diff mercurial/copies.py @ 44758:45f3f35cefe7

copies: fix the changeset based algorithm regarding merge

In 99ebde4fec99, we changed the list of files stored into the `files` field.
This lead to the changeset centric copy algorithm to break in various merge
situation involving merge. Older information could reach the merge through
`p1`, and while information from `p2` was strictly fresher, it would get
overwritten anyway.

We update the situation with more details about which revision introduces rename
information. This help use making the right decision in case of merge.

We are now running a more comprehensive suite of test with include this kind of
situation. The behavior differ slightly from the filelog based in a couple of
instance. There is mostly two distinct cases:

1) there are conflicting rename information in a merge (different rename history
on each side). In this case the filelog based implementation arbitrarily pick a
side based on the file-revision-number. So it depends on a local factor. The
changeset centric algorithm will use a deterministic approach, by picking the
information coming from the first parent of the merge. This is stable across
different clone.

2) rename information related to file that exist in both source and destination.
The filelog based implementation do not even try to detect these, however the
changeset centric one get them for "free" (it is simpler to detect them than
not).

The new implementation focus on correctness. Performance improvement will come
later.

Differential Revision: https://phab.mercurial-scm.org/D8244

--- a/mercurial/copies.py	Fri Apr 24 15:06:42 2020 -0400
+++ b/mercurial/copies.py	Thu Mar 05 17:55:05 2020 +0100
@@ -183,10 +183,27 @@
     * p1copies: mapping of copies from p1
     * p2copies: mapping of copies from p2
     * removed: a list of removed files
+    * ismerged: a callback to know if file was merged in that revision
     """
     cl = repo.changelog
     parents = cl.parentrevs
 
+    def get_ismerged(rev):
+        ctx = repo[rev]
+
+        def ismerged(path):
+            if path not in ctx.files():
+                return False
+            fctx = ctx[path]
+            parents = fctx._filelog.parents(fctx._filenode)
+            nb_parents = 0
+            for n in parents:
+                if n != node.nullid:
+                    nb_parents += 1
+            return nb_parents >= 2
+
+        return ismerged
+
     if repo.filecopiesmode == b'changeset-sidedata':
         changelogrevision = cl.changelogrevision
         flags = cl.flags
@@ -218,6 +235,7 @@
 
         def revinfo(rev):
             p1, p2 = parents(rev)
+            value = None
             if flags(rev) & REVIDX_SIDEDATA:
                 e = merge_caches.pop(rev, None)
                 if e is not None:
@@ -228,12 +246,22 @@
                 removed = c.filesremoved
                 if p1 != node.nullrev and p2 != node.nullrev:
                     # XXX some case we over cache, IGNORE
-                    merge_caches[rev] = (p1, p2, p1copies, p2copies, removed)
+                    value = merge_caches[rev] = (
+                        p1,
+                        p2,
+                        p1copies,
+                        p2copies,
+                        removed,
+                        get_ismerged(rev),
+                    )
             else:
                 p1copies = {}
                 p2copies = {}
                 removed = []
-            return p1, p2, p1copies, p2copies, removed
+
+            if value is None:
+                value = (p1, p2, p1copies, p2copies, removed, get_ismerged(rev))
+            return value
 
     else:
 
@@ -242,7 +270,7 @@
             ctx = repo[rev]
             p1copies, p2copies = ctx._copies
             removed = ctx.filesremoved()
-            return p1, p2, p1copies, p2copies, removed
+            return p1, p2, p1copies, p2copies, removed, get_ismerged(rev)
 
     return revinfo
 
@@ -256,6 +284,7 @@
     revinfo = _revinfogetter(repo)
 
     cl = repo.changelog
+    isancestor = cl.isancestorrev  # XXX we should had chaching to this.
     missingrevs = cl.findmissingrevs(common=[a.rev()], heads=[b.rev()])
     mrset = set(missingrevs)
     roots = set()
@@ -283,10 +312,14 @@
     iterrevs.update(roots)
     iterrevs.remove(b.rev())
     revs = sorted(iterrevs)
-    return _combinechangesetcopies(revs, children, b.rev(), revinfo, match)
+    return _combinechangesetcopies(
+        revs, children, b.rev(), revinfo, match, isancestor
+    )
 
 
-def _combinechangesetcopies(revs, children, targetrev, revinfo, match):
+def _combinechangesetcopies(
+    revs, children, targetrev, revinfo, match, isancestor
+):
     """combine the copies information for each item of iterrevs
 
     revs: sorted iterable of revision to visit
@@ -305,7 +338,7 @@
             # this is a root
             copies = {}
         for i, c in enumerate(children[r]):
-            p1, p2, p1copies, p2copies, removed = revinfo(c)
+            p1, p2, p1copies, p2copies, removed, ismerged = revinfo(c)
             if r == p1:
                 parent = 1
                 childcopies = p1copies
@@ -319,9 +352,12 @@
                 }
             newcopies = copies
             if childcopies:
-                newcopies = _chain(newcopies, childcopies)
-                # _chain makes a copies, we can avoid doing so in some
-                # simple/linear cases.
+                newcopies = copies.copy()
+                for dest, source in pycompat.iteritems(childcopies):
+                    prev = copies.get(source)
+                    if prev is not None and prev[1] is not None:
+                        source = prev[1]
+                    newcopies[dest] = (c, source)
                 assert newcopies is not copies
             for f in removed:
                 if f in newcopies:
@@ -330,7 +366,7 @@
                         # branches.  when there are no other branches, this
                         # could be avoided.
                         newcopies = copies.copy()
-                    del newcopies[f]
+                    newcopies[f] = (c, None)
             othercopies = all_copies.get(c)
             if othercopies is None:
                 all_copies[c] = newcopies
@@ -338,21 +374,55 @@
                 # we are the second parent to work on c, we need to merge our
                 # work with the other.
                 #
-                # Unlike when copies are stored in the filelog, we consider
-                # it a copy even if the destination already existed on the
-                # other branch. It's simply too expensive to check if the
-                # file existed in the manifest.
-                #
                 # In case of conflict, parent 1 take precedence over parent 2.
                 # This is an arbitrary choice made anew when implementing
                 # changeset based copies. It was made without regards with
                 # potential filelog related behavior.
                 if parent == 1:
-                    othercopies.update(newcopies)
+                    _merge_copies_dict(
+                        othercopies, newcopies, isancestor, ismerged
+                    )
                 else:
-                    newcopies.update(othercopies)
+                    _merge_copies_dict(
+                        newcopies, othercopies, isancestor, ismerged
+                    )
                     all_copies[c] = newcopies
-    return all_copies[targetrev]
+
+    final_copies = {}
+    for dest, (tt, source) in all_copies[targetrev].items():
+        if source is not None:
+            final_copies[dest] = source
+    return final_copies
+
+
+def _merge_copies_dict(minor, major, isancestor, ismerged):
+    """merge two copies-mapping together, minor and major
+
+    In case of conflict, value from "major" will be picked.
+
+    - `isancestors(low_rev, high_rev)`: callable return True if `low_rev` is an
+                                        ancestors of `high_rev`,
+
+    - `ismerged(path)`: callable return True if `path` have been merged in the
+                        current revision,
+    """
+    for dest, value in major.items():
+        other = minor.get(dest)
+        if other is None:
+            minor[dest] = value
+        else:
+            new_tt = value[0]
+            other_tt = other[0]
+            if value[1] == other[1]:
+                continue
+            # content from "major" wins, unless it is older
+            # than the branch point or there is a merge
+            if (
+                new_tt == other_tt
+                or not isancestor(new_tt, other_tt)
+                or ismerged(dest)
+            ):
+                minor[dest] = value
 
 
 def _forwardcopies(a, b, base=None, match=None):