[Clang] Workaround dependent source location issues

In #78436 we made some SourceLocExpr dependent to
deal with the fact that their value should reflect the name of
specialized function - rather than the rtemplate in which they
are first used.

However SourceLocExpr are unusual in two ways
 - They don't depend on template argumente
 - They morally depend on the context in which they are used
   (rather than called from).

It's fair to say that this is quite novels and confuses
clang. In particular, in some cases, we used to create
dependent SourceLocExpr and never subsequently transform them,
leaving dependent objects in instantiated functions types.
To work around that we avoid replacing SourceLocExpr when we think
they could remain dependent.
It's certainly not perfect but it fixes a number of reported bugs,
and seem to only affect scenarios in which the value of the
SourceLocExpr does not matter (overload resolution).

Fixes #106428
Fixes #81155

clang/docs/ReleaseNotes.rst

@@ -326,6 +326,7 @@ Bug Fixes to C++ Support
 - Fix evaluation of the index of dependent pack indexing expressions/types specifiers (#GH105900)
 - Correctly handle subexpressions of an immediate invocation in the presence of implicit casts. (#GH105558)
 - Clang now correctly handles direct-list-initialization of a structured bindings from an array. (#GH31813)
+- Fix an issue with dependent source location expressions (#GH106428), (#GH81155)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaExpr.cpp

@@ -5441,11 +5441,24 @@ struct EnsureImmediateInvocationInDefaultArgs
 
   // Rewrite to source location to refer to the context in which they are used.
   ExprResult TransformSourceLocExpr(SourceLocExpr *E) {
-    if (E->getParentContext() == SemaRef.CurContext)
+    DeclContext *DC = E->getParentContext();
+    if (DC == SemaRef.CurContext)
       return E;
-    return getDerived().RebuildSourceLocExpr(E->getIdentKind(), E->getType(),
-                                             E->getBeginLoc(), E->getEndLoc(),
-                                             SemaRef.CurContext);
+
+    // FIXME: During instantiation, because the rebuild of defaults arguments
+    // is not always done in the context of the template instantiator,
+    // we run the risk of producing a dependent source location
+    // that would never be rebuilt.
+    // This usually happen during overload resolution, or in contexts
+    // where the value of the source location does not matter.
+    // However, we should find a better way to deal with source location
+    // of function template.
+    if (!SemaRef.CurrentInstantiationScope ||
+        !SemaRef.CurContext->isDependentContext() || DC->isDependentContext())
+      DC = SemaRef.CurContext;
+
+    return getDerived().RebuildSourceLocExpr(
+        E->getIdentKind(), E->getType(), E->getBeginLoc(), E->getEndLoc(), DC);
   }
 };
 

clang/test/SemaCXX/source_location.cpp

@@ -929,3 +929,63 @@ void test() {
 }
 
 }
+
+namespace GH106428 {
+
+struct add_fn {
+    template <typename T>
+    constexpr auto operator()(T lhs, T rhs,
+                              const std::source_location loc = std::source_location::current())
+        const -> T
+    {
+        return lhs + rhs;
+    }
+};
+
+
+template <class _Fp, class... _Args>
+decltype(_Fp{}(0, 0))
+__invoke(_Fp&& __f);
+
+template<typename T>
+struct type_identity { using type = T; };
+
+template<class Fn>
+struct invoke_result : type_identity<decltype(__invoke(Fn{}))> {};
+
+using i = invoke_result<add_fn>::type;
+static_assert(__is_same(i, int));
+
+}
+
+#if __cplusplus >= 202002L
+
+namespace GH81155 {
+struct buff {
+  buff(buff &, const char * = __builtin_FUNCTION());
+};
+
+template <class Ty>
+Ty declval();
+
+template <class Fx>
+auto Call(buff arg) -> decltype(Fx{}(arg));
+
+template <typename>
+struct F {};
+
+template <class Fx>
+struct InvocableR : F<decltype(Call<Fx>(declval<buff>()))> {
+  static constexpr bool value = false;
+};
+
+template <class Fx, bool = InvocableR<Fx>::value>
+void Help(Fx) {}
+
+void Test() {
+  Help([](buff) {});
+}
+
+}
+
+#endif