[PATCH V3] copy: add flag for disabling copy tracing

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1422386787 28800
#      Tue Jan 27 11:26:27 2015 -0800
# Node ID 4ca99cf25f530edf9114c9aa24a7b2e41c7d6b20
# Parent  52ff737c63d2b2cb41185549aa9c35bc47317032
copy: add flag for disabling copy tracing

Copy tracing can be up to 80% of rebase time when rebasing stacks
of commits in large repos (hundreds of thousands of files).
This provides the option of turning off the majority of copy tracing. It
does not turn off _forwardcopies() since that is used to carry copy
information inside a commit across a rebase.

This will affect the situation where a user edits a file, then rebases on top of
commits that have moved that file. The move will not be detected and the user
will have to manually resolve the issue (possibly by redoing the rebase with
this flag off).

This takes rebasing a 3 commit stack that's a couple weeks old from 65s to 12s.

diff --git a/mercurial/copies.py b/mercurial/copies.py
--- a/mercurial/copies.py
+++ b/mercurial/copies.py
@@ -186,6 +186,9 @@ def _forwardcopies(a, b):
     return cm
 
 def _backwardrenames(a, b):
+    if a._repo.ui.configbool('experimental', 'disablecopytrace'):
+        return {}
+
     # Even though we're not taking copies into account, 1:n rename situations
     # can still exist (e.g. hg cp a b; hg mv a c). In those cases we
     # arbitrarily pick one of the renames.
@@ -258,6 +261,13 @@ def mergecopies(repo, c1, c2, ca):
     if c2.node() is None and c1.node() == repo.dirstate.p1():
         return repo.dirstate.copies(), {}, {}, {}
 
+    if repo.ui.configbool('experimental', 'disablecopytrace'):
+        # If we're just tracking against the parent, do a simple check.
+        # This is necessary to ensure copies survive rebasing.
+        if ca in c2.parents():
+            return pathcopies(ca, c2), {}, {}, {}
+        return {}, {}, {}, {}
+
     limit = _findlimit(repo, c1.rev(), c2.rev())
     if limit is None:
         # no common ancestor, no copies
@@ -506,7 +516,8 @@ def duplicatecopies(repo, rev, fromrev, 
     copies between fromrev and rev.
     '''
     exclude = {}
-    if skiprev is not None:
+    if (skiprev is not None and
+        repo.ui.configbool('experimental', 'disablecopytrace')):
         exclude = pathcopies(repo[fromrev], repo[skiprev])
     for dst, src in pathcopies(repo[fromrev], repo[rev]).iteritems():
         # copies.pathcopies returns backward renames, so dst might not
diff --git a/tests/test-copy-move-merge.t b/tests/test-copy-move-merge.t
--- a/tests/test-copy-move-merge.t
+++ b/tests/test-copy-move-merge.t
@@ -61,4 +61,73 @@ file c
   1
   2
 
+Test disabling copy tracing
+
+- first verify copy metadata was kept
+
+  $ hg up -qC 2
+  $ hg rebase --keep -d 1 -b 2 --config extensions.rebase=
+  rebasing 2:add3f11052fa "other" (tip)
+  merging b and a to b
+  merging c and a to c
+
+  $ cat b
+  0
+  1
+  2
+
+- next verify copy metadata is lost when disabled
+
+  $ hg strip -r . --config extensions.strip=
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  saved backup bundle to $TESTTMP/t/.hg/strip-backup/550bd84c0cd3-fc575957-backup.hg (glob)
+  $ hg up -qC 2
+  $ hg rebase --keep -d 1 -b 2 --config extensions.rebase= --config experimental.disablecopytrace=True
+  rebasing 2:add3f11052fa "other" (tip)
+  remote changed a which local deleted
+  use (c)hanged version or leave (d)eleted? c
+
+  $ cat b
+  1
+  2
+
   $ cd ..
+
+Verify disabling copy tracing still keeps copies from rebase source
+
+  $ hg init copydisable
+  $ cd copydisable
+  $ touch a
+  $ hg ci -Aqm a
+  $ touch b
+  $ touch c
+  $ hg ci -Aqm b
+  $ hg cp b x
+  $ hg cp c y
+  $ echo x >> x
+  $ hg ci -qm xy
+  $ hg up -q 1
+  $ hg cp b x
+  $ touch z
+  $ hg ci -Aqm xz
+  $ hg log -G -T '{rev} {desc}\n'
+  @  3 xz
+  |
+  | o  2 xy
+  |/
+  o  1 b
+  |
+  o  0 a
+  
+  $ hg rebase -d . -b 2 --config extensions.rebase= --config experimental.disablecopytrace=True
+  rebasing 2:002ca7a9f426 "xy"
+  merging x
+  saved backup bundle to $TESTTMP/copydisable/.hg/strip-backup/002ca7a9f426-19f9ad1e-backup.hg (glob)
+  $ hg up -q 3
+  $ hg log -f x -T '{rev} {desc}\n'
+  3 xy
+  2 xz
+  1 b
+  $ hg log -f y -T '{rev} {desc}\n'
+  3 xy
+  1 b