[PATCH STABLE] revert: properly revert to ancestor of p2 during merge

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1456224107 -3600
#      Tue Feb 23 11:41:47 2016 +0100
# Branch stable
# Node ID aa94f42b742e958bd9c3f2f7a82722a7058aee76
# Parent  1bcb4f34b9f91a2e330966182f691664fbada1bc
# Available At http://hg.netv6.net/marmoute-wip/mercurial/
#              hg pull http://hg.netv6.net/marmoute-wip/mercurial/ -r aa94f42b742e
revert: properly revert to ancestor of p2 during merge

During merge, added (from one perspective) file can be reported as "modified".
To work around that, revert was testing if modified file where present in the
parent manifest and marking them as "added" in this case. However, we should be
checking against the target revision manifest instead. Otherwise see file as
"newly added" even if they exist in the target revision.

That revert behavior regressed in 06fbd9518bc5.

Note: in this patch we can notice that we are building a set out of a manifest,
breaking effort for manifest laziness introduced since this code was written.
Fixing it is another adventure.

diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2844,14 +2844,10 @@ def revert(ui, repo, ctx, parents, *pats
     node = ctx.node()
 
     mf = ctx.manifest()
     if node == p2:
         parent = p2
-    if node == parent:
-        pmf = mf
-    else:
-        pmf = None
 
     # need all matching names in dirstate and manifest of target rev,
     # so have to walk both. do not print errors if files exist in one
     # but not other. in both cases, filesets should be evaluated against
     # workingctx to get consistent result (issue4497). this means 'set:**'
@@ -2962,15 +2958,11 @@ def revert(ui, repo, ctx, parents, *pats
             dsadded = added
 
         # in case of merge, files that are actually added can be reported as
         # modified, we need to post process the result
         if p2 != nullid:
-            if pmf is None:
-                # only need parent manifest in the merge case,
-                # so do not read by default
-                pmf = repo[parent].manifest()
-            mergeadd = dsmodified - set(pmf)
+            mergeadd = dsmodified - set(mf)
             dsadded |= mergeadd
             dsmodified -= mergeadd
 
         # if f is a rename, update `names` to also revert the source
         cwd = repo.getcwd()
diff --git a/tests/test-revert.t b/tests/test-revert.t
--- a/tests/test-revert.t
+++ b/tests/test-revert.t
@@ -1074,5 +1074,74 @@ check resulting directory against the --
 
   $ python ../dircontent.py > ../content-base-explicit.txt
   $ cd ..
   $ diff -U 0 -- content-base-all.txt content-base-explicit.txt | grep _
   [1]
+
+Revert to an ancestor of P2 during a merge (issue5052)
+-----------------------------------------------------
+
+(prepare the repository)
+
+  $ hg init issue5052
+  $ cd issue5052
+  $ echo '.\.orig' > .hgignore
+  $ echo 0 > root
+  $ hg ci -qAm C0
+  $ echo 0 > A
+  $ hg ci -qAm C1
+  $ echo 1 >> A
+  $ hg ci -qm C2
+  $ hg up -q 0
+  $ echo 1 > B
+  $ hg ci -qAm C3
+  $ hg status --rev 'ancestor(.,2)' --rev 2
+  A A
+  $ hg log -G -T '{rev} ({files})\n'
+  @  3 (B)
+  |
+  | o  2 (A)
+  | |
+  | o  1 (A)
+  |/
+  o  0 (.hgignore root)
+  
+
+actual tests: reverting to something else than a merge parent
+
+  $ hg merge
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+
+  $ hg status --rev 'p1()'
+  M A
+  $ hg status --rev 'p2()'
+  A B
+  $ hg status --rev '1'
+  M A
+  A B
+  $ hg revert --rev 1 --all
+  reverting A
+  removing B
+  $ hg status --rev 1
+
+From the other parents
+
+  $ hg up -C 'p2()'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+
+  $ hg status --rev 'p1()'
+  M B
+  $ hg status --rev 'p2()'
+  A A
+  $ hg status --rev '1'
+  M A
+  A B
+  $ hg revert --rev 1 --all
+  reverting A
+  removing B
+  $ hg status --rev 1
+
+  $ cd ..