In ExprRequirement building, treat OverloadExpr as dependent (#66683)

As reported in #66612, we aren't correctly treating the placeholder
expression type correctly, so we ended up trying to get a reference
version of it, and this resulted in an assertion, since the placeholder
type cannot have a reference added.

Fixes: #66612

Author: erichkeane

clang/docs/ReleaseNotes.rst

@@ -305,6 +305,9 @@ Bug Fixes to C++ Support
   that contains a `return`.
   (`#48527 <https://github.com/llvm/llvm-project/issues/48527>`_)
 
+- Clang now no longer asserts when an UnresolvedLookupExpr is used as an
+  expression requirement. (`#66612 https://github.com/llvm/llvm-project/issues/66612`)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.

clang/lib/Sema/SemaExprCXX.cpp

@@ -9063,7 +9063,8 @@ Sema::BuildExprRequirement(
     concepts::ExprRequirement::ReturnTypeRequirement ReturnTypeRequirement) {
   auto Status = concepts::ExprRequirement::SS_Satisfied;
   ConceptSpecializationExpr *SubstitutedConstraintExpr = nullptr;
-  if (E->isInstantiationDependent() || ReturnTypeRequirement.isDependent())
+  if (E->isInstantiationDependent() || E->getType()->isPlaceholderType() ||
+      ReturnTypeRequirement.isDependent())
     Status = concepts::ExprRequirement::SS_Dependent;
   else if (NoexceptLoc.isValid() && canThrow(E) == CanThrowResult::CT_Can)
     Status = concepts::ExprRequirement::SS_NoexceptNotMet;

clang/test/SemaTemplate/concepts.cpp

@@ -1031,3 +1031,20 @@ void test() {
     fff(42UL); // expected-error {{no matching function}}
 }
 }
+
+namespace GH66612 {
+  template<typename C>
+    auto end(C c) ->int;
+
+  template <typename T>
+    concept Iterator = true;
+
+  template <typename CT>
+    concept Container = requires(CT b) {
+        { end } -> Iterator; // #66612GH_END
+    };
+
+  static_assert(Container<int>);// expected-error{{static assertion failed}}
+  // expected-note@-1{{because 'int' does not satisfy 'Container'}}
+  // expected-note@#66612GH_END{{because 'end' would be invalid: reference to overloaded function could not be resolved; did you mean to call it?}}
+}