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namespaces: let namespaces override singlenode() definition...

namespaces: let namespaces override singlenode() definition Some namespaces have multiple nodes per name (meaning that their namemap() returns multiple nodes). One such namespace is the "topics" namespace (from the evolve repo). We also have our own internal namespace at Google (for review units) that has multiple nodes per name. These namespaces may not want to use the default "pick highest revnum" resolution that we currently use when resolving a name to a single node. As an example, they may decide that `hg co <name>` should check out a commit that's last in some sense even if an earlier commit had just been amended and thus had a higher revnum [1]. This patch gives the namespace the option to continue to return multiple nodes and to override how the best node is picked. Allowing namespaces to override that may also be useful as an optimization (it may be cheaper for the namespace to find just that node). I have been arguing (in D3715) for using all the nodes returned from namemap() when resolving the symbol to a revset, so e.g. `hg log -r stable` would resolve to *all* nodes on stable, not just the one with the highest revnum (except that I don't actually think we should change it for the branch namespace because of BC). Most people seem opposed to that. If we decide not to do it, I think we can deprecate the namemap() function in favor of the new singlenode() (I find it weird to have namespaces, like the branch namespace, where namemap() isn't nodemap()'s inverse). I therefore think this patch makes sense regardless of what we decide on that issue. [1] Actually, even the branch namespace would have wanted to override singlenode() if it had supported multiple nodes. That's because closes branch heads are mostly ignored, so "hg co default" will not check out the highest-revnum node if that's a closed head. Differential Revision: https://phab.mercurial-scm.org/D3852

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      # txnutil.py - transaction related utilities

      #

      #  Copyright FUJIWARA Katsunori <foozy@lares.dti.ne.jp> and others

      #

      # This software may be used and distributed according to the terms of the

      # GNU General Public License version 2 or any later version.

      from __future__ import absolute_import

      import errno

      from . import (

          encoding,

      )

      def mayhavepending(root):

          '''return whether 'root' may have pending changes, which are

          visible to this process.

          '''

          return root == encoding.environ.get('HG_PENDING')

      def trypending(root, vfs, filename, **kwargs):

          '''Open  file to be read according to HG_PENDING environment variable

          This opens '.pending' of specified 'filename' only when HG_PENDING

          is equal to 'root'.

          This returns '(fp, is_pending_opened)' tuple.

          '''

          if mayhavepending(root):

              try:

                  return (vfs('%s.pending' % filename, **kwargs), True)

              except IOError as inst:

                  if inst.errno != errno.ENOENT:

                      raise

          return (vfs(filename, **kwargs), False)

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				# txnutil.py - transaction related utilities
				#
				# Copyright FUJIWARA Katsunori <foozy@lares.dti.ne.jp> and others
				#
				# This software may be used and distributed according to the terms of the
				# GNU General Public License version 2 or any later version.

				from __future__ import absolute_import

				import errno

				from . import (
				encoding,
				)

				def mayhavepending(root):
				'''return whether 'root' may have pending changes, which are
				visible to this process.
				'''
				return root == encoding.environ.get('HG_PENDING')

				def trypending(root, vfs, filename, **kwargs):
				'''Open file to be read according to HG_PENDING environment variable

				This opens '.pending' of specified 'filename' only when HG_PENDING
				is equal to 'root'.

				This returns '(fp, is_pending_opened)' tuple.
				'''
				if mayhavepending(root):
				try:
				return (vfs('%s.pending' % filename, **kwargs), True)
				except IOError as inst:
				if inst.errno != errno.ENOENT:
				raise
				return (vfs(filename, **kwargs), False)