[Clang][Sema] Use StructuralValues to model dependent NTTP arguments (#93556)

This patch takes Richard's approach of no longer modeling dependent NTTP
arguments with TemplateParamObjectDecls. Clang used to do so, which left
behind a problem in that we might mess up dependent and non-dependent
arguments that boil down to the same canonical type because there's a
default argument on the NTTP.

The problem of "canonical expression" is still present because this
patch doesn't touch the profiling part. Namely, #92292 seems different.

Fixes https://github.com/llvm/llvm-project/issues/84052

1 files changed, 6 insertions, 1 deletions

diff --git a/clang/lib/AST/TemplateBase.cpp b/clang/lib/AST/TemplateBase.cpp
index a7ee973..b50daf5 100644
--- a/clang/lib/AST/TemplateBase.cpp
+++ b/clang/lib/AST/TemplateBase.cpp
@@ -221,8 +221,13 @@ static const ValueDecl *getAsSimpleValueDeclRef(const ASTContext &Ctx,
 
   // We model class non-type template parameters as their template parameter
   // object declaration.
-  if (V.isStruct() || V.isUnion())
+  if (V.isStruct() || V.isUnion()) {
+    // Dependent types are not supposed to be described as
+    // TemplateParamObjectDecls.
+    if (T->isDependentType() || T->isInstantiationDependentType())
+      return nullptr;
     return Ctx.getTemplateParamObjectDecl(T, V);
+  }
 
   // Pointers and references with an empty path use the special 'Declaration'
   // representation.