icasefs: make case-folding collision detection as deletion aware (issue3648)

Before this patch, case-folding collision is checked simply between
manifests of each merged revisions.

So, files may be considered as colliding each other, even though one
of them is already deleted on one of merged branches: in such case,
merge causes deleting it, so case-folding collision doesn't occur.

This patch checks whether both of files colliding each other still
remain after merge or not, and ignores collision if at least one of
them is deleted by merge.

In the case that one of colliding files is deleted on one of merged
branches and changed on another, file is considered to still remain
after merge, even though it may be deleted by merge, if "deleting" of
it is chosen in "manifestmerge()".

This avoids fail to merge by case-folding collisions after choices
from "changing" and "deleting" of files.

This patch adds only tests for "removed remotely" code paths in
"_remains()", because other ones are tested by existing tests in
"test-casecollision-merge.t".

mercurial/merge.py

@@ -99,7 +99,26 b' def _checkunknown(repo, wctx, mctx):'
         raise util.Abort(_("untracked files in working directory differ "
                            "from files in requested revision"))
 
-def _checkcollision(mctx, wctx):
+def _remains(f, m, ma, workingctx=False):
+    """check whether specified file remains after merge.
+
+    It is assumed that specified file is not contained in the manifest
+    of the other context.
+    """
+    if f in ma:
+        n = m[f]
+        if n != ma[f]:
+            return True # because it is changed locally
+            # even though it doesn't remain, if "remote deleted" is
+            # chosen in manifestmerge()
+        elif workingctx and n[20:] == "a":
+            return True # because it is added locally (linear merge specific)
+        else:
+            return False # because it is removed remotely
+    else:
+        return True # because it is added locally
+
+def _checkcollision(mctx, extractxs):
     "check for case folding collisions in the destination context"
     folded = {}
     for fn in mctx:
@@ -109,7 +128,8 b' def _checkcollision(mctx, wctx):'
                              % (fn, folded[fold]))
         folded[fold] = fn
 
-    if wctx:
+    if extractxs:
+        wctx, actx = extractxs
         # class to delay looking up copy mapping
         class pathcopies(object):
             @util.propertycache
@@ -121,7 +141,9 b' def _checkcollision(mctx, wctx):'
         for fn in wctx:
             fold = util.normcase(fn)
             mfn = folded.get(fold, None)
-            if mfn and mfn != fn and pc.map.get(mfn) != fn:
+            if (mfn and mfn != fn and pc.map.get(mfn) != fn and
+                _remains(fn, wctx.manifest(), actx.manifest(), True) and
+                _remains(mfn, mctx.manifest(), actx.manifest())):
                 raise util.Abort(_("case-folding collision between %s and %s")
                                  % (mfn, fn))
 
@@ -595,7 +617,7 b' def update(repo, node, branchmerge, forc'
                 (force or not wc.dirty(missing=True, branch=False))):
                 _checkcollision(p2, None)
             else:
-                _checkcollision(p2, wc)
+                _checkcollision(p2, (wc, pa))
         if not force:
             _checkunknown(repo, wc, p2)
         action += _forgetremoved(wc, p2, branchmerge)

tests/test-casecollision-merge.t

@@ -11,8 +11,8 b' test for rename awareness of case-foldin'
 (1) colliding file is one renamed from collided file:
 this is also case for issue3370.
 
-  $ hg init merge_renameaware_1
-  $ cd merge_renameaware_1
+  $ hg init branch_merge_renaming
+  $ cd branch_merge_renaming
 
   $ echo a > a
   $ hg add a
@@ -53,8 +53,8 b' this is also case for issue3370.'
 
 (2) colliding file is not related to collided file
 
-  $ hg init merge_renameaware_2
-  $ cd merge_renameaware_2
+  $ hg init branch_merge_collding
+  $ cd branch_merge_collding
 
   $ echo a > a
   $ hg add a
@@ -66,22 +66,26 b' this is also case for issue3370.'
   $ hg commit -m '#2'
   $ hg update --clean 0
   1 files updated, 0 files merged, 1 files removed, 0 files unresolved
-  $ echo 'modified at #3' > a
+  $ echo x > x
+  $ hg add x
   $ hg commit -m '#3'
   created new head
+  $ echo 'modified at #4' > a
+  $ hg commit -m '#4'
 
   $ hg merge
   abort: case-folding collision between A and a
   [255]
   $ hg parents --template '{rev}\n'
-  3
+  4
   $ hg status -A
   C a
+  C x
   $ cat a
-  modified at #3
+  modified at #4
 
   $ hg update --clean 2
-  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  1 files updated, 0 files merged, 2 files removed, 0 files unresolved
   $ hg merge
   abort: case-folding collision between a and A
   [255]
@@ -92,6 +96,29 b' this is also case for issue3370.'
   $ cat A
   A
 
+test for deletion awareness of case-folding collision check (issue3648):
+revision '#3' doesn't change 'a', so 'a' should be recognized as
+safely removed in merging between #2 and #3.
+
+  $ hg update --clean 3
+  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge 2
+  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg status -A
+  M A
+  R a
+  C x
+
+  $ hg update --clean 2
+  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge 3
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg status -A
+  M x
+  C A
+
   $ cd ..