Patchwork [1,of,7] dirstate: introduce new context manager for marking dirstate parent changes

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Submitter Augie Fackler
Date May 18, 2017, 10:19 p.m.
Message ID <a69ba7abd7c7396205bb.1495145986@augie-macbookpro2.roam.corp.google.com>
Download mbox | patch
Permalink /patch/20693/
State Superseded
Headers show

Comments

Augie Fackler - May 18, 2017, 10:19 p.m.
# HG changeset patch
# User Augie Fackler <augie@google.com>
# Date 1495141830 14400
#      Thu May 18 17:10:30 2017 -0400
# Node ID a69ba7abd7c7396205bbf44984fc5bd028a7f815
# Parent  1f3972ed06833775ada5b23d9c90d1cbb240e4fd
dirstate: introduce new context manager for marking dirstate parent changes
Gregory Szorc - May 19, 2017, 12:37 a.m.
On Thu, May 18, 2017 at 3:19 PM, Augie Fackler <raf@durin42.com> wrote:

> # HG changeset patch
> # User Augie Fackler <augie@google.com>
> # Date 1495141830 14400
> #      Thu May 18 17:10:30 2017 -0400
> # Node ID a69ba7abd7c7396205bbf44984fc5bd028a7f815
> # Parent  1f3972ed06833775ada5b23d9c90d1cbb240e4fd
> dirstate: introduce new context manager for marking dirstate parent changes
>
> diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
> --- a/mercurial/dirstate.py
> +++ b/mercurial/dirstate.py
> @@ -8,6 +8,7 @@
>  from __future__ import absolute_import
>
>  import collections
> +import contextlib
>  import errno
>  import os
>  import stat
> @@ -99,6 +100,18 @@ class dirstate(object):
>          # for consistent view between _pl() and _read() invocations
>          self._pendingmode = None
>
> +    @contextlib.contextmanager
> +    def parentchange(self):
> +        '''Context manager for handling dirstate parents.
> +
> +        If an exception occurs in the scope of the context manager,
> +        the incoherent dirstate won't be written when wlock is
> +        released.
> +        '''
> +        self._parentwriters += 1
> +        yield
> +        self._parentwriters -= 1
>
>
I assume the docstring explains why this isn't a try..finally, as one would
expect in most @contextmanager's. While the context is literally right
there today, I can't help but wonder if it warrants an inline comment
instead in case the docstring no longer shows up in the context of a future
diff. Or maybe it should be written to something like:

self._parentwriters += 1
try:
    yield
except Exception:
    # Don't decrement writer count because it shouldn't be written after
error.
    raise
else:
    self._parentwriters -= 1

(Yes, I'm likely being overly pedantic here. But not seeing try..finally in
@contextmanager really bothers my reviewer brain. IMO we should have a
style rule to enforce the pattern because it is such an easy mistake to
make.)


>      def beginparentchange(self):
>          '''Marks the beginning of a set of changes that involve changing
>          the dirstate parents. If there is an exception during this time,
> _______________________________________________
> Mercurial-devel mailing list
> Mercurial-devel@mercurial-scm.org
> https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel
>

Patch

diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -8,6 +8,7 @@ 
 from __future__ import absolute_import
 
 import collections
+import contextlib
 import errno
 import os
 import stat
@@ -99,6 +100,18 @@  class dirstate(object):
         # for consistent view between _pl() and _read() invocations
         self._pendingmode = None
 
+    @contextlib.contextmanager
+    def parentchange(self):
+        '''Context manager for handling dirstate parents.
+
+        If an exception occurs in the scope of the context manager,
+        the incoherent dirstate won't be written when wlock is
+        released.
+        '''
+        self._parentwriters += 1
+        yield
+        self._parentwriters -= 1
+
     def beginparentchange(self):
         '''Marks the beginning of a set of changes that involve changing
         the dirstate parents. If there is an exception during this time,