rebase: while rewriting desc hashes, ignore ambiguous prefix "hashes"

If a repo is sufficiently large, a six digit number "hash prefix" can somewhat
easily reference an ambiguous hash prefix.

Differential Revision: https://phab.mercurial-scm.org/D12552

mercurial/rewriteutil.py

@@ -215,9 +215,9 def update_hash_refs(repo, commitmsg, pe
     for h in hashes:
         try:
             fullnode = scmutil.resolvehexnodeidprefix(unfi, h)
-        except error.WdirUnsupported:
-            # Someone has an fffff... in a commit message we're
-            # rewriting. Don't try rewriting that.
+        except (error.WdirUnsupported, error.AmbiguousPrefixLookupError):
+            # Someone has an fffff... or some other prefix that's ambiguous in a
+            # commit message we're rewriting. Don't try rewriting that.
             continue
         if fullnode is None:
             continue

tests/test-rebase-inmemory.t

@@ -1027,8 +1027,7 scheme ever changes:
   $ hg ci -qAm 'The previous two (parentless) commits had a hash prefix of b04363. Check that rewrite_hash_refs will not fail because of that.'
   $ hg rebase -r . -d 5
   rebasing 8:5c4cdabf5769 tip "The previous two (parentless) commits had a hash prefix of b04363. Check that rewrite_hash_refs will not fail because of that."
-  abort: 00changelog@b04363: ambiguous identifier (known-bad-output !)
-  [50]
+  saved backup bundle to $TESTTMP/keep_merge/.hg/strip-backup/5c4cdabf5769-335e1828-rebase.hg
 
   $ cd ..