[Clang][Sema] Make UnresolvedLookupExprs in class scope explicit specializations instantiation dependent (#100392)

A class member named by an expression in a member function that may instantiate to a static _or_ non-static member is represented by a `UnresolvedLookupExpr` in order to defer the implicit transformation to a class member access expression until instantiation. Since `ASTContext::getDecltypeType` only creates a `DecltypeType` that has a `DependentDecltypeType` as its canonical type when the operand is instantiation dependent, and since we do not transform types unless they are instantiation dependent, we need to mark the `UnresolvedLookupExpr` as instantiation dependent in order to correctly build a `DecltypeType` using the expression as its operand with a `DependentDecltypeType` canonical type. Fixes #99873. 

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index 2070f3b..f1ba26f 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -331,7 +331,8 @@ ExprResult Sema::BuildPossibleImplicitMemberExpr(
     return UnresolvedLookupExpr::Create(
         Context, R.getNamingClass(), SS.getWithLocInContext(Context),
         TemplateKWLoc, R.getLookupNameInfo(), /*RequiresADL=*/false,
-        TemplateArgs, R.begin(), R.end(), /*KnownDependent=*/true);
+        TemplateArgs, R.begin(), R.end(), /*KnownDependent=*/true,
+        /*KnownInstantiationDependent=*/true);
 
   case IMA_Error_StaticOrExplicitContext:
   case IMA_Error_Unrelated: