[PATCH 1 of 2] copies: create and use _loose_next function for _related

[Gábor Stefanik]

# HG changeset patch
# User Gábor Stefanik <gabor.stefanik at nng.com>
# Date 1522848489 -7200
#      Wed Apr 04 15:28:09 2018 +0200
# Node ID d72ca973100a1f1a4451a7d1efdc3e43ebc2912e
# Parent  656ac240f39284eec4435d25c01d71056aa4e8a5
copies: create and use _loose_next function for _related

_loose_next is going to be a variant of the next function that tries to follow
grafts and similar relationship when the regular next raises StopIteration.
This is needed for bug 5834.

diff -r 656ac240f392 -r d72ca973100a mercurial/copies.py
--- a/mercurial/copies.py       Sat Mar 24 01:30:50 2018 -0400
+++ b/mercurial/copies.py       Wed Apr 04 15:28:09 2018 +0200
@@ -731,6 +731,12 @@

     return copies, {}, {}, {}, {}

+def _loose_next(g):
+    try:
+        return next(g), g
+    except StopIteration:
+        raise
+
 def _related(f1, f2, limit):
     """return True if f1 and f2 filectx have a common ancestor

@@ -748,16 +754,16 @@
         f1r, f2r = f1.linkrev(), f2.linkrev()

         if f1r is None:
-            f1 = next(g1)
+            f1, g1 = _loose_next(g1)
         if f2r is None:
-            f2 = next(g2)
+            f1, g1 = _loose_next(g1)

         while True:
             f1r, f2r = f1.linkrev(), f2.linkrev()
             if f1r > f2r:
-                f1 = next(g1)
+                f1, g1 = _loose_next(g1)
             elif f2r > f1r:
-                f2 = next(g2)
+                f1, g1 = _loose_next(g1)
             elif f1 == f2:
                 return f1 # a match
             elif f1r == f2r or f1r < limit or f2r < limit:
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