[PATCH] c++: constinit on pointer to function [PR104066]

[Marek Polacek <polacek@redhat.com>]

[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.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
I think I'd like to backport this all the way back to 10.

	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.
---
 gcc/cp/decl.cc                           |  2 +-
 gcc/testsuite/g++.dg/cpp2a/constinit18.C | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/constinit18.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index d28889ed865..9a7b1a6c381 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -13071,7 +13071,7 @@ 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" }

base-commit: ee892832ea19b21a3420ef042e582204fac852a2
-- 
2.38.1