rust: using policy.importrust from Python callers

rust: using policy.importrust from Python callers

This commit converts all current Python callers of
mercurial.rustext to the new policy.importrust system.

After this point, going through policy.importrust
or policy.importmod (in some more distant future)
is mandatory for callers of Rust code outside of
Python tests.

We felt it to be appropriate to keep Rust-specific tests
run inconditionally if the Rust extensions are present.

--- a/mercurial/dirstate.py	Wed May 29 13:27:56 2019 +0200
+++ b/mercurial/dirstate.py	Thu May 30 09:14:41 2019 +0200
@@ -27,13 +27,8 @@
     util,
 )
 
-try:
-    from . import rustext
-    rustext.__name__  # force actual import (see hgdemandimport)
-except ImportError:
-    rustext = None
-
 parsers = policy.importmod(r'parsers')
+dirstatemod = policy.importrust(r'dirstate', default=parsers)
 
 propertycache = util.propertycache
 filecache = scmutil.filecache
@@ -1468,12 +1463,7 @@
         # parsing the dirstate.
         #
         # (we cannot decorate the function directly since it is in a C module)
-        if rustext is not None:
-            parse_dirstate = rustext.dirstate.parse_dirstate
-        else:
-            parse_dirstate = parsers.parse_dirstate
-
-        parse_dirstate = util.nogc(parse_dirstate)
+        parse_dirstate = util.nogc(dirstatemod.parse_dirstate)
         p = parse_dirstate(self._map, self.copymap, st)
         if not self._dirtyparents:
             self.setparents(*p)
@@ -1484,13 +1474,8 @@
         self.get = self._map.get
 
     def write(self, st, now):
-        if rustext is not None:
-            pack_dirstate = rustext.dirstate.pack_dirstate
-        else:
-            pack_dirstate = parsers.pack_dirstate
-
-        st.write(pack_dirstate(self._map, self.copymap,
-                                       self.parents(), now))
+        st.write(dirstatemod.pack_dirstate(self._map, self.copymap,
+                                           self.parents(), now))
         st.close()
         self._dirtyparents = False
         self.nonnormalset, self.otherparentset = self.nonnormalentries()

--- a/mercurial/match.py	Wed May 29 13:27:56 2019 +0200
+++ b/mercurial/match.py	Thu May 30 09:14:41 2019 +0200
@@ -17,6 +17,7 @@
     encoding,
     error,
     pathutil,
+    policy,
     pycompat,
     util,
 )
@@ -24,11 +25,7 @@
     stringutil,
 )
 
-try:
-    from . import rustext
-    rustext.__name__  # force actual import (see hgdemandimport)
-except ImportError:
-    rustext = None
+rustmod = policy.importrust('filepatterns')
 
 allpatternkinds = ('re', 'glob', 'path', 'relglob', 'relpath', 'relre',
                    'rootglob',
@@ -1197,14 +1194,14 @@
     regular expression.
     globsuffix is appended to the regexp of globs.'''
 
-    if rustext is not None:
+    if rustmod is not None:
         try:
-            return rustext.filepatterns.build_single_regex(
+            return rustmod.build_single_regex(
                 kind,
                 pat,
                 globsuffix
             )
-        except rustext.filepatterns.PatternError:
+        except rustmod.PatternError:
             raise error.ProgrammingError(
                 'not a regex pattern: %s:%s' % (kind, pat)
             )
@@ -1460,8 +1457,8 @@
     This is useful to debug ignore patterns.
     '''
 
-    if rustext is not None:
-        result, warnings = rustext.filepatterns.read_pattern_file(
+    if rustmod is not None:
+        result, warnings = rustmod.read_pattern_file(
             filepath,
             bool(warn),
             sourceinfo,

--- a/mercurial/revlog.py	Wed May 29 13:27:56 2019 +0200
+++ b/mercurial/revlog.py	Thu May 30 09:14:41 2019 +0200
@@ -97,11 +97,8 @@
 REVIDX_RAWTEXT_CHANGING_FLAGS
 
 parsers = policy.importmod(r'parsers')
-try:
-    from . import rustext
-    rustext.__name__  # force actual import (see hgdemandimport)
-except ImportError:
-    rustext = None
+rustancestor = policy.importrust(r'ancestor')
+rustdagop = policy.importrust(r'dagop')
 
 # Aliased for performance.
 _zlibdecompress = zlib.decompress
@@ -825,8 +822,8 @@
             checkrev(r)
         # and we're sure ancestors aren't filtered as well
 
-        if rustext is not None:
-            lazyancestors = rustext.ancestor.LazyAncestors
+        if rustancestor is not None:
+            lazyancestors = rustancestor.LazyAncestors
             arg = self.index
         elif util.safehasattr(parsers, 'rustlazyancestors'):
             lazyancestors = ancestor.rustlazyancestors
@@ -915,8 +912,8 @@
         if common is None:
             common = [nullrev]
 
-        if rustext is not None:
-            return rustext.ancestor.MissingAncestors(self.index, common)
+        if rustancestor is not None:
+            return rustancestor.MissingAncestors(self.index, common)
         return ancestor.incrementalmissingancestors(self.parentrevs, common)
 
     def findmissingrevs(self, common=None, heads=None):
@@ -1130,8 +1127,8 @@
                 return self.index.headrevs()
             except AttributeError:
                 return self._headrevs()
-        if rustext is not None:
-            return rustext.dagop.headrevs(self.index, revs)
+        if rustdagop is not None:
+            return rustdagop.headrevs(self.index, revs)
         return dagop.headrevs(revs, self._uncheckedparentrevs)
 
     def computephases(self, roots):