[gcc r12-8270] c++: decltype of non-dependent call of class type [PR105386]

[Patrick Palka]

https://gcc.gnu.org/g:b6a48401da51e9042b6f0822d532b3b472492658

commit r12-8270-gb6a48401da51e9042b6f0822d532b3b472492658
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Apr 26 10:53:38 2022 -0400

    c++: decltype of non-dependent call of class type [PR105386]
    
    We need to pass tf_decltype when instantiating a non-dependent decltype
    operand, like tsubst does in the dependent case, so that we don't force
    completion of a prvalue operand's class type.
    
            PR c++/105386
    
    gcc/cp/ChangeLog:
    
            * semantics.cc (finish_decltype_type): Pass tf_decltype to
            instantiate_non_dependent_expr_sfinae.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/decltype81.C: New test.

Diff:
---
 gcc/cp/semantics.cc                     |  2 +-
 gcc/testsuite/g++.dg/cpp0x/decltype81.C | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index f08c0b6281f..ab48f11c9be 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -11252,7 +11252,7 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
     }
   else if (processing_template_decl)
     {
-      expr = instantiate_non_dependent_expr_sfinae (expr, complain);
+      expr = instantiate_non_dependent_expr_sfinae (expr, complain|tf_decltype);
       if (expr == error_mark_node)
 	return error_mark_node;
       /* Keep processing_template_decl cleared for the rest of the function
diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype81.C b/gcc/testsuite/g++.dg/cpp0x/decltype81.C
new file mode 100644
index 00000000000..7d25db39d9c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/decltype81.C
@@ -0,0 +1,15 @@
+// PR c++/105386
+// { dg-do compile { target c++11 } }
+
+template<class T> struct NoInst {
+  static_assert(sizeof(T) == 9999, "NoInst instantiated");
+};
+
+template<class T> NoInst<T> f(T);
+
+template<class>
+struct A {
+  using type = decltype(f(0));
+};
+
+A<int> a;