[PATCH] changelog: document the 'readpending' method

Pierre-Yves David pierre-yves.david at ens-lyon.org
Sat Jun 20 01:33:14 CDT 2015

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1411960723 25200
#      Sun Sep 28 20:18:43 2014 -0700
# Node ID 4ee6cb9d4164b381a98359815eaf615a3e207c7e
# Parent  2748bf78a5bf610da4f2d90fd1eea19a3b360c04
changelog: document the 'readpending' method

I happen to have spend some time understanding this logic, so I'm leaving
documentation for the next poor fellow.

diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -257,10 +257,22 @@ class changelog(revlog.revlog):
         self._divert = False
         # split when we're done
     def readpending(self, file):
+        """read index data from a "pending" file
+        During transaction, the actual changesets' data are still stored in the
+        main file, but are not referenced in the official index. Instead a
+        "pending" index is written by the transaction logic. If this function
+        is running, we are likely in a subprocess invoked in a hook. The
+        subprocess is informed that it is within a transaction and need to
+        access it's content.
+        This function will read all the index data out of the pending file and
+        overide the local ones. We just overide a handful of key index related
+        data because everything else is still relevant."""
         if not self.opener.exists(file):
             return # no pending data for changelog
         r = revlog.revlog(self.opener, file)
         self.index = r.index
         self.nodemap = r.nodemap

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