[gcc r13-7172] c++: make trait of incomplete type a permerror [PR109277]

[gcc r13-7172] c++: make trait of incomplete type a permerror [PR109277]

[Jason Merrill]

https://gcc.gnu.org/g:f32f7881fb0db085479525b5a23db5dabd990c3b

commit r13-7172-gf32f7881fb0db085479525b5a23db5dabd990c3b
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Apr 3 23:20:13 2023 -0400

    c++: make trait of incomplete type a permerror [PR109277]
    
    An incomplete type argument to several traits is specified to be undefined
    behavior in the library; since it's a compile-time property, we diagnose
    it.  But apparently some code was relying on the previous behavior of not
    diagnosing.  So let's make it a permerror.
    
    The assert in cxx_incomplete_type_diagnostic didn't like that, and I don't
    see the point of having the assert, so let's just remove it.
    
            PR c++/109277
    
    gcc/cp/ChangeLog:
    
            * semantics.cc (check_trait_type): Handle incomplete type directly.
            * typeck2.cc (cxx_incomplete_type_diagnostic): Remove assert.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/ext/is_convertible5.C: New test.

Diff:
---
 gcc/cp/semantics.cc                        | 7 ++++++-
 gcc/cp/typeck2.cc                          | 4 ----
 gcc/testsuite/g++.dg/ext/is_convertible5.C | 7 +++++++
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 99a76e3ed65..45e0b0e81d3 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12107,7 +12107,12 @@ check_trait_type (tree type, int kind = 1)
   if (VOID_TYPE_P (type))
     return true;
 
-  return !!complete_type_or_else (strip_array_types (type), NULL_TREE);
+  type = complete_type (strip_array_types (type));
+  if (!COMPLETE_TYPE_P (type)
+      && cxx_incomplete_type_diagnostic (NULL_TREE, type, DK_PERMERROR)
+      && !flag_permissive)
+    return false;
+  return true;
 }
 
 /* Process a trait expression.  */
diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 76a7a7f6b98..bf03967a71f 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -298,10 +298,6 @@ cxx_incomplete_type_diagnostic (location_t loc, const_tree value,
 {
   bool is_decl = false, complained = false;
 
-  gcc_assert (diag_kind == DK_WARNING 
-	      || diag_kind == DK_PEDWARN 
-	      || diag_kind == DK_ERROR);
-
   /* Avoid duplicate error message.  */
   if (TREE_CODE (type) == ERROR_MARK)
     return false;
diff --git a/gcc/testsuite/g++.dg/ext/is_convertible5.C b/gcc/testsuite/g++.dg/ext/is_convertible5.C
new file mode 100644
index 00000000000..ab9be05afea
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_convertible5.C
@@ -0,0 +1,7 @@
+// PR c++/109277
+// { dg-do compile { target c++11 } }
+// { dg-options -fpermissive }
+
+struct a;
+struct b{};
+static_assert (!__is_convertible (a, b), ""); // { dg-warning "incomplete" }