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

8 files changed, 20 insertions, 2 deletions

diff --git a/tests/frontend/consistencyerror/bug.bst b/tests/frontend/consistencyerror/bug.bst
index a66002046..5639abee2 100644
--- a/tests/frontend/consistencyerror/bug.bst
+++ b/tests/frontend/consistencyerror/bug.bst
@@ -1,4 +1,4 @@
 kind: import
-description: An element with an unhandled exception at get_consistency time
+description: An element with an unhandled exception in checking whether it is cached or not
 sources:
 - kind: consistencybug
diff --git a/tests/frontend/consistencyerror/error.bst b/tests/frontend/consistencyerror/error.bst
index ccf11c942..e377aa97a 100644
--- a/tests/frontend/consistencyerror/error.bst
+++ b/tests/frontend/consistencyerror/error.bst
@@ -1,4 +1,4 @@
 kind: import
-description: An element with a failing source at get_consistency time
+description: An element with a failing source when checking whether it is cached or not
 sources:
 - kind: consistencyerror
diff --git a/tests/frontend/consistencyerror/plugins/consistencybug.py b/tests/frontend/consistencyerror/plugins/consistencybug.py
index c4a3217ec..7f0bd9211 100644
--- a/tests/frontend/consistencyerror/plugins/consistencybug.py
+++ b/tests/frontend/consistencyerror/plugins/consistencybug.py
@@ -14,6 +14,9 @@ class ConsistencyBugSource(Source):
     def is_resolved(self):
         return True
 
+    def is_cached(self):
+        return True
+
     def get_consistency(self):
 
         # Raise an unhandled exception (not a BstError)
diff --git a/tests/frontend/consistencyerror/plugins/consistencyerror.py b/tests/frontend/consistencyerror/plugins/consistencyerror.py
index d7433e368..523ac0b6f 100644
--- a/tests/frontend/consistencyerror/plugins/consistencyerror.py
+++ b/tests/frontend/consistencyerror/plugins/consistencyerror.py
@@ -14,6 +14,9 @@ class ConsistencyErrorSource(Source):
     def is_resolved(self):
         return True
 
+    def is_cached(self):
+        return True
+
     def get_consistency(self):
 
         # Raise an error unconditionally
diff --git a/tests/frontend/project/sources/fetch_source.py b/tests/frontend/project/sources/fetch_source.py
index d634adfa3..60b4ba95d 100644
--- a/tests/frontend/project/sources/fetch_source.py
+++ b/tests/frontend/project/sources/fetch_source.py
@@ -69,6 +69,9 @@ class FetchSource(Source):
     def is_resolved(self):
         return True
 
+    def is_cached(self) -> bool:
+        return self.get_consistency() == Consistency.CACHED
+
     def get_consistency(self):
         if not os.path.exists(self.output_file):
             return Consistency.RESOLVED
diff --git a/tests/sources/no-fetch-cached/plugins/sources/always_cached.py b/tests/sources/no-fetch-cached/plugins/sources/always_cached.py
index 5f05b592b..6267a99eb 100644
--- a/tests/sources/no-fetch-cached/plugins/sources/always_cached.py
+++ b/tests/sources/no-fetch-cached/plugins/sources/always_cached.py
@@ -23,6 +23,9 @@ class AlwaysCachedSource(Source):
     def is_resolved(self):
         return True
 
+    def is_cached(self):
+        return True
+
     def get_consistency(self):
         return Consistency.CACHED
 
diff --git a/tests/sources/previous_source_access/plugins/sources/foo_transform.py b/tests/sources/previous_source_access/plugins/sources/foo_transform.py
index 906a8f6be..c59c81e63 100644
--- a/tests/sources/previous_source_access/plugins/sources/foo_transform.py
+++ b/tests/sources/previous_source_access/plugins/sources/foo_transform.py
@@ -39,6 +39,9 @@ class FooTransformSource(Source):
     def get_unique_key(self):
         return (self.ref,)
 
+    def is_cached(self):
+        return self.get_consistency() == Consistency.CACHED
+
     def get_consistency(self):
         if self.ref is None:
             return Consistency.INCONSISTENT
diff --git a/tests/sources/project_key_test/plugins/sources/key-test.py b/tests/sources/project_key_test/plugins/sources/key-test.py
index 30256929c..98dd380ef 100644
--- a/tests/sources/project_key_test/plugins/sources/key-test.py
+++ b/tests/sources/project_key_test/plugins/sources/key-test.py
@@ -20,6 +20,9 @@ class KeyTest(Source):
         assert self.ref
         return "abcdefg"
 
+    def is_cached(self):
+        return False
+
     def get_consistency(self):
         if self.ref:
             return Consistency.RESOLVED