sparse: override dirstate.walk() instead of dirstate._ignore

sparse: override dirstate.walk() instead of dirstate._ignore

Instead of treating files that are outside the sparse config as
ignored, this makes it so we list only those that are within the
sparse config by passing the sparse matcher to dirstate.walk().

Once we add support for narrow (sparseness applied to history, not
just working copy), we will need to do a similar restriction of the
walk over manifests, so this will be more consistent then. It also
simplifies the code a bit.

Note that a side-effect of this change is that files outside the
sparse config used to be listed as ignored, but they will now not be
listed at all. This can be seen in the test case where "hg purge" no
longer has any effect because it doesn't see that the files outside
the space config exist. To fix that, I think we should add an option
to dirstate.walk() to walk outside the sparse config. We might expose
that to the user as --no-sparse flag to e.g. "hg status" and "hg
purge", but that's work for another day.

Differential Revision: https://phab.mercurial-scm.org/D59

--- a/hgext/sparse.py	Wed Jul 12 15:24:47 2017 -0700
+++ b/hgext/sparse.py	Tue Jul 11 10:46:35 2017 -0700
@@ -192,36 +192,11 @@
     and to prevent modifications to files outside the checkout.
     """
 
-    # The atrocity below is needed to wrap dirstate._ignore. It is a cached
-    # property, which means normal function wrapping doesn't work.
-    class ignorewrapper(object):
-        def __init__(self, orig):
-            self.orig = orig
-            self.origignore = None
-            self.func = None
-            self.sparsematch = None
-
-        def __get__(self, obj, type=None):
-            origignore = self.orig.__get__(obj)
+    def walk(orig, self, match, subrepos, unknown, ignored, full=True):
+        match = matchmod.intersectmatchers(match, self._sparsematcher)
+        return orig(self, match, subrepos, unknown, ignored, full)
 
-            sparsematch = obj._sparsematcher
-            if sparsematch.always():
-                return origignore
-
-            if self.sparsematch != sparsematch or self.origignore != origignore:
-                self.func = matchmod.unionmatcher([
-                    origignore, matchmod.negatematcher(sparsematch)])
-                self.sparsematch = sparsematch
-                self.origignore = origignore
-            return self.func
-
-        def __set__(self, obj, value):
-            return self.orig.__set__(obj, value)
-
-        def __delete__(self, obj):
-            return self.orig.__delete__(obj)
-
-    replacefilecache(dirstate.dirstate, '_ignore', ignorewrapper)
+    extensions.wrapfunction(dirstate.dirstate, 'walk', walk)
 
     # dirstate.rebuild should not add non-matching files
     def _rebuild(orig, self, parent, allfiles, changedfiles=None):

--- a/tests/test-sparse.t	Wed Jul 12 15:24:47 2017 -0700
+++ b/tests/test-sparse.t	Tue Jul 11 10:46:35 2017 -0700
@@ -144,10 +144,15 @@
   M show
 
   $ hg up -qC .
+TODO: add an option to purge to also purge files outside the sparse config?
   $ hg purge --all --config extensions.purge=
   $ ls
+  hide
+  hide3
   show
   show2
+For now, manually remove the files
+  $ rm hide hide3
 
 Verify rebase temporarily includes excluded files