element.py: Introduce __update_strict_cache_key_of_rdeps()

Once an Element's strict cache key is determined, we should
attempt to update the strict cache key of it's reverse
dependencies. The state of a reverse dependency will be
updated once all of its dependencies have strict cache keys

This patch introduces the potential for a RecursionError because
_update_state() can now trigger further _update_state calls (on
reverse dependencies). Therefore, the maximum recursion limit
for our "test_max_recursion_depth" test has been lowered.

If this becomes a problem, we can always consider setting a
larger recursion limit, for now, this change has been tested
with the Debian stack and works as expected.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/buildstream/_pipeline.py b/src/buildstream/_pipeline.py
index a96a3f731..a9d88befd 100644
--- a/src/buildstream/_pipeline.py
+++ b/src/buildstream/_pipeline.py
@@ -124,6 +124,11 @@ class Pipeline():
     #
     def resolve_elements(self, targets):
         with self._context.messenger.timed_activity("Resolving cached state", silent_nested=True):
+            # XXX: Now that Element._update_state() can trigger recursive update_state calls
+            # it is possible that we could get a RecursionError. However, this is unlikely
+            # to happen, even for large projects (tested with the Debian stack). Although,
+            # if it does become a problem we may have to set the recursion limit to a
+            # greater value.
             for element in self.dependencies(targets, Scope.ALL):
                 # Determine initial element state.
                 element._update_state()