filecache: create an entry in _filecache when __set__ is called for a missing one

Preserve the invariant that if P is a filecached property on X then
P in X.__dict__ => P in X._filecache.

Previously, it was possible for a filecached property to become out of sync
with the filesystem if it was set before getting it first, since the initial
filecacheentry was created in __get__.

Old behaviour:

  repo.prop = x
  repo.invalidate() # prop has no entry in _filecache, it's not removed
                    # from __dict__
  repo.prop         # returns x like before without checking with the
                    # filesystem

New:

  repo.prop = x     # an empty entry is created in _filecache
  repo.invalidate() # prop is removed from __dict__
  repo.prop         # recreates prop

mercurial/scmutil.py

@@ -950,6 +950,7 b' class filecache(object):'
     def __get__(self, obj, type=None):
         # do we need to check if the file changed?
         if self.name in obj.__dict__:
+            assert self.name in obj._filecache, self.name
             return obj.__dict__[self.name]
 
         entry = obj._filecache.get(self.name)
@@ -971,8 +972,15 b' class filecache(object):'
         return entry.obj
 
     def __set__(self, obj, value):
-        if self.name in obj._filecache:
-            obj._filecache[self.name].obj = value # update cached copy
+        if self.name not in obj._filecache:
+            # we add an entry for the missing value because X in __dict__
+            # implies X in _filecache
+            ce = filecacheentry(self.join(obj, self.path), False)
+            obj._filecache[self.name] = ce
+        else:
+            ce = obj._filecache[self.name]
+
+        ce.obj = value # update cached copy
         obj.__dict__[self.name] = value # update copy returned by obj.x
 
     def __delete__(self, obj):

tests/test-filecache.py

@@ -101,6 +101,17 b' def test_filecache_synced():'
     # it
     repo.commit('.')
 
+def setbeforeget(repo):
+    os.remove('x')
+    repo.cached = 0
+    repo.invalidate()
+    print repo.cached
+    repo.invalidate()
+    f = open('x', 'w')
+    f.write('a')
+    f.close()
+    print repo.cached
+
 print 'basic:'
 print
 basic(fakerepo())
@@ -109,3 +120,7 b" print 'fakeuncacheable:'"
 print
 fakeuncacheable()
 test_filecache_synced()
+print
+print 'setbeforeget:'
+print
+setbeforeget(fakerepo())

tests/test-filecache.py.out

@@ -17,3 +17,9 b' repository tip rolled back to revision -'
 working directory now based on revision -1
 repository tip rolled back to revision -1 (undo commit)
 working directory now based on revision -1
+
+setbeforeget:
+
+0
+creating
+None