[Capability System] Fix bug where capabilities do not correctly propegate if AST-parent has target+set the AST-child does not (#8175)

Fixes: #8174

Changes:
* To determine if we propagate capabilities, we need to ensure that a
`join` will do nothing (optimization since `join` is expensive + caching
data for the `join` adds up to be expensive). This logic was changed in
`slang-check-decl.cpp` since the current logic was incorrect.
* A parent could have the set `metal+glsl` and the use-site could have
`glsl`. In this case, we will not remove `metal` from the parent since
`{metal+glsl}.implies({glsl})` is true.

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 0a9853012..507e12fa6 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -14268,7 +14268,11 @@ static void _propagateRequirement(
         ensureDecl(visitor, referencedDecl, DeclCheckState::CapabilityChecked);
     }
 
-    if (resultCaps.implies(nodeCaps))
+    // If we do not have the same target+stage, we need to `join` to remove excess target+stage.
+    //
+    // If we have the same target+stage but current capabilities do not imply incoming capabilities,
+    // we need to `join`.
+    if (!resultCaps.joinWithOtherWillChangeThis(nodeCaps))
         return;
 
     auto oldCaps = resultCaps;