[PATCH V6] 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
# Branch stable
# Node ID 6ef23dd36dfd7ccd467b55f0ad59ccbe07e4b08c
# Parent  79f0cb97d7537a7c2948f8f9b0a89148825a3a1d
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
@@ -185,6 +185,9 @@ def _forwardcopies(a, b, match=None):
     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 +261,12 @@ def mergecopies(repo, c1, c2, ca):
     if c2.node() is None and c1.node() == repo.dirstate.p1():
         return repo.dirstate.copies(), {}, {}, {}
 
+    # Copy trace disabling is explicitly below the node == p1 logic above
+    # because the logic above is required for a simple copy to be kept across a
+    # rebase.
+    if repo.ui.configbool('experimental', 'disablecopytrace'):
+        return {}, {}, {}, {}
+
     limit = _findlimit(repo, c1.rev(), c2.rev())
     if limit is None:
         # no common ancestor, no copies
@@ -507,7 +516,12 @@ def duplicatecopies(repo, rev, fromrev, 
     copies between fromrev and rev.
     '''
     exclude = {}
-    if skiprev is not None:
+    if (skiprev is not None and
+        not repo.ui.configbool('experimental', 'disablecopytrace')):
+        # disablecopytrace skips this line, but not the entire function because
+        # the line below is O(size of the repo) during a rebase, while the rest
+        # of the function is much faster (and is required for carrying copy
+        # metadata across the rebase anyway).
         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
@@ -59,4 +59,107 @@ 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 'add a'
+  $ touch b
+  $ hg ci -Aqm 'add b, c'
+  $ hg cp b x
+  $ echo x >> x
+  $ hg ci -qm 'copy b->x'
+  $ hg up -q 1
+  $ touch z
+  $ hg ci -Aqm 'add z'
+  $ hg log -G -T '{rev} {desc}\n'
+  @  3 add z
+  |
+  | o  2 copy b->x
+  |/
+  o  1 add b, c
+  |
+  o  0 add a
+  
+  $ hg rebase -d . -b 2 --config extensions.rebase= --config experimental.disablecopytrace=True
+  rebasing 2:6adcf8c12e7d "copy b->x"
+  saved backup bundle to $TESTTMP/copydisable/.hg/strip-backup/6adcf8c12e7d-ce4b3e75-backup.hg (glob)
+  $ hg up -q 3
+  $ hg log -f x -T '{rev} {desc}\n'
+  3 copy b->x
+  1 add b, c
+
+  $ cd ../
+
+Verify we duplicate existing copies, instead of detecting them
+
+  $ hg init copydisable3
+  $ cd copydisable3
+  $ touch a
+  $ hg ci -Aqm 'add a'
+  $ hg cp a b
+  $ hg ci -Aqm 'copy a->b'
+  $ hg mv b c
+  $ hg ci -Aqm 'move b->c'
+  $ hg up -q 0
+  $ hg cp a b
+  $ echo b >> b
+  $ hg ci -Aqm 'copy a->b (2)'
+  $ hg log -G -T '{rev} {desc}\n'
+  @  3 copy a->b (2)
+  |
+  | o  2 move b->c
+  | |
+  | o  1 copy a->b
+  |/
+  o  0 add a
+  
+  $ hg rebase -d 2 -s 3 --config extensions.rebase= --config experimental.disablecopytrace=True
+  rebasing 3:47e1a9e6273b "copy a->b (2)" (tip)
+  saved backup bundle to $TESTTMP/copydisable3/.hg/strip-backup/47e1a9e6273b-2d099c59-backup.hg (glob)
+
+  $ hg log -G -f b
+  @  changeset:   3:76024fb4b05b
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     copy a->b (2)
+  |
+  o  changeset:   0:ac82d8b1f7c4
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     add a
+