rust-dirstate: call parse/pack bindings from Python

rust-dirstate: call parse/pack bindings from Python

A future patch will need to address the issue of Rust module policy,
to avoid having ugly duplicate imports and conditionals all over the place.

As the rewrite of dirstate in Rust progresses, we will need fewer of those
"contact points".

Differential Revision: https://phab.mercurial-scm.org/D6350

--- a/mercurial/dirstate.py	Mon May 06 22:50:34 2019 +0200
+++ b/mercurial/dirstate.py	Mon May 06 22:51:10 2019 +0200
@@ -27,6 +27,12 @@
     util,
 )
 
+try:
+    from . import rustext
+    rustext.__name__  # force actual import (see hgdemandimport)
+except ImportError:
+    rustext = None
+
 parsers = policy.importmod(r'parsers')
 
 propertycache = util.propertycache
@@ -1465,7 +1471,12 @@
         # parsing the dirstate.
         #
         # (we cannot decorate the function directly since it is in a C module)
-        parse_dirstate = util.nogc(parsers.parse_dirstate)
+        if rustext is not None:
+            parse_dirstate = rustext.dirstate.parse_dirstate
+        else:
+            parse_dirstate = parsers.parse_dirstate
+
+        parse_dirstate = util.nogc(parse_dirstate)
         p = parse_dirstate(self._map, self.copymap, st)
         if not self._dirtyparents:
             self.setparents(*p)
@@ -1476,7 +1487,12 @@
         self.get = self._map.get
 
     def write(self, st, now):
-        st.write(parsers.pack_dirstate(self._map, self.copymap,
+        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.close()
         self._dirtyparents = False

--- a/tests/fakedirstatewritetime.py	Mon May 06 22:50:34 2019 +0200
+++ b/tests/fakedirstatewritetime.py	Mon May 06 22:51:10 2019 +0200
@@ -16,6 +16,12 @@
 )
 from mercurial.utils import dateutil
 
+try:
+    from mercurial import rustext
+    rustext.__name__  # force actual import (see hgdemandimport)
+except ImportError:
+    rustext = None
+
 configtable = {}
 configitem = registrar.configitem(configtable)
 
@@ -51,16 +57,22 @@
     # 'fakenow' value and 'touch -t YYYYmmddHHMM' argument easy
     fakenow = dateutil.parsedate(fakenow, [b'%Y%m%d%H%M'])[0]
 
-    orig_pack_dirstate = parsers.pack_dirstate
+    if rustext is not None:
+        orig_module = rustext.dirstate
+        orig_pack_dirstate = rustext.dirstate.pack_dirstate
+    else:
+        orig_module = parsers
+        orig_pack_dirstate = parsers.pack_dirstate
+
     orig_dirstate_getfsnow = dirstate._getfsnow
     wrapper = lambda *args: pack_dirstate(fakenow, orig_pack_dirstate, *args)
 
-    parsers.pack_dirstate = wrapper
+    orig_module.pack_dirstate = wrapper
     dirstate._getfsnow = lambda *args: fakenow
     try:
         return func()
     finally:
-        parsers.pack_dirstate = orig_pack_dirstate
+        orig_module.pack_dirstate = orig_pack_dirstate
         dirstate._getfsnow = orig_dirstate_getfsnow
 
 def _poststatusfixup(orig, workingctx, status, fixup):