fix a crash when using type equality constaint (#8515)

Close #8193.

When constructing `TransitiveTypeWitness` node, we should check if there
is operand that represents two equal times. Currently, we only check
whether the operand is `TypeEqualityWitness`, which is not good enough,
because a `DeclaredSubtypeWitness` could also be representing two same
types, in that case, we should also const fold this kind of witness.

Fails to do so, we could finally ends up with a generating a lookup
witness IR on a generic parameter that is not supposed to be looked up.

1 files changed, 8 insertions, 0 deletions

diff --git a/source/slang/slang-ast-decl-ref.cpp b/source/slang/slang-ast-decl-ref.cpp
index 7eec32a3a..c054ef994 100644
--- a/source/slang/slang-ast-decl-ref.cpp
+++ b/source/slang/slang-ast-decl-ref.cpp
@@ -426,6 +426,14 @@ SourceLoc DeclRefBase::getLoc() const
     return getDecl()->loc;
 }
 
+// Keep this function here for better debuggin purpose
+String DeclRefBase::toString() const
+{
+    StringBuilder sb;
+    const_cast<DeclRefBase*>(this)->toText(sb);
+    return sb.produceString();
+}
+
 DeclRefBase* DeclRefBase::getParent()
 {
     auto astBuilder = getCurrentASTBuilder();