D2553: templatefilters: avoid infinite recursion bug in stringify

[durin42 (Augie Fackler)]

durin42 created this revision.
Herald added a subscriber: mercurial-devel.
Herald added a reviewer: hg-reviewers.

REVISION SUMMARY
  This doesn't ever happen on Python 2, but it's been a persistent pain
  on Python 3. Adding this helped produce some of my upcoming Python 3
  fixes.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D2553

AFFECTED FILES
  mercurial/templatefilters.py

CHANGE DETAILS

diff --git a/mercurial/templatefilters.py b/mercurial/templatefilters.py
--- a/mercurial/templatefilters.py
+++ b/mercurial/templatefilters.py
@@ -376,6 +376,12 @@
     """
     thing = templatekw.unwraphybrid(thing)
     if util.safehasattr(thing, '__iter__') and not isinstance(thing, bytes):
+        if isinstance(thing, str):
+            # This is only reachable on Python 3 (otherwise
+            # isinstance(thing, bytes) would have been true), and is
+            # here to prevent infinite recursion bugs on Python 3.
+            raise error.ProgrammingError(
+                'stringify got unexpected unicode string: %r' % thing)
         return "".join([stringify(t) for t in thing if t is not None])
     if thing is None:
         return ""



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