From: Jakub Jelinek <jakub@redhat.com>
Date: Fri, 6 Feb 2026 10:27:52 +0000 (+0100)
Subject: tree: Fix up build_function_type for (...) fntypes [PR123977]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5f75fc37b131c701a5b5c627239fa4e4dfabe230;p=thirdparty%2Fgcc.git

tree: Fix up build_function_type for (...) fntypes [PR123977]

The following testcase ICEs in -std=c++26 mode since my r16-4338 C++26
va_start changes.
The problem is that if we have anything non-canonical in a function
type with (...) in C++26 (or C23/C2Y) mode, in this case the R typedef
on return type rather than void, then we try to build TYPE_CANONICAL
for that, but weren't passing in the no_named_args_stdarg_p, so
a type with TYPE_NO_NAMED_ARGS_STDARG_P flag set got TYPE_CANONICAL
with TYPE_NO_NAMED_ARGS_STDARG_P flag cleared and comptypes then
didn't like that as those aren't really compatible types
(...) vs. the C89-ish () which even C++ uses for some type-generic
etc. builtins.

2026-02-05  Jakub Jelinek  <jakub@redhat.com>

	PR c++/123977
	* tree.cc (build_function_type): Pass no_named_args_stdarg_p
	as last argument to recursive call.

	* g++.dg/cpp26/stdarg10.C: New test.
---

diff --git a/gcc/testsuite/g++.dg/cpp26/stdarg10.C b/gcc/testsuite/g++.dg/cpp26/stdarg10.C
new file mode 100644
index 00000000000..a8e1ddaee1e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/stdarg10.C
@@ -0,0 +1,19 @@
+// PR c++/123977
+// { dg-do compile }
+
+typedef void R;
+struct A {
+  R foo (...) const volatile;
+  void foo ();
+};
+
+template <class T>
+struct B {
+  static void bar () { (T (A::*)) &A::foo; }
+};
+
+void
+baz ()
+{
+  B <R (...) const volatile>::bar;
+}
diff --git a/gcc/tree.cc b/gcc/tree.cc
index cf47f0ee64d..22effa6bcd1 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -7780,7 +7780,8 @@ build_function_type (tree value_type, tree arg_types,
     gcc_assert (TYPE_STRUCTURAL_EQUALITY_P (t));
   else if (any_noncanonical_p)
     TYPE_CANONICAL (t) = build_function_type (TYPE_CANONICAL (value_type),
-					      canon_argtypes);
+					      canon_argtypes,
+					      no_named_args_stdarg_p);
 
   if (!COMPLETE_TYPE_P (t))
     layout_type (t);