Patchwork [2,of,2] revset: new predicates to find key merge revisions

diff --git a/mercurial/mergestate.py b/mercurial/mergestate.py
--- a/mercurial/mergestate.py
+++ b/mercurial/mergestate.py
@@ -304,6 +304,22 @@ 
             if entry[0] == 'u':
                 yield f
 
+    def ancestorchangectx(self, dfile):
+        extras = self.extras(dfile)
+        anccommitnode = extras.get('ancestorlinknode')
+        if anccommitnode:
+            return self._repo[anccommitnode]
+        else:
+            return None
+
+    def otherfilectx(self, dfile):
+        entry = self._state[dfile]
+        return self.otherctx.filectx(entry[5], fileid=entry[6])
+
+    def localfilectx(self, dfile):
+        entry = self._state[dfile]
+        return self.localctx.filectx(entry[2])
+
     def driverresolved(self):
         """Obtain the paths of driver-resolved files."""
 
diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -17,6 +17,7 @@ 
     error,
     hbisect,
     match as matchmod,
+    mergestate as mergestatemod,
     node,
     obsolete as obsmod,
     parser,
@@ -816,6 +817,54 @@ 
     getargs(x, 0, 0, _("closed takes no arguments"))
     return subset.filter(lambda r: repo[r].closesbranch())
 
+@predicate('conflict(type,[pattern])')
+def conflict(repo, subset, x):
+    """The type revision for any merge conflict matching pattern.
+    See :hg:`help patterns` for information about file patterns.
+
+    type should be one of "ancestor", "other" or "local", for the three-way
+    merge ancestor, the "other" tree, or the "local" tree.
+
+    The pattern without explicit kind like ``glob:`` is expected to be
+    relative to the current directory and match against a file exactly
+    for efficiency. If pattern is omitted, all conflicts are included.
+    """
+    # i18n: "conflict" is a keyword
+    l = getargs(x, 1, 2, _('conflict takes one or two arguments'))
+    t = getstring(l[0], _("conflict requires a type"))
+    if t not in ["ancestor", "other", "local"]:
+        msg = _('conflict file types are "ancestor", "other" or "local"')
+        raise error.Abort(msg)
+    if len(l) == 2:
+        pat = getstring(l[1], _("conflict takes a string pattern"))
+    else:
+        pat = None
+
+    ms = mergestatemod.mergestatereadonly.read(repo)
+
+    if pat is None:
+        files = ms.files()
+    elif not matchmod.patkind(pat):
+        f = pathutil.canonpath(repo.root, repo.getcwd(), pat)
+        if f in ms:
+            files = [f]
+        else:
+            files = []
+    else:
+        m = matchmod.match(repo.root, repo.getcwd(), [pat], ctx=repo[None])
+        files = (f for f in ms if m(f))
+
+    s = set()
+    for f in files:
+        if t == "ancestor":
+            s.add(ms.ancestorchangectx(f).rev())
+        elif t == "local":
+            s.add(ms.localfilectx(f).introrev())
+        elif t == "other":
+            s.add(ms.otherfilectx(f).introrev())
+
+    return subset & s
+
 @predicate('contains(pattern)')
 def contains(repo, subset, x):
     """The revision's manifest contains a file matching pattern (but might not
diff --git a/tests/test-revset.t b/tests/test-revset.t
--- a/tests/test-revset.t
+++ b/tests/test-revset.t
@@ -2230,3 +2230,94 @@ 
   2
 
   $ cd ..
+
+Test merge conflict predicates
+
+  $ hg init conflictrepo
+  $ cd conflictrepo
+  $ echo file1 > file1
+  $ echo file2 > file2
+  $ hg commit -qAm first
+  $ echo line2 >> file1
+  $ hg commit -qAm second
+  $ hg bookmark base
+  $ hg bookmark tree1
+  $ echo line1 > file1
+  $ hg commit -qAm tree1-file1
+  $ echo tree1-file2 > file2
+  $ hg commit -qAm tree1-file2
+  $ echo file3 > file3
+  $ hg commit -qAm tree1-file3
+  $ hg update base
+  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  (activating bookmark base)
+  $ hg bookmark tree2
+  $ echo lineA > file1
+  $ echo line2 >> file1
+  $ hg commit -qAm tree2
+  $ hg bookmark tree2
+  $ echo tree2-file2 > file2
+  $ hg commit -qAm tree2-file2
+  $ echo file4 > file4
+  $ hg commit -qAm tree2-file4
+
+There are no markers before a merge conflict exists
+
+  $ hg debugrevspec 'conflict("ancestor","glob:*")'
+  $ hg debugrevspec 'conflict("local","glob:*")'
+  $ hg debugrevspec 'conflict("other","glob:*")'
+
+Merge and test that the expected set of markers exist and work with patterns
+
+  $ hg merge --rev tree1 --tool :fail
+  1 files updated, 0 files merged, 0 files removed, 2 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
+  [1]
+  $ hg resolve --list
+  U file1
+  U file2
+  $ hg debugrevspec 'conflict("ancestor","glob:*")'
+  1
+  $ hg debugrevspec 'conflict("local","glob:*")'
+  5
+  6
+  $ hg debugrevspec 'conflict("other","glob:*")'
+  2
+  3
+  $ hg debugrevspec 'conflict("ancestor", "file1")'
+  1
+  $ hg debugrevspec 'conflict("local", "file1")'
+  5
+  $ hg debugrevspec 'conflict("other", "file1")'
+  2
+  $ hg debugrevspec 'conflict("ancestor", "file2")'
+  1
+  $ hg debugrevspec 'conflict("local", "file2")'
+  6
+  $ hg debugrevspec 'conflict("other", "file2")'
+  3
+
+There are no markers on files not in conflict
+  $ hg debugrevspec 'conflict("ancestor", "file4")'
+  $ hg debugrevspec 'conflict("local", "file4")'
+  $ hg debugrevspec 'conflict("other","file4")'
+
+It's possible to get interesting sets from markers
+
+  $ hg debugrevspec 'conflict("ancestor", "glob:*"):conflict("local", "file1")'
+  1
+  2
+  3
+  4
+  5
+  $ hg debugrevspec 'conflict("ancestor", "file2"):conflict("other", "re:file[1234]")'
+  1
+  2
+  3
+
+We get a nice error if we ask for a non-existent marker
+
+  $ hg debugrevspec 'conflict("mercurial-versus-sccs", "glob:*")'
+  abort: conflict file types are "ancestor", "other" or "local"
+  [255]
+  $ cd ..