copies: filter invalid copies only at end of pathcopies() (issue6163)

copies._filter() filters out copies whose source file does not exist
in the start commit or whose target file does not exist in the end
commit. We do that after chaining copies with dirstate copies or
backward renames from another branch. We also do at the end of the
changeset-centric copy tracing. The filtering means that we will
remove copies to/from files that did not exist in some intermediate
commit. That is inconsistent with what we do if a file has been
deleted and then re-added (we allow updating across that).

Copying the two first examples from issue6163:

  @  4 'rename x to y'
  |
  o  3 'add x again'
  |
  o  2 'remove x'
  |
  | o  1 'modify x'
  |/
  o  0 'add x'

  @  4 'rename x to y'
  |
  o  3 'add x again'
  |
  | o  2 'modify x'
  | |
  | o  1 'add x'
  |/
  o  0 'base'

When doing `hg rebase -r 1 -d 4` in the first case, it succeeds, but
`hg rebase -r 2 -d 4` in the second case does not. That's because we
chain and filter via commit 0, which does not have file 'x' in the
second case. IMO, that's clearly inconsistent. So this patch removes
the filtering step so it only happens at the end. If a file was
temporarily removed, whether via a merge base or not, it will now
still be considered the same file. That fixes issue6163 for the
changeset-centric case.

Differential Revision: https://phab.mercurial-scm.org/D6603

mercurial/copies.py

@@ -285,7 +285,6 b' def _changesetforwardcopies(a, b, match)'
                     # that side, even if it was also copied on the p2 side.
                     copies[dst] = copies2[dst]
         if r == b.rev():
-            _filter(a, b, copies)
             return copies
         for i, c in enumerate(children[r]):
             childctx = repo[c]
@@ -321,7 +320,6 b' def _forwardcopies(a, b, match=None):'
         cm = _committedforwardcopies(a, b.p1(), match)
         # combine copies from dirstate if necessary
         copies = _chain(cm, _dirstatecopies(b._repo, match))
-        _filter(a, b, copies)
     else:
         copies  = _committedforwardcopies(a, b, match)
     return copies
@@ -373,7 +371,7 b' def pathcopies(x, y, match=None):'
             repo.ui.debug('debug.copies: search mode: combined\n')
         copies = _chain(_backwardrenames(x, a, match=match),
                         _forwardcopies(a, y, match=match))
-        _filter(x, y, copies)
+    _filter(x, y, copies)
     return copies
 
 def mergecopies(repo, c1, c2, base):

tests/test-copies-unrelated.t

@@ -299,6 +299,8 b' above, but here the break in history is '
   o  0 base
      a
   $ hg debugpathcopies 1 4
+  x -> y (no-filelog !)
+#if filelog
 BROKEN: This should succeed and merge the changes from x into y
   $ hg graft -r 2
   grafting 2:* "modify x" (glob)
@@ -308,6 +310,11 b' BROKEN: This should succeed and merge th'
   abort: unresolved conflicts, can't continue
   (use 'hg resolve' and 'hg graft --continue')
   [255]
+#else
+  $ hg graft -r 2
+  grafting 2:* "modify x" (glob)
+  merging y and x to y
+#endif
   $ hg co -qC 2
   $ hg graft -r 4
   grafting 4:* "rename x to y"* (glob)
@@ -345,6 +352,8 b' different between the branches.'
   o  0 base
      a
   $ hg debugpathcopies 1 5
+  x -> y (no-filelog !)
+#if filelog
 BROKEN: This should succeed and merge the changes from x into y
   $ hg graft -r 2
   grafting 2:* "modify x" (glob)
@@ -354,6 +363,11 b' BROKEN: This should succeed and merge th'
   abort: unresolved conflicts, can't continue
   (use 'hg resolve' and 'hg graft --continue')
   [255]
+#else
+  $ hg graft -r 2
+  grafting 2:* "modify x" (glob)
+  merging y and x to y
+#endif
   $ hg co -qC 2
 BROKEN: This should succeed and merge the changes from x into y
   $ hg graft -r 5

tests/test-copies.t

@@ -354,8 +354,7 b' of the merge to the merge should include'
   $ hg debugpathcopies 1 3
   x -> z
 
-Copy x to y on one side of merge, create y and rename to z on the other side. Pathcopies from the
-first side should not include the y->z rename since y didn't exist in the merge base.
+Copy x to y on one side of merge, create y and rename to z on the other side.
   $ newrepo
   $ echo x > x
   $ hg ci -Aqm 'add x'
@@ -385,6 +384,7 b' first side should not include the y->z r'
   $ hg debugpathcopies 2 3
   y -> z
   $ hg debugpathcopies 1 3
+  y -> z (no-filelog !)
 
 Create x and y, then rename x to z on one side of merge, and rename y to z and
 modify z on the other side. When storing copies in the changeset, we don't