[PATCH v2 STABLE] amend: fix amending rename commit with obsolescence markers (issue4405)

[Ryan McElroy]

# HG changeset patch
# User Ryan McElroy <rmcelroy at fb.com>
# Date 1413466506 25200
#      Thu Oct 16 06:35:06 2014 -0700
# Node ID d4c47f740c3e1e51789ee976de7dcaa6974e815a
# Parent  f10019d2ee0afa2cc629a5e5409803e14fb40697
amend: fix amending rename commit with obsolescence markers (issue4405)

This addresses the bug described in issue4405: when obsolescence markers are
enabled, amending a commit with a file move can lead to the copy information
being lost.

diff --git a/mercurial/copies.py b/mercurial/copies.py
--- a/mercurial/copies.py
+++ b/mercurial/copies.py
@@ -19,7 +19,12 @@
     return f[:s]
 
 def _findlimit(repo, a, b):
-    """Find the earliest revision that's an ancestor of a or b but not both,
+    """
+    Find the last revision that needs to be checked to ensure that a full
+    transitive closure for file copies can be properly calculated.
+    Generally, this means finding the earliest revision number that's an
+    ancestor of a or b but not both, except when a or b is a direct descendent
+    of the other, in which case we can return the minimum revnum of a and b.
     None if no such revision exists.
     """
     # basic idea:
@@ -73,7 +78,32 @@
 
     if not hascommonancestor:
         return None
-    return limit
+
+    # Consider the following flow (see test-commit-amend.t under issue4405):
+    # 1/ File 'a' committed
+    # 2/ File renamed from 'a' to 'b' in a new commit
+    # 3/ Commit messaged updated with amend
+    # 4/ File renamed from 'b' to 'c' and commit (2) amended
+    #
+    # When obsolescence markers are enabled, this would create a graph like:
+    # @  4 mv b c
+    # |
+    # | x  3 temporary amend commit for 60e352014901
+    # | |
+    # | x  2 change message
+    # |/
+    # | x  1 mv a b
+    # |/
+    # o  0 add a
+    #
+    # During the second amend (step 4), limit is calculated to be 3, which does
+    # not look back far enough to reconstruct the full transitive closure of the
+    # renames.
+    #
+    # In this case, a is rev 4 and b is rev 0; taking the minimum of these three
+    # ensures that we always look back far enough when we have obsolescence
+    # markers enabled.
+    return min(limit, a, b)
 
 def _chain(src, dst, a, b):
     '''chain two sets of copies a->b'''
diff --git a/tests/test-commit-amend.t b/tests/test-commit-amend.t
--- a/tests/test-commit-amend.t
+++ b/tests/test-commit-amend.t
@@ -854,3 +854,38 @@
   HG: changed foo
   $ hg parents --template "{desc}\n"
   editor should be invoked
+
+Check for issue4405
+  $ cat > obs.py << EOF
+  > import mercurial.obsolete
+  > mercurial.obsolete._enabled = True
+  > EOF
+  $ cat >> $HGRCPATH <<EOF
+  > [extensions]
+  > EOF
+  $ echo "obs=${TESTTMP}/obs.py" >> $HGRCPATH
+  $ hg init repo
+  $ cd repo
+  $ echo a > a
+  $ hg add a
+  $ hg commit -m a
+  $ hg mv a b
+  $ hg commit -m 'mv a b'
+  $ hg st -C --change .
+  A b
+    a
+  R a
+  $ hg commit --amend -m 'change commit message'
+  $ hg st -C --change .
+  A b
+    a
+  R a
+  $ hg mv b c
+  $ hg commit --amend -m 'mv b c'
+  $ hg st -C --change .
+  A c
+    a
+  R a
+  $ rm ${TESTTMP}/obs.py
+  $ rm $HGRCPATH
+  $ cd ..