merge: do early copy to deal with issue636

Without copies/renames, merges source names are 1:1 with their
targets. Copies and renames introduce the possibility that there will
be two merges with the same input but different output. By doing the
copy to the destination name before the merge, the actual merge
becomes 1:1 again, and no source is the input to two different merges.

- add a preliminary scan to applyupdates to do copies
- for the merge action, pass the old name (for finding ancestors) and
  the new name (for input to the merge) to filemerge
- eliminate the old post-merge copy
- lookup file contents from new name in filemerge
- pass new name to external merge helper
- report merge failure at new name
- add a test

tests/test-double-merge

@@ -0,0 +1,30 b''
+#!/bin/sh
+
+hg init repo
+cd repo
+
+echo line 1 > foo
+hg ci -qAm 'add foo' -d "1000000 0"
+
+# copy foo to bar and change both files
+hg cp foo bar
+echo line 2-1 >> foo
+echo line 2-2 >> bar
+hg ci -m 'cp foo bar; change both' -d "1000000 0"
+
+# in another branch, change foo in a way that doesn't conflict with
+# the other changes
+hg up -qC 0
+echo line 0 >| foo
+hg cat foo >> foo
+hg ci -m 'change foo' -d "1000000 0"
+
+# we get conflicts that shouldn't be there
+hg merge --debug
+
+echo "-- foo --"
+cat foo
+
+echo "-- bar --"
+cat bar
+

tests/test-double-merge.out

@@ -0,0 +1,20 b''
+resolving manifests
+ overwrite None partial False
+ ancestor 310fd17130da local 2092631ce82b+ remote 7731dad1c2b9
+ foo: versions differ -> m
+ foo: remote copied to bar -> m
+copying foo to bar
+merging foo and bar
+my foo@2092631ce82b+ other bar@7731dad1c2b9 ancestor foo@310fd17130da
+merging foo
+my foo@2092631ce82b+ other foo@7731dad1c2b9 ancestor foo@310fd17130da
+0 files updated, 2 files merged, 0 files removed, 0 files unresolved
+(branch merge, don't forget to commit)
+-- foo --
+line 0
+line 1
+line 2-1
+-- bar --
+line 0
+line 1
+line 2-2

mercurial/merge.py

@@ -9,10 +9,11 b' from node import *'
 from i18n import _
 import errno, util, os, tempfile, context
 
-def filemerge(repo, fw, fo, wctx, mctx):
+def filemerge(repo, fw, fd, fo, wctx, mctx):
     """perform a 3-way merge in the working directory
 
-    fw = filename in the working directory
+    fw = original filename in the working directory
+    fd = destination filename in the working directory
     fo = filename in other parent
     wctx, mctx = working and merge changecontexts
     """
@@ -27,15 +28,16 b' def filemerge(repo, fw, fo, wctx, mctx):'
         return name
 
     fcm = wctx.filectx(fw)
+    fcmdata = wctx.filectx(fd).data()
     fco = mctx.filectx(fo)
 
-    if not fco.cmp(fcm.data()): # files identical?
+    if not fco.cmp(fcmdata): # files identical?
         return None
 
     fca = fcm.ancestor(fco)
     if not fca:
         fca = repo.filectx(fw, fileid=nullrev)
-    a = repo.wjoin(fw)
+    a = repo.wjoin(fd)
     b = temp("base", fca)
     c = temp("other", fco)
 
@@ -49,11 +51,11 b' def filemerge(repo, fw, fo, wctx, mctx):'
     cmd = (os.environ.get("HGMERGE") or repo.ui.config("ui", "merge")
            or "hgmerge")
     r = util.system('%s "%s" "%s" "%s"' % (cmd, a, b, c), cwd=repo.root,
-                    environ={'HG_FILE': fw,
+                    environ={'HG_FILE': fd,
                              'HG_MY_NODE': str(wctx.parents()[0]),
                              'HG_OTHER_NODE': str(mctx)})
     if r:
-        repo.ui.warn(_("merging %s failed!\n") % fw)
+        repo.ui.warn(_("merging %s failed!\n") % fd)
 
     os.unlink(b)
     os.unlink(c)
@@ -380,6 +382,15 b' def applyupdates(repo, action, wctx, mct'
 
     updated, merged, removed, unresolved = 0, 0, 0, 0
     action.sort()
+    # prescan for copy/renames
+    for a in action:
+        f, m = a[:2]
+        if m == 'm': # merge
+            f2, fd, flags, move = a[2:]
+            if f != fd:
+                repo.ui.debug(_("copying %s to %s\n") % (f, fd))
+                repo.wwrite(fd, repo.wread(f), flags)
+
     for a in action:
         f, m = a[:2]
         if f and f[0] == "/":
@@ -396,7 +407,7 b' def applyupdates(repo, action, wctx, mct'
             removed += 1
         elif m == "m": # merge
             f2, fd, flags, move = a[2:]
-            r = filemerge(repo, f, f2, wctx, mctx)
+            r = filemerge(repo, f, fd, f2, wctx, mctx)
             if r > 0:
                 unresolved += 1
             else:
@@ -404,10 +415,7 b' def applyupdates(repo, action, wctx, mct'
                     updated += 1
                 else:
                     merged += 1
-            if f != fd:
-                repo.ui.debug(_("copying %s to %s\n") % (f, fd))
-                repo.wwrite(fd, repo.wread(f), flags)
-                if move:
+            if f != fd and move:
                     repo.ui.debug(_("removing %s\n") % f)
                     os.unlink(repo.wjoin(f))
             util.set_exec(repo.wjoin(fd), "x" in flags)

tests/test-merge9.out

@@ -5,7 +5,7 b' adding quux2'
 merging bar
 merging bar failed!
 merging foo and baz
-merging foo failed!
+merging baz failed!
 1 files updated, 0 files merged, 0 files removed, 2 files unresolved
 There are unresolved merges, you can redo the full merge using:
   hg update -C 2

tests/test-rename-merge1.out

@@ -7,9 +7,9 b' resolving manifests'
  a2: divergent renames -> dr
  a: remote moved to b -> m
  b2: remote created -> g
+copying a to b
 merging a and b
 my a@f26ec4fc3fa3+ other b@8e765a822af2 ancestor a@af1939970a1c
-copying a to b
 removing a
 warning: detected divergent renames of a2 to:
  c2

tests/test-rename-merge2.out

@@ -6,17 +6,17 b' resolving manifests'
  ancestor 924404dff337 local e300d1c794ec+ remote 735846fee2d7
  rev: versions differ -> m
  a: remote copied to b -> m
+copying a to b
 merging a and b
 my a@e300d1c794ec+ other b@735846fee2d7 ancestor a@924404dff337
-copying a to b
 merging rev
 my rev@e300d1c794ec+ other rev@735846fee2d7 ancestor rev@924404dff337
 0 files updated, 2 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
 --------------
-M a
 M b
   a
+C a
 --------------
 
 --------------
@@ -49,9 +49,9 b' resolving manifests'
  ancestor 924404dff337 local e300d1c794ec+ remote e03727d2d66b
  rev: versions differ -> m
  a: remote moved to b -> m
+copying a to b
 merging a and b
 my a@e300d1c794ec+ other b@e03727d2d66b ancestor a@924404dff337
-copying a to b
 removing a
 merging rev
 my rev@e300d1c794ec+ other rev@e03727d2d66b ancestor rev@924404dff337
@@ -357,9 +357,9 b' resolving manifests'
  ancestor 924404dff337 local e300d1c794ec+ remote 79cc6877a3b7
  rev: versions differ -> m
  a: remote moved to b -> m
+copying a to b
 merging a and b
 my a@e300d1c794ec+ other b@79cc6877a3b7 ancestor a@924404dff337
-copying a to b
 removing a
 merging rev
 my rev@e300d1c794ec+ other rev@79cc6877a3b7 ancestor rev@924404dff337