[gcc r16-3287] c++: Fix ICE on mangling invalid compound requirement [PR120618]

[Jason Merrill via Gcc-cvs]

https://gcc.gnu.org/g:54bf72ebfe983c611673bcc4368b5834773fcc7d

commit r16-3287-g54bf72ebfe983c611673bcc4368b5834773fcc7d
Author: Ben Wu <soggysocks...@gmail.com>
Date:   Tue Aug 19 13:49:41 2025 -0400

    c++: Fix ICE on mangling invalid compound requirement [PR120618]
    
    This testcase caused an ICE when mangling the invalid type-constraint in
    write_requirement since write_type_constraint expects a TEMPLATE_TYPE_PARM.
    
    Setting the trailing return type to NULL_TREE when a
    return-type-requirement is found in place of a type-constraint prevents the
    failed assertion in write_requirement. It also allows the invalid
    constraint to be satisfied in some contexts to prevent redundant errors,
    e.g. in concepts-requires5.C.
    
    Bootstrapped and tested on x86_64-linux-gnu.
    
            PR c++/120618
    
    gcc/cp/ChangeLog:
    
            * parser.cc (cp_parser_compound_requirement): Set type to
            NULL_TREE for invalid type-constraint.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/concepts-requires5.C: Don't require
            redundant diagnostic in static assertion.
            * g++.dg/concepts/pr120618.C: New test.
    
    Suggested-by: Jason Merrill <ja...@redhat.com>

Diff:
---
 gcc/cp/parser.cc                                |  9 ++++++---
 gcc/testsuite/g++.dg/concepts/pr120618.C        | 13 +++++++++++++
 gcc/testsuite/g++.dg/cpp2a/concepts-requires5.C |  2 +-
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index d66b658b748f..40223bedcc1c 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -33403,9 +33403,12 @@ cp_parser_compound_requirement (cp_parser *parser)
            }
        }
       else
-       /* P1452R2 removed the trailing-return-type option.  */
-       error_at (type_loc,
-                 "return-type-requirement is not a type-constraint");
+       {
+         /* P1452R2 removed the trailing-return-type option.  */
+         error_at (type_loc,
+                   "return-type-requirement is not a type-constraint");
+         type = NULL_TREE;
+       }
     }
 
   location_t loc = make_location (expr_token->location,
diff --git a/gcc/testsuite/g++.dg/concepts/pr120618.C 
b/gcc/testsuite/g++.dg/concepts/pr120618.C
new file mode 100644
index 000000000000..85d2532a9d67
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/pr120618.C
@@ -0,0 +1,13 @@
+// { dg-do compile { target c++17 } }
+// { dg-options "-fconcepts" }
+
+class B{};
+
+template <typename T>
+requires (!requires(T t) { { t } -> bool; }) // { dg-error 
"return-type-requirement is not a type-constraint" }
+void foo(T t) {}
+
+int main() {
+  B b;
+  foo(b); // { dg-prune-output "no matching function" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires5.C 
b/gcc/testsuite/g++.dg/cpp2a/concepts-requires5.C
index 524eadbf5ddb..3c5a9135c181 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-requires5.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires5.C
@@ -41,5 +41,5 @@ class D : /*private*/ B { };
 void driver_2()
 {
   static_assert(ConvertibleTo<D, B>()); // { dg-error "cannot call" }
-  static_assert(ConvertibleTo<D, B>); // { dg-error "static assertion failed" }
+  static_assert(ConvertibleTo<D, B>); // { dg-prune-output "static assertion 
failed" }
 }