store: add union stores

Future patches will refactor the storage logic into a more abstract API. This
patch adds a union store, which will allow us to check both local client storage and
shared cache storage, without exposing the difference at higher levels.

remotefilelog/contentstore.py

@@ -3,6 +3,46 @@ import basestore, ioutil
 from mercurial import util
 from mercurial.node import hex
 
+class unioncontentstore(object):
+    def __init__(self, local, shared):
+        self._local = local
+        self._shared = shared
+
+    def get(self, name, node):
+        try:
+            return self._shared.get(name, node)
+        except KeyError:
+            pass
+
+        try:
+            return self._local.get(name, node)
+        except KeyError:
+            pass
+
+        self._shared.triggerfetches([(name, node)])
+        try:
+            return self._shared.get(name, node)
+        except KeyError:
+            pass
+
+        raise error.LookupError(id, self.filename, _('no node'))
+
+    def add(self, name, node, data):
+        raise Exception("cannot add content only to remotefilelog "
+                        "contentstore")
+
+    def contains(self, keys):
+        missing = self._local.contains(keys)
+        if missing:
+            missing = self._shared.contains(missing)
+        return missing
+
+    def addfetcher(self, fetchfunc):
+        self._shared.addfetcher(fetchfunc)
+
+    def triggerfetches(self, keys):
+        self._shared.triggerfetches(keys)
+
 class remotefilelogcontentstore(basestore.basestore):
     def get(self, name, node):
         pass

remotefilelog/metadatastore.py

@@ -3,6 +3,61 @@ import basestore, ioutil
 from mercurial import util
 from mercurial.node import hex
 
+class unionmetadatastore(object):
+    def __init__(self, local, shared):
+        self._local = local
+        self._shared = shared
+
+    def getparents(self, name, node):
+        """Returns the immediate parents of the node."""
+        pass
+
+    def getancestors(self, name, node):
+        """Returns as many ancestors as we're aware of.
+
+        return value: {
+           node: (p1, p2, linknode),
+           ...
+        }
+        """
+        try:
+            return self._shared.getancestors(name, node)
+        except KeyError:
+            pass
+
+        try:
+            return self._local.getancestors(name, node)
+        except KeyError:
+            pass
+
+        self._shared.triggerfetches([(name, node)])
+        try:
+            return self._shared.getancestors(name, node)
+        except KeyError:
+            pass
+
+        raise error.LookupError(node, name, _('no valid file history'))
+
+    def getlinknode(self, name, node):
+        ancestors = self.getancestors(name, node)
+        return ancestors[node][3]
+
+    def add(self, name, node, data):
+        raise Exception("cannot add content only to remotefilelog "
+                        "contentstore")
+
+    def contains(self, keys):
+        missing = self._local.contains(keys)
+        if missing:
+            missing = self._shared.contains(missing)
+        return missing
+
+    def addfetcher(self, fetchfunc):
+        self._shared.addfetcher(fetchfunc)
+
+    def triggerfetches(self, keys):
+        self._shared.triggerfetches(keys)
+
 class remotefilelogmetadatastore(basestore.basestore):
     def getparents(self, name, node):
         """Returns the immediate parents of the node."""