keyword: restore kwtemplater.restrict at the end of wrapped patch.diff

Before this patch, kwdiff doesn't restore kwtemplater.restrict after
invocation of wrapped patch.diff(). This suppresses keyword expansion
at subsequent filelog.read().

Typical usecase of this issue is "hg cat" after "hg diff" with command
server. In this case, kwtemplater.restrict=True is kept in command
server process even after "hg diff".

To ensure kwtemplater.restrict=True while original patch.diff()
running, this patch makes kwdiff() yield values returned by it,
because it returns generator object.

Strictly speaking, if filelog.read() is invoked before completely
evaluating the result of previous patch.diff(), keyword expansion is
still suppressed, because kwtemplater.restrict isn't restored yet.

But this fixing should be reasonable enough, because patch.diff() is
consumed immediately, AFAIK.

hgext/keyword.py

@@ -665,8 +665,13 b' def reposetup(ui, repo):'
 
     def kwdiff(orig, *args, **kwargs):
         '''Monkeypatch patch.diff to avoid expansion.'''
+        restrict = kwt.restrict
         kwt.restrict = True
-        return orig(*args, **kwargs)
+        try:
+            for chunk in orig(*args, **kwargs):
+                yield chunk
+        finally:
+            kwt.restrict = restrict
 
     def kwweb_skip(orig, web, req, tmpl):
         '''Wraps webcommands.x turning off keyword expansion.'''

tests/test-keyword.t

@@ -1378,4 +1378,35 b' Test restricted mode with fetch (with me'
    $Xinfo$
   +xxxx
 
+Test that patch.diff(), which is implied by "hg diff" or so, doesn't
+suppress expanding keywords at subsequent commands
+
+#if windows
+  $ PYTHONPATH="$TESTDIR/../contrib;$PYTHONPATH"
+#else
+  $ PYTHONPATH="$TESTDIR/../contrib:$PYTHONPATH"
+#endif
+  $ export PYTHONPATH
+
+  $ grep -v '^promptecho ' < $HGRCPATH >> $HGRCPATH.new
+  $ mv $HGRCPATH.new $HGRCPATH
+
+  >>> from __future__ import print_function
+  >>> from hgclient import readchannel, runcommand, check
+  >>> @check
+  ... def check(server):
+  ...     # hello block
+  ...     readchannel(server)
+  ... 
+  ...     runcommand(server, ['cat', 'm'])
+  ...     runcommand(server, ['diff', '-c', '.', 'm'])
+  ...     runcommand(server, ['cat', 'm'])
+  *** runcommand cat m
+  $Id: m 800511b3a22d Thu, 01 Jan 1970 00:00:00 +0000 test $
+  bar
+  *** runcommand diff -c . m
+  *** runcommand cat m
+  $Id: m 800511b3a22d Thu, 01 Jan 1970 00:00:00 +0000 test $
+  bar
+
   $ cd ..