filectx.parents: enforce changeid of parent to be in own changectx ancestors Because of the way filenodes are computed, you can have multiple changesets "introducing" the same file revision. For example, in the changeset graph below, changeset 2 and 3 both change a file -to- and -from- the same content. o 3: content = new | | o 2: content = new |/ o 1: content = old In such cases, the file revision is create once, when 2 is added, and just reused for 3. So the file change in '3' (from "old" to "new)" has no linkrev pointing to it). We'll call this situation "linkrev-shadowing". As the linkrev is used for optimization purposes when walking a file history, the linkrev-shadowing results in an unexpected jump to another branch during such a walk.. This leads to multiple bugs with log, annotate and rename detection. One element to fix such bugs is to ensure that walking the file history sticks on the same topology as the changeset's history. For this purpose, we extend the logic in 'basefilectx.parents' so that it always defines the proper changeset to associate the parent file revision with. This "proper" changeset has to be an ancestor of the changeset associated with the child file revision. This logic is performed in the '_adjustlinkrev' function. This function is given the starting changeset and all the information regarding the parent file revision. If the linkrev for the file revision is an ancestor of the starting changeset, the linkrev is valid and will be used. If it is not, we detected a topological jump caused by linkrev shadowing, we are going to walk the ancestors of the starting changeset until we find one setting the file to the revision we are trying to create. The performance impact appears acceptable: - We are walking the changelog once for each filelog traversal (as there should be no overlap between searches), - changelog traversal itself is fairly cheap, compared to what is likely going to be perform on the result on the filelog traversal, - We only touch the manifest for ancestors touching the file, And such changesets are likely to be the one introducing the file. (except in pathological cases involving merge), - We use manifest diff instead of full manifest unpacking to check manifest content, so it does not involve applying multiple diffs in most case. - linkrev shadowing is not the common case. Tests for fixed issues in log, annotate and rename detection have been added. But this changeset does not solve all problems. It fixes -ancestry- computation, but if the linkrev-shadowed changesets is the starting one, we'll still get things wrong. We'll have to fix the bootstrapping of such operations in a later changeset. Also, the usage of `hg log FILE` without --follow still has issues with linkrev pointing to hidden changesets, because it relies on the `filelog` revset which implement its own traversal logic that is still to be fixed. Thanks goes to: - Matt Mackall: for nudging me in the right direction - Julien Cristau and R?mi Cardona: for keep telling me linkrev bug were an evolution show stopper for 3 years. - Durham Goode: for finding a new linkrev issue every few weeks - Mads Kiilerich: for that last rename bug who raise this topic over my anoyance limit.

--- a/mercurial/context.py	Wed Dec 31 17:55:43 2014 +0900
+++ b/mercurial/context.py	Tue Dec 23 15:30:38 2014 -0800
@@ -22,6 +22,40 @@
 # dirty in the working copy.
 _newnode = '!' * 21
 
+def _adjustlinkrev(repo, path, filelog, fnode, srcrev):
+    """return the first ancestor of <srcrev> introducting <fnode>
+
+    If the linkrev of the file revision does not point to an ancestor of
+    srcrev, we'll walk down the ancestors until we find one introducing this
+    file revision.
+
+    :repo: a localrepository object (used to access changelog and manifest)
+    :path: the file path
+    :fnode: the nodeid of the file revision
+    :filelog: the filelog of this path
+    :srcrev: the changeset revision we search ancestors from
+    """
+    cl = repo.unfiltered().changelog
+    ma = repo.manifest
+    # fetch the linkrev
+    fr = filelog.rev(fnode)
+    lkr = filelog.linkrev(fr)
+    # check if this linkrev is an ancestor of srcrev
+    anc = cl.ancestors([srcrev], lkr)
+    if lkr not in anc:
+        for a in anc:
+            ac = cl.read(a) # get changeset data (we avoid object creation).
+            if path in ac[3]: # checking the 'files' field.
+                # The file has been touched, check if the content is similar
+                # to the one we search for.
+                if fnode == ma.readdelta(ac[0]).get(path):
+                    return a
+        # In theory, we should never get out of that loop without a result. But
+        # if manifest uses a buggy file revision (not children of the one it
+        # replaces) we could. Such a buggy situation will likely result is crash
+        # somewhere else at to some point.
+    return lkr
+
 class basectx(object):
     """A basectx object represents the common logic for its children:
     changectx: read-only context that is already present in the repo,
@@ -739,7 +773,7 @@
         parents = self._filelog.parents(self._filenode)
         pl = [(_path, node, fl) for node in parents if node != nullid]
 
-        r = self._filelog.renamed(self._filenode)
+        r = fl.renamed(self._filenode)
         if r:
             # - In the simple rename case, both parent are nullid, pl is empty.
             # - In case of merge, only one of the parent is null id and should
@@ -751,7 +785,19 @@
             # first nullid parent with rename information.
             pl.insert(0, (r[0], r[1], self._repo.file(r[0])))
 
-        return [filectx(self._repo, p, fileid=n, filelog=l) for p, n, l in pl]
+        ret = []
+        for path, fnode, l in pl:
+            if '_changeid' in vars(self) or '_changectx' in vars(self):
+                # If self is associated with a changeset (probably explicitly
+                # fed), ensure the created filectx is associated with a
+                # changeset that is an ancestor of self.changectx.
+                rev = _adjustlinkrev(self._repo, path, l, fnode, self.rev())
+                fctx = filectx(self._repo, path, fileid=fnode, filelog=l,
+                               changeid=rev)
+            else:
+                fctx = filectx(self._repo, path, fileid=fnode, filelog=l)
+            ret.append(fctx)
+        return ret
 
     def p1(self):
         return self.parents()[0]