dagop: add smartset interface to filectxancestors()

The original filectx API is kept public since we'll need it to walk ancestor
(rev, match) pairs efficiently. The current implementation scans ancestors
twice for 'hg log -fp FILE'.

mercurial/dagop.py

@@ -77,7 +77,10 b' def _walkrevtree(pfunc, revs, startdepth'
 
 def filectxancestors(fctxs, followfirst=False):
     """Like filectx.ancestors(), but can walk from multiple files/revisions,
-    and includes the given fctxs themselves"""
+    and includes the given fctxs themselves
+
+    Yields (rev, {fctx, ...}) pairs in descending order.
+    """
     visit = {}
     def addvisit(fctx):
         rev = fctx.rev()
@@ -93,13 +96,21 b' def filectxancestors(fctxs, followfirst='
     for c in fctxs:
         addvisit(c)
     while visit:
-        rev = max(visit)
-        c = visit[rev].pop()
-        if not visit[rev]:
-            del visit[rev]
-        yield c
-        for parent in c.parents()[:cut]:
-            addvisit(parent)
+        currev = max(visit)
+        curfctxs = visit.pop(currev)
+        yield currev, curfctxs
+        for c in curfctxs:
+            for parent in c.parents()[:cut]:
+                addvisit(parent)
+
+def filerevancestors(fctxs, followfirst=False):
+    """Like filectx.ancestors(), but can walk from multiple files/revisions,
+    and includes the given fctxs themselves
+
+    Returns a smartset.
+    """
+    gen = (rev for rev, _cs in filectxancestors(fctxs, followfirst))
+    return generatorset(gen, iterasc=False)
 
 def _genrevancestors(repo, revs, followfirst, startdepth, stopdepth, cutfunc):
     if followfirst:

mercurial/revset.py

@@ -928,8 +928,7 b' def _follow(repo, subset, x, name, follo'
         files = c.manifest().walk(matcher)
 
         fctxs = [c[f].introfilectx() for f in files]
-        a = dagop.filectxancestors(fctxs, followfirst)
-        s = set(c.rev() for c in a)
+        s = dagop.filerevancestors(fctxs, followfirst)
     else:
         s = dagop.revancestors(repo, baseset([c.rev()]), followfirst)