[PATCH 2/2] c++: make trait of incomplete type a permerror [PR109277]

[Jason Merrill <jason@redhat.com>]

Tested x86_64-pc-linux-gnu, applying to trunk.

-- 8< --

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.
---
 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(-)
 create mode 100644 gcc/testsuite/g++.dg/ext/is_convertible5.C

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" }
-- 
2.31.1