sparse: use None as the sparse matcher value when disabled

This create a clear signal for when the feature is unused. We could also create
an `alwaysmatcher`, but using None is more explicit, so I went for it.

hgext/sparse.py

@@ -216,6 +216,8 b' def _setupdirstate(ui):'
     def walk(orig, self, match, subrepos, unknown, ignored, full=True):
         # hack to not exclude explicitly-specified paths so that they can
         # be warned later on e.g. dirstate.add()
+        sparse_matcher = self._sparsematcher
+        if sparse_matcher is not None:
         em = matchmod.exact(match.files())
         sm = matchmod.unionmatcher([self._sparsematcher, em])
         match = matchmod.intersectmatchers(match, sm)
@@ -226,7 +228,7 b' def _setupdirstate(ui):'
     # dirstate.rebuild should not add non-matching files
     def _rebuild(orig, self, parent, allfiles, changedfiles=None):
         matcher = self._sparsematcher
-        if not matcher.always():
+        if matcher is not None and not matcher.always():
             allfiles = [f for f in allfiles if matcher(f)]
             if changedfiles:
                 changedfiles = [f for f in changedfiles if matcher(f)]
@@ -255,7 +257,7 b' def _setupdirstate(ui):'
 
         def _wrapper(orig, self, *args, **kwargs):
             sparsematch = self._sparsematcher
-            if not sparsematch.always():
+            if sparsematch is not None and not sparsematch.always():
                 for f in args:
                     if f is not None and not sparsematch(f) and f not in self:
                         raise error.Abort(

mercurial/dirstate.py

@@ -27,7 +27,6 b' from . import ('
     policy,
     pycompat,
     scmutil,
-    sparse,
     util,
 )
 
@@ -113,6 +112,7 b' class dirstate:'
         self._opener = opener
         self._validate = validate
         self._root = root
+        # Either build a sparse-matcher or None if sparse is disabled
         self._sparsematchfn = sparsematchfn
         # ntpath.join(root, '') of Python 2.7.9 does not add sep if root is
         # UNC path pointing to root share (issue4557)
@@ -184,7 +184,11 b' class dirstate:'
         The working directory may not include every file from a manifest. The
         matcher obtained by this property will match a path if it is to be
         included in the working directory.
+
+        When sparse if disabled, return None.
         """
+        if self._sparsematchfn is None:
+            return None
         # TODO there is potential to cache this property. For now, the matcher
         # is resolved on every access. (But the called function does use a
         # cache to keep the lookup fast.)
@@ -1259,7 +1263,7 b' class dirstate:'
             use_rust = False
         elif subrepos:
             use_rust = False
-        elif sparse.enabled:
+        elif self._sparsematchfn is not None:
             use_rust = False
         elif not isinstance(match, allowed_matchers):
             # Some matchers have yet to be implemented

mercurial/localrepo.py

@@ -1747,6 +1747,8 b' class localrepository:'
 
     def _makedirstate(self):
         """Extension point for wrapping the dirstate per-repo."""
+        sparsematchfn = None
+        if sparse.use_sparse(self):
         sparsematchfn = lambda: sparse.matcher(self)
         v2_req = requirementsmod.DIRSTATE_V2_REQUIREMENT
         th = requirementsmod.DIRSTATE_TRACKED_HINT_V1