context: don't hex encode all unknown 20 char revision specs (issue4890)

d3908c911d5e introduced nice hexified display of missing nodes. It did however
also make missing 20 character revision specifications be shown as hex - very
confusing.

Users are often wrong and somehow specify revisions that don't exist. Nodes
will however rarely be missing ... and they will only look like a user provided
revision specification and be all ascii in 1 of 4*10**9.

With this change, missing revisions will only be hexified if they really look
like binary nodes. This change will thus improve the error reporting UI in the
common case and only very rarely make it confusing in the opposite direction of
how it was before.

mercurial/context.py

@@ -5,6 +5,8 b''
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
+import re
+
 from node import nullid, nullrev, wdirid, short, hex, bin
 from i18n import _
 import mdiff, error, util, scmutil, subrepo, patch, encoding, phases
@@ -22,6 +24,8 b' propertycache = util.propertycache'
 # dirty in the working copy.
 _newnode = '!' * 21
 
+nonascii = re.compile(r'[^\x21-\x7f]').search
+
 class basectx(object):
     """A basectx object represents the common logic for its children:
     changectx: read-only context that is already present in the repo,
@@ -466,7 +470,7 b' class changectx(basectx):'
                 msg = _("working directory has unknown parent '%s'!")
                 raise error.Abort(msg % short(changeid))
             try:
-                if len(changeid) == 20:
+                if len(changeid) == 20 and nonascii(changeid):
                     changeid = hex(changeid)
             except TypeError:
                 pass

tests/test-pull.t

@@ -52,6 +52,18 b''
   $ hg rollback --dry-run --verbose
   repository tip rolled back to revision -1 (undo pull: http://foo:***@localhost:$HGPORT/)
 
+Test pull of non-existing 20 character revision specification, making sure plain ascii identifiers
+not are encoded like a node:
+
+  $ hg pull -r 'xxxxxxxxxxxxxxxxxxxy'
+  pulling from http://foo@localhost:$HGPORT/
+  abort: unknown revision 'xxxxxxxxxxxxxxxxxxxy'!
+  [255]
+  $ hg pull -r 'xxxxxxxxxxxxxxxxxx y'
+  pulling from http://foo@localhost:$HGPORT/
+  abort: unknown revision '7878787878787878787878787878787878782079'!
+  [255]
+
 Issue622: hg init && hg pull -u URL doesn't checkout default branch
 
   $ cd ..