[gcc r11-8220] c++: ICE with bogus late return type [PR99803]

[Marek Polacek <mpolacek@gcc.gnu.org>]

https://gcc.gnu.org/g:70f2bff43aadd2fcc0595bf9f4bab72647529655

commit r11-8220-g70f2bff43aadd2fcc0595bf9f4bab72647529655
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Apr 14 17:57:15 2021 -0400

    c++: ICE with bogus late return type [PR99803]
    
    Here we ICE when compiling this code in C++20, because we're trying to
    slam a 'typename' after the ->.  The cp_parser_template_id call just
    before the spot I'm changing parsed A::template A<int> as a BASELINK
    that contains a constructor, but make_typename_type crashes on that.
    
    This patch makes make_typename_type more robust instead of checking
    for is_overloaded_fn prior calling it.
    
    gcc/cp/ChangeLog:
    
            PR c++/99803
            * decl.c (make_typename_type): Give an error and return when
            name is is_overloaded_fn.
            * parser.c (cp_parser_class_name): Don't check is_overloaded_fn
            before calling make_typename_type.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/99803
            * g++.dg/cpp2a/typename14.C: Don't expect particular error
            messages.
            * g++.dg/cpp2a/typename19.C: New test.

Diff:
---
 gcc/cp/decl.c                           | 8 +++++++-
 gcc/cp/parser.c                         | 4 +---
 gcc/testsuite/g++.dg/cpp2a/typename14.C | 4 ++--
 gcc/testsuite/g++.dg/cpp2a/typename19.C | 5 +++++
 4 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index d40b7a7da5f..942eb318f2c 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4055,6 +4055,12 @@ make_typename_type (tree context, tree name, enum tag_types tag_type,
 	error ("%qD used without template arguments", name);
       return error_mark_node;
     }
+  else if (is_overloaded_fn (name))
+    {
+      if (complain & tf_error)
+	error ("%qD is a function, not a type", name);
+      return error_mark_node;
+    }
   gcc_assert (identifier_p (name));
   gcc_assert (TYPE_P (context));
 
@@ -4066,7 +4072,7 @@ make_typename_type (tree context, tree name, enum tag_types tag_type,
 	error ("%q#T is not a class", context);
       return error_mark_node;
     }
-  
+
   /* When the CONTEXT is a dependent type,  NAME could refer to a
      dependent base class of CONTEXT.  But look inside it anyway
      if CONTEXT is a currently open scope, in case it refers to a
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index dfc9b8251a7..99eccf0c5e4 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -24730,9 +24730,7 @@ cp_parser_class_name (cp_parser *parser,
   decl = cp_parser_maybe_treat_template_as_class (decl, class_head_p);
 
   /* If this is a typename, create a TYPENAME_TYPE.  */
-  if (typename_p
-      && decl != error_mark_node
-      && !is_overloaded_fn (decl))
+  if (typename_p && decl != error_mark_node)
     {
       decl = make_typename_type (scope, decl, typename_type,
 				 /*complain=*/tf_error);
diff --git a/gcc/testsuite/g++.dg/cpp2a/typename14.C b/gcc/testsuite/g++.dg/cpp2a/typename14.C
index 8d82b6b8d34..ba7dad8245f 100644
--- a/gcc/testsuite/g++.dg/cpp2a/typename14.C
+++ b/gcc/testsuite/g++.dg/cpp2a/typename14.C
@@ -8,7 +8,7 @@ template<typename> struct A
 
 template<typename T>
 template<typename U>
-A<T>::A<U> () // { dg-error "partial specialization" }
+A<T>::A<U> () // { dg-error "" }
 {
 }
 
@@ -19,7 +19,7 @@ template<typename> struct B
 
 template<typename T>
 template<typename U>
-B<T>::foo<int>(int) // { dg-error "partial specialization|declaration" }
+B<T>::foo<int>(int) // { dg-error "" }
 {
   return 1;
 }
diff --git a/gcc/testsuite/g++.dg/cpp2a/typename19.C b/gcc/testsuite/g++.dg/cpp2a/typename19.C
new file mode 100644
index 00000000000..320a14d6a0c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/typename19.C
@@ -0,0 +1,5 @@
+// PR c++/99803
+// { dg-do compile { target c++20 } }
+
+struct A { template<typename T> A(T); };
+auto A(unsigned) -> A::template A<int>; // { dg-error "not a type" }