Ensure genindex output is deterministic.

See also <https://github.com/sphinx-doc/sphinx/pull/1694>

Signed-off-by: Chris Lamb <chris@chris-lamb.co.uk>

sphinx/environment.py

@@ -14,6 +14,7 @@ import os
 import sys
 import time
 import types
+import bisect
 import codecs
 import imghdr
 import string
@@ -1800,7 +1801,8 @@ class BuildEnvironment:
                 except NoUri:
                     pass
                 else:
-                    entry[0].append((main, uri))
+                    # maintain links in sorted/deterministic order
+                    bisect.insort(entry[0], (main, uri))
 
         for fn, entries in iteritems(self.indexentries):
             # new entry types must be listed in directives/other.py!
@@ -1838,8 +1840,10 @@ class BuildEnvironment:
         def keyfunc(entry, lcletters=string.ascii_lowercase + '_'):
             lckey = unicodedata.normalize('NFD', entry[0].lower())
             if lckey[0:1] in lcletters:
-                return chr(127) + lckey
-            return lckey
+                lckey = chr(127) + lckey
+            # ensure a determinstic order *within* letters by also sorting on
+            # the entry itself
+            return (lckey, entry[0])
         newlist = sorted(new.items(), key=keyfunc)
 
         if group_entries: