shortest: make {shortest("fffffffff")} work again

{shortest("fffffffff")} should shorten it to the shortest unambiguous
prefix for the working directory. It used to do that until I broke it
in 7b2955624777 (scmutil: make shortesthexnodeidprefix() take a full
binary nodeid, 2018-04-14), when we started returning the full hex
nodeid for any working directory prefix shorter than 40 hex
digits. This patch fixes it by catching WdirUnsupported
specifically.

Differential Revision: https://phab.mercurial-scm.org/D3455

mercurial/templatefuncs.py

@@ -12,6 +12,7 b' import re'
 from .i18n import _
 from .node import (
     bin,
+    wdirid,
 )
 from . import (
     color,
@@ -601,7 +602,9 b' def shortest(context, mapping, args):'
     else:
         try:
             node = scmutil.resolvehexnodeidprefix(repo, hexnode)
-        except (error.LookupError, error.WdirUnsupported):
+        except error.WdirUnsupported:
+            node = wdirid
+        except error.LookupError:
             return hexnode
         if not node:
             return hexnode

tests/test-command-template.t

@@ -3916,6 +3916,15 b' Test shortest(node) function:'
   $ hg log --template '{shortest("not a hex string, but it'\''s 40 bytes long")}\n' -l1
   not a hex string, but it's 40 bytes long
 
+  $ hg log --template '{shortest("ffffffffffffffffffffffffffffffffffffffff")}\n' -l1
+  ffff
+
+  $ hg log --template '{shortest("fffffff")}\n' -l1
+  ffff
+
+  $ hg log --template '{shortest("ff")}\n' -l1
+  ffff
+
   $ cd ..
 
 Test shortest(node) with the repo having short hash collision: