convert: add a mode where mercurial_sink skips empty revisions.

The getchanges function of some converter_source classes can return
some false positives.  I.e. they sometimes claim that a file "foo"
was changed in some revision, even though its contents are still the
same.

convert_svn is particularly bad, but I think this can also happen with
convert_cvs and, at least in theory, with mercurial_source.

For regular conversions this is not really a problem - as long as
getfile returns the right contents, we'll get a converted revision
with the right contents.  But when we use --filemap, this could lead
to superfluous revisions being converted.

Instead of fixing every converter_source, I decided to change
mercurial_sink to work around this problem.

When --filemap is used, we're interested only in revisions that touch
some specific files.  If a revision doesn't change any of these files,
then we're not interested in it (at least for revisions with a single
parent; merges are special).

For mercurial_sink, we abuse this property and rollback a commit if
the manifest text hasn't changed.  This avoids duplicating the logic
from localrepo.filecommit to detect unchanged files.

hgext/convert/__init__.py

@@ -382,6 +382,7 b' def convert(ui, src, dest=None, revmapfi'
     fmap = opts.get('filemap')
     if fmap:
         srcc = filemap.filemap_source(ui, srcc, fmap)
+        destc.setfilemapmode(True)
 
     if not revmapfile:
         try:

hgext/convert/common.py

@@ -167,3 +167,13 b' class converter_sink(object):'
         pbranch: branch name of parent commit
         parents: destination revisions of parent"""
         pass
+
+    def setfilemapmode(self, active):
+        """Tell the destination that we're using a filemap
+
+        Some converter_sources (svn in particular) can claim that a file
+        was changed in a revision, even if there was no change.  This method
+        tells the destination that we're using a filemap and that it should
+        filter empty revisions.
+        """
+        pass

hgext/convert/hg.py

@@ -28,6 +28,7 b' class mercurial_sink(converter_sink):'
             raise NoRepo("could not open hg repo %s as sink" % path)
         self.lock = None
         self.wlock = None
+        self.filemapmode = False
 
     def before(self):
         self.wlock = self.repo.wlock()
@@ -96,6 +97,10 b' class mercurial_sink(converter_sink):'
                 pl.append(p)
                 seen[p] = 1
         parents = pl
+        nparents = len(parents)
+        if self.filemapmode and nparents == 1:
+            m1node = self.repo.changelog.read(bin(parents[0]))[0]
+            parent = parents[0]
 
         if len(parents) < 2: parents.append("0" * 40)
         if len(parents) < 2: parents.append("0" * 40)
@@ -117,6 +122,13 b' class mercurial_sink(converter_sink):'
             text = "(octopus merge fixup)\n"
             p2 = hg.hex(self.repo.changelog.tip())
 
+        if self.filemapmode and nparents == 1:
+            man = self.repo.manifest
+            mnode = self.repo.changelog.read(bin(p2))[0]
+            if not man.cmp(m1node, man.revision(mnode)):
+                self.repo.rollback()
+                self.repo.dirstate.clear()
+                return parent
         return p2
 
     def puttags(self, tags):
@@ -153,6 +165,9 b' class mercurial_sink(converter_sink):'
                                 date, tagparent, nullid)
             return hex(self.repo.changelog.tip())
 
+    def setfilemapmode(self, active):
+        self.filemapmode = active
+
 class mercurial_source(converter_source):
     def __init__(self, ui, path, rev=None):
         converter_source.__init__(self, ui, path, rev)