[gcc r12-8916] c++: constinit on pointer to function [PR104066]

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

https://gcc.gnu.org/g:14faa5f585f6025df1e04c8c8b34340ff5e4d494

commit r12-8916-g14faa5f585f6025df1e04c8c8b34340ff5e4d494
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Nov 17 11:59:29 2022 -0500

    c++: constinit on pointer to function [PR104066]
    
    [dcl.constinit]: "The constinit specifier shall be applied only to
    a declaration of a variable with static or thread storage duration."
    
    Thus, this ought to be OK:
    
      constinit void (*p)() = nullptr;
    
    but the error message I introduced when implementing constinit was
    not looking at funcdecl_p, so the code above was rejected.
    
    Fixed thus.  I'm checking constinit_p first because I think that's
    far more likely to be false than funcdecl_p.
    
            PR c++/104066
    
    gcc/cp/ChangeLog:
    
            * decl.cc (grokdeclarator): Check funcdecl_p before complaining
            about constinit.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/constinit18.C: New test.
    
    (cherry picked from commit 7b3b2f50953c5143d4b14b59d322d8a793f411dd)

Diff:
---
 gcc/cp/decl.cc                           |  2 +-
 gcc/testsuite/g++.dg/cpp2a/constinit18.C | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index cd1522f9a9f..ed47d262078 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -12963,7 +12963,7 @@ grokdeclarator (const cp_declarator *declarator,
 			  "an array", name);
 		return error_mark_node;
 	      }
-	    if (constinit_p)
+	    if (constinit_p && funcdecl_p)
 	      {
 		error_at (declspecs->locations[ds_constinit],
 			  "%<constinit%> on function return type is not "
diff --git a/gcc/testsuite/g++.dg/cpp2a/constinit18.C b/gcc/testsuite/g++.dg/cpp2a/constinit18.C
new file mode 100644
index 00000000000..51b4f0273be
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constinit18.C
@@ -0,0 +1,12 @@
+// PR c++/104066
+// { dg-do compile { target c++20 } }
+
+constinit void (*p)() = nullptr;
+constinit void (*pp)() = nullptr;
+void fn();
+constinit void (&r)() = fn;
+
+extern constinit long (* const syscall_reexported) (long, ...);
+
+constinit void bad (); // { dg-error ".constinit. on function return type is not allowed" }
+constinit void bad () { } // { dg-error ".constinit. on function return type is not allowed" }