fastpartialmatch: handle nullid correctly

Summary: Special case for nullid

Test Plan: arc unit

Reviewers: #mercurial, simpkins, ikostia

Reviewed By: ikostia

Subscribers: net-systems-diffs@fb.com, mjpieters, #sourcecontrol

Differential Revision: https://phabricator.intern.facebook.com/D4945927

Tasks: 17622253

Signature: t1:4945927:1493123209:712990c1e883241d99c0aeb4af8d48e18e1baa3d

hgext3rd/fastpartialmatch.py

@@ -52,6 +52,9 @@ from mercurial.i18n import _
 from mercurial.node import (
     bin,
     hex,
+    nullhex,
+    nullid,
+    nullrev,
 )
 
 from operator import itemgetter
@@ -405,6 +408,8 @@ def _findcandidates(ui, vfs, id):
     candidates = {}
     if not (isinstance(id, str) and len(id) >= 4 and _maybehash(id)):
         return candidates
+    if nullhex.startswith(id):
+        candidates[nullid] = nullrev
     filename = id[:2]
     fullpath = os.path.join(_partialindexdir, filename)
     try:

tests/test-fastpartialmatch.t

@@ -462,3 +462,6 @@ Try to create empty commit
   $ hg ci -m empty
   nothing changed
   [1]
+
+Try to checkout nullid
+  $ hg up --config fastpartialmatch.raiseifinconsistent=True -q 0000000000