Patchwork D3994: fastannotate: initial import from Facebook's hg-experimental

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Submitter phabricator
Date Aug. 1, 2018, 10:48 p.m.
Message ID <67280b3e895a3c7517f5403cf1fe39fe@localhost.localdomain>
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Permalink /patch/33081/
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phabricator - Aug. 1, 2018, 10:48 p.m.
durin42 updated this revision to Diff 9767.

REPOSITORY
  rHG Mercurial

CHANGES SINCE LAST UPDATE
  https://phab.mercurial-scm.org/D3994?vs=9685&id=9767

REVISION DETAIL
  https://phab.mercurial-scm.org/D3994

AFFECTED FILES
  hgext/fastannotate/__init__.py
  hgext/fastannotate/commands.py
  hgext/fastannotate/context.py
  hgext/fastannotate/error.py
  hgext/fastannotate/formatter.py
  hgext/fastannotate/protocol.py
  hgext/fastannotate/revmap.py
  hgext/fastannotate/support.py
  setup.py
  tests/test-fastannotate-corrupt.t
  tests/test-fastannotate-diffopts.t
  tests/test-fastannotate-hg.t
  tests/test-fastannotate-perfhack.t
  tests/test-fastannotate-protocol.t
  tests/test-fastannotate-renames.t
  tests/test-fastannotate-revmap.py
  tests/test-fastannotate.t

CHANGE DETAILS




To: durin42, #hg-reviewers
Cc: quark, mercurial-devel

Patch

diff --git a/tests/test-fastannotate.t b/tests/test-fastannotate.t
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate.t
@@ -0,0 +1,263 @@ 
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > fastannotate=
+  > EOF
+
+  $ HGMERGE=true; export HGMERGE
+
+  $ hg init repo
+  $ cd repo
+
+a simple merge case
+
+  $ echo 1 > a
+  $ hg commit -qAm 'append 1'
+  $ echo 2 >> a
+  $ hg commit -m 'append 2'
+  $ echo 3 >> a
+  $ hg commit -m 'append 3'
+  $ hg up 1 -q
+  $ cat > a << EOF
+  > 0
+  > 1
+  > 2
+  > EOF
+  $ hg commit -qm 'insert 0'
+  $ hg merge 2 -q
+  $ echo 4 >> a
+  $ hg commit -m merge
+  $ hg log -G -T '{rev}: {desc}'
+  @    4: merge
+  |\
+  | o  3: insert 0
+  | |
+  o |  2: append 3
+  |/
+  o  1: append 2
+  |
+  o  0: append 1
+  
+  $ hg fastannotate a
+  3: 0
+  0: 1
+  1: 2
+  2: 3
+  4: 4
+  $ hg fastannotate -r 0 a
+  0: 1
+  $ hg fastannotate -r 1 a
+  0: 1
+  1: 2
+  $ hg fastannotate -udnclf a
+  test 3 d641cb51f61e Thu Jan 01 00:00:00 1970 +0000 a:1: 0
+  test 0 4994017376d3 Thu Jan 01 00:00:00 1970 +0000 a:1: 1
+  test 1 e940cb6d9a06 Thu Jan 01 00:00:00 1970 +0000 a:2: 2
+  test 2 26162a884ba6 Thu Jan 01 00:00:00 1970 +0000 a:3: 3
+  test 4 3ad7bcd2815f Thu Jan 01 00:00:00 1970 +0000 a:5: 4
+  $ hg fastannotate --linear a
+  3: 0
+  0: 1
+  1: 2
+  4: 3
+  4: 4
+
+incrementally updating
+
+  $ hg fastannotate -r 0 a --debug
+  fastannotate: a: using fast path (resolved fctx: True)
+  0: 1
+  $ hg fastannotate -r 0 a --debug --rebuild
+  fastannotate: a: 1 new changesets in the main branch
+  0: 1
+  $ hg fastannotate -r 1 a --debug
+  fastannotate: a: 1 new changesets in the main branch
+  0: 1
+  1: 2
+  $ hg fastannotate -r 3 a --debug
+  fastannotate: a: 1 new changesets in the main branch
+  3: 0
+  0: 1
+  1: 2
+  $ hg fastannotate -r 4 a --debug
+  fastannotate: a: 1 new changesets in the main branch
+  3: 0
+  0: 1
+  1: 2
+  2: 3
+  4: 4
+  $ hg fastannotate -r 1 a --debug
+  fastannotate: a: using fast path (resolved fctx: True)
+  0: 1
+  1: 2
+
+rebuild happens automatically if unable to update
+
+  $ hg fastannotate -r 2 a --debug
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 3 new changesets in the main branch
+  0: 1
+  1: 2
+  2: 3
+
+config option "fastannotate.mainbranch"
+
+  $ hg fastannotate -r 1 --rebuild --config fastannotate.mainbranch=tip a --debug
+  fastannotate: a: 4 new changesets in the main branch
+  0: 1
+  1: 2
+  $ hg fastannotate -r 4 a --debug
+  fastannotate: a: using fast path (resolved fctx: True)
+  3: 0
+  0: 1
+  1: 2
+  2: 3
+  4: 4
+
+config option "fastannotate.modes"
+
+  $ hg annotate -r 1 --debug a
+  0: 1
+  1: 2
+  $ hg annotate --config fastannotate.modes=fctx -r 1 --debug a
+  fastannotate: a: using fast path (resolved fctx: False)
+  0: 1
+  1: 2
+  $ hg fastannotate --config fastannotate.modes=fctx -h -q
+  hg: unknown command 'fastannotate'
+  (did you mean *) (glob)
+  [255]
+
+rename
+
+  $ hg mv a b
+  $ cat > b << EOF
+  > 0
+  > 11
+  > 3
+  > 44
+  > EOF
+  $ hg commit -m b -q
+  $ hg fastannotate -ncf --long-hash b
+  3 d641cb51f61e331c44654104301f8154d7865c89 a: 0
+  5 d44dade239915bc82b91e4556b1257323f8e5824 b: 11
+  2 26162a884ba60e8c87bf4e0d6bb8efcc6f711a4e a: 3
+  5 d44dade239915bc82b91e4556b1257323f8e5824 b: 44
+  $ hg fastannotate -r 26162a884ba60e8c87bf4e0d6bb8efcc6f711a4e a
+  0: 1
+  1: 2
+  2: 3
+
+fastannotate --deleted
+
+  $ hg fastannotate --deleted -nf b
+  3 a:  0
+  5 b:  11
+  0 a: -1
+  1 a: -2
+  2 a:  3
+  5 b:  44
+  4 a: -4
+  $ hg fastannotate --deleted -r 3 -nf a
+  3 a:  0
+  0 a:  1
+  1 a:  2
+
+file and directories with ".l", ".m" suffixes
+
+  $ cd ..
+  $ hg init repo2
+  $ cd repo2
+
+  $ mkdir a.l b.m c.lock a.l.hg b.hg
+  $ for i in a b c d d.l d.m a.l/a b.m/a c.lock/a a.l.hg/a b.hg/a; do
+  >   echo $i > $i
+  > done
+  $ hg add . -q
+  $ hg commit -m init
+  $ hg fastannotate a.l/a b.m/a c.lock/a a.l.hg/a b.hg/a d.l d.m a b c d
+  0: a
+  0: a.l.hg/a
+  0: a.l/a
+  0: b
+  0: b.hg/a
+  0: b.m/a
+  0: c
+  0: c.lock/a
+  0: d
+  0: d.l
+  0: d.m
+
+empty file
+
+  $ touch empty
+  $ hg commit -A empty -m empty
+  $ hg fastannotate empty
+
+json format
+
+  $ hg fastannotate -Tjson -cludn b a empty
+  [
+   {
+    "date": [0.0, 0],
+    "line": "a\n",
+    "line_number": 1,
+    "node": "1fd620b16252aecb54c6aa530dff5ed6e6ec3d21",
+    "rev": 0,
+    "user": "test"
+   },
+   {
+    "date": [0.0, 0],
+    "line": "b\n",
+    "line_number": 1,
+    "node": "1fd620b16252aecb54c6aa530dff5ed6e6ec3d21",
+    "rev": 0,
+    "user": "test"
+   }
+  ]
+
+  $ hg fastannotate -Tjson -cludn empty
+  [
+  ]
+  $ hg fastannotate -Tjson --no-content -n a
+  [
+   {
+    "rev": 0
+   }
+  ]
+
+working copy
+
+  $ echo a >> a
+  $ hg fastannotate -r 'wdir()' a
+  abort: cannot update linelog to wdir()
+  (set fastannotate.mainbranch)
+  [255]
+  $ cat >> $HGRCPATH << EOF
+  > [fastannotate]
+  > mainbranch = .
+  > EOF
+  $ hg fastannotate -r 'wdir()' a
+  0 : a
+  1+: a
+  $ hg fastannotate -cludn -r 'wdir()' a
+  test 0 1fd620b16252  Thu Jan 01 00:00:00 1970 +0000:1: a
+  test 1 720582f5bdb6+ *:2: a (glob)
+  $ hg fastannotate -cludn -r 'wdir()' -Tjson a
+  [
+   {
+    "date": [0.0, 0],
+    "line": "a\n",
+    "line_number": 1,
+    "node": "1fd620b16252aecb54c6aa530dff5ed6e6ec3d21",
+    "rev": 0,
+    "user": "test"
+   },
+   {
+    "date": [*, 0], (glob)
+    "line": "a\n",
+    "line_number": 2,
+    "node": null,
+    "rev": null,
+    "user": "test"
+   }
+  ]
diff --git a/tests/test-fastannotate-revmap.py b/tests/test-fastannotate-revmap.py
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate-revmap.py
@@ -0,0 +1,191 @@ 
+from __future__ import absolute_import, print_function
+
+import os
+import tempfile
+
+from mercurial import util
+from hgext.fastannotate import error, revmap
+
+def genhsh(i):
+    return chr(i) + b'\0' * 19
+
+def gettemppath():
+    fd, path = tempfile.mkstemp()
+    os.unlink(path)
+    os.close(fd)
+    return path
+
+def ensure(condition):
+    if not condition:
+        raise RuntimeError('Unexpected')
+
+def testbasicreadwrite():
+    path = gettemppath()
+
+    rm = revmap.revmap(path)
+    ensure(rm.maxrev == 0)
+    for i in xrange(5):
+        ensure(rm.rev2hsh(i) is None)
+    ensure(rm.hsh2rev(b'\0' * 20) is None)
+
+    paths = ['', 'a', None, 'b', 'b', 'c', 'c', None, 'a', 'b', 'a', 'a']
+    for i in xrange(1, 5):
+        ensure(rm.append(genhsh(i), sidebranch=(i & 1), path=paths[i]) == i)
+
+    ensure(rm.maxrev == 4)
+    for i in xrange(1, 5):
+        ensure(rm.hsh2rev(genhsh(i)) == i)
+        ensure(rm.rev2hsh(i) == genhsh(i))
+
+    # re-load and verify
+    rm.flush()
+    rm = revmap.revmap(path)
+    ensure(rm.maxrev == 4)
+    for i in xrange(1, 5):
+        ensure(rm.hsh2rev(genhsh(i)) == i)
+        ensure(rm.rev2hsh(i) == genhsh(i))
+        ensure(bool(rm.rev2flag(i) & revmap.sidebranchflag) == bool(i & 1))
+
+    # append without calling save() explicitly
+    for i in xrange(5, 12):
+        ensure(rm.append(genhsh(i), sidebranch=(i & 1), path=paths[i],
+                         flush=True) == i)
+
+    # re-load and verify
+    rm = revmap.revmap(path)
+    ensure(rm.maxrev == 11)
+    for i in xrange(1, 12):
+        ensure(rm.hsh2rev(genhsh(i)) == i)
+        ensure(rm.rev2hsh(i) == genhsh(i))
+        ensure(rm.rev2path(i) == paths[i] or paths[i - 1])
+        ensure(bool(rm.rev2flag(i) & revmap.sidebranchflag) == bool(i & 1))
+
+    os.unlink(path)
+
+    # missing keys
+    ensure(rm.rev2hsh(12) is None)
+    ensure(rm.rev2hsh(0) is None)
+    ensure(rm.rev2hsh(-1) is None)
+    ensure(rm.rev2flag(12) is None)
+    ensure(rm.rev2path(12) is None)
+    ensure(rm.hsh2rev(b'\1' * 20) is None)
+
+    # illformed hash (not 20 bytes)
+    try:
+        rm.append(b'\0')
+        ensure(False)
+    except Exception:
+        pass
+
+def testcorruptformat():
+    path = gettemppath()
+
+    # incorrect header
+    with open(path, 'w') as f:
+        f.write(b'NOT A VALID HEADER')
+    try:
+        revmap.revmap(path)
+        ensure(False)
+    except error.CorruptedFileError:
+        pass
+
+    # rewrite the file
+    os.unlink(path)
+    rm = revmap.revmap(path)
+    rm.append(genhsh(0), flush=True)
+
+    rm = revmap.revmap(path)
+    ensure(rm.maxrev == 1)
+
+    # corrupt the file by appending a byte
+    size = os.stat(path).st_size
+    with open(path, 'a') as f:
+        f.write('\xff')
+    try:
+        revmap.revmap(path)
+        ensure(False)
+    except error.CorruptedFileError:
+        pass
+
+    # corrupt the file by removing the last byte
+    ensure(size > 0)
+    with open(path, 'w') as f:
+        f.truncate(size - 1)
+    try:
+        revmap.revmap(path)
+        ensure(False)
+    except error.CorruptedFileError:
+        pass
+
+    os.unlink(path)
+
+def testcopyfrom():
+    path = gettemppath()
+    rm = revmap.revmap(path)
+    for i in xrange(1, 10):
+        ensure(rm.append(genhsh(i), sidebranch=(i & 1), path=str(i // 3)) == i)
+    rm.flush()
+
+    # copy rm to rm2
+    rm2 = revmap.revmap()
+    rm2.copyfrom(rm)
+    path2 = gettemppath()
+    rm2.path = path2
+    rm2.flush()
+
+    # two files should be the same
+    ensure(len(set(util.readfile(p) for p in [path, path2])) == 1)
+
+    os.unlink(path)
+    os.unlink(path2)
+
+class fakefctx(object):
+    def __init__(self, node, path=None):
+        self._node = node
+        self._path = path
+
+    def node(self):
+        return self._node
+
+    def path(self):
+        return self._path
+
+def testcontains():
+    path = gettemppath()
+
+    rm = revmap.revmap(path)
+    for i in xrange(1, 5):
+        ensure(rm.append(genhsh(i), sidebranch=(i & 1)) == i)
+
+    for i in xrange(1, 5):
+        ensure(((genhsh(i), None) in rm) == ((i & 1) == 0))
+        ensure((fakefctx(genhsh(i)) in rm) == ((i & 1) == 0))
+    for i in xrange(5, 10):
+        ensure(fakefctx(genhsh(i)) not in rm)
+        ensure((genhsh(i), None) not in rm)
+
+    # "contains" checks paths
+    rm = revmap.revmap()
+    for i in xrange(1, 5):
+        ensure(rm.append(genhsh(i), path=str(i // 2)) == i)
+    for i in xrange(1, 5):
+        ensure(fakefctx(genhsh(i), path=str(i // 2)) in rm)
+        ensure(fakefctx(genhsh(i), path='a') not in rm)
+
+def testlastnode():
+    path = gettemppath()
+    ensure(revmap.getlastnode(path) is None)
+    rm = revmap.revmap(path)
+    ensure(revmap.getlastnode(path) is None)
+    for i in xrange(1, 10):
+        hsh = genhsh(i)
+        rm.append(hsh, path=str(i // 2), flush=True)
+        ensure(revmap.getlastnode(path) == hsh)
+        rm2 = revmap.revmap(path)
+        ensure(rm2.rev2hsh(rm2.maxrev) == hsh)
+
+testbasicreadwrite()
+testcorruptformat()
+testcopyfrom()
+testcontains()
+testlastnode()
diff --git a/tests/test-fastannotate-renames.t b/tests/test-fastannotate-renames.t
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate-renames.t
@@ -0,0 +1,168 @@ 
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > fastannotate=
+  > [fastannotate]
+  > mainbranch=main
+  > EOF
+
+  $ hg init repo
+  $ cd repo
+
+add or rename files on top of the master branch
+
+  $ echo a1 > a
+  $ echo b1 > b
+  $ hg commit -qAm 1
+  $ hg bookmark -i main
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: 1 new changesets in the main branch
+  0 b: b1
+  $ hg fastannotate --debug -nf a
+  fastannotate: a: 1 new changesets in the main branch
+  0 a: a1
+  $ echo a2 >> a
+  $ cat > b << EOF
+  > b0
+  > b1
+  > EOF
+  $ hg mv a t
+  $ hg mv b a
+  $ hg mv t b
+  $ hg commit -m 'swap names'
+
+existing linelogs are not helpful with such renames in side branches
+
+  $ hg fastannotate --debug -nf a
+  fastannotate: a: linelog cannot help in annotating this revision
+  1 a: b0
+  0 b: b1
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: linelog cannot help in annotating this revision
+  0 a: a1
+  1 b: a2
+
+move main branch forward, rebuild should happen
+
+  $ hg bookmark -i main -r . -q
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: cache broken and deleted
+  fastannotate: b: 2 new changesets in the main branch
+  0 a: a1
+  1 b: a2
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: using fast path (resolved fctx: True)
+  0 a: a1
+  1 b: a2
+
+for rev 0, the existing linelog is still useful for a, but not for b
+
+  $ hg fastannotate --debug -nf a -r 0
+  fastannotate: a: using fast path (resolved fctx: True)
+  0 a: a1
+  $ hg fastannotate --debug -nf b -r 0
+  fastannotate: b: linelog cannot help in annotating this revision
+  0 b: b1
+
+a rebuild can also be triggered if "the main branch last time" mismatches
+
+  $ echo a3 >> a
+  $ hg commit -m a3
+  $ cat >> b << EOF
+  > b3
+  > b4
+  > EOF
+  $ hg commit -m b4
+  $ hg bookmark -i main -q
+  $ hg fastannotate --debug -nf a
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 3 new changesets in the main branch
+  1 a: b0
+  0 b: b1
+  2 a: a3
+  $ hg fastannotate --debug -nf a
+  fastannotate: a: using fast path (resolved fctx: True)
+  1 a: b0
+  0 b: b1
+  2 a: a3
+
+linelog can be updated without being helpful
+
+  $ hg mv a t
+  $ hg mv b a
+  $ hg mv t b
+  $ hg commit -m 'swap names again'
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: 1 new changesets in the main branch
+  1 a: b0
+  0 b: b1
+  2 a: a3
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: linelog cannot help in annotating this revision
+  1 a: b0
+  0 b: b1
+  2 a: a3
+
+move main branch forward again, rebuilds are one-time
+
+  $ hg bookmark -i main -q
+  $ hg fastannotate --debug -nf a
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 4 new changesets in the main branch
+  0 a: a1
+  1 b: a2
+  3 b: b3
+  3 b: b4
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: cache broken and deleted
+  fastannotate: b: 4 new changesets in the main branch
+  1 a: b0
+  0 b: b1
+  2 a: a3
+  $ hg fastannotate --debug -nf a
+  fastannotate: a: using fast path (resolved fctx: True)
+  0 a: a1
+  1 b: a2
+  3 b: b3
+  3 b: b4
+  $ hg fastannotate --debug -nf b
+  fastannotate: b: using fast path (resolved fctx: True)
+  1 a: b0
+  0 b: b1
+  2 a: a3
+
+list changeset hashes to improve readability
+
+  $ hg log -T '{rev}:{node}\n'
+  4:980e1ab8c516350172928fba95b49ede3b643dca
+  3:14e123fedad9f491f5dde0beca2a767625a0a93a
+  2:96495c41e4c12218766f78cdf244e768d7718b0f
+  1:35c2b781234c994896aba36bd3245d3104e023df
+  0:653e95416ebb5dbcc25bbc7f75568c9e01f7bd2f
+
+annotate a revision not in the linelog. linelog cannot be used, but does not get rebuilt either
+
+  $ hg fastannotate --debug -nf a -r 96495c41e4c12218766f78cdf244e768d7718b0f
+  fastannotate: a: linelog cannot help in annotating this revision
+  1 a: b0
+  0 b: b1
+  2 a: a3
+  $ hg fastannotate --debug -nf a -r 2
+  fastannotate: a: linelog cannot help in annotating this revision
+  1 a: b0
+  0 b: b1
+  2 a: a3
+  $ hg fastannotate --debug -nf a -r .
+  fastannotate: a: using fast path (resolved fctx: True)
+  0 a: a1
+  1 b: a2
+  3 b: b3
+  3 b: b4
+
+annotate an ancient revision where the path matches. linelog can be used
+
+  $ hg fastannotate --debug -nf a -r 0
+  fastannotate: a: using fast path (resolved fctx: True)
+  0 a: a1
+  $ hg fastannotate --debug -nf a -r 653e95416ebb5dbcc25bbc7f75568c9e01f7bd2f
+  fastannotate: a: using fast path (resolved fctx: False)
+  0 a: a1
diff --git a/tests/test-fastannotate-protocol.t b/tests/test-fastannotate-protocol.t
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate-protocol.t
@@ -0,0 +1,216 @@ 
+  $ cat >> $HGRCPATH << EOF
+  > [ui]
+  > ssh = $PYTHON "$TESTDIR/dummyssh"
+  > [extensions]
+  > fastannotate=
+  > [fastannotate]
+  > mainbranch=@
+  > EOF
+
+  $ HGMERGE=true; export HGMERGE
+
+setup the server repo
+
+  $ hg init repo-server
+  $ cd repo-server
+  $ cat >> .hg/hgrc << EOF
+  > [fastannotate]
+  > server=1
+  > EOF
+  $ for i in 1 2 3 4; do
+  >   echo $i >> a
+  >   hg commit -A -m $i a
+  > done
+  $ [ -d .hg/fastannotate ]
+  [1]
+  $ hg bookmark @
+  $ cd ..
+
+setup the local repo
+
+  $ hg clone 'ssh://user@dummy/repo-server' repo-local -q
+  $ cd repo-local
+  $ cat >> .hg/hgrc << EOF
+  > [fastannotate]
+  > client=1
+  > clientfetchthreshold=0
+  > EOF
+  $ [ -d .hg/fastannotate ]
+  [1]
+  $ hg fastannotate a --debug
+  running * (glob)
+  sending hello command
+  sending between command
+  remote: * (glob) (?)
+  remote: capabilities: * (glob)
+  remote: * (glob) (?)
+  sending protocaps command
+  fastannotate: requesting 1 files
+  sending getannotate command
+  fastannotate: writing 112 bytes to fastannotate/default/a.l (?)
+  fastannotate: server returned
+  fastannotate: writing 112 bytes to fastannotate/default/a.l (?)
+  fastannotate: writing 94 bytes to fastannotate/default/a.m
+  fastannotate: a: using fast path (resolved fctx: True)
+  0: 1
+  1: 2
+  2: 3
+  3: 4
+
+the cache could be reused and no download is necessary
+
+  $ hg fastannotate a --debug
+  fastannotate: a: using fast path (resolved fctx: True)
+  0: 1
+  1: 2
+  2: 3
+  3: 4
+
+if the client agrees where the head of the master branch is, no re-download
+happens even if the client has more commits
+
+  $ echo 5 >> a
+  $ hg commit -m 5
+  $ hg bookmark -r 3 @ -f
+  $ hg fastannotate a --debug
+  0: 1
+  1: 2
+  2: 3
+  3: 4
+  4: 5
+
+if the client has a different "@" (head of the master branch) and "@" is ahead
+of the server, the server can detect things are unchanged and does not return
+full contents (not that there is no "writing ... to fastannotate"), but the
+client can also build things up on its own (causing diverge)
+
+  $ hg bookmark -r 4 @ -f
+  $ hg fastannotate a --debug
+  running * (glob)
+  sending hello command
+  sending between command
+  remote: * (glob) (?)
+  remote: capabilities: * (glob)
+  remote: * (glob) (?)
+  sending protocaps command
+  fastannotate: requesting 1 files
+  sending getannotate command
+  fastannotate: server returned
+  fastannotate: a: 1 new changesets in the main branch
+  0: 1
+  1: 2
+  2: 3
+  3: 4
+  4: 5
+
+if the client has a different "@" which is behind the server. no download is
+necessary
+
+  $ hg fastannotate a --debug --config fastannotate.mainbranch=2
+  fastannotate: a: using fast path (resolved fctx: True)
+  0: 1
+  1: 2
+  2: 3
+  3: 4
+  4: 5
+
+define fastannotate on-disk paths
+
+  $ p1=.hg/fastannotate/default
+  $ p2=../repo-server/.hg/fastannotate/default
+
+revert bookmark change so the client is behind the server
+
+  $ hg bookmark -r 2 @ -f
+
+in the "fctx" mode with the "annotate" command, the client also downloads the
+cache. but not in the (default) "fastannotate" mode.
+
+  $ rm $p1/a.l $p1/a.m
+  $ hg annotate a --debug | grep 'fastannotate: writing'
+  [1]
+  $ hg annotate a --config fastannotate.modes=fctx --debug | grep 'fastannotate: writing' | sort
+  fastannotate: writing 112 bytes to fastannotate/default/a.l
+  fastannotate: writing 94 bytes to fastannotate/default/a.m
+
+the fastannotate cache (built server-side, downloaded client-side) in two repos
+have the same content (because the client downloads from the server)
+
+  $ diff $p1/a.l $p2/a.l
+  $ diff $p1/a.m $p2/a.m
+
+in the "fctx" mode, the client could also build the cache locally
+
+  $ hg annotate a --config fastannotate.modes=fctx --debug --config fastannotate.mainbranch=4 | grep fastannotate
+  fastannotate: requesting 1 files
+  fastannotate: server returned
+  fastannotate: a: 1 new changesets in the main branch
+
+the server would rebuild broken cache automatically
+
+  $ cp $p2/a.m $p2/a.m.bak
+  $ echo BROKEN1 > $p1/a.m
+  $ echo BROKEN2 > $p2/a.m
+  $ hg fastannotate a --debug | grep 'fastannotate: writing' | sort
+  fastannotate: writing 112 bytes to fastannotate/default/a.l
+  fastannotate: writing 94 bytes to fastannotate/default/a.m
+  $ diff $p1/a.m $p2/a.m
+  $ diff $p2/a.m $p2/a.m.bak
+
+use the "debugbuildannotatecache" command to build annotate cache
+
+  $ rm -rf $p1 $p2
+  $ hg --cwd ../repo-server debugbuildannotatecache a --debug
+  fastannotate: a: 4 new changesets in the main branch
+  $ hg --cwd ../repo-local debugbuildannotatecache a --debug
+  running * (glob)
+  sending hello command
+  sending between command
+  remote: * (glob) (?)
+  remote: capabilities: * (glob)
+  remote: * (glob) (?)
+  sending protocaps command
+  fastannotate: requesting 1 files
+  sending getannotate command
+  fastannotate: server returned
+  fastannotate: writing * (glob)
+  fastannotate: writing * (glob)
+  $ diff $p1/a.l $p2/a.l
+  $ diff $p1/a.m $p2/a.m
+
+with the clientfetchthreshold config option, the client can build up the cache
+without downloading from the server
+
+  $ rm -rf $p1
+  $ hg fastannotate a --debug --config fastannotate.clientfetchthreshold=10
+  fastannotate: a: 3 new changesets in the main branch
+  0: 1
+  1: 2
+  2: 3
+  3: 4
+  4: 5
+
+if the fastannotate directory is not writable, the fctx mode still works
+
+  $ rm -rf $p1
+  $ touch $p1
+  $ hg annotate a --debug --traceback --config fastannotate.modes=fctx
+  fastannotate: a: cache broken and deleted
+  fastannotate: prefetch failed: * (glob)
+  fastannotate: a: cache broken and deleted
+  fastannotate: falling back to the vanilla annotate: * (glob)
+  0: 1
+  1: 2
+  2: 3
+  3: 4
+  4: 5
+
+with serverbuildondemand=False, the server will not build anything
+
+  $ cat >> ../repo-server/.hg/hgrc <<EOF
+  > [fastannotate]
+  > serverbuildondemand=False
+  > EOF
+  $ rm -rf $p1 $p2
+  $ hg fastannotate a --debug | grep 'fastannotate: writing'
+  [1]
diff --git a/tests/test-fastannotate-perfhack.t b/tests/test-fastannotate-perfhack.t
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate-perfhack.t
@@ -0,0 +1,182 @@ 
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > fastannotate=
+  > [fastannotate]
+  > perfhack=1
+  > EOF
+
+  $ HGMERGE=true; export HGMERGE
+
+  $ hg init repo
+  $ cd repo
+
+a simple merge case
+
+  $ echo 1 > a
+  $ hg commit -qAm 'append 1'
+  $ echo 2 >> a
+  $ hg commit -m 'append 2'
+  $ echo 3 >> a
+  $ hg commit -m 'append 3'
+  $ hg up 1 -q
+  $ cat > a << EOF
+  > 0
+  > 1
+  > 2
+  > EOF
+  $ hg commit -qm 'insert 0'
+  $ hg merge 2 -q
+  $ echo 4 >> a
+  $ hg commit -m merge
+  $ hg log -G -T '{rev}: {desc}'
+  @    4: merge
+  |\
+  | o  3: insert 0
+  | |
+  o |  2: append 3
+  |/
+  o  1: append 2
+  |
+  o  0: append 1
+  
+  $ hg fastannotate a
+  3: 0
+  0: 1
+  1: 2
+  2: 3
+  4: 4
+  $ hg fastannotate -r 0 a
+  0: 1
+  $ hg fastannotate -r 1 a
+  0: 1
+  1: 2
+  $ hg fastannotate -udnclf a
+  test 3 d641cb51f61e Thu Jan 01 00:00:00 1970 +0000 a:1: 0
+  test 0 4994017376d3 Thu Jan 01 00:00:00 1970 +0000 a:1: 1
+  test 1 e940cb6d9a06 Thu Jan 01 00:00:00 1970 +0000 a:2: 2
+  test 2 26162a884ba6 Thu Jan 01 00:00:00 1970 +0000 a:3: 3
+  test 4 3ad7bcd2815f Thu Jan 01 00:00:00 1970 +0000 a:5: 4
+  $ hg fastannotate --linear a
+  3: 0
+  0: 1
+  1: 2
+  4: 3
+  4: 4
+
+incrementally updating
+
+  $ hg fastannotate -r 0 a --debug
+  fastannotate: a: using fast path (resolved fctx: True)
+  0: 1
+  $ hg fastannotate -r 0 a --debug --rebuild
+  fastannotate: a: 1 new changesets in the main branch
+  0: 1
+  $ hg fastannotate -r 1 a --debug
+  fastannotate: a: 1 new changesets in the main branch
+  0: 1
+  1: 2
+  $ hg fastannotate -r 3 a --debug
+  fastannotate: a: 1 new changesets in the main branch
+  3: 0
+  0: 1
+  1: 2
+  $ hg fastannotate -r 4 a --debug
+  fastannotate: a: 1 new changesets in the main branch
+  3: 0
+  0: 1
+  1: 2
+  2: 3
+  4: 4
+  $ hg fastannotate -r 1 a --debug
+  fastannotate: a: using fast path (resolved fctx: True)
+  0: 1
+  1: 2
+
+rebuild happens automatically if unable to update
+
+  $ hg fastannotate -r 2 a --debug
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 3 new changesets in the main branch
+  0: 1
+  1: 2
+  2: 3
+
+config option "fastannotate.mainbranch"
+
+  $ hg fastannotate -r 1 --rebuild --config fastannotate.mainbranch=tip a --debug
+  fastannotate: a: 4 new changesets in the main branch
+  0: 1
+  1: 2
+  $ hg fastannotate -r 4 a --debug
+  fastannotate: a: using fast path (resolved fctx: True)
+  3: 0
+  0: 1
+  1: 2
+  2: 3
+  4: 4
+
+rename
+
+  $ hg mv a b
+  $ cat > b << EOF
+  > 0
+  > 11
+  > 3
+  > 44
+  > EOF
+  $ hg commit -m b -q
+  $ hg fastannotate -ncf --long-hash b
+  3 d641cb51f61e331c44654104301f8154d7865c89 a: 0
+  5 d44dade239915bc82b91e4556b1257323f8e5824 b: 11
+  2 26162a884ba60e8c87bf4e0d6bb8efcc6f711a4e a: 3
+  5 d44dade239915bc82b91e4556b1257323f8e5824 b: 44
+  $ hg fastannotate -r 26162a884ba60e8c87bf4e0d6bb8efcc6f711a4e a
+  0: 1
+  1: 2
+  2: 3
+
+fastannotate --deleted
+
+  $ hg fastannotate --deleted -nf b
+  3 a:  0
+  5 b:  11
+  0 a: -1
+  1 a: -2
+  2 a:  3
+  5 b:  44
+  4 a: -4
+  $ hg fastannotate --deleted -r 3 -nf a
+  3 a:  0
+  0 a:  1
+  1 a:  2
+
+file and directories with ".l", ".m" suffixes
+
+  $ cd ..
+  $ hg init repo2
+  $ cd repo2
+
+  $ mkdir a.l b.m c.lock a.l.hg b.hg
+  $ for i in a b c d d.l d.m a.l/a b.m/a c.lock/a a.l.hg/a b.hg/a; do
+  >   echo $i > $i
+  > done
+  $ hg add . -q
+  $ hg commit -m init
+  $ hg fastannotate a.l/a b.m/a c.lock/a a.l.hg/a b.hg/a d.l d.m a b c d
+  0: a
+  0: a.l.hg/a
+  0: a.l/a
+  0: b
+  0: b.hg/a
+  0: b.m/a
+  0: c
+  0: c.lock/a
+  0: d
+  0: d.l
+  0: d.m
+
+empty file
+
+  $ touch empty
+  $ hg commit -A empty -m empty
+  $ hg fastannotate empty
diff --git a/tests/test-fastannotate-hg.t b/tests/test-fastannotate-hg.t
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate-hg.t
@@ -0,0 +1,777 @@ 
+(this file is backported from core hg tests/test-annotate.t)
+
+  $ cat >> $HGRCPATH << EOF
+  > [diff]
+  > git=1
+  > [extensions]
+  > fastannotate=
+  > [fastannotate]
+  > modes=fctx
+  > forcefollow=False
+  > mainbranch=.
+  > EOF
+
+  $ HGMERGE=true; export HGMERGE
+
+init
+
+  $ hg init repo
+  $ cd repo
+
+commit
+
+  $ echo 'a' > a
+  $ hg ci -A -m test -u nobody -d '1 0'
+  adding a
+
+annotate -c
+
+  $ hg annotate -c a
+  8435f90966e4: a
+
+annotate -cl
+
+  $ hg annotate -cl a
+  8435f90966e4:1: a
+
+annotate -d
+
+  $ hg annotate -d a
+  Thu Jan 01 00:00:01 1970 +0000: a
+
+annotate -n
+
+  $ hg annotate -n a
+  0: a
+
+annotate -nl
+
+  $ hg annotate -nl a
+  0:1: a
+
+annotate -u
+
+  $ hg annotate -u a
+  nobody: a
+
+annotate -cdnu
+
+  $ hg annotate -cdnu a
+  nobody 0 8435f90966e4 Thu Jan 01 00:00:01 1970 +0000: a
+
+annotate -cdnul
+
+  $ hg annotate -cdnul a
+  nobody 0 8435f90966e4 Thu Jan 01 00:00:01 1970 +0000:1: a
+
+annotate (JSON)
+
+  $ hg annotate -Tjson a
+  [
+   {
+    "abspath": "a",
+    "lines": [{"line": "a\n", "rev": 0}],
+    "path": "a"
+   }
+  ]
+
+  $ hg annotate -Tjson -cdfnul a
+  [
+   {
+    "abspath": "a",
+    "lines": [{"date": [1.0, 0], "file": "a", "line": "a\n", "line_number": 1, "node": "8435f90966e442695d2ded29fdade2bac5ad8065", "rev": 0, "user": "nobody"}],
+    "path": "a"
+   }
+  ]
+
+  $ cat <<EOF >>a
+  > a
+  > a
+  > EOF
+  $ hg ci -ma1 -d '1 0'
+  $ hg cp a b
+  $ hg ci -mb -d '1 0'
+  $ cat <<EOF >> b
+  > b4
+  > b5
+  > b6
+  > EOF
+  $ hg ci -mb2 -d '2 0'
+
+annotate -n b
+
+  $ hg annotate -n b
+  0: a
+  1: a
+  1: a
+  3: b4
+  3: b5
+  3: b6
+
+annotate --no-follow b
+
+  $ hg annotate --no-follow b
+  2: a
+  2: a
+  2: a
+  3: b4
+  3: b5
+  3: b6
+
+annotate -nl b
+
+  $ hg annotate -nl b
+  0:1: a
+  1:2: a
+  1:3: a
+  3:4: b4
+  3:5: b5
+  3:6: b6
+
+annotate -nf b
+
+  $ hg annotate -nf b
+  0 a: a
+  1 a: a
+  1 a: a
+  3 b: b4
+  3 b: b5
+  3 b: b6
+
+annotate -nlf b
+
+  $ hg annotate -nlf b
+  0 a:1: a
+  1 a:2: a
+  1 a:3: a
+  3 b:4: b4
+  3 b:5: b5
+  3 b:6: b6
+
+  $ hg up -C 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ cat <<EOF >> b
+  > b4
+  > c
+  > b5
+  > EOF
+  $ hg ci -mb2.1 -d '2 0'
+  created new head
+  $ hg merge
+  merging b
+  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg ci -mmergeb -d '3 0'
+
+annotate after merge
+(note: the first one falls back to the vanilla annotate which does not use linelog)
+
+  $ hg annotate -nf b --debug
+  fastannotate: b: rebuilding broken cache
+  fastannotate: b: 5 new changesets in the main branch
+  0 a: a
+  1 a: a
+  1 a: a
+  3 b: b4
+  4 b: c
+  3 b: b5
+
+(difference explained below)
+
+  $ hg annotate -nf b --debug
+  fastannotate: b: using fast path (resolved fctx: False)
+  0 a: a
+  1 a: a
+  1 a: a
+  4 b: b4
+  4 b: c
+  4 b: b5
+
+annotate after merge with -l
+(fastannotate differs from annotate)
+
+  $ hg log -Gp -T '{rev}:{node}' -r '2..5'
+  @    5:64afcdf8e29e063c635be123d8d2fb160af00f7e
+  |\
+  | o  4:5fbdc1152d97597717021ad9e063061b200f146bdiff --git a/b b/b
+  | |  --- a/b
+  | |  +++ b/b
+  | |  @@ -1,3 +1,6 @@
+  | |   a
+  | |   a
+  | |   a
+  | |  +b4
+  | |  +c
+  | |  +b5
+  | |
+  o |  3:37ec9f5c3d1f99572d7075971cb4876e2139b52fdiff --git a/b b/b
+  |/   --- a/b
+  |    +++ b/b
+  |    @@ -1,3 +1,6 @@
+  |     a
+  |     a
+  |     a
+  |    +b4
+  |    +b5
+  |    +b6
+  |
+  o  2:3086dbafde1ce745abfc8d2d367847280aabae9ddiff --git a/a b/b
+  |  copy from a
+  ~  copy to b
+  
+
+(in this case, "b4", "b5" could be considered introduced by either rev 3, or rev 4.
+ and that causes the rev number difference)
+
+  $ hg annotate -nlf b --config fastannotate.modes=
+  0 a:1: a
+  1 a:2: a
+  1 a:3: a
+  3 b:4: b4
+  4 b:5: c
+  3 b:5: b5
+
+  $ hg annotate -nlf b
+  0 a:1: a
+  1 a:2: a
+  1 a:3: a
+  4 b:4: b4
+  4 b:5: c
+  4 b:6: b5
+
+  $ hg up -C 1
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg cp a b
+  $ cat <<EOF > b
+  > a
+  > z
+  > a
+  > EOF
+  $ hg ci -mc -d '3 0'
+  created new head
+  $ hg merge
+  merging b
+  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ cat <<EOF >> b
+  > b4
+  > c
+  > b5
+  > EOF
+  $ echo d >> b
+  $ hg ci -mmerge2 -d '4 0'
+
+annotate after rename merge
+
+  $ hg annotate -nf b
+  0 a: a
+  6 b: z
+  1 a: a
+  3 b: b4
+  4 b: c
+  3 b: b5
+  7 b: d
+
+annotate after rename merge with -l
+(fastannotate differs from annotate)
+
+  $ hg log -Gp -T '{rev}:{node}' -r '0+1+6+7'
+  @    7:6284bb6c38fef984a929862a53bbc71ce9eafa81diff --git a/b b/b
+  |\   --- a/b
+  | :  +++ b/b
+  | :  @@ -1,3 +1,7 @@
+  | :   a
+  | :   z
+  | :   a
+  | :  +b4
+  | :  +c
+  | :  +b5
+  | :  +d
+  | :
+  o :  6:b80e3e32f75a6a67cd4ac85496a11511e9112816diff --git a/a b/b
+  :/   copy from a
+  :    copy to b
+  :    --- a/a
+  :    +++ b/b
+  :    @@ -1,3 +1,3 @@
+  :    -a (?)
+  :     a
+  :    +z
+  :     a
+  :    -a (?)
+  :
+  o  1:762f04898e6684ff713415f7b8a8d53d33f96c92diff --git a/a b/a
+  |  --- a/a
+  |  +++ b/a
+  |  @@ -1,1 +1,3 @@
+  |   a
+  |  +a
+  |  +a
+  |
+  o  0:8435f90966e442695d2ded29fdade2bac5ad8065diff --git a/a b/a
+     new file mode 100644
+     --- /dev/null
+     +++ b/a
+     @@ -0,0 +1,1 @@
+     +a
+  
+
+(note on question marks:
+ the upstream bdiff change (96f2f50d923f+3633403888ae+8c0c75aa3ff4+5c4e2636c1a9
+ +38ed54888617) alters the output so deletion is not always at the end of the
+ output. for example:
+ | a | b | old | new | # old: e1d6aa0e4c3a, new: 8836f13e3c5b
+ |-------------------|
+ | a | a |  a  | -a  |
+ | a | z | +z  |  a  |
+ | a | a |  a  | +z  |
+ |   |   | -a  |  a  |
+ |-------------------|
+ | a | a |     a     |
+ | a | a |     a     |
+ | a |   |    -a     |
+ this leads to more question marks below)
+
+(rev 1 adds two "a"s and rev 6 deletes one "a".
+ the "a" that rev 6 deletes could be either the first or the second "a" of those two "a"s added by rev 1.
+ and that causes the line number difference)
+
+  $ hg annotate -nlf b --config fastannotate.modes=
+  0 a:1: a
+  6 b:2: z
+  1 a:3: a
+  3 b:4: b4
+  4 b:5: c
+  3 b:5: b5
+  7 b:7: d
+
+  $ hg annotate -nlf b
+  0 a:1: a (?)
+  1 a:2: a (?)
+  6 b:2: z
+  1 a:2: a (?)
+  1 a:3: a (?)
+  3 b:4: b4
+  4 b:5: c
+  3 b:5: b5
+  7 b:7: d
+
+Issue2807: alignment of line numbers with -l
+(fastannotate differs from annotate, same reason as above)
+
+  $ echo more >> b
+  $ hg ci -mmore -d '5 0'
+  $ echo more >> b
+  $ hg ci -mmore -d '6 0'
+  $ echo more >> b
+  $ hg ci -mmore -d '7 0'
+  $ hg annotate -nlf b
+   0 a: 1: a (?)
+   1 a: 2: a (?)
+   6 b: 2: z
+   1 a: 2: a (?)
+   1 a: 3: a (?)
+   3 b: 4: b4
+   4 b: 5: c
+   3 b: 5: b5
+   7 b: 7: d
+   8 b: 8: more
+   9 b: 9: more
+  10 b:10: more
+
+linkrev vs rev
+
+  $ hg annotate -r tip -n a
+  0: a
+  1: a
+  1: a
+
+linkrev vs rev with -l
+
+  $ hg annotate -r tip -nl a
+  0:1: a
+  1:2: a
+  1:3: a
+
+Issue589: "undelete" sequence leads to crash
+
+annotate was crashing when trying to --follow something
+
+like A -> B -> A
+
+generate ABA rename configuration
+
+  $ echo foo > foo
+  $ hg add foo
+  $ hg ci -m addfoo
+  $ hg rename foo bar
+  $ hg ci -m renamefoo
+  $ hg rename bar foo
+  $ hg ci -m renamebar
+
+annotate after ABA with follow
+
+  $ hg annotate --follow foo
+  foo: foo
+
+missing file
+
+  $ hg ann nosuchfile
+  abort: nosuchfile: no such file in rev e9e6b4fa872f
+  [255]
+
+annotate file without '\n' on last line
+
+  $ printf "" > c
+  $ hg ci -A -m test -u nobody -d '1 0'
+  adding c
+  $ hg annotate c
+  $ printf "a\nb" > c
+  $ hg ci -m test
+  $ hg annotate c
+  [0-9]+: a (re)
+  [0-9]+: b (re)
+
+Issue3841: check annotation of the file of which filelog includes
+merging between the revision and its ancestor
+
+to reproduce the situation with recent Mercurial, this script uses (1)
+"hg debugsetparents" to merge without ancestor check by "hg merge",
+and (2) the extension to allow filelog merging between the revision
+and its ancestor by overriding "repo._filecommit".
+
+  $ cat > ../legacyrepo.py <<EOF
+  > from mercurial import node, error
+  > def reposetup(ui, repo):
+  >     class legacyrepo(repo.__class__):
+  >         def _filecommit(self, fctx, manifest1, manifest2,
+  >                         linkrev, tr, changelist):
+  >             fname = fctx.path()
+  >             text = fctx.data()
+  >             flog = self.file(fname)
+  >             fparent1 = manifest1.get(fname, node.nullid)
+  >             fparent2 = manifest2.get(fname, node.nullid)
+  >             meta = {}
+  >             copy = fctx.renamed()
+  >             if copy and copy[0] != fname:
+  >                 raise error.Abort('copying is not supported')
+  >             if fparent2 != node.nullid:
+  >                 changelist.append(fname)
+  >                 return flog.add(text, meta, tr, linkrev,
+  >                                 fparent1, fparent2)
+  >             raise error.Abort('only merging is supported')
+  >     repo.__class__ = legacyrepo
+  > EOF
+
+  $ cat > baz <<EOF
+  > 1
+  > 2
+  > 3
+  > 4
+  > 5
+  > EOF
+  $ hg add baz
+  $ hg commit -m "baz:0"
+
+  $ cat > baz <<EOF
+  > 1 baz:1
+  > 2
+  > 3
+  > 4
+  > 5
+  > EOF
+  $ hg commit -m "baz:1"
+
+  $ cat > baz <<EOF
+  > 1 baz:1
+  > 2 baz:2
+  > 3
+  > 4
+  > 5
+  > EOF
+  $ hg debugsetparents 17 17
+  $ hg --config extensions.legacyrepo=../legacyrepo.py  commit -m "baz:2"
+  $ hg debugindexdot .hg/store/data/baz.i
+  digraph G {
+  	-1 -> 0
+  	0 -> 1
+  	1 -> 2
+  	1 -> 2
+  }
+  $ hg annotate baz
+  17: 1 baz:1
+  18: 2 baz:2
+  16: 3
+  16: 4
+  16: 5
+
+  $ cat > baz <<EOF
+  > 1 baz:1
+  > 2 baz:2
+  > 3 baz:3
+  > 4
+  > 5
+  > EOF
+  $ hg commit -m "baz:3"
+
+  $ cat > baz <<EOF
+  > 1 baz:1
+  > 2 baz:2
+  > 3 baz:3
+  > 4 baz:4
+  > 5
+  > EOF
+  $ hg debugsetparents 19 18
+  $ hg --config extensions.legacyrepo=../legacyrepo.py  commit -m "baz:4"
+  $ hg debugindexdot .hg/store/data/baz.i
+  digraph G {
+  	-1 -> 0
+  	0 -> 1
+  	1 -> 2
+  	1 -> 2
+  	2 -> 3
+  	3 -> 4
+  	2 -> 4
+  }
+  $ hg annotate baz
+  17: 1 baz:1
+  18: 2 baz:2
+  19: 3 baz:3
+  20: 4 baz:4
+  16: 5
+
+annotate clean file
+
+  $ hg annotate -ncr "wdir()" foo
+  11 472b18db256d : foo
+
+annotate modified file
+
+  $ echo foofoo >> foo
+  $ hg annotate -r "wdir()" foo
+  11 : foo
+  20+: foofoo
+
+  $ hg annotate -cr "wdir()" foo
+  472b18db256d : foo
+  b6bedd5477e7+: foofoo
+
+  $ hg annotate -ncr "wdir()" foo
+  11 472b18db256d : foo
+  20 b6bedd5477e7+: foofoo
+
+  $ hg annotate --debug -ncr "wdir()" foo
+  11 472b18db256d1e8282064eab4bfdaf48cbfe83cd : foo
+  20 b6bedd5477e797f25e568a6402d4697f3f895a72+: foofoo
+
+  $ hg annotate -udr "wdir()" foo
+  test Thu Jan 01 00:00:00 1970 +0000: foo
+  test [A-Za-z0-9:+ ]+: foofoo (re)
+
+  $ hg annotate -ncr "wdir()" -Tjson foo
+  [
+   {
+    "abspath": "foo",
+    "lines": [{"line": "foo\n", "node": "472b18db256d1e8282064eab4bfdaf48cbfe83cd", "rev": 11}, {"line": "foofoo\n", "node": null, "rev": null}],
+    "path": "foo"
+   }
+  ]
+
+annotate added file
+
+  $ echo bar > bar
+  $ hg add bar
+  $ hg annotate -ncr "wdir()" bar
+  20 b6bedd5477e7+: bar
+
+annotate renamed file
+
+  $ hg rename foo renamefoo2
+  $ hg annotate -ncr "wdir()" renamefoo2
+  11 472b18db256d : foo
+  20 b6bedd5477e7+: foofoo
+
+annotate missing file
+
+  $ rm baz
+#if windows
+  $ hg annotate -ncr "wdir()" baz
+  abort: $TESTTMP\repo\baz: The system cannot find the file specified
+  [255]
+#else
+  $ hg annotate -ncr "wdir()" baz
+  abort: $ENOENT$: $TESTTMP/repo/baz
+  [255]
+#endif
+
+annotate removed file
+
+  $ hg rm baz
+#if windows
+  $ hg annotate -ncr "wdir()" baz
+  abort: $TESTTMP\repo\baz: The system cannot find the file specified
+  [255]
+#else
+  $ hg annotate -ncr "wdir()" baz
+  abort: $ENOENT$: $TESTTMP/repo/baz
+  [255]
+#endif
+
+Test annotate with whitespace options
+
+  $ cd ..
+  $ hg init repo-ws
+  $ cd repo-ws
+  $ cat > a <<EOF
+  > aa
+  > 
+  > b b
+  > EOF
+  $ hg ci -Am "adda"
+  adding a
+  $ sed 's/EOL$//g' > a <<EOF
+  > a  a
+  > 
+  >  EOL
+  > b  b
+  > EOF
+  $ hg ci -m "changea"
+
+Annotate with no option
+
+  $ hg annotate a
+  1: a  a
+  0: 
+  1:  
+  1: b  b
+
+Annotate with --ignore-space-change
+
+  $ hg annotate --ignore-space-change a
+  1: a  a
+  1: 
+  0:  
+  0: b  b
+
+Annotate with --ignore-all-space
+
+  $ hg annotate --ignore-all-space a
+  0: a  a
+  0: 
+  1:  
+  0: b  b
+
+Annotate with --ignore-blank-lines (similar to no options case)
+
+  $ hg annotate --ignore-blank-lines a
+  1: a  a
+  0: 
+  1:  
+  1: b  b
+
+  $ cd ..
+
+Annotate with linkrev pointing to another branch
+------------------------------------------------
+
+create history with a filerev whose linkrev points to another branch
+
+  $ hg init branchedlinkrev
+  $ cd branchedlinkrev
+  $ echo A > a
+  $ hg commit -Am 'contentA'
+  adding a
+  $ echo B >> a
+  $ hg commit -m 'contentB'
+  $ hg up --rev 'desc(contentA)'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ echo unrelated > unrelated
+  $ hg commit -Am 'unrelated'
+  adding unrelated
+  created new head
+  $ hg graft -r 'desc(contentB)'
+  grafting 1:fd27c222e3e6 "contentB"
+  $ echo C >> a
+  $ hg commit -m 'contentC'
+  $ echo W >> a
+  $ hg log -G
+  @  changeset:   4:072f1e8df249
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     contentC
+  |
+  o  changeset:   3:ff38df03cc4b
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     contentB
+  |
+  o  changeset:   2:62aaf3f6fc06
+  |  parent:      0:f0932f74827e
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     unrelated
+  |
+  | o  changeset:   1:fd27c222e3e6
+  |/   user:        test
+  |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    summary:     contentB
+  |
+  o  changeset:   0:f0932f74827e
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     contentA
+  
+
+Annotate should list ancestor of starting revision only
+
+  $ hg annotate a
+  0: A
+  3: B
+  4: C
+
+  $ hg annotate a -r 'wdir()'
+  0 : A
+  3 : B
+  4 : C
+  4+: W
+
+Even when the starting revision is the linkrev-shadowed one:
+
+  $ hg annotate a -r 3
+  0: A
+  3: B
+
+  $ cd ..
+
+Issue5360: Deleted chunk in p1 of a merge changeset
+
+  $ hg init repo-5360
+  $ cd repo-5360
+  $ echo 1 > a
+  $ hg commit -A a -m 1
+  $ echo 2 >> a
+  $ hg commit -m 2
+  $ echo a > a
+  $ hg commit -m a
+  $ hg update '.^' -q
+  $ echo 3 >> a
+  $ hg commit -m 3 -q
+  $ hg merge 2 -q
+  $ cat > a << EOF
+  > b
+  > 1
+  > 2
+  > 3
+  > a
+  > EOF
+  $ hg resolve --mark -q
+  $ hg commit -m m
+  $ hg annotate a
+  4: b
+  0: 1
+  1: 2
+  3: 3
+  2: a
+
+  $ cd ..
diff --git a/tests/test-fastannotate-diffopts.t b/tests/test-fastannotate-diffopts.t
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate-diffopts.t
@@ -0,0 +1,33 @@ 
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > fastannotate=
+  > EOF
+
+  $ hg init repo
+  $ cd repo
+
+changes to whitespaces
+
+  $ cat >> a << EOF
+  > 1
+  > 
+  >  
+  >  2
+  > EOF
+  $ hg commit -qAm '1'
+  $ cat > a << EOF
+  >  1
+  > 
+  > 2
+  > 
+  > 
+  > 3
+  > EOF
+  $ hg commit -m 2
+  $ hg fastannotate -wB a
+  0:  1
+  0: 
+  1: 2
+  0: 
+  1: 
+  1: 3
diff --git a/tests/test-fastannotate-corrupt.t b/tests/test-fastannotate-corrupt.t
new file mode 100644
--- /dev/null
+++ b/tests/test-fastannotate-corrupt.t
@@ -0,0 +1,83 @@ 
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > fastannotate=
+  > EOF
+
+  $ hg init repo
+  $ cd repo
+  $ for i in 0 1 2 3 4; do
+  >   echo $i >> a
+  >   echo $i >> b
+  >   hg commit -A -m $i a b
+  > done
+
+use the "debugbuildannotatecache" command to build annotate cache at rev 0
+
+  $ hg debugbuildannotatecache --debug --config fastannotate.mainbranch=0
+  fastannotate: a: 1 new changesets in the main branch
+  fastannotate: b: 1 new changesets in the main branch
+
+"debugbuildannotatecache" should work with broken cache (and other files would
+be built without being affected). note: linelog being broken is only noticed
+when we try to append to it.
+
+  $ echo 'CORRUPT!' >> .hg/fastannotate/default/a.m
+  $ hg debugbuildannotatecache --debug --config fastannotate.mainbranch=1
+  fastannotate: a: rebuilding broken cache
+  fastannotate: a: 2 new changesets in the main branch
+  fastannotate: b: 1 new changesets in the main branch
+
+  $ echo 'CANNOT REUSE!' > .hg/fastannotate/default/a.l
+  $ hg debugbuildannotatecache --debug --config fastannotate.mainbranch=2
+  fastannotate: a: rebuilding broken cache
+  fastannotate: a: 3 new changesets in the main branch
+  fastannotate: b: 1 new changesets in the main branch
+
+  $ rm .hg/fastannotate/default/a.m
+  $ hg debugbuildannotatecache --debug --config fastannotate.mainbranch=3
+  fastannotate: a: rebuilding broken cache
+  fastannotate: a: 4 new changesets in the main branch
+  fastannotate: b: 1 new changesets in the main branch
+
+  $ rm .hg/fastannotate/default/a.l
+  $ hg debugbuildannotatecache --debug --config fastannotate.mainbranch=3
+  $ hg debugbuildannotatecache --debug --config fastannotate.mainbranch=4
+  fastannotate: a: rebuilding broken cache
+  fastannotate: a: 5 new changesets in the main branch
+  fastannotate: b: 1 new changesets in the main branch
+
+"fastannotate" should deal with file corruption as well
+
+  $ rm -rf .hg/fastannotate
+  $ hg fastannotate --debug -r 0 a
+  fastannotate: a: 1 new changesets in the main branch
+  0: 0
+
+  $ echo 'CORRUPT!' >> .hg/fastannotate/default/a.m
+  $ hg fastannotate --debug -r 0 a
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 1 new changesets in the main branch
+  0: 0
+
+  $ echo 'CORRUPT!' > .hg/fastannotate/default/a.l
+  $ hg fastannotate --debug -r 1 a
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 2 new changesets in the main branch
+  0: 0
+  1: 1
+
+  $ rm .hg/fastannotate/default/a.l
+  $ hg fastannotate --debug -r 1 a
+  fastannotate: a: using fast path (resolved fctx: True)
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 2 new changesets in the main branch
+  0: 0
+  1: 1
+
+  $ rm .hg/fastannotate/default/a.m
+  $ hg fastannotate --debug -r 2 a
+  fastannotate: a: cache broken and deleted
+  fastannotate: a: 3 new changesets in the main branch
+  0: 0
+  1: 1
+  2: 2
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -818,6 +818,7 @@ 
             'mercurial.thirdparty.zope.interface',
             'mercurial.utils',
             'hgext', 'hgext.convert', 'hgext.fsmonitor',
+            'hgext.fastannotate',
             'hgext.fsmonitor.pywatchman',
             'hgext.infinitepush',
             'hgext.highlight',
diff --git a/hgext/fastannotate/support.py b/hgext/fastannotate/support.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/support.py
@@ -0,0 +1,131 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# support: fastannotate support for hgweb, and filectx
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+from mercurial import (
+    context as hgcontext,
+    dagop,
+    extensions,
+    hgweb,
+    patch,
+    util,
+)
+
+from . import (
+    context,
+    revmap,
+)
+
+class _lazyfctx(object):
+    """delegates to fctx but do not construct fctx when unnecessary"""
+
+    def __init__(self, repo, node, path):
+        self._node = node
+        self._path = path
+        self._repo = repo
+
+    def node(self):
+        return self._node
+
+    def path(self):
+        return self._path
+
+    @util.propertycache
+    def _fctx(self):
+        return context.resolvefctx(self._repo, self._node, self._path)
+
+    def __getattr__(self, name):
+        return getattr(self._fctx, name)
+
+def _convertoutputs(repo, annotated, contents):
+    """convert fastannotate outputs to vanilla annotate format"""
+    # fastannotate returns: [(nodeid, linenum, path)], [linecontent]
+    # convert to what fctx.annotate returns: [annotateline]
+    results = []
+    fctxmap = {}
+    annotateline = dagop.annotateline
+    for i, (hsh, linenum, path) in enumerate(annotated):
+        if (hsh, path) not in fctxmap:
+            fctxmap[(hsh, path)] = _lazyfctx(repo, hsh, path)
+        # linenum: the user wants 1-based, we have 0-based.
+        lineno = linenum + 1
+        fctx = fctxmap[(hsh, path)]
+        line = contents[i]
+        results.append(annotateline(fctx=fctx, lineno=lineno, text=line))
+    return results
+
+def _getmaster(fctx):
+    """(fctx) -> str"""
+    return fctx._repo.ui.config('fastannotate', 'mainbranch') or 'default'
+
+def _doannotate(fctx, follow=True, diffopts=None):
+    """like the vanilla fctx.annotate, but do it via fastannotate, and make
+    the output format compatible with the vanilla fctx.annotate.
+    may raise Exception, and always return line numbers.
+    """
+    master = _getmaster(fctx)
+    annotated = contents = None
+
+    with context.fctxannotatecontext(fctx, follow, diffopts) as ac:
+        try:
+            annotated, contents = ac.annotate(fctx.rev(), master=master,
+                                              showpath=True, showlines=True)
+        except Exception:
+            ac.rebuild() # try rebuild once
+            fctx._repo.ui.debug('fastannotate: %s: rebuilding broken cache\n'
+                                % fctx._path)
+            try:
+                annotated, contents = ac.annotate(fctx.rev(), master=master,
+                                                  showpath=True, showlines=True)
+            except Exception:
+                raise
+
+    assert annotated and contents
+    return _convertoutputs(fctx._repo, annotated, contents)
+
+def _hgwebannotate(orig, fctx, ui):
+    diffopts = patch.difffeatureopts(ui, untrusted=True,
+                                     section='annotate', whitespace=True)
+    return _doannotate(fctx, diffopts=diffopts)
+
+def _fctxannotate(orig, self, follow=False, linenumber=False, skiprevs=None,
+                  diffopts=None):
+    if skiprevs:
+        # skiprevs is not supported yet
+        return orig(self, follow, linenumber, skiprevs=skiprevs,
+                    diffopts=diffopts)
+    try:
+        return _doannotate(self, follow, diffopts)
+    except Exception as ex:
+        self._repo.ui.debug('fastannotate: falling back to the vanilla '
+                            'annotate: %r\n' % ex)
+        return orig(self, follow=follow, skiprevs=skiprevs,
+                    diffopts=diffopts)
+
+def _remotefctxannotate(orig, self, follow=False, skiprevs=None, diffopts=None):
+    # skipset: a set-like used to test if a fctx needs to be downloaded
+    skipset = None
+    with context.fctxannotatecontext(self, follow, diffopts) as ac:
+        skipset = revmap.revmap(ac.revmappath)
+    return orig(self, follow, skiprevs=skiprevs, diffopts=diffopts,
+                prefetchskip=skipset)
+
+def replacehgwebannotate():
+    extensions.wrapfunction(hgweb.webutil, 'annotate', _hgwebannotate)
+
+def replacefctxannotate():
+    extensions.wrapfunction(hgcontext.basefilectx, 'annotate', _fctxannotate)
+
+def replaceremotefctxannotate():
+    try:
+        r = extensions.find('remotefilelog')
+    except KeyError:
+        return
+    else:
+        extensions.wrapfunction(r.remotefilectx.remotefilectx, 'annotate',
+                                _remotefctxannotate)
diff --git a/hgext/fastannotate/revmap.py b/hgext/fastannotate/revmap.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/revmap.py
@@ -0,0 +1,254 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# revmap: trivial hg hash - linelog rev bidirectional map
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+import bisect
+import os
+import struct
+
+from mercurial.node import hex
+from mercurial import (
+    error as hgerror,
+    pycompat,
+)
+from . import error
+
+# the revmap file format is straightforward:
+#
+#    8 bytes: header
+#    1 byte : flag for linelog revision 1
+#    ? bytes: (optional) '\0'-terminated path string
+#             only exists if (flag & renameflag) != 0
+#   20 bytes: hg hash for linelog revision 1
+#    1 byte : flag for linelog revision 2
+#    ? bytes: (optional) '\0'-terminated path string
+#   20 bytes: hg hash for linelog revision 2
+#   ....
+#
+# the implementation is kinda stupid: __init__ loads the whole revmap.
+# no laziness. benchmark shows loading 10000 revisions is about 0.015
+# seconds, which looks enough for our use-case. if this implementation
+# becomes a bottleneck, we can change it to lazily read the file
+# from the end.
+
+# whether the changeset is in the side branch. i.e. not in the linear main
+# branch but only got referenced by lines in merge changesets.
+sidebranchflag = 1
+
+# whether the changeset changes the file path (ie. is a rename)
+renameflag = 2
+
+# len(mercurial.node.nullid)
+_hshlen = 20
+
+class revmap(object):
+    """trivial hg bin hash - linelog rev bidirectional map
+
+    also stores a flag (uint8) for each revision, and track renames.
+    """
+
+    HEADER = b'REVMAP1\0'
+
+    def __init__(self, path=None):
+        """create or load the revmap, optionally associate to a file
+
+        if path is None, the revmap is entirely in-memory. the caller is
+        responsible for locking. concurrent writes to a same file is unsafe.
+        the caller needs to make sure one file is associated to at most one
+        revmap object at a time."""
+        self.path = path
+        self._rev2hsh = [None]
+        self._rev2flag = [None]
+        self._hsh2rev = {}
+        # since rename does not happen frequently, do not store path for every
+        # revision. self._renamerevs can be used for bisecting.
+        self._renamerevs = [0]
+        self._renamepaths = ['']
+        self._lastmaxrev = -1
+        if path:
+            if os.path.exists(path):
+                self._load()
+            else:
+                # write the header so "append" can do incremental updates
+                self.flush()
+
+    def copyfrom(self, rhs):
+        """copy the map data from another revmap. do not affect self.path"""
+        self._rev2hsh = rhs._rev2hsh[:]
+        self._rev2flag = rhs._rev2flag[:]
+        self._hsh2rev = rhs._hsh2rev.copy()
+        self._renamerevs = rhs._renamerevs[:]
+        self._renamepaths = rhs._renamepaths[:]
+        self._lastmaxrev = -1
+
+    @property
+    def maxrev(self):
+        """return max linelog revision number"""
+        return len(self._rev2hsh) - 1
+
+    def append(self, hsh, sidebranch=False, path=None, flush=False):
+        """add a binary hg hash and return the mapped linelog revision.
+        if flush is True, incrementally update the file.
+        """
+        if hsh in self._hsh2rev:
+            raise error.CorruptedFileError('%r is in revmap already' % hex(hsh))
+        if len(hsh) != _hshlen:
+            raise hgerror.ProgrammingError('hsh must be %d-char long' % _hshlen)
+        idx = len(self._rev2hsh)
+        flag = 0
+        if sidebranch:
+            flag |= sidebranchflag
+        if path is not None and path != self._renamepaths[-1]:
+            flag |= renameflag
+            self._renamerevs.append(idx)
+            self._renamepaths.append(path)
+        self._rev2hsh.append(hsh)
+        self._rev2flag.append(flag)
+        self._hsh2rev[hsh] = idx
+        if flush:
+            self.flush()
+        return idx
+
+    def rev2hsh(self, rev):
+        """convert linelog revision to hg hash. return None if not found."""
+        if rev > self.maxrev or rev < 0:
+            return None
+        return self._rev2hsh[rev]
+
+    def rev2flag(self, rev):
+        """get the flag (uint8) for a given linelog revision.
+        return None if revision does not exist.
+        """
+        if rev > self.maxrev or rev < 0:
+            return None
+        return self._rev2flag[rev]
+
+    def rev2path(self, rev):
+        """get the path for a given linelog revision.
+        return None if revision does not exist.
+        """
+        if rev > self.maxrev or rev < 0:
+            return None
+        idx = bisect.bisect_right(self._renamerevs, rev) - 1
+        return self._renamepaths[idx]
+
+    def hsh2rev(self, hsh):
+        """convert hg hash to linelog revision. return None if not found."""
+        return self._hsh2rev.get(hsh)
+
+    def clear(self, flush=False):
+        """make the map empty. if flush is True, write to disk"""
+        # rev 0 is reserved, real rev starts from 1
+        self._rev2hsh = [None]
+        self._rev2flag = [None]
+        self._hsh2rev = {}
+        self._rev2path = ['']
+        self._lastmaxrev = -1
+        if flush:
+            self.flush()
+
+    def flush(self):
+        """write the state down to the file"""
+        if not self.path:
+            return
+        if self._lastmaxrev == -1: # write the entire file
+            with open(self.path, 'wb') as f:
+                f.write(self.HEADER)
+                for i in pycompat.xrange(1, len(self._rev2hsh)):
+                    self._writerev(i, f)
+        else: # append incrementally
+            with open(self.path, 'ab') as f:
+                for i in pycompat.xrange(self._lastmaxrev + 1,
+                                         len(self._rev2hsh)):
+                    self._writerev(i, f)
+        self._lastmaxrev = self.maxrev
+
+    def _load(self):
+        """load state from file"""
+        if not self.path:
+            return
+        # use local variables in a loop. CPython uses LOAD_FAST for them,
+        # which is faster than both LOAD_CONST and LOAD_GLOBAL.
+        flaglen = 1
+        hshlen = _hshlen
+        with open(self.path, 'rb') as f:
+            if f.read(len(self.HEADER)) != self.HEADER:
+                raise error.CorruptedFileError()
+            self.clear(flush=False)
+            while True:
+                buf = f.read(flaglen)
+                if not buf:
+                    break
+                flag = ord(buf)
+                rev = len(self._rev2hsh)
+                if flag & renameflag:
+                    path = self._readcstr(f)
+                    self._renamerevs.append(rev)
+                    self._renamepaths.append(path)
+                hsh = f.read(hshlen)
+                if len(hsh) != hshlen:
+                    raise error.CorruptedFileError()
+                self._hsh2rev[hsh] = rev
+                self._rev2flag.append(flag)
+                self._rev2hsh.append(hsh)
+        self._lastmaxrev = self.maxrev
+
+    def _writerev(self, rev, f):
+        """append a revision data to file"""
+        flag = self._rev2flag[rev]
+        hsh = self._rev2hsh[rev]
+        f.write(struct.pack('B', flag))
+        if flag & renameflag:
+            path = self.rev2path(rev)
+            if path is None:
+                raise error.CorruptedFileError('cannot find path for %s' % rev)
+            f.write(path + '\0')
+        f.write(hsh)
+
+    @staticmethod
+    def _readcstr(f):
+        """read a C-language-like '\0'-terminated string"""
+        buf = ''
+        while True:
+            ch = f.read(1)
+            if not ch: # unexpected eof
+                raise error.CorruptedFileError()
+            if ch == '\0':
+                break
+            buf += ch
+        return buf
+
+    def __contains__(self, f):
+        """(fctx or (node, path)) -> bool.
+        test if (node, path) is in the map, and is not in a side branch.
+        f can be either a tuple of (node, path), or a fctx.
+        """
+        if isinstance(f, tuple): # f: (node, path)
+            hsh, path = f
+        else: # f: fctx
+            hsh, path = f.node(), f.path()
+        rev = self.hsh2rev(hsh)
+        if rev is None:
+            return False
+        if path is not None and path != self.rev2path(rev):
+            return False
+        return (self.rev2flag(rev) & sidebranchflag) == 0
+
+def getlastnode(path):
+    """return the last hash in a revmap, without loading its full content.
+    this is equivalent to `m = revmap(path); m.rev2hsh(m.maxrev)`, but faster.
+    """
+    hsh = None
+    try:
+        with open(path, 'rb') as f:
+            f.seek(-_hshlen, 2)
+            if f.tell() > len(revmap.HEADER):
+                hsh = f.read(_hshlen)
+    except IOError:
+        pass
+    return hsh
diff --git a/hgext/fastannotate/protocol.py b/hgext/fastannotate/protocol.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/protocol.py
@@ -0,0 +1,250 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# protocol: logic for a server providing fastannotate support
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+from __future__ import absolute_import
+
+import contextlib
+import os
+
+from mercurial.i18n import _
+from mercurial import (
+    error,
+    extensions,
+    hg,
+    localrepo,
+    scmutil,
+    wireprotov1peer,
+    wireprotov1server,
+)
+from . import context
+
+# common
+
+def _getmaster(ui):
+    """get the mainbranch, and enforce it is set"""
+    master = ui.config('fastannotate', 'mainbranch')
+    if not master:
+        raise error.Abort(_('fastannotate.mainbranch is required '
+                            'for both the client and the server'))
+    return master
+
+# server-side
+
+def _capabilities(orig, repo, proto):
+    result = orig(repo, proto)
+    result.append('getannotate')
+    return result
+
+def _getannotate(repo, proto, path, lastnode):
+    # output:
+    #   FILE := vfspath + '\0' + str(size) + '\0' + content
+    #   OUTPUT := '' | FILE + OUTPUT
+    result = ''
+    buildondemand = repo.ui.configbool('fastannotate', 'serverbuildondemand',
+                                       True)
+    with context.annotatecontext(repo, path) as actx:
+        if buildondemand:
+            # update before responding to the client
+            master = _getmaster(repo.ui)
+            try:
+                if not actx.isuptodate(master):
+                    actx.annotate(master, master)
+            except Exception:
+                # non-fast-forward move or corrupted. rebuild automically.
+                actx.rebuild()
+                try:
+                    actx.annotate(master, master)
+                except Exception:
+                    actx.rebuild() # delete files
+            finally:
+                # although the "with" context will also do a close/flush, we
+                # need to do it early so we can send the correct respond to
+                # client.
+                actx.close()
+        # send back the full content of revmap and linelog, in the future we
+        # may want to do some rsync-like fancy updating.
+        # the lastnode check is not necessary if the client and the server
+        # agree where the main branch is.
+        if actx.lastnode != lastnode:
+            for p in [actx.revmappath, actx.linelogpath]:
+                if not os.path.exists(p):
+                    continue
+                content = ''
+                with open(p, 'rb') as f:
+                    content = f.read()
+                vfsbaselen = len(repo.vfs.base + '/')
+                relpath = p[vfsbaselen:]
+                result += '%s\0%s\0%s' % (relpath, len(content), content)
+    return result
+
+def _registerwireprotocommand():
+    if 'getannotate' in wireprotov1server.commands:
+        return
+    wireprotov1server.wireprotocommand(
+        'getannotate', 'path lastnode')(_getannotate)
+
+def serveruisetup(ui):
+    _registerwireprotocommand()
+    extensions.wrapfunction(wireprotov1server, '_capabilities', _capabilities)
+
+# client-side
+
+def _parseresponse(payload):
+    result = {}
+    i = 0
+    l = len(payload) - 1
+    state = 0 # 0: vfspath, 1: size
+    vfspath = size = ''
+    while i < l:
+        ch = payload[i]
+        if ch == '\0':
+            if state == 1:
+                result[vfspath] = buffer(payload, i + 1, int(size))
+                i += int(size)
+                state = 0
+                vfspath = size = ''
+            elif state == 0:
+                state = 1
+        else:
+            if state == 1:
+                size += ch
+            elif state == 0:
+                vfspath += ch
+        i += 1
+    return result
+
+def peersetup(ui, peer):
+    class fastannotatepeer(peer.__class__):
+        @wireprotov1peer.batchable
+        def getannotate(self, path, lastnode=None):
+            if not self.capable('getannotate'):
+                ui.warn(_('remote peer cannot provide annotate cache\n'))
+                yield None, None
+            else:
+                args = {'path': path, 'lastnode': lastnode or ''}
+                f = wireprotov1peer.future()
+                yield args, f
+                yield _parseresponse(f.value)
+    peer.__class__ = fastannotatepeer
+
+@contextlib.contextmanager
+def annotatepeer(repo):
+    ui = repo.ui
+
+    # fileservice belongs to remotefilelog
+    fileservice = getattr(repo, 'fileservice', None)
+    sharepeer = ui.configbool('fastannotate', 'clientsharepeer', True)
+
+    if sharepeer and fileservice:
+        ui.debug('fastannotate: using remotefilelog connection pool\n')
+        conn = repo.connectionpool.get(repo.fallbackpath)
+        peer = conn.peer
+        stolen = True
+    else:
+        remotepath = ui.expandpath(
+            ui.config('fastannotate', 'remotepath', 'default'))
+        peer = hg.peer(ui, {}, remotepath)
+        stolen = False
+
+    try:
+        # Note: fastannotate requests should never trigger a remotefilelog
+        # "getfiles" request, because "getfiles" puts the stream into a state
+        # that does not exit. See "clientfetch": it does "getannotate" before
+        # any hg stuff that could potentially trigger a "getfiles".
+        yield peer
+    finally:
+        if not stolen:
+            for i in ['close', 'cleanup']:
+                getattr(peer, i, lambda: None)()
+        else:
+            conn.__exit__(None, None, None)
+
+def clientfetch(repo, paths, lastnodemap=None, peer=None):
+    """download annotate cache from the server for paths"""
+    if not paths:
+        return
+
+    if peer is None:
+        with annotatepeer(repo) as peer:
+            return clientfetch(repo, paths, lastnodemap, peer)
+
+    if lastnodemap is None:
+        lastnodemap = {}
+
+    ui = repo.ui
+    results = []
+    with peer.commandexecutor() as batcher:
+        ui.debug('fastannotate: requesting %d files\n' % len(paths))
+        for p in paths:
+            results.append(batcher.callcommand(
+                'getannotate',
+                {'path': p, 'lastnode':lastnodemap.get(p)}))
+
+    ui.debug('fastannotate: server returned\n')
+    for result in results:
+        for path, content in result.result().iteritems():
+            # ignore malicious paths
+            if not path.startswith('fastannotate/') or '/../' in (path + '/'):
+                ui.debug('fastannotate: ignored malicious path %s\n' % path)
+                continue
+            if ui.debugflag:
+                ui.debug('fastannotate: writing %d bytes to %s\n'
+                         % (len(content), path))
+            repo.vfs.makedirs(os.path.dirname(path))
+            with repo.vfs(path, 'wb') as f:
+                f.write(content)
+
+def _filterfetchpaths(repo, paths):
+    """return a subset of paths whose history is long and need to fetch linelog
+    from the server. works with remotefilelog and non-remotefilelog repos.
+    """
+    threshold = repo.ui.configint('fastannotate', 'clientfetchthreshold', 10)
+    if threshold <= 0:
+        return paths
+
+    master = repo.ui.config('fastannotate', 'mainbranch') or 'default'
+
+    if 'remotefilelog' in repo.requirements:
+        ctx = scmutil.revsingle(repo, master)
+        f = lambda path: len(ctx[path].ancestormap())
+    else:
+        f = lambda path: len(repo.file(path))
+
+    result = []
+    for path in paths:
+        try:
+            if f(path) >= threshold:
+                result.append(path)
+        except Exception: # file not found etc.
+            result.append(path)
+
+    return result
+
+def localreposetup(ui, repo):
+    class fastannotaterepo(repo.__class__):
+        def prefetchfastannotate(self, paths, peer=None):
+            master = _getmaster(self.ui)
+            needupdatepaths = []
+            lastnodemap = {}
+            try:
+                for path in _filterfetchpaths(self, paths):
+                    with context.annotatecontext(self, path) as actx:
+                        if not actx.isuptodate(master, strict=False):
+                            needupdatepaths.append(path)
+                            lastnodemap[path] = actx.lastnode
+                if needupdatepaths:
+                    clientfetch(self, needupdatepaths, lastnodemap, peer)
+            except Exception as ex:
+                # could be directory not writable or so, not fatal
+                self.ui.debug('fastannotate: prefetch failed: %r\n' % ex)
+    repo.__class__ = fastannotaterepo
+
+def clientreposetup(ui, repo):
+    _registerwireprotocommand()
+    if isinstance(repo, localrepo.localrepository):
+        localreposetup(ui, repo)
+    if peersetup not in hg.wirepeersetupfuncs:
+        hg.wirepeersetupfuncs.append(peersetup)
diff --git a/hgext/fastannotate/formatter.py b/hgext/fastannotate/formatter.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/formatter.py
@@ -0,0 +1,161 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# format: defines the format used to output annotate result
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+from __future__ import absolute_import
+
+from mercurial import (
+    encoding,
+    node,
+    pycompat,
+    templatefilters,
+    util,
+)
+from mercurial.utils import (
+        dateutil,
+)
+
+# imitating mercurial.commands.annotate, not using the vanilla formatter since
+# the data structures are a bit different, and we have some fast paths.
+class defaultformatter(object):
+    """the default formatter that does leftpad and support some common flags"""
+
+    def __init__(self, ui, repo, opts):
+        self.ui = ui
+        self.opts = opts
+
+        if ui.quiet:
+            datefunc = dateutil.shortdate
+        else:
+            datefunc = dateutil.datestr
+        datefunc = util.cachefunc(datefunc)
+        getctx = util.cachefunc(lambda x: repo[x[0]])
+        hexfunc = self._hexfunc
+
+        # special handling working copy "changeset" and "rev" functions
+        if self.opts.get('rev') == 'wdir()':
+            orig = hexfunc
+            hexfunc = lambda x: None if x is None else orig(x)
+            wnode = hexfunc(repo[None].p1().node()) + '+'
+            wrev = str(repo[None].p1().rev())
+            wrevpad = ''
+            if not opts.get('changeset'): # only show + if changeset is hidden
+                wrev += '+'
+                wrevpad = ' '
+            revenc = lambda x: wrev if x is None else str(x) + wrevpad
+            csetenc = lambda x: wnode if x is None else str(x) + ' '
+        else:
+            revenc = csetenc = str
+
+        # opt name, separator, raw value (for json/plain), encoder (for plain)
+        opmap = [('user', ' ', lambda x: getctx(x).user(), ui.shortuser),
+                 ('number', ' ', lambda x: getctx(x).rev(), revenc),
+                 ('changeset', ' ', lambda x: hexfunc(x[0]), csetenc),
+                 ('date', ' ', lambda x: getctx(x).date(), datefunc),
+                 ('file', ' ', lambda x: x[2], str),
+                 ('line_number', ':', lambda x: x[1] + 1, str)]
+        fieldnamemap = {'number': 'rev', 'changeset': 'node'}
+        funcmap = [(get, sep, fieldnamemap.get(op, op), enc)
+                   for op, sep, get, enc in opmap
+                   if opts.get(op)]
+        # no separator for first column
+        funcmap[0] = list(funcmap[0])
+        funcmap[0][1] = ''
+        self.funcmap = funcmap
+
+    def write(self, annotatedresult, lines=None, existinglines=None):
+        """(annotateresult, [str], set([rev, linenum])) -> None. write output.
+        annotateresult can be [(node, linenum, path)], or [(node, linenum)]
+        """
+        pieces = [] # [[str]]
+        maxwidths = [] # [int]
+
+        # calculate padding
+        for f, sep, name, enc in self.funcmap:
+            l = [enc(f(x)) for x in annotatedresult]
+            pieces.append(l)
+            if name in ['node', 'date']: # node and date has fixed size
+                l = l[:1]
+            widths = map(encoding.colwidth, set(l))
+            maxwidth = (max(widths) if widths else 0)
+            maxwidths.append(maxwidth)
+
+        # buffered output
+        result = ''
+        for i in pycompat.xrange(len(annotatedresult)):
+            for j, p in enumerate(pieces):
+                sep = self.funcmap[j][1]
+                padding = ' ' * (maxwidths[j] - len(p[i]))
+                result += sep + padding + p[i]
+            if lines:
+                if existinglines is None:
+                    result += ': ' + lines[i]
+                else: # extra formatting showing whether a line exists
+                    key = (annotatedresult[i][0], annotatedresult[i][1])
+                    if key in existinglines:
+                        result += ':  ' + lines[i]
+                    else:
+                        result += ': ' + self.ui.label('-' + lines[i],
+                                                       'diff.deleted')
+
+            if result[-1] != '\n':
+                result += '\n'
+
+        self.ui.write(result)
+
+    @util.propertycache
+    def _hexfunc(self):
+        if self.ui.debugflag or self.opts.get('long_hash'):
+            return node.hex
+        else:
+            return node.short
+
+    def end(self):
+        pass
+
+class jsonformatter(defaultformatter):
+    def __init__(self, ui, repo, opts):
+        super(jsonformatter, self).__init__(ui, repo, opts)
+        self.ui.write('[')
+        self.needcomma = False
+
+    def write(self, annotatedresult, lines=None, existinglines=None):
+        if annotatedresult:
+            self._writecomma()
+
+        pieces = [(name, map(f, annotatedresult))
+                  for f, sep, name, enc in self.funcmap]
+        if lines is not None:
+            pieces.append(('line', lines))
+        pieces.sort()
+
+        seps = [','] * len(pieces[:-1]) + ['']
+
+        result = ''
+        lasti = len(annotatedresult) - 1
+        for i in pycompat.xrange(len(annotatedresult)):
+            result += '\n {\n'
+            for j, p in enumerate(pieces):
+                k, vs = p
+                result += ('  "%s": %s%s\n'
+                           % (k, templatefilters.json(vs[i], paranoid=False),
+                              seps[j]))
+            result += ' }%s' % ('' if i == lasti else ',')
+        if lasti >= 0:
+            self.needcomma = True
+
+        self.ui.write(result)
+
+    def _writecomma(self):
+        if self.needcomma:
+            self.ui.write(',')
+            self.needcomma = False
+
+    @util.propertycache
+    def _hexfunc(self):
+        return node.hex
+
+    def end(self):
+        self.ui.write('\n]\n')
diff --git a/hgext/fastannotate/error.py b/hgext/fastannotate/error.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/error.py
@@ -0,0 +1,13 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# error: errors used in fastannotate
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+from __future__ import absolute_import
+
+class CorruptedFileError(Exception):
+    pass
+
+class CannotReuseError(Exception):
+    """cannot reuse or update the cache incrementally"""
diff --git a/hgext/fastannotate/context.py b/hgext/fastannotate/context.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/context.py
@@ -0,0 +1,823 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# context: context needed to annotate a file
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+import collections
+import contextlib
+import hashlib
+import os
+
+from mercurial.i18n import _
+from mercurial import (
+    error,
+    linelog as linelogmod,
+    lock as lockmod,
+    mdiff,
+    node,
+    pycompat,
+    scmutil,
+    util,
+)
+
+from . import (
+    error as faerror,
+    revmap as revmapmod,
+)
+
+# given path, get filelog, cached
+@util.lrucachefunc
+def _getflog(repo, path):
+    return repo.file(path)
+
+# extracted from mercurial.context.basefilectx.annotate
+def _parents(f, follow=True):
+    # Cut _descendantrev here to mitigate the penalty of lazy linkrev
+    # adjustment. Otherwise, p._adjustlinkrev() would walk changelog
+    # from the topmost introrev (= srcrev) down to p.linkrev() if it
+    # isn't an ancestor of the srcrev.
+    f._changeid
+    pl = f.parents()
+
+    # Don't return renamed parents if we aren't following.
+    if not follow:
+        pl = [p for p in pl if p.path() == f.path()]
+
+    # renamed filectx won't have a filelog yet, so set it
+    # from the cache to save time
+    for p in pl:
+        if not '_filelog' in p.__dict__:
+            p._filelog = _getflog(f._repo, p.path())
+
+    return pl
+
+# extracted from mercurial.context.basefilectx.annotate. slightly modified
+# so it takes a fctx instead of a pair of text and fctx.
+def _decorate(fctx):
+    text = fctx.data()
+    linecount = text.count('\n')
+    if text and not text.endswith('\n'):
+        linecount += 1
+    return ([(fctx, i) for i in pycompat.xrange(linecount)], text)
+
+# extracted from mercurial.context.basefilectx.annotate. slightly modified
+# so it takes an extra "blocks" parameter calculated elsewhere, instead of
+# calculating diff here.
+def _pair(parent, child, blocks):
+    for (a1, a2, b1, b2), t in blocks:
+        # Changed blocks ('!') or blocks made only of blank lines ('~')
+        # belong to the child.
+        if t == '=':
+            child[0][b1:b2] = parent[0][a1:a2]
+    return child
+
+# like scmutil.revsingle, but with lru cache, so their states (like manifests)
+# could be reused
+_revsingle = util.lrucachefunc(scmutil.revsingle)
+
+def resolvefctx(repo, rev, path, resolverev=False, adjustctx=None):
+    """(repo, str, str) -> fctx
+
+    get the filectx object from repo, rev, path, in an efficient way.
+
+    if resolverev is True, "rev" is a revision specified by the revset
+    language, otherwise "rev" is a nodeid, or a revision number that can
+    be consumed by repo.__getitem__.
+
+    if adjustctx is not None, the returned fctx will point to a changeset
+    that introduces the change (last modified the file). if adjustctx
+    is 'linkrev', trust the linkrev and do not adjust it. this is noticeably
+    faster for big repos but is incorrect for some cases.
+    """
+    if resolverev and not isinstance(rev, int) and rev is not None:
+        ctx = _revsingle(repo, rev)
+    else:
+        ctx = repo[rev]
+
+    # If we don't need to adjust the linkrev, create the filectx using the
+    # changectx instead of using ctx[path]. This means it already has the
+    # changectx information, so blame -u will be able to look directly at the
+    # commitctx object instead of having to resolve it by going through the
+    # manifest. In a lazy-manifest world this can prevent us from downloading a
+    # lot of data.
+    if adjustctx is None:
+        # ctx.rev() is None means it's the working copy, which is a special
+        # case.
+        if ctx.rev() is None:
+            fctx = ctx[path]
+        else:
+            fctx = repo.filectx(path, changeid=ctx.rev())
+    else:
+        fctx = ctx[path]
+        if adjustctx == 'linkrev':
+            introrev = fctx.linkrev()
+        else:
+            introrev = fctx.introrev()
+        if introrev != ctx.rev():
+            fctx._changeid = introrev
+            fctx._changectx = repo[introrev]
+    return fctx
+
+# like mercurial.store.encodedir, but use linelog suffixes: .m, .l, .lock
+def encodedir(path):
+    return (path
+            .replace('.hg/', '.hg.hg/')
+            .replace('.l/', '.l.hg/')
+            .replace('.m/', '.m.hg/')
+            .replace('.lock/', '.lock.hg/'))
+
+def hashdiffopts(diffopts):
+    diffoptstr = str(sorted(
+        (k, getattr(diffopts, k))
+        for k in mdiff.diffopts.defaults.iterkeys()
+    ))
+    return hashlib.sha1(diffoptstr).hexdigest()[:6]
+
+_defaultdiffopthash = hashdiffopts(mdiff.defaultopts)
+
+class annotateopts(object):
+    """like mercurial.mdiff.diffopts, but is for annotate
+
+    followrename: follow renames, like "hg annotate -f"
+    followmerge: follow p2 of a merge changeset, otherwise p2 is ignored
+    """
+
+    defaults = {
+        'diffopts': None,
+        'followrename': True,
+        'followmerge': True,
+    }
+
+    def __init__(self, **opts):
+        for k, v in self.defaults.iteritems():
+            setattr(self, k, opts.get(k, v))
+
+    @util.propertycache
+    def shortstr(self):
+        """represent opts in a short string, suitable for a directory name"""
+        result = ''
+        if not self.followrename:
+            result += 'r0'
+        if not self.followmerge:
+            result += 'm0'
+        if self.diffopts is not None:
+            assert isinstance(self.diffopts, mdiff.diffopts)
+            diffopthash = hashdiffopts(self.diffopts)
+            if diffopthash != _defaultdiffopthash:
+                result += 'i' + diffopthash
+        return result or 'default'
+
+defaultopts = annotateopts()
+
+class _annotatecontext(object):
+    """do not use this class directly as it does not use lock to protect
+    writes. use "with annotatecontext(...)" instead.
+    """
+
+    def __init__(self, repo, path, linelogpath, revmappath, opts):
+        self.repo = repo
+        self.ui = repo.ui
+        self.path = path
+        self.opts = opts
+        self.linelogpath = linelogpath
+        self.revmappath = revmappath
+        self._linelog = None
+        self._revmap = None
+        self._node2path = {} # {str: str}
+
+    @property
+    def linelog(self):
+        if self._linelog is None:
+            if os.path.exists(self.linelogpath):
+                with open(self.linelogpath, 'rb') as f:
+                    try:
+                        self._linelog = linelogmod.linelog.fromdata(f.read())
+                    except linelogmod.LineLogError:
+                        self._linelog = linelogmod.linelog()
+            else:
+                self._linelog = linelogmod.linelog()
+        return self._linelog
+
+    @property
+    def revmap(self):
+        if self._revmap is None:
+            self._revmap = revmapmod.revmap(self.revmappath)
+        return self._revmap
+
+    def close(self):
+        if self._revmap is not None:
+            self._revmap.flush()
+            self._revmap = None
+        if self._linelog is not None:
+            with open(self.linelogpath, 'wb') as f:
+                f.write(self._linelog.encode())
+            self._linelog = None
+
+    __del__ = close
+
+    def rebuild(self):
+        """delete linelog and revmap, useful for rebuilding"""
+        self.close()
+        self._node2path.clear()
+        _unlinkpaths([self.revmappath, self.linelogpath])
+
+    @property
+    def lastnode(self):
+        """return last node in revmap, or None if revmap is empty"""
+        if self._revmap is None:
+            # fast path, read revmap without loading its full content
+            return revmapmod.getlastnode(self.revmappath)
+        else:
+            return self._revmap.rev2hsh(self._revmap.maxrev)
+
+    def isuptodate(self, master, strict=True):
+        """return True if the revmap / linelog is up-to-date, or the file
+        does not exist in the master revision. False otherwise.
+
+        it tries to be fast and could return false negatives, because of the
+        use of linkrev instead of introrev.
+
+        useful for both server and client to decide whether to update
+        fastannotate cache or not.
+
+        if strict is True, even if fctx exists in the revmap, but is not the
+        last node, isuptodate will return False. it's good for performance - no
+        expensive check was done.
+
+        if strict is False, if fctx exists in the revmap, this function may
+        return True. this is useful for the client to skip downloading the
+        cache if the client's master is behind the server's.
+        """
+        lastnode = self.lastnode
+        try:
+            f = self._resolvefctx(master, resolverev=True)
+            # choose linkrev instead of introrev as the check is meant to be
+            # *fast*.
+            linknode = self.repo.changelog.node(f.linkrev())
+            if not strict and lastnode and linknode != lastnode:
+                # check if f.node() is in the revmap. note: this loads the
+                # revmap and can be slow.
+                return self.revmap.hsh2rev(linknode) is not None
+            # avoid resolving old manifest, or slow adjustlinkrev to be fast,
+            # false negatives are acceptable in this case.
+            return linknode == lastnode
+        except LookupError:
+            # master does not have the file, or the revmap is ahead
+            return True
+
+    def annotate(self, rev, master=None, showpath=False, showlines=False):
+        """incrementally update the cache so it includes revisions in the main
+        branch till 'master'. and run annotate on 'rev', which may or may not be
+        included in the main branch.
+
+        if master is None, do not update linelog.
+
+        the first value returned is the annotate result, it is [(node, linenum)]
+        by default. [(node, linenum, path)] if showpath is True.
+
+        if showlines is True, a second value will be returned, it is a list of
+        corresponding line contents.
+        """
+
+        # the fast path test requires commit hash, convert rev number to hash,
+        # so it may hit the fast path. note: in the "fctx" mode, the "annotate"
+        # command could give us a revision number even if the user passes a
+        # commit hash.
+        if isinstance(rev, int):
+            rev = node.hex(self.repo.changelog.node(rev))
+
+        # fast path: if rev is in the main branch already
+        directly, revfctx = self.canannotatedirectly(rev)
+        if directly:
+            if self.ui.debugflag:
+                self.ui.debug('fastannotate: %s: using fast path '
+                              '(resolved fctx: %s)\n'
+                              % (self.path, util.safehasattr(revfctx, 'node')))
+            return self.annotatedirectly(revfctx, showpath, showlines)
+
+        # resolve master
+        masterfctx = None
+        if master:
+            try:
+                masterfctx = self._resolvefctx(master, resolverev=True,
+                                               adjustctx=True)
+            except LookupError: # master does not have the file
+                pass
+            else:
+                if masterfctx in self.revmap: # no need to update linelog
+                    masterfctx = None
+
+        #                  ... - @ <- rev (can be an arbitrary changeset,
+        #                 /                not necessarily a descendant
+        #      master -> o                 of master)
+        #                |
+        #     a merge -> o         'o': new changesets in the main branch
+        #                |\        '#': revisions in the main branch that
+        #                o *            exist in linelog / revmap
+        #                | .       '*': changesets in side branches, or
+        # last master -> # .            descendants of master
+        #                | .
+        #                # *       joint: '#', and is a parent of a '*'
+        #                |/
+        #     a joint -> # ^^^^ --- side branches
+        #                |
+        #                ^ --- main branch (in linelog)
+
+        # these DFSes are similar to the traditional annotate algorithm.
+        # we cannot really reuse the code for perf reason.
+
+        # 1st DFS calculates merges, joint points, and needed.
+        # "needed" is a simple reference counting dict to free items in
+        # "hist", reducing its memory usage otherwise could be huge.
+        initvisit = [revfctx]
+        if masterfctx:
+            if masterfctx.rev() is None:
+                raise error.Abort(_('cannot update linelog to wdir()'),
+                                  hint=_('set fastannotate.mainbranch'))
+            initvisit.append(masterfctx)
+        visit = initvisit[:]
+        pcache = {}
+        needed = {revfctx: 1}
+        hist = {} # {fctx: ([(llrev or fctx, linenum)], text)}
+        while visit:
+            f = visit.pop()
+            if f in pcache or f in hist:
+                continue
+            if f in self.revmap: # in the old main branch, it's a joint
+                llrev = self.revmap.hsh2rev(f.node())
+                self.linelog.annotate(llrev)
+                result = self.linelog.annotateresult
+                hist[f] = (result, f.data())
+                continue
+            pl = self._parentfunc(f)
+            pcache[f] = pl
+            for p in pl:
+                needed[p] = needed.get(p, 0) + 1
+                if p not in pcache:
+                    visit.append(p)
+
+        # 2nd (simple) DFS calculates new changesets in the main branch
+        # ('o' nodes in # the above graph), so we know when to update linelog.
+        newmainbranch = set()
+        f = masterfctx
+        while f and f not in self.revmap:
+            newmainbranch.add(f)
+            pl = pcache[f]
+            if pl:
+                f = pl[0]
+            else:
+                f = None
+                break
+
+        # f, if present, is the position where the last build stopped at, and
+        # should be the "master" last time. check to see if we can continue
+        # building the linelog incrementally. (we cannot if diverged)
+        if masterfctx is not None:
+            self._checklastmasterhead(f)
+
+        if self.ui.debugflag:
+            if newmainbranch:
+                self.ui.debug('fastannotate: %s: %d new changesets in the main'
+                              ' branch\n' % (self.path, len(newmainbranch)))
+            elif not hist: # no joints, no updates
+                self.ui.debug('fastannotate: %s: linelog cannot help in '
+                              'annotating this revision\n' % self.path)
+
+        # prepare annotateresult so we can update linelog incrementally
+        self.linelog.annotate(self.linelog.maxrev)
+
+        # 3rd DFS does the actual annotate
+        visit = initvisit[:]
+        progress = 0
+        while visit:
+            f = visit[-1]
+            if f in hist:
+                visit.pop()
+                continue
+
+            ready = True
+            pl = pcache[f]
+            for p in pl:
+                if p not in hist:
+                    ready = False
+                    visit.append(p)
+            if not ready:
+                continue
+
+            visit.pop()
+            blocks = None # mdiff blocks, used for appending linelog
+            ismainbranch = (f in newmainbranch)
+            # curr is the same as the traditional annotate algorithm,
+            # if we only care about linear history (do not follow merge),
+            # then curr is not actually used.
+            assert f not in hist
+            curr = _decorate(f)
+            for i, p in enumerate(pl):
+                bs = list(self._diffblocks(hist[p][1], curr[1]))
+                if i == 0 and ismainbranch:
+                    blocks = bs
+                curr = _pair(hist[p], curr, bs)
+                if needed[p] == 1:
+                    del hist[p]
+                    del needed[p]
+                else:
+                    needed[p] -= 1
+
+            hist[f] = curr
+            del pcache[f]
+
+            if ismainbranch: # need to write to linelog
+                if not self.ui.quiet:
+                    progress += 1
+                    self.ui.progress(_('building cache'), progress,
+                                     total=len(newmainbranch))
+                bannotated = None
+                if len(pl) == 2 and self.opts.followmerge: # merge
+                    bannotated = curr[0]
+                if blocks is None: # no parents, add an empty one
+                    blocks = list(self._diffblocks('', curr[1]))
+                self._appendrev(f, blocks, bannotated)
+            elif showpath: # not append linelog, but we need to record path
+                self._node2path[f.node()] = f.path()
+
+        if progress: # clean progress bar
+            self.ui.write()
+
+        result = [
+            ((self.revmap.rev2hsh(fr) if isinstance(fr, int) else fr.node()), l)
+            for fr, l in hist[revfctx][0]] # [(node, linenumber)]
+        return self._refineannotateresult(result, revfctx, showpath, showlines)
+
+    def canannotatedirectly(self, rev):
+        """(str) -> bool, fctx or node.
+        return (True, f) if we can annotate without updating the linelog, pass
+        f to annotatedirectly.
+        return (False, f) if we need extra calculation. f is the fctx resolved
+        from rev.
+        """
+        result = True
+        f = None
+        if not isinstance(rev, int) and rev is not None:
+            hsh = {20: bytes, 40: node.bin}.get(len(rev), lambda x: None)(rev)
+            if hsh is not None and (hsh, self.path) in self.revmap:
+                f = hsh
+        if f is None:
+            adjustctx = 'linkrev' if self._perfhack else True
+            f = self._resolvefctx(rev, adjustctx=adjustctx, resolverev=True)
+            result = f in self.revmap
+            if not result and self._perfhack:
+                # redo the resolution without perfhack - as we are going to
+                # do write operations, we need a correct fctx.
+                f = self._resolvefctx(rev, adjustctx=True, resolverev=True)
+        return result, f
+
+    def annotatealllines(self, rev, showpath=False, showlines=False):
+        """(rev : str) -> [(node : str, linenum : int, path : str)]
+
+        the result has the same format with annotate, but include all (including
+        deleted) lines up to rev. call this after calling annotate(rev, ...) for
+        better performance and accuracy.
+        """
+        revfctx = self._resolvefctx(rev, resolverev=True, adjustctx=True)
+
+        # find a chain from rev to anything in the mainbranch
+        if revfctx not in self.revmap:
+            chain = [revfctx]
+            a = ''
+            while True:
+                f = chain[-1]
+                pl = self._parentfunc(f)
+                if not pl:
+                    break
+                if pl[0] in self.revmap:
+                    a = pl[0].data()
+                    break
+                chain.append(pl[0])
+
+            # both self.linelog and self.revmap is backed by filesystem. now
+            # we want to modify them but do not want to write changes back to
+            # files. so we create in-memory objects and copy them. it's like
+            # a "fork".
+            linelog = linelogmod.linelog()
+            linelog.copyfrom(self.linelog)
+            linelog.annotate(linelog.maxrev)
+            revmap = revmapmod.revmap()
+            revmap.copyfrom(self.revmap)
+
+            for f in reversed(chain):
+                b = f.data()
+                blocks = list(self._diffblocks(a, b))
+                self._doappendrev(linelog, revmap, f, blocks)
+                a = b
+        else:
+            # fastpath: use existing linelog, revmap as we don't write to them
+            linelog = self.linelog
+            revmap = self.revmap
+
+        lines = linelog.getalllines()
+        hsh = revfctx.node()
+        llrev = revmap.hsh2rev(hsh)
+        result = [(revmap.rev2hsh(r), l) for r, l in lines if r <= llrev]
+        # cannot use _refineannotateresult since we need custom logic for
+        # resolving line contents
+        if showpath:
+            result = self._addpathtoresult(result, revmap)
+        if showlines:
+            linecontents = self._resolvelines(result, revmap, linelog)
+            result = (result, linecontents)
+        return result
+
+    def _resolvelines(self, annotateresult, revmap, linelog):
+        """(annotateresult) -> [line]. designed for annotatealllines.
+        this is probably the most inefficient code in the whole fastannotate
+        directory. but we have made a decision that the linelog does not
+        store line contents. so getting them requires random accesses to
+        the revlog data, since they can be many, it can be very slow.
+        """
+        # [llrev]
+        revs = [revmap.hsh2rev(l[0]) for l in annotateresult]
+        result = [None] * len(annotateresult)
+        # {(rev, linenum): [lineindex]}
+        key2idxs = collections.defaultdict(list)
+        for i in pycompat.xrange(len(result)):
+            key2idxs[(revs[i], annotateresult[i][1])].append(i)
+        while key2idxs:
+            # find an unresolved line and its linelog rev to annotate
+            hsh = None
+            try:
+                for (rev, _linenum), idxs in key2idxs.iteritems():
+                    if revmap.rev2flag(rev) & revmapmod.sidebranchflag:
+                        continue
+                    hsh = annotateresult[idxs[0]][0]
+                    break
+            except StopIteration: # no more unresolved lines
+                return result
+            if hsh is None:
+                # the remaining key2idxs are not in main branch, resolving them
+                # using the hard way...
+                revlines = {}
+                for (rev, linenum), idxs in key2idxs.iteritems():
+                    if rev not in revlines:
+                        hsh = annotateresult[idxs[0]][0]
+                        if self.ui.debugflag:
+                            self.ui.debug('fastannotate: reading %s line #%d '
+                                          'to resolve lines %r\n'
+                                          % (node.short(hsh), linenum, idxs))
+                        fctx = self._resolvefctx(hsh, revmap.rev2path(rev))
+                        lines = mdiff.splitnewlines(fctx.data())
+                        revlines[rev] = lines
+                    for idx in idxs:
+                        result[idx] = revlines[rev][linenum]
+                assert all(x is not None for x in result)
+                return result
+
+            # run the annotate and the lines should match to the file content
+            self.ui.debug('fastannotate: annotate %s to resolve lines\n'
+                          % node.short(hsh))
+            linelog.annotate(rev)
+            fctx = self._resolvefctx(hsh, revmap.rev2path(rev))
+            annotated = linelog.annotateresult
+            lines = mdiff.splitnewlines(fctx.data())
+            if len(lines) != len(annotated):
+                raise faerror.CorruptedFileError('unexpected annotated lines')
+            # resolve lines from the annotate result
+            for i, line in enumerate(lines):
+                k = annotated[i]
+                if k in key2idxs:
+                    for idx in key2idxs[k]:
+                        result[idx] = line
+                    del key2idxs[k]
+        return result
+
+    def annotatedirectly(self, f, showpath, showlines):
+        """like annotate, but when we know that f is in linelog.
+        f can be either a 20-char str (node) or a fctx. this is for perf - in
+        the best case, the user provides a node and we don't need to read the
+        filelog or construct any filecontext.
+        """
+        if isinstance(f, str):
+            hsh = f
+        else:
+            hsh = f.node()
+        llrev = self.revmap.hsh2rev(hsh)
+        if not llrev:
+            raise faerror.CorruptedFileError('%s is not in revmap'
+                                             % node.hex(hsh))
+        if (self.revmap.rev2flag(llrev) & revmapmod.sidebranchflag) != 0:
+            raise faerror.CorruptedFileError('%s is not in revmap mainbranch'
+                                             % node.hex(hsh))
+        self.linelog.annotate(llrev)
+        result = [(self.revmap.rev2hsh(r), l)
+                  for r, l in self.linelog.annotateresult]
+        return self._refineannotateresult(result, f, showpath, showlines)
+
+    def _refineannotateresult(self, result, f, showpath, showlines):
+        """add the missing path or line contents, they can be expensive.
+        f could be either node or fctx.
+        """
+        if showpath:
+            result = self._addpathtoresult(result)
+        if showlines:
+            if isinstance(f, str): # f: node or fctx
+                llrev = self.revmap.hsh2rev(f)
+                fctx = self._resolvefctx(f, self.revmap.rev2path(llrev))
+            else:
+                fctx = f
+            lines = mdiff.splitnewlines(fctx.data())
+            if len(lines) != len(result): # linelog is probably corrupted
+                raise faerror.CorruptedFileError()
+            result = (result, lines)
+        return result
+
+    def _appendrev(self, fctx, blocks, bannotated=None):
+        self._doappendrev(self.linelog, self.revmap, fctx, blocks, bannotated)
+
+    def _diffblocks(self, a, b):
+        return mdiff.allblocks(a, b, self.opts.diffopts)
+
+    @staticmethod
+    def _doappendrev(linelog, revmap, fctx, blocks, bannotated=None):
+        """append a revision to linelog and revmap"""
+
+        def getllrev(f):
+            """(fctx) -> int"""
+            # f should not be a linelog revision
+            if isinstance(f, int):
+                raise error.ProgrammingError('f should not be an int')
+            # f is a fctx, allocate linelog rev on demand
+            hsh = f.node()
+            rev = revmap.hsh2rev(hsh)
+            if rev is None:
+                rev = revmap.append(hsh, sidebranch=True, path=f.path())
+            return rev
+
+        # append sidebranch revisions to revmap
+        siderevs = []
+        siderevmap = {} # node: int
+        if bannotated is not None:
+            for (a1, a2, b1, b2), op in blocks:
+                if op != '=':
+                    # f could be either linelong rev, or fctx.
+                    siderevs += [f for f, l in bannotated[b1:b2]
+                                 if not isinstance(f, int)]
+        siderevs = set(siderevs)
+        if fctx in siderevs: # mainnode must be appended seperately
+            siderevs.remove(fctx)
+        for f in siderevs:
+            siderevmap[f] = getllrev(f)
+
+        # the changeset in the main branch, could be a merge
+        llrev = revmap.append(fctx.node(), path=fctx.path())
+        siderevmap[fctx] = llrev
+
+        for (a1, a2, b1, b2), op in reversed(blocks):
+            if op == '=':
+                continue
+            if bannotated is None:
+                linelog.replacelines(llrev, a1, a2, b1, b2)
+            else:
+                blines = [((r if isinstance(r, int) else siderevmap[r]), l)
+                          for r, l in bannotated[b1:b2]]
+                linelog.replacelines_vec(llrev, a1, a2, blines)
+
+    def _addpathtoresult(self, annotateresult, revmap=None):
+        """(revmap, [(node, linenum)]) -> [(node, linenum, path)]"""
+        if revmap is None:
+            revmap = self.revmap
+
+        def _getpath(nodeid):
+            path = self._node2path.get(nodeid)
+            if path is None:
+                path = revmap.rev2path(revmap.hsh2rev(nodeid))
+                self._node2path[nodeid] = path
+            return path
+
+        return [(n, l, _getpath(n)) for n, l in annotateresult]
+
+    def _checklastmasterhead(self, fctx):
+        """check if fctx is the master's head last time, raise if not"""
+        if fctx is None:
+            llrev = 0
+        else:
+            llrev = self.revmap.hsh2rev(fctx.node())
+            if not llrev:
+                raise faerror.CannotReuseError()
+        if self.linelog.maxrev != llrev:
+            raise faerror.CannotReuseError()
+
+    @util.propertycache
+    def _parentfunc(self):
+        """-> (fctx) -> [fctx]"""
+        followrename = self.opts.followrename
+        followmerge = self.opts.followmerge
+        def parents(f):
+            pl = _parents(f, follow=followrename)
+            if not followmerge:
+                pl = pl[:1]
+            return pl
+        return parents
+
+    @util.propertycache
+    def _perfhack(self):
+        return self.ui.configbool('fastannotate', 'perfhack')
+
+    def _resolvefctx(self, rev, path=None, **kwds):
+        return resolvefctx(self.repo, rev, (path or self.path), **kwds)
+
+def _unlinkpaths(paths):
+    """silent, best-effort unlink"""
+    for path in paths:
+        try:
+            util.unlink(path)
+        except OSError:
+            pass
+
+class pathhelper(object):
+    """helper for getting paths for lockfile, linelog and revmap"""
+
+    def __init__(self, repo, path, opts=defaultopts):
+        # different options use different directories
+        self._vfspath = os.path.join('fastannotate',
+                                     opts.shortstr, encodedir(path))
+        self._repo = repo
+
+    @property
+    def dirname(self):
+        return os.path.dirname(self._repo.vfs.join(self._vfspath))
+
+    @property
+    def linelogpath(self):
+        return self._repo.vfs.join(self._vfspath + '.l')
+
+    def lock(self):
+        return lockmod.lock(self._repo.vfs, self._vfspath + '.lock')
+
+    @contextlib.contextmanager
+    def _lockflock(self):
+        """the same as 'lock' but use flock instead of lockmod.lock, to avoid
+        creating temporary symlinks."""
+        import fcntl
+        lockpath = self.linelogpath
+        util.makedirs(os.path.dirname(lockpath))
+        lockfd = os.open(lockpath, os.O_RDONLY | os.O_CREAT, 0o664)
+        fcntl.flock(lockfd, fcntl.LOCK_EX)
+        try:
+            yield
+        finally:
+            fcntl.flock(lockfd, fcntl.LOCK_UN)
+            os.close(lockfd)
+
+    @property
+    def revmappath(self):
+        return self._repo.vfs.join(self._vfspath + '.m')
+
+@contextlib.contextmanager
+def annotatecontext(repo, path, opts=defaultopts, rebuild=False):
+    """context needed to perform (fast) annotate on a file
+
+    an annotatecontext of a single file consists of two structures: the
+    linelog and the revmap. this function takes care of locking. only 1
+    process is allowed to write that file's linelog and revmap at a time.
+
+    when something goes wrong, this function will assume the linelog and the
+    revmap are in a bad state, and remove them from disk.
+
+    use this function in the following way:
+
+        with annotatecontext(...) as actx:
+            actx. ....
+    """
+    helper = pathhelper(repo, path, opts)
+    util.makedirs(helper.dirname)
+    revmappath = helper.revmappath
+    linelogpath = helper.linelogpath
+    actx = None
+    try:
+        with helper.lock():
+            actx = _annotatecontext(repo, path, linelogpath, revmappath, opts)
+            if rebuild:
+                actx.rebuild()
+            yield actx
+    except Exception:
+        if actx is not None:
+            actx.rebuild()
+        repo.ui.debug('fastannotate: %s: cache broken and deleted\n' % path)
+        raise
+    finally:
+        if actx is not None:
+            actx.close()
+
+def fctxannotatecontext(fctx, follow=True, diffopts=None, rebuild=False):
+    """like annotatecontext but get the context from a fctx. convenient when
+    used in fctx.annotate
+    """
+    repo = fctx._repo
+    path = fctx._path
+    if repo.ui.configbool('fastannotate', 'forcefollow', True):
+        follow = True
+    aopts = annotateopts(diffopts=diffopts, followrename=follow)
+    return annotatecontext(repo, path, aopts, rebuild)
diff --git a/hgext/fastannotate/commands.py b/hgext/fastannotate/commands.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/commands.py
@@ -0,0 +1,281 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# commands: fastannotate commands
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+import os
+
+from mercurial.i18n import _
+from mercurial import (
+    commands,
+    error,
+    extensions,
+    patch,
+    pycompat,
+    registrar,
+    scmutil,
+    util,
+)
+
+from . import (
+    context as facontext,
+    error as faerror,
+    formatter as faformatter,
+)
+
+cmdtable = {}
+command = registrar.command(cmdtable)
+
+def _matchpaths(repo, rev, pats, opts, aopts=facontext.defaultopts):
+    """generate paths matching given patterns"""
+    perfhack = repo.ui.configbool('fastannotate', 'perfhack')
+
+    # disable perfhack if:
+    # a) any walkopt is used
+    # b) if we treat pats as plain file names, some of them do not have
+    #    corresponding linelog files
+    if perfhack:
+        # cwd related to reporoot
+        reporoot = os.path.dirname(repo.path)
+        reldir = os.path.relpath(pycompat.getcwd(), reporoot)
+        if reldir == '.':
+            reldir = ''
+        if any(opts.get(o[1]) for o in commands.walkopts): # a)
+            perfhack = False
+        else: # b)
+            relpats = [os.path.relpath(p, reporoot) if os.path.isabs(p) else p
+                       for p in pats]
+            # disable perfhack on '..' since it allows escaping from the repo
+            if any(('..' in f or
+                    not os.path.isfile(
+                        facontext.pathhelper(repo, f, aopts).linelogpath))
+                   for f in relpats):
+                perfhack = False
+
+    # perfhack: emit paths directory without checking with manifest
+    # this can be incorrect if the rev dos not have file.
+    if perfhack:
+        for p in relpats:
+            yield os.path.join(reldir, p)
+    else:
+        def bad(x, y):
+            raise error.Abort("%s: %s" % (x, y))
+        ctx = scmutil.revsingle(repo, rev)
+        m = scmutil.match(ctx, pats, opts, badfn=bad)
+        for p in ctx.walk(m):
+            yield p
+
+fastannotatecommandargs = {
+    'options': [
+        ('r', 'rev', '.', _('annotate the specified revision'), _('REV')),
+        ('u', 'user', None, _('list the author (long with -v)')),
+        ('f', 'file', None, _('list the filename')),
+        ('d', 'date', None, _('list the date (short with -q)')),
+        ('n', 'number', None, _('list the revision number (default)')),
+        ('c', 'changeset', None, _('list the changeset')),
+        ('l', 'line-number', None, _('show line number at the first '
+                                     'appearance')),
+        ('e', 'deleted', None, _('show deleted lines (slow) (EXPERIMENTAL)')),
+        ('', 'no-content', None, _('do not show file content (EXPERIMENTAL)')),
+        ('', 'no-follow', None, _("don't follow copies and renames")),
+        ('', 'linear', None, _('enforce linear history, ignore second parent '
+                               'of merges (EXPERIMENTAL)')),
+        ('', 'long-hash', None, _('show long changeset hash (EXPERIMENTAL)')),
+        ('', 'rebuild', None, _('rebuild cache even if it exists '
+                                '(EXPERIMENTAL)')),
+    ] + commands.diffwsopts + commands.walkopts + commands.formatteropts,
+    'synopsis': _('[-r REV] [-f] [-a] [-u] [-d] [-n] [-c] [-l] FILE...'),
+    'inferrepo': True,
+}
+
+def fastannotate(ui, repo, *pats, **opts):
+    """show changeset information by line for each file
+
+    List changes in files, showing the revision id responsible for each line.
+
+    This command is useful for discovering when a change was made and by whom.
+
+    By default this command prints revision numbers. If you include --file,
+    --user, or --date, the revision number is suppressed unless you also
+    include --number. The default format can also be customized by setting
+    fastannotate.defaultformat.
+
+    Returns 0 on success.
+
+    .. container:: verbose
+
+        This command uses an implementation different from the vanilla annotate
+        command, which may produce slightly different (while still reasonable)
+        outputs for some cases.
+
+        Unlike the vanilla anootate, fastannotate follows rename regardless of
+        the existence of --file.
+
+        For the best performance when running on a full repo, use -c, -l,
+        avoid -u, -d, -n. Use --linear and --no-content to make it even faster.
+
+        For the best performance when running on a shallow (remotefilelog)
+        repo, avoid --linear, --no-follow, or any diff options. As the server
+        won't be able to populate annotate cache when non-default options
+        affecting results are used.
+    """
+    if not pats:
+        raise error.Abort(_('at least one filename or pattern is required'))
+
+    # performance hack: filtered repo can be slow. unfilter by default.
+    if ui.configbool('fastannotate', 'unfilteredrepo'):
+        repo = repo.unfiltered()
+
+    rev = opts.get('rev', '.')
+    rebuild = opts.get('rebuild', False)
+
+    diffopts = patch.difffeatureopts(ui, opts, section='annotate',
+                                     whitespace=True)
+    aopts = facontext.annotateopts(
+        diffopts=diffopts,
+        followmerge=not opts.get('linear', False),
+        followrename=not opts.get('no_follow', False))
+
+    if not any(opts.get(s)
+               for s in ['user', 'date', 'file', 'number', 'changeset']):
+        # default 'number' for compatibility. but fastannotate is more
+        # efficient with "changeset", "line-number" and "no-content".
+        for name in ui.configlist('fastannotate', 'defaultformat', ['number']):
+            opts[name] = True
+
+    ui.pager('fastannotate')
+    template = opts.get('template')
+    if template == 'json':
+        formatter = faformatter.jsonformatter(ui, repo, opts)
+    else:
+        formatter = faformatter.defaultformatter(ui, repo, opts)
+    showdeleted = opts.get('deleted', False)
+    showlines = not bool(opts.get('no_content'))
+    showpath = opts.get('file', False)
+
+    # find the head of the main (master) branch
+    master = ui.config('fastannotate', 'mainbranch') or rev
+
+    # paths will be used for prefetching and the real annotating
+    paths = list(_matchpaths(repo, rev, pats, opts, aopts))
+
+    # for client, prefetch from the server
+    if util.safehasattr(repo, 'prefetchfastannotate'):
+        repo.prefetchfastannotate(paths)
+
+    for path in paths:
+        result = lines = existinglines = None
+        while True:
+            try:
+                with facontext.annotatecontext(repo, path, aopts, rebuild) as a:
+                    result = a.annotate(rev, master=master, showpath=showpath,
+                                        showlines=(showlines and
+                                                   not showdeleted))
+                    if showdeleted:
+                        existinglines = set((l[0], l[1]) for l in result)
+                        result = a.annotatealllines(
+                            rev, showpath=showpath, showlines=showlines)
+                break
+            except (faerror.CannotReuseError, faerror.CorruptedFileError):
+                # happens if master moves backwards, or the file was deleted
+                # and readded, or renamed to an existing name, or corrupted.
+                if rebuild: # give up since we have tried rebuild already
+                    raise
+                else: # try a second time rebuilding the cache (slow)
+                    rebuild = True
+                    continue
+
+        if showlines:
+            result, lines = result
+
+        formatter.write(result, lines, existinglines=existinglines)
+    formatter.end()
+
+_newopts = set([])
+_knownopts = set([opt[1].replace('-', '_') for opt in
+                  (fastannotatecommandargs['options'] + commands.globalopts)])
+
+def _annotatewrapper(orig, ui, repo, *pats, **opts):
+    """used by wrapdefault"""
+    # we need this hack until the obsstore has 0.0 seconds perf impact
+    if ui.configbool('fastannotate', 'unfilteredrepo'):
+        repo = repo.unfiltered()
+
+    # treat the file as text (skip the isbinary check)
+    if ui.configbool('fastannotate', 'forcetext'):
+        opts['text'] = True
+
+    # check if we need to do prefetch (client-side)
+    rev = opts.get('rev')
+    if util.safehasattr(repo, 'prefetchfastannotate') and rev is not None:
+        paths = list(_matchpaths(repo, rev, pats, opts))
+        repo.prefetchfastannotate(paths)
+
+    return orig(ui, repo, *pats, **opts)
+
+def registercommand():
+    """register the fastannotate command"""
+    name = '^fastannotate|fastblame|fa'
+    command(name, **fastannotatecommandargs)(fastannotate)
+
+def wrapdefault():
+    """wrap the default annotate command, to be aware of the protocol"""
+    extensions.wrapcommand(commands.table, 'annotate', _annotatewrapper)
+
+@command('debugbuildannotatecache',
+         [('r', 'rev', '', _('build up to the specific revision'), _('REV'))
+         ] + commands.walkopts,
+         _('[-r REV] FILE...'))
+def debugbuildannotatecache(ui, repo, *pats, **opts):
+    """incrementally build fastannotate cache up to REV for specified files
+
+    If REV is not specified, use the config 'fastannotate.mainbranch'.
+
+    If fastannotate.client is True, download the annotate cache from the
+    server. Otherwise, build the annotate cache locally.
+
+    The annotate cache will be built using the default diff and follow
+    options and lives in '.hg/fastannotate/default'.
+    """
+    rev = opts.get('REV') or ui.config('fastannotate', 'mainbranch')
+    if not rev:
+        raise error.Abort(_('you need to provide a revision'),
+                          hint=_('set fastannotate.mainbranch or use --rev'))
+    if ui.configbool('fastannotate', 'unfilteredrepo'):
+        repo = repo.unfiltered()
+    ctx = scmutil.revsingle(repo, rev)
+    m = scmutil.match(ctx, pats, opts)
+    paths = list(ctx.walk(m))
+    if util.safehasattr(repo, 'prefetchfastannotate'):
+        # client
+        if opts.get('REV'):
+            raise error.Abort(_('--rev cannot be used for client'))
+        repo.prefetchfastannotate(paths)
+    else:
+        # server, or full repo
+        for i, path in enumerate(paths):
+            ui.progress(_('building'), i, total=len(paths))
+            with facontext.annotatecontext(repo, path) as actx:
+                try:
+                    if actx.isuptodate(rev):
+                        continue
+                    actx.annotate(rev, rev)
+                except (faerror.CannotReuseError, faerror.CorruptedFileError):
+                    # the cache is broken (could happen with renaming so the
+                    # file history gets invalidated). rebuild and try again.
+                    ui.debug('fastannotate: %s: rebuilding broken cache\n'
+                             % path)
+                    actx.rebuild()
+                    try:
+                        actx.annotate(rev, rev)
+                    except Exception as ex:
+                        # possibly a bug, but should not stop us from building
+                        # cache for other files.
+                        ui.warn(_('fastannotate: %s: failed to '
+                                  'build cache: %r\n') % (path, ex))
+        # clear the progress bar
+        ui.write()
diff --git a/hgext/fastannotate/__init__.py b/hgext/fastannotate/__init__.py
new file mode 100644
--- /dev/null
+++ b/hgext/fastannotate/__init__.py
@@ -0,0 +1,185 @@ 
+# Copyright 2016-present Facebook. All Rights Reserved.
+#
+# fastannotate: faster annotate implementation using linelog
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""yet another annotate implementation that might be faster (EXPERIMENTAL)
+
+The fastannotate extension provides a 'fastannotate' command that makes
+use of the linelog data structure as a cache layer and is expected to
+be faster than the vanilla 'annotate' if the cache is present.
+
+In most cases, fastannotate requires a setup that mainbranch is some pointer
+that always moves forward, to be most efficient.
+
+Using fastannotate together with linkrevcache would speed up building the
+annotate cache greatly. Run "debugbuildlinkrevcache" before
+"debugbuildannotatecache".
+
+::
+
+    [fastannotate]
+    # specify the main branch head. the internal linelog will only contain
+    # the linear (ignoring p2) "mainbranch". since linelog cannot move
+    # backwards without a rebuild, this should be something that always moves
+    # forward, usually it is "master" or "@".
+    mainbranch = master
+
+    # fastannotate supports different modes to expose its feature.
+    # a list of combination:
+    # - fastannotate: expose the feature via the "fastannotate" command which
+    #   deals with everything in a most efficient way, and provides extra
+    #   features like --deleted etc.
+    # - fctx: replace fctx.annotate implementation. note:
+    #     a. it is less efficient than the "fastannotate" command
+    #     b. it will make it practically impossible to access the old (disk
+    #        side-effect free) annotate implementation
+    #     c. it implies "hgweb".
+    # - hgweb: replace hgweb's annotate implementation. conflict with "fctx".
+    # (default: fastannotate)
+    modes = fastannotate
+
+    # default format when no format flags are used (default: number)
+    defaultformat = changeset, user, date
+
+    # serve the annotate cache via wire protocol (default: False)
+    # tip: the .hg/fastannotate directory is portable - can be rsynced
+    server = True
+
+    # build annotate cache on demand for every client request (default: True)
+    # disabling it could make server response faster, useful when there is a
+    # cronjob building the cache.
+    serverbuildondemand = True
+
+    # update local annotate cache from remote on demand
+    # (default: True for remotefilelog repo, False otherwise)
+    client = True
+
+    # path to use when connecting to the remote server (default: default)
+    remotepath = default
+
+    # share sshpeer with remotefilelog. this would allow fastannotate to peek
+    # into remotefilelog internals, and steal its sshpeer, or in the reversed
+    # direction: donate its sshpeer to remotefilelog. disable this if
+    # fastannotate and remotefilelog should not share a sshpeer when their
+    # endpoints are different and incompatible. (default: True)
+    clientsharepeer = True
+
+    # minimal length of the history of a file required to fetch linelog from
+    # the server. (default: 10)
+    clientfetchthreshold = 10
+
+    # use flock instead of the file existence lock
+    # flock may not work well on some network filesystems, but they avoid
+    # creating and deleting files frequently, which is faster when updating
+    # the annotate cache in batch. if you have issues with this option, set it
+    # to False. (default: True if flock is supported, False otherwise)
+    useflock = True
+
+    # for "fctx" mode, always follow renames regardless of command line option.
+    # this is a BC with the original command but will reduced the space needed
+    # for annotate cache, and is useful for client-server setup since the
+    # server will only provide annotate cache with default options (i.e. with
+    # follow). do not affect "fastannotate" mode. (default: True)
+    forcefollow = True
+
+    # for "fctx" mode, always treat file as text files, to skip the "isbinary"
+    # check. this is consistent with the "fastannotate" command and could help
+    # to avoid a file fetch if remotefilelog is used. (default: True)
+    forcetext = True
+
+    # use unfiltered repo for better performance.
+    unfilteredrepo = True
+
+    # sacrifice correctness in some corner cases for performance. it does not
+    # affect the correctness of the annotate cache being built. the option
+    # is experimental and may disappear in the future (default: False)
+    perfhack = True
+"""
+
+from __future__ import absolute_import
+
+from mercurial.i18n import _
+from mercurial import (
+    error as hgerror,
+    localrepo,
+    registrar,
+    util,
+)
+
+from . import (
+    commands,
+    context,
+    protocol,
+)
+
+# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
+# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
+# be specifying the version(s) of Mercurial they are tested with, or
+# leave the attribute unspecified.
+testedwith = 'ships-with-hg-core'
+
+cmdtable = commands.cmdtable
+
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('fastannotate', 'modes', default=['fastannotate'])
+configitem('fastannotate', 'server', default=False)
+configitem('fastannotate', 'useflock', default=True)
+configitem('fastannotate', 'client')
+configitem('fastannotate', 'unfilteredrepo', default=True)
+configitem('fastannotate', 'defaultformat', default=['number'])
+configitem('fastannotate', 'perfhack', default=False)
+configitem('fastannotate', 'mainbranch')
+configitem('fastannotate', 'forcetext', default=True)
+configitem('fastannotate', 'forcefollow', default=True)
+configitem('fastannotate', 'clientfetchthreshold', default=10)
+configitem('fastannotate', 'clientsharepeer', default=True)
+configitem('fastannotate', 'serverbuildondemand', default=True)
+configitem('fastannotate', 'remotepath', default='default')
+
+def _flockavailable():
+    try:
+        import fcntl
+        fcntl.flock
+    except StandardError:
+        return False
+    else:
+        return True
+
+def uisetup(ui):
+    modes = set(ui.configlist('fastannotate', 'modes'))
+    if 'fctx' in modes:
+        modes.discard('hgweb')
+    for name in modes:
+        if name == 'fastannotate':
+            commands.registercommand()
+        elif name == 'hgweb':
+            from . import support
+            support.replacehgwebannotate()
+        elif name == 'fctx':
+            from . import support
+            support.replacefctxannotate()
+            support.replaceremotefctxannotate()
+            commands.wrapdefault()
+        else:
+            raise hgerror.Abort(_('fastannotate: invalid mode: %s') % name)
+
+    if ui.configbool('fastannotate', 'server'):
+        protocol.serveruisetup(ui)
+
+    if ui.configbool('fastannotate', 'useflock', _flockavailable()):
+        context.pathhelper.lock = context.pathhelper._lockflock
+
+    # fastannotate has its own locking, without depending on repo lock
+    localrepo.localrepository._wlockfreeprefix.add('fastannotate/')
+
+def reposetup(ui, repo):
+    client = ui.configbool('fastannotate', 'client', default=None)
+    if client is None:
+        if util.safehasattr(repo, 'requirements'):
+            client = 'remotefilelog' in repo.requirements
+    if client:
+        protocol.clientreposetup(ui, repo)