Re: [PATCH] c++: Fix up diagnostics of wrong constexpr bodies in C++11 in templates [PR123889]

[Jakub Jelinek]

On Sun, Feb 08, 2026 at 11:27:40AM +0900, Jason Merrill wrote:
> > +         && !DECL_CONSTRUCTOR_P (fun))
> > +       error ("body of %<constexpr%> function %qD not a return-statement",
> > +              fun);
> >       require_potential_rvalue_constant_expression (massaged);
> >       if (DECL_CONSTRUCTOR_P (fun))
> 
> Since we have this DECL_CONSTRUCTOR_P check already, let's make the new code
> an else?

Thanks, here is what I've committed after another x86_64/i686-linux
bootstrap/regtest:

2026-02-09  Jakub Jelinek  <ja...@redhat.com>

        PR c++/123889
        * constexpr.cc (explain_invalid_constexpr_fn): Diagnose
        NULL or error_mark_node massaged on non-constructor.

        * g++.dg/cpp0x/constexpr-123889.C: New test.

--- gcc/cp/constexpr.cc.jj      2026-02-04 11:21:46.975769787 +0100
+++ gcc/cp/constexpr.cc 2026-02-08 21:04:44.816563912 +0100
@@ -1124,6 +1124,9 @@ explain_invalid_constexpr_fn (tree fun)
                /* Also check the body, not just the ctor-initializer.  */
                require_potential_rvalue_constant_expression (body);
            }
+         else if (massaged == NULL_TREE || massaged == error_mark_node)
+           error ("body of %<constexpr%> function %qD not a return-statement",
+                  fun);
        }
     }
 }
--- gcc/testsuite/g++.dg/cpp0x/constexpr-123889.C.jj    2026-02-02 
14:42:30.345152859 +0100
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-123889.C       2026-02-02 
14:44:10.958435899 +0100
@@ -0,0 +1,14 @@
+// PR c++/123889
+// { dg-do compile { target c++11 } }
+
+template <class T>
+constexpr int func (T) {
+// { dg-message "'constexpr int func\\\(T\\\) \\\[with T = int\\\]' is not 
usable as a 'constexpr' function because:" "" { target c++11_only } .-1 }
+// { dg-error "body of 'constexpr' function 'constexpr int func\\\(T\\\) 
\\\[with T = int\\\]' not a return-statement" "" { target c++11_only } .-2 }
+  return 1;
+  return 2;
+}
+
+static_assert (func (1) == 1, "");
+// { dg-error "non-constant condition for static assertion" "" { target 
c++11_only } .-1 }
+// { dg-error "'constexpr int func\\\(T\\\) \\\[with T = int\\\]' called in a 
constant expression" "" { target c++11_only } .-2 }


        Jakub