dirstate: move parents source of truth to dirstatemap

dirstate: move parents source of truth to dirstatemap

As part of moving dirstate storage to its own class, let's move the source of
truth for the dirstate parents to dirstatemap. This requires that dirstate._pl
no longer be a cache, and that all sets go through dirstatemap.setparents.

Differential Revision: https://phab.mercurial-scm.org/D759

--- a/mercurial/dirstate.py	Tue Sep 26 03:56:20 2017 -0700
+++ b/mercurial/dirstate.py	Tue Sep 26 03:56:20 2017 -0700
@@ -71,7 +71,6 @@
         # UNC path pointing to root share (issue4557)
         self._rootdir = pathutil.normasprefix(root)
         self._dirty = False
-        self._dirtypl = False
         self._lastnormaltime = 0
         self._ui = ui
         self._filecache = {}
@@ -184,7 +183,7 @@
                 raise
             return "default"
 
-    @propertycache
+    @property
     def _pl(self):
         return self._map.parents()
 
@@ -343,11 +342,11 @@
             raise ValueError("cannot set dirstate parent without "
                              "calling dirstate.beginparentchange")
 
-        self._dirty = self._dirtypl = True
+        self._dirty = True
         oldp2 = self._pl[1]
         if self._origpl is None:
             self._origpl = self._pl
-        self._pl = p1, p2
+        self._map.setparents(p1, p2)
         copies = {}
         if oldp2 != nullid and p2 == nullid:
             candidatefiles = self._nonnormalset.union(self._otherparentset)
@@ -432,8 +431,8 @@
         # (we cannot decorate the function directly since it is in a C module)
         parse_dirstate = util.nogc(parsers.parse_dirstate)
         p = parse_dirstate(self._map._map, self._map.copymap, st)
-        if not self._dirtypl:
-            self._pl = p
+        if not self._map._dirtyparents:
+            self._map.setparents(*p)
 
     def invalidate(self):
         '''Causes the next access to reread the dirstate.
@@ -444,7 +443,7 @@
 
         for a in ("_map", "_identity",
                   "_filefoldmap", "_dirfoldmap", "_branch",
-                  "_pl", "_dirs", "_ignore", "_nonnormalset",
+                  "_dirs", "_ignore", "_nonnormalset",
                   "_otherparentset"):
             if a in self.__dict__:
                 delattr(self, a)
@@ -679,7 +678,7 @@
         self._otherparentset = set()
         if "_dirs" in self.__dict__:
             delattr(self, "_dirs")
-        self._pl = [nullid, nullid]
+        self._map.setparents(nullid, nullid)
         self._lastnormaltime = 0
         self._updatedfiles.clear()
         self._dirty = True
@@ -694,7 +693,7 @@
 
         if self._origpl is None:
             self._origpl = self._pl
-        self._pl = (parent, nullid)
+        self._map.setparents(parent, nullid)
         for f in changedfiles:
             if f in allfiles:
                 self.normallookup(f)
@@ -787,7 +786,7 @@
         self._nonnormalset, self._otherparentset = self._map.nonnormalentries()
         st.close()
         self._lastnormaltime = 0
-        self._dirty = self._dirtypl = False
+        self._dirty = self._map._dirtyparents = False
 
     def _dirignore(self, f):
         if f == '.':
@@ -1292,6 +1291,8 @@
 
         self._map = {}
         self.copymap = {}
+        self._parents = None
+        self._dirtyparents = False
 
         # for consistent view between _pl() and _read() invocations
         self._pendingmode = None
@@ -1370,16 +1371,28 @@
         return fp
 
     def parents(self):
-        try:
-            fp = self._opendirstatefile()
-            st = fp.read(40)
-            fp.close()
+        if not self._parents:
+            try:
+                fp = self._opendirstatefile()
+                st = fp.read(40)
+                fp.close()
+            except IOError as err:
+                if err.errno != errno.ENOENT:
+                    raise
+                # File doesn't exist, so the current state is empty
+                st = ''
+
             l = len(st)
             if l == 40:
-                return st[:20], st[20:40]
-            elif l > 0 and l < 40:
-                raise error.Abort(_('working directory state appears damaged!'))
-        except IOError as err:
-            if err.errno != errno.ENOENT:
-                raise
-        return [nullid, nullid]
+                self._parents = st[:20], st[20:40]
+            elif l == 0:
+                self._parents = [nullid, nullid]
+            else:
+                raise error.Abort(_('working directory state appears '
+                                    'damaged!'))
+
+        return self._parents
+
+    def setparents(self, p1, p2):
+        self._parents = (p1, p2)
+        self._dirtyparents = True