copies: clean up _related logic

The limit parameter was never actually used, since the only way the 4th case
could be reached was if f1r and f2r converged. The new code makes this clear,
and additionally reduces the conditional block to just 3 cases.

mercurial/copies.py

@@ -698,9 +698,6 b' def _heuristicscopytracing(repo, c1, c2,'
             basenametofilename[basename].append(f)
             dirnametofilename[dirname].append(f)
 
-        # in case of a rebase/graft, base may not be a common ancestor
-        anc = c1.ancestor(c2)
-
         for f in missingfiles:
             basename = os.path.basename(f)
             dirname = os.path.dirname(f)
@@ -723,7 +720,7 b' def _heuristicscopytracing(repo, c1, c2,'
 
             for candidate in movecandidates:
                 f1 = c1.filectx(candidate)
-                if _related(f1, f2, anc.rev()):
+                if _related(f1, f2):
                     # if there are a few related copies then we'll merge
                     # changes into all of them. This matches the behaviour
                     # of upstream copytracing
@@ -731,7 +728,7 b' def _heuristicscopytracing(repo, c1, c2,'
 
     return copies, {}, {}, {}, {}
 
-def _related(f1, f2, limit):
+def _related(f1, f2):
     """return True if f1 and f2 filectx have a common ancestor
 
     Walk back to common ancestor to see if the two files originate
@@ -758,10 +755,8 b' def _related(f1, f2, limit):'
                 f1 = next(g1)
             elif f2r > f1r:
                 f2 = next(g2)
-            elif f1 == f2:
-                return f1 # a match
-            elif f1r == f2r or f1r < limit or f2r < limit:
-                return False # copy no longer relevant
+            else: # f1 and f2 point to files in the same linkrev
+                return f1 == f2 # true if they point to the same file
     except StopIteration:
         return False
 
@@ -829,7 +824,7 b' def _checkcopies(srcctx, dstctx, f, base'
         c2 = getdstfctx(of, mdst[of])
         # c2 might be a plain new file on added on destination side that is
         # unrelated to the droids we are looking for.
-        cr = _related(oc, c2, tca.rev())
+        cr = _related(oc, c2)
         if cr and (of == f or of == c2.path()): # non-divergent
             if backwards:
                 data['copy'][of] = f