source.py: Remove the reliance on consistency to get whether a source is cached

This removes the need to use consistency in Sources, by asking
explicitely whether the source is cached or not.

This introduces a new public method on source: `is_cached` that needs
implementation and that should return whether the source has a local
copy or not.

- On fetch, also reset whether the source was cached or set if as
  cached when we know it was.

- Validate the cache's source after fetching it

  This doesn't need to be run in the scheduler's process and can be
  offloaded to the child, which will allow better multiprocessing

1 files changed, 3 insertions, 0 deletions

diff --git a/src/buildstream/_gitsourcebase.py b/src/buildstream/_gitsourcebase.py
index ce2ef9731..125d34df4 100644
--- a/src/buildstream/_gitsourcebase.py
+++ b/src/buildstream/_gitsourcebase.py
@@ -527,6 +527,9 @@ class _GitSourceBase(Source):
     def is_resolved(self):
         return self.mirror.ref is not None
 
+    def is_cached(self):
+        return self._have_all_refs()
+
     def load_ref(self, node):
         self.mirror.ref = node.get_str("ref", None)
         self.mirror.tags = self._load_tags(node)