[PATCH 1 of 9] changegroup: use `iter(callable, sentinel)` instead of while True

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1470419998 14400
#      Fri Aug 05 13:59:58 2016 -0400
# Node ID 84bc06986855488a7237adc057655baa1e3c3e09
# Parent  91b2f21763955063b994b07a1060305e0fe93031
changegroup: use `iter(callable, sentinel)` instead of while True

This is functionally equivalent, but is a little more concise.

diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -475,10 +475,7 @@ class cg3unpacker(cg2unpacker):
     def _unpackmanifests(self, repo, revmap, trp, prog, numchanges):
         super(cg3unpacker, self)._unpackmanifests(repo, revmap, trp, prog,
                                                   numchanges)
-        while True:
-            chunkdata = self.filelogheader()
-            if not chunkdata:
-                break
+        for chunkdata in iter(self.filelogheader, {}):
             # If we get here, there are directory manifests in the changegroup
             d = chunkdata["filename"]
             repo.ui.debug("adding %s revisions\n" % d)
@@ -1012,10 +1009,7 @@ def changegroup(repo, basenodes, source)
 def _addchangegroupfiles(repo, source, revmap, trp, expectedfiles, needfiles):
     revisions = 0
     files = 0
-    while True:
-        chunkdata = source.filelogheader()
-        if not chunkdata:
-            break
+    for chunkdata in iter(source.filelogheader, {}):
         files += 1
         f = chunkdata["filename"]
         repo.ui.debug("adding %s revisions\n" % f)