refactor: prefer checks against nullrev over nullid

A common pattern is using a changeset context and obtaining the node to
compare against nullid. Change this to obtain the nullrev instead. In
the future, the nullid becomes a property of the repository and is no
longer a global constant, so using nullrev is much easier to reason
about. Python function call overhead makes the difference moot, but
future changes will result in more dictionary lookups otherwise, so
prefer the simpler pattern.

Differential Revision: https://phab.mercurial-scm.org/D10290

hgext/extdiff.py

@@ -91,7 +91,7 b' import subprocess'
 
 from mercurial.i18n import _
 from mercurial.node import (
-    nullid,
+    nullrev,
     short,
 )
 from mercurial import (
@@ -565,18 +565,18 b' def dodiff(ui, repo, cmdline, pats, opts'
             repo, [from_rev] + [to_rev], b'nowarn'
         )
         ctx1a = scmutil.revsingle(repo, from_rev, None)
-        ctx1b = repo[nullid]
+        ctx1b = repo[nullrev]
         ctx2 = scmutil.revsingle(repo, to_rev, None)
     else:
         ctx1a, ctx2 = scmutil.revpair(repo, revs)
         if not revs:
             ctx1b = repo[None].p2()
         else:
-            ctx1b = repo[nullid]
+            ctx1b = repo[nullrev]
 
     # Disable 3-way merge if there is only one parent
     if do3way:
-        if ctx1b.node() == nullid:
+        if ctx1b.rev() == nullrev:
             do3way = False
 
     matcher = scmutil.match(ctx2, pats, opts)

hgext/split.py

@@ -12,7 +12,7 b' from __future__ import absolute_import'
 from mercurial.i18n import _
 
 from mercurial.node import (
-    nullid,
+    nullrev,
     short,
 )
 
@@ -80,12 +80,12 b' def split(ui, repo, *revs, **opts):'
                 raise error.InputError(_(b'cannot split multiple revisions'))
 
             rev = revs.first()
-            ctx = repo[rev]
-            # Handle nullid specially here (instead of leaving for precheck()
+            # Handle nullrev specially here (instead of leaving for precheck()
             # below) so we get a nicer message and error code.
-            if rev is None or ctx.node() == nullid:
+            if rev is None or rev == nullrev:
                 ui.status(_(b'nothing to split\n'))
                 return 1
+            ctx = repo[rev]
             if ctx.node() is None:
                 raise error.InputError(_(b'cannot split working directory'))
 

mercurial/context.py

@@ -2885,7 +2885,7 b' class memctx(committablectx):'
         # "1 < len(self._parents)" can't be used for checking
         # existence of the 2nd parent, because "memctx._parents" is
         # explicitly initialized by the list, of which length is 2.
-        if p2.node() != nullid:
+        if p2.rev() != nullrev:
             man2 = p2.manifest()
             managing = lambda f: f in man1 or f in man2
         else:
@@ -2903,7 +2903,7 b' class memctx(committablectx):'
         return scmutil.status(modified, added, removed, [], [], [], [])
 
     def parents(self):
-        if self._parents[1].node() == nullid:
+        if self._parents[1].rev() == nullrev:
             return [self._parents[0]]
         return self._parents
 
@@ -3052,7 +3052,7 b' class metadataonlyctx(committablectx):'
         # "1 < len(self._parents)" can't be used for checking
         # existence of the 2nd parent, because "metadataonlyctx._parents" is
         # explicitly initialized by the list, of which length is 2.
-        if p2.node() != nullid:
+        if p2.rev() != nullrev:
             man2 = p2.manifest()
             managing = lambda f: f in man1 or f in man2
         else:

mercurial/copies.py

@@ -149,7 +149,7 b' def _committedforwardcopies(a, b, base, '
     # optimization, since the ctx.files() for a merge commit is not correct for
     # this comparison.
     forwardmissingmatch = match
-    if b.p1() == a and b.p2().node() == nullid:
+    if b.p1() == a and b.p2().rev() == nullrev:
         filesmatcher = matchmod.exact(b.files())
         forwardmissingmatch = matchmod.intersectmatchers(match, filesmatcher)
     if repo.ui.configbool(b'devel', b'copy-tracing.trace-all-files'):

mercurial/logcmdutil.py

@@ -14,6 +14,7 b' import posixpath'
 from .i18n import _
 from .node import (
     nullid,
+    nullrev,
     wdirid,
     wdirrev,
 )
@@ -82,7 +83,7 b' def diff_parent(ctx):'
     If diff.merge is enabled, an overlayworkingctx of the auto-merged parents will be returned.
     """
     repo = ctx.repo()
-    if repo.ui.configbool(b"diff", b"merge") and ctx.p2().node() != nullid:
+    if repo.ui.configbool(b"diff", b"merge") and ctx.p2().rev() != nullrev:
         # avoid cycle context -> subrepo -> cmdutil -> logcmdutil
         from . import context
 

mercurial/mergestate.py

@@ -11,6 +11,7 b' from .node import ('
     hex,
     nullhex,
     nullid,
+    nullrev,
 )
 from . import (
     error,
@@ -341,7 +342,7 b' class _mergestate_base(object):'
         flo = fco.flags()
         fla = fca.flags()
         if b'x' in flags + flo + fla and b'l' not in flags + flo + fla:
-            if fca.node() == nullid and flags != flo:
+            if fca.rev() == nullrev and flags != flo:
                 if preresolve:
                     self._repo.ui.warn(
                         _(

mercurial/shelve.py

@@ -534,7 +534,7 b' def _docreatecmd(ui, repo, pats, opts):'
     parent = parents[0]
     origbranch = wctx.branch()
 
-    if parent.node() != nullid:
+    if parent.rev() != nullrev:
         desc = b"changes to: %s" % parent.description().split(b'\n', 1)[0]
     else:
         desc = b'(changes in empty repository)'

mercurial/simplemerge.py

@@ -19,7 +19,7 b''
 from __future__ import absolute_import
 
 from .i18n import _
-from .node import nullid
+from .node import nullrev
 from . import (
     error,
     mdiff,
@@ -427,7 +427,7 b' def _picklabels(defaults, overrides):'
 def is_not_null(ctx):
     if not util.safehasattr(ctx, "node"):
         return False
-    return ctx.node() != nullid
+    return ctx.rev() != nullrev
 
 
 def _mergediff(m3, name_a, name_b, name_base):