c++: Implement C++26 P2741R3 - user-generated static_assert messages [PR110348]

The following patch implements the user generated static_assert messages next
to string literals.

As I wrote already in the PR, in addition to looking through the paper
I looked at the clang++ testcase for this feature implemented there from
paper's author and on godbolt played with various parts of the testcase
coverage below, and there are some differences between what the patch
implements and what clang++ implements.

The first is that clang++ diagnoses if M.size () or M.data () methods
are present, but aren't constexpr; while the paper introduction talks about
that, the standard wording changes don't seem to require that, all they say
is that those methods need to exist (assuming accessible and the like)
and be implicitly convertible to std::size_t or const char *, but rest is
only if the static assertion fails.  If there is intent to change that
wording, the question is how far to go, e.g. while M.size () could be
constexpr, they could e.g. return some class object which wouldn't have
constexpr conversion operator to size_t/const char * and tons of other
reasons why the constant evaluation could fail.  Without actually evaluating
it I don't see how we could guarantee anything for non-failed static_assert.

The second difference is that
static_assert (false, "foo"_myd);
in the testcase is normal failed static assertion and
static_assert (true, "foo"_myd);
would be accepted, while clang++ rejects it.  IMHO
"foo"_myd doesn't match the syntactic requirements of unevaluated-string
as mentioned in http://eel.is/c++draft/dcl.pre#10 , and because
a constexpr udlit operator can return something which is valid, it shouldn't
be rejected just in case.
Last is clang++ ICEs on non-static data members size/data.

The first version of this support had a difference where M.data () was not
a constant expression but a core constant expression, but if M.size () != 0
M.data ()[0] ... M.data ()[M.size () - 1] were integer constant expressions.
We don't have any routine to test whether an expression is a core constant
expression, so what the code does is try silently whether M.data () is
a constant expression (maybe_constant_value), if it is, nice, we can use
that result to attempt to optimize the extraction of the message from it
if it is some recognized form involving a STRING_CST and just to double-check
try to constant evaluate M.data ()[0] and M.data ()[M.size () - 1] expressions
as boundaries but not anything in between.  If M.data () is not a constant
expression, we don't fail, but use a slower method of evaluating M.data ()[i]
for i 0, 1, ... M.size () - 1.  And if M.size () == 0, the above wouldn't
evaluate anything, so we try to constant evaluate (M.data (), 0) as constant
expression, which should succeed if M.data () is a core constant expression
and fail otherwise.

The patch assumes that these expressions are manifestly constant evaluated.

The patch implements what I see in the paper, because it is unclear what
further changes will be voted in (and the changes can be done at that
point).
The initial patch used tf_none in 6 spots so that just the static_assert
specific errors were emitted and not others, but during review this has been
changed, so that we emit both the more detailed errors why something wasn't
found or wasn't callable or wasn't convertible and diagnostics that
static_assert second argument needs to satisfy some of the needed properties.

2023-11-23  Jakub Jelinek  <jakub@redhat.com>

	PR c++/110348
gcc/
	* doc/invoke.texi (-Wno-c++26-extensions): Document.
gcc/c-family/
	* c.opt (Wc++26-extensions): New option.
	* c-cppbuiltin.cc (c_cpp_builtins): For C++26 predefine
	__cpp_static_assert to 202306L rather than 201411L.
gcc/cp/
	* parser.cc: Implement C++26 P2741R3 - user-generated static_assert
	messages.
	(cp_parser_static_assert): Parse message argument as
	conditional-expression if it is not a pure string literal or
	several of them concatenated followed by closing paren.
	* semantics.cc (finish_static_assert): Handle message which is not
	STRING_CST.  For condition with bare parameter packs return early.
	* pt.cc (tsubst_expr) <case STATIC_ASSERT>: Also tsubst_expr
	message and make sure that if it wasn't originally STRING_CST, it
	isn't after tsubst_expr either.
gcc/testsuite/
	* g++.dg/cpp26/static_assert1.C: New test.
	* g++.dg/cpp26/feat-cxx26.C (__cpp_static_assert): Expect
	202306L rather than 201411L.
	* g++.dg/cpp0x/udlit-error1.C: Expect different diagnostics for
	static_assert with user-defined literal.

diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
index 8d2f07a96ce0c701c7fced1e1d22b70d990c17d0..56c4d63718637a13be05a5a5d7ace458ef1bc554 100644 (file)
--- a/gcc/c-family/c-cppbuiltin.cc
+++ b/gcc/c-family/c-cppbuiltin.cc
@@ -1023,7 +1023,8 @@ c_cpp_builtins (cpp_reader *pfile)
        {
          /* Set feature test macros for C++17.  */
          cpp_define (pfile, "__cpp_unicode_characters=201411L");
-         cpp_define (pfile, "__cpp_static_assert=201411L");
+         if (cxx_dialect <= cxx23)
+           cpp_define (pfile, "__cpp_static_assert=201411L");
          cpp_define (pfile, "__cpp_namespace_attributes=201411L");
          cpp_define (pfile, "__cpp_enumerator_attributes=201411L");
          cpp_define (pfile, "__cpp_nested_namespace_definitions=201411L");
@@ -1086,6 +1087,7 @@ c_cpp_builtins (cpp_reader *pfile)
        {
          /* Set feature test macros for C++26.  */
          cpp_define (pfile, "__cpp_constexpr=202306L");
+         cpp_define (pfile, "__cpp_static_assert=202306L");
        }
       if (flag_concepts)
         {

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index b10c6057cd153afa981a4b9d0881dd5425e82b46..3848f378de1ac72d60c3fbbd3c97d05127db6c2a 100644 (file)
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -498,6 +498,10 @@ Wc++23-extensions
 C++ ObjC++ Var(warn_cxx23_extensions) Warning Init(1)
 Warn about C++23 constructs in code compiled with an older standard.
 
+Wc++26-extensions
+C++ ObjC++ Var(warn_cxx26_extensions) Warning Init(1)
+Warn about C++26 constructs in code compiled with an older standard.
+
 Wcast-function-type
 C ObjC C++ ObjC++ Var(warn_cast_function_type) Warning EnabledBy(Wextra)
 Warn about casts between incompatible function types.

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index f556b8f3c0157958f70e8d44cabc90e533eb287c..f6d088bc73f5363ba4807ed2295290b2f6b23c95 100644 (file)
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -16616,6 +16616,7 @@ cp_parser_linkage_specification (cp_parser* parser, tree prefix_attr)
    static_assert-declaration:
      static_assert ( constant-expression , string-literal ) ;
      static_assert ( constant-expression ) ; (C++17)
+     static_assert ( constant-expression, conditional-expression ) ; (C++26)
 
    If MEMBER_P, this static_assert is a class member.  */
 
@@ -16646,10 +16647,10 @@ cp_parser_static_assert (cp_parser *parser, bool member_p)
 
   /* Parse the constant-expression.  Allow a non-constant expression
      here in order to give better diagnostics in finish_static_assert.  */
-  condition =
-    cp_parser_constant_expression (parser,
-                                   /*allow_non_constant_p=*/true,
-                                  /*non_constant_p=*/nullptr);
+  condition
+    = cp_parser_constant_expression (parser,
+                                    /*allow_non_constant_p=*/true,
+                                    /*non_constant_p=*/nullptr);
 
   if (cp_lexer_peek_token (parser->lexer)->type == CPP_CLOSE_PAREN)
     {
@@ -16668,8 +16669,32 @@ cp_parser_static_assert (cp_parser *parser, bool member_p)
       /* Parse the separating `,'.  */
       cp_parser_require (parser, CPP_COMMA, RT_COMMA);
 
-      /* Parse the string-literal message.  */
-      if (cxx_dialect >= cxx26)
+      /* Parse the message expression.  */
+      bool string_lit = true;
+      for (unsigned int i = 1; ; ++i)
+       {
+         cp_token *tok = cp_lexer_peek_nth_token (parser->lexer, i);
+         if (cp_parser_is_pure_string_literal (tok))
+           continue;
+         else if (tok->type == CPP_CLOSE_PAREN)
+           break;
+         string_lit = false;
+         break;
+       }
+      if (!string_lit)
+       {
+         location_t loc = cp_lexer_peek_token (parser->lexer)->location;
+         if (cxx_dialect < cxx26)
+           pedwarn (loc, OPT_Wc__26_extensions,
+                    "%<static_assert%> with non-string message only "
+                    "available with %<-std=c++2c%> or %<-std=gnu++2c%>");
+
+         message = cp_parser_conditional_expression (parser);
+         if (TREE_CODE (message) == STRING_CST)
+           message = build1_loc (loc, PAREN_EXPR, TREE_TYPE (message),
+                                 message);
+       }
+      else if (cxx_dialect >= cxx26)
        message = cp_parser_unevaluated_string_literal (parser);
       else
        message = cp_parser_string_literal (parser, /*translate=*/false,

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 68ce4a87372945243e4d9b0149161a16379687c3..092e6fdfd36999ca416ff92e9758ff916d7208df 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -18702,15 +18702,20 @@ tsubst_stmt (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 
     case STATIC_ASSERT:
       {
-       tree condition;
+       tree condition, message;
 
        ++c_inhibit_evaluation_warnings;
        condition = tsubst_expr (STATIC_ASSERT_CONDITION (t), args,
                                 complain, in_decl);
+       message = tsubst_expr (STATIC_ASSERT_MESSAGE (t), args,
+                              complain, in_decl);
+       if (TREE_CODE (STATIC_ASSERT_MESSAGE (t)) != STRING_CST
+           && TREE_CODE (message) == STRING_CST)
+         message = build1_loc (STATIC_ASSERT_SOURCE_LOCATION (t),
+                               PAREN_EXPR, TREE_TYPE (message), message);
        --c_inhibit_evaluation_warnings;
 
-        finish_static_assert (condition,
-                              STATIC_ASSERT_MESSAGE (t),
+       finish_static_assert (condition, message,
                               STATIC_ASSERT_SOURCE_LOCATION (t),
                              /*member_p=*/false, /*show_expr_p=*/true);
       }

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 8090c71809fefc6de4e3acf1722e4cd2318b6478..f0a8372683db4b4b4453e8b477e61ce5b4e1f082 100644 (file)
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -11434,6 +11434,7 @@ finish_static_assert (tree condition, tree message, location_t location,
                      bool member_p, bool show_expr_p)
 {
   tsubst_flags_t complain = tf_warning_or_error;
+  tree message_sz = NULL_TREE, message_data = NULL_TREE;
 
   if (message == NULL_TREE
       || message == error_mark_node
@@ -11441,13 +11442,61 @@ finish_static_assert (tree condition, tree message, location_t location,
       || condition == error_mark_node)
     return;
 
-  if (check_for_bare_parameter_packs (condition))
-    condition = error_mark_node;
+  if (check_for_bare_parameter_packs (condition)
+      || check_for_bare_parameter_packs (message))
+    return;
+
+  if (TREE_CODE (message) != STRING_CST
+      && !type_dependent_expression_p (message))
+    {
+      message_sz
+       = finish_class_member_access_expr (message,
+                                          get_identifier ("size"),
+                                          false, complain);
+      if (message_sz != error_mark_node)
+       message_data
+         = finish_class_member_access_expr (message,
+                                            get_identifier ("data"),
+                                            false, complain);
+      if (message_sz == error_mark_node || message_data == error_mark_node)
+       {
+         error_at (location, "%<static_assert%> message must be a string "
+                             "literal or object with %<size%> and "
+                             "%<data%> members");
+         return;
+       }
+      releasing_vec size_args, data_args;
+      message_sz = finish_call_expr (message_sz, &size_args, false, false,
+                                    complain);
+      message_data = finish_call_expr (message_data, &data_args, false, false,
+                                      complain);
+      if (message_sz == error_mark_node || message_data == error_mark_node)
+       return;
+      message_sz = build_converted_constant_expr (size_type_node, message_sz,
+                                                 complain);
+      if (message_sz == error_mark_node)
+       {
+         error_at (location, "%<static_assert%> message %<size()%> "
+                             "must be implicitly convertible to "
+                             "%<std::size_t%>");
+         return;
+       }
+      message_data = build_converted_constant_expr (const_string_type_node,
+                                                   message_data, complain);
+      if (message_data == error_mark_node)
+       {
+         error_at (location, "%<static_assert%> message %<data()%> "
+                             "must be implicitly convertible to "
+                             "%<const char*%>");
+         return;
+       }
+    }
 
   /* Save the condition in case it was a concept check.  */
   tree orig_condition = condition;
 
-  if (instantiation_dependent_expression_p (condition))
+  if (instantiation_dependent_expression_p (condition)
+      || instantiation_dependent_expression_p (message))
     {
       /* We're in a template; build a STATIC_ASSERT and put it in
          the right place. */
@@ -11485,9 +11534,89 @@ finish_static_assert (tree condition, tree message, location_t location,
          if (processing_template_decl)
            goto defer;
 
-         int sz = TREE_INT_CST_LOW (TYPE_SIZE_UNIT
-                                    (TREE_TYPE (TREE_TYPE (message))));
-         int len = TREE_STRING_LENGTH (message) / sz - 1;
+         int len;
+         const char *msg = NULL;
+         char *buf = NULL;
+         if (message_sz && message_data)
+           {
+             tree msz = cxx_constant_value (message_sz, NULL_TREE, complain);
+             if (!tree_fits_uhwi_p (msz))
+               {
+                 error_at (location,
+                           "%<static_assert%> message %<size()%> "
+                           "must be a constant expression");
+                 return;
+               }
+             else if ((unsigned HOST_WIDE_INT) (int) tree_to_uhwi (msz)
+                      != tree_to_uhwi (msz))
+               {
+                 error_at (location,
+                           "%<static_assert%> message %<size()%> "
+                           "%qE too large", msz);
+                 return;
+               }
+             len = tree_to_uhwi (msz);
+             tree data = maybe_constant_value (message_data, NULL_TREE,
+                                               mce_true);
+             if (!reduced_constant_expression_p (data))
+               data = NULL_TREE;
+             if (len)
+               {
+                 if (data)
+                   msg = c_getstr (data);
+                 if (msg == NULL)
+                   buf = XNEWVEC (char, len);
+                 for (int i = 0; i < len; ++i)
+                   {
+                     tree t = message_data;
+                     if (i)
+                       t = build2 (POINTER_PLUS_EXPR,
+                                   TREE_TYPE (message_data), message_data,
+                                   size_int (i));
+                     t = build1 (INDIRECT_REF, TREE_TYPE (TREE_TYPE (t)), t);
+                     tree t2 = cxx_constant_value (t, NULL_TREE, complain);
+                     if (!tree_fits_shwi_p (t2))
+                       {
+                         error_at (location,
+                                   "%<static_assert%> message %<data()[%d]%> "
+                                   "must be a constant expression", i);
+                         return;
+                       }
+                     if (msg == NULL)
+                       buf[i] = tree_to_shwi (t2);
+                     /* If c_getstr worked, just verify the first and
+                        last characters using constant evaluation.  */
+                     else if (len > 2 && i == 0)
+                       i = len - 2;
+                   }
+                 if (msg == NULL)
+                   msg = buf;
+               }
+             else if (!data)
+               {
+                 /* We don't have any function to test whether some
+                    expression is a core constant expression.  So, instead
+                    test whether (message.data (), 0) is a constant
+                    expression.  */
+                 data = build2 (COMPOUND_EXPR, integer_type_node,
+                                message_data, integer_zero_node);
+                 tree t = cxx_constant_value (data, NULL_TREE, complain);
+                 if (!integer_zerop (t))
+                   {
+                     error_at (location,
+                               "%<static_assert%> message %<data()%> "
+                               "must be a core constant expression");
+                     return;
+                   }
+               }
+           }
+         else
+           {
+             tree eltype = TREE_TYPE (TREE_TYPE (message));
+             int sz = TREE_INT_CST_LOW (TYPE_SIZE_UNIT (eltype));
+             msg = TREE_STRING_POINTER (message);
+             len = TREE_STRING_LENGTH (message) / sz - 1;
+           }
 
          /* See if we can find which clause was failing (for logical AND).  */
          tree bad = find_failing_clause (NULL, orig_condition);
@@ -11497,12 +11626,13 @@ finish_static_assert (tree condition, tree message, location_t location,
 
          auto_diagnostic_group d;
 
-          /* Report the error. */
+         /* Report the error. */
          if (len == 0)
            error_at (cloc, "static assertion failed");
          else
-           error_at (cloc, "static assertion failed: %s",
-                     TREE_STRING_POINTER (message));
+           error_at (cloc, "static assertion failed: %.*s", len, msg);
+
+         XDELETEVEC (buf);
 
          diagnose_failing_condition (bad, cloc, show_expr_p);
        }

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 7666de1e9b274ef4fdda408637eeb10e9d9e3eee..54c42c9659ca0ef809bf951a09560d1fc55750ab 100644 (file)
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -9107,6 +9107,13 @@ Do not warn about C++23 constructs in code being compiled using
 an older C++ standard.  Even without this option, some C++23 constructs
 will only be diagnosed if @option{-Wpedantic} is used.
 
+@opindex Wc++26-extensions
+@opindex Wno-c++26-extensions
+@item -Wno-c++26-extensions @r{(C++ and Objective-C++ only)}
+Do not warn about C++26 constructs in code being compiled using
+an older C++ standard.  Even without this option, some C++26 constructs
+will only be diagnosed if @option{-Wpedantic} is used.
+
 @opindex Wcast-qual
 @opindex Wno-cast-qual
 @item -Wcast-qual

diff --git a/gcc/testsuite/g++.dg/cpp0x/udlit-error1.C b/gcc/testsuite/g++.dg/cpp0x/udlit-error1.C
index 40566e0572f31de5ad7750f4075488ae3065285b..6d6cd454540a7a0c0fb0590edb9ef43f0e0c2339 100644 (file)
--- a/gcc/testsuite/g++.dg/cpp0x/udlit-error1.C
+++ b/gcc/testsuite/g++.dg/cpp0x/udlit-error1.C
@@ -11,7 +11,9 @@ void operator""_x(const char *, decltype(sizeof(0)));
 #pragma message "hi"_x   // { dg-warning "string literal with user-defined suffix is invalid in this context" }
 
 extern "C"_x { void g(); } // { dg-error "before user-defined string literal" }
-static_assert(true, "foo"_x); // { dg-error "string literal with user-defined suffix is invalid in this context|expected" }
+static_assert(true, "foo"_x);  // { dg-error "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "invalid use of 'void'" "" { target *-*-* } .-2 }
 
 [[deprecated("oof"_x)]]        // { dg-error "string literal with user-defined suffix is invalid in this context" "" { target c++26 } }
 void

diff --git a/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C b/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
index 0977d964fe09f16978ad5f399e804d20064beb41..80e8ef680d9dd7142d61a5950ddc09222186c66a 100644 (file)
--- a/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
+++ b/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
@@ -304,8 +304,8 @@
 
 #ifndef __cpp_static_assert
 #  error "__cpp_static_assert"
-#elif __cpp_static_assert != 201411
-#  error "__cpp_static_assert != 201411"
+#elif __cpp_static_assert != 202306
+#  error "__cpp_static_assert != 202306"
 #endif
 
 #ifndef __cpp_namespace_attributes

diff --git a/gcc/testsuite/g++.dg/cpp26/static_assert1.C b/gcc/testsuite/g++.dg/cpp26/static_assert1.C
new file mode 100644 (file)
index 0000000..9dec52b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/static_assert1.C
@@ -0,0 +1,309 @@
+// C++26 P2741R3 - user-generated static_assert messages
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+static_assert (true, "");
+static_assert (true, (""));    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "request for member 'size' in '\\\(\\\"\\\"\\\)', which is of non-class type 'const char \\\[1\\\]'" "" { target *-*-* } .-2 }
+static_assert (true, "" + 0);  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "request for member 'size' in '\\\(const char\\\*\\\)\\\"\\\"', which is of non-class type 'const char\\\*'" "" { target *-*-* } .-2 }
+static_assert (true, 0);       // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "request for member 'size' in '0', which is of non-class type 'int'" "" { target *-*-* } .-2 }
+struct A {};
+static_assert (true, A {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "'struct A' has no member named 'size'" "" { target *-*-* } .-2 }
+struct B { int size; };
+static_assert (true, B {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "'struct B' has no member named 'data'" "" { target *-*-* } .-2 }
+struct C { constexpr int size () const { return 0; } };
+static_assert (true, C {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "'struct C' has no member named 'data'" "" { target *-*-* } .-2 }
+struct D { constexpr int size () const { return 0; } int data; };
+static_assert (true, D {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'D\\\(\\\).D::data' cannot be used as a function" "" { target *-*-* } .-1 }
+struct E { int size = 0;
+          constexpr const char *data () const { return ""; } };
+static_assert (true, E {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'E\\\(\\\).E::size' cannot be used as a function" "" { target c++11_only } .-1 }
+                               // { dg-error "'E\\\{0\\\}.E::size' cannot be used as a function" "" { target c++14 } .-2 }
+struct F { constexpr const char *size () const { return ""; }
+          constexpr const char *data () const { return ""; } };
+static_assert (true, F {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message 'size\\\(\\\)' must be implicitly convertible to 'std::size_t'" "" { target *-*-* } .-1 }
+                               // { dg-error "could not convert 'F\\\(\\\).F::size\\\(\\\)' from 'const char\\\*' to '\[^']*'" "" { target *-*-* } .-2 }
+                               // { dg-error "conversion from 'const char\\\*' to '\[^']*' in a converted constant expression" "" { target *-*-* } .-3 }
+struct G { constexpr long size () const { return 0; }
+          constexpr float data () const { return 0.0f; } };
+static_assert (true, G {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message 'data\\\(\\\)' must be implicitly convertible to 'const char\\\*'" "" { target *-*-* } .-1 }
+                               // { dg-error "could not convert 'G\\\(\\\).G::data\\\(\\\)' from 'float' to 'const char\\\*'" "" { target *-*-* } .-2 }
+struct H { short size () const { return 0; }
+          constexpr const char *data () const { return ""; } };
+static_assert (true, H {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+struct I { constexpr signed char size () const { return 0; }
+          const char *data () const { return ""; } };
+static_assert (true, I {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+struct J { constexpr int size () const { return j ? throw 1 : 0; }     // { dg-error "expression '<throw-expression>' is not a constant expression" }
+          constexpr const char *data () const { return ""; };
+          constexpr J (int x) : j (x) {}
+          int j; };
+static_assert (true, J (1));   // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+static_assert (false, J (0));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed" "" { target *-*-* } .-1 }
+static_assert (false, J (1));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "'static_assert' message 'size\\\(\\\)' must be a constant expression" "" { target *-*-* } .-1 }
+struct K { constexpr operator int () { return 4; } };
+struct L { constexpr operator const char * () { return "test"; } };
+struct M { constexpr K size () const { return {}; }
+          constexpr L data () const { return {}; } };
+static_assert (true, M {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+static_assert (false, M {});   // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+#if  __cpp_constexpr_dynamic_alloc >= 201907L
+struct N { constexpr int size () const { return 3; }
+          constexpr const char *data () const { return new char[3] { 'b', 'a', 'd' }; } }; // { dg-error "'\\\* N\\\(\\\).N::data\\\(\\\)' is not a constant expression because allocated storage has not been deallocated" "" { target c++20 } }
+static_assert (true, N {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++20 && c++23_down } } }
+static_assert (false, N {});   // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++20 && c++23_down } } }
+                               // { dg-error "'static_assert' message 'data\\\(\\\)\\\[0\\\]' must be a constant expression" "" { target c++20 } .-1 }
+#endif
+constexpr const char a[] = { 't', 'e', 's', 't' };
+struct O { constexpr int size () const { return 4; }
+          constexpr const char *data () const { return a; } };
+static_assert (false, O {});   // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+struct P { constexpr int size () const { return 4 - p; }
+          constexpr const char *data () const { return &a[p]; }
+          constexpr P (int x) : p (x) {}
+          int p; };
+static_assert (false, P (0));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+static_assert (false, P (2));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: st" "" { target *-*-* } .-1 }
+struct Q { constexpr int size () const { return 4 - q; }
+          constexpr const char *data () const { return &"test"[q]; }
+          constexpr Q (int x) : q (x) {}
+          int q; };
+static_assert (false, Q (0));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+static_assert (false, Q (1));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: est" "" { target *-*-* } .-1 }
+struct R { constexpr int size () const { return 4 - r; }
+          constexpr const char *d () const { return "test"; }
+          constexpr const char *data () const { return d () + r; }
+          constexpr R (int x) : r (x) {}
+          int r; };
+static_assert (false, R (0));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+static_assert (false, R (2));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: st" "" { target *-*-* } .-1 }
+struct S { constexpr float size (float) const { return 42.0f; }
+          constexpr int size (void * = nullptr) const { return 4; }
+          constexpr double data (double) const { return 42.0; }
+          constexpr const char *data (int = 0) const { return "test"; } };
+static_assert (true, S {});    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+static_assert (false, S {});   // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+
+using size_t = decltype (sizeof (0));
+struct string_view {
+  size_t s;
+  const char *d;
+  constexpr string_view () : s (0), d (nullptr) {}
+  constexpr string_view (const char *p) : s (__builtin_strlen (p)), d (p) {}
+  constexpr string_view (size_t l, const char *p) : s (l), d (p) {}
+  constexpr size_t size () const noexcept { return s; }
+  constexpr const char *data () const noexcept { return d; }
+};
+static_assert (true, string_view{});                           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+static_assert (false, string_view ("test"));                   // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+static_assert (false, string_view ("א"));                     // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                                               // { dg-error "static assertion failed: א" "" { target *-*-* } .-1 }
+static_assert (false, string_view (0, nullptr));               // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                                               // { dg-error "static assertion failed" "" { target *-*-* } .-1 }
+static_assert (false, string_view (4, "testwithextrachars"));  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+static_assert (false, string_view (42, "test"));               // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                                               // { dg-error "array subscript value '41' is outside the bounds of array type 'const char \\\[5\\\]'" "" { target *-*-* } .-1 }
+                                                               // { dg-error "'static_assert' message 'data\\\(\\\)\\\[41\\\]' must be a constant expression" "" { target *-*-* } .-2 }
+
+template <typename T, size_t N>
+struct array {
+  constexpr size_t size () const { return N; }
+  constexpr const T *data () const { return a; }
+  const T a[N];
+};
+static_assert (true, array<char, 2> { 'O', 'K' });             // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+static_assert (true, array<wchar_t, 2> { L'O', L'K' });                // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                                               // { dg-error "'static_assert' message 'data\\\(\\\)' must be implicitly convertible to 'const char\\\*'" "" { target *-*-* } .-1 }
+                                                               // { dg-error "could not convert 'array<wchar_t, 2>{const wchar_t \\\[2\\\]{\[0-9]+, \[0-9]+}}.array<wchar_t, 2>::data\\\(\\\)' from 'const wchar_t\\\*' to 'const char\\\*'" "" { target *-*-* } .-2 }
+static_assert (false, array<char, 4> { 't', 'e', 's', 't' });  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                                               // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+
+void
+foo ()
+{
+  constexpr auto a = array<char, 4> { 't', 'e', 's', 't' };
+  static_assert (false, a);                                    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+}                                                              // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+
+#if  __cpp_constexpr_dynamic_alloc >= 201907L
+struct T {
+  const char *d = init ();
+  constexpr int size () const { return 4; }
+  constexpr const char *data () const { return d; }
+  constexpr const char *init () const { return new char[4] { 't', 'e', 's', 't' }; }
+  constexpr ~T () { delete[] d; }
+};
+static_assert (false, T{});            // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++20 && c++23_down } } }
+                                       // { dg-error "static assertion failed: test" "" { target c++20 } .-1 }
+#endif
+struct U { constexpr operator const char * () const { return u; }
+          char u[5] = "test"; };
+#if __cplusplus >= 201402L
+struct V { constexpr auto size () const { return K{}; }
+          constexpr auto data () const { return U{}; } };
+static_assert (false, V{});            // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++14 && c++23_down } } }
+                                       // { dg-error "static assertion failed: test" "" { target c++14 } .-1 }
+#endif
+struct W { constexpr int size (int) const { return 4; }
+          constexpr const char *data () const { return "test"; } };
+static_assert (true, W{});             // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "no matching function for call to 'W::size\\\(\\\)'" "" { target *-*-* } .-1 }
+struct X { constexpr int size () const { return 4; }
+          constexpr const char *data (int) const { return "test"; } };
+static_assert (true, X{});             // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "no matching function for call to 'X::data\\\(\\\)'" "" { target *-*-* } .-1 }
+struct Y { constexpr int size () { return 4; }
+          constexpr const char *data (int) { return "test"; } };
+static_assert (true, Y{});             // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "no matching function for call to 'Y::data\\\(\\\)'" "" { target *-*-* } .-1 }
+#if __cpp_concepts >= 201907L
+struct Z { constexpr int size (auto...) const { return 4; }
+          constexpr const char *data (auto...) const { return "test"; } };
+static_assert (false, Z{});            // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++20 && c++23_down } } }
+                                       // { dg-error "static assertion failed: test" "" { target c++20 } .-1 }
+#endif
+
+namespace NN
+{
+  template <typename T>
+  struct A {
+    constexpr int size () const = delete;
+    constexpr const char *data () const { return "test"; } };
+  static_assert (true, A<int>{});      // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "use of deleted function 'constexpr int NN::A<T>::size\\\(\\\) const \\\[with T = int\\\]'" "" { target *-*-* } .-1 }
+#if __cpp_concepts >= 201907L
+  template <typename T>
+  struct B {
+    constexpr int size () const { return 4; }
+    constexpr const char *data () const requires false { return "test"; } };
+  static_assert (true, B<short>{});    // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++20 && c++23_down } } }
+                                       // { dg-error "no matching function for call to 'NN::B<short int>::data\\\(\\\)'" "" { target c++20 } .-1 }
+#endif
+  class C {
+    constexpr int size () const = delete;
+    constexpr const char *data () const { return "test"; } };
+  static_assert (true, C{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "use of deleted function 'constexpr int NN::C::size\\\(\\\) const'" "" { target *-*-* } .-1 }
+                                       // { dg-error "'constexpr const char\\\* NN::C::data\\\(\\\) const' is private within this context" "" { target *-*-* } .-2 }
+#if __cplusplus >= 201402L
+  struct D {
+    constexpr int size () { return 4; }
+    constexpr int size () const { return 3; }
+    constexpr const char *data () { return "test"; }
+    constexpr const char *data () const { return "ehlo"; } };
+  static_assert (true, D{});   // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++14 && c++23_down } } }
+  static_assert (false, D{});  // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++14 && c++23_down } } }
+                               // { dg-error "static assertion failed: test" "" { target c++14 } .-1 }
+#endif
+  struct E {
+    constexpr int size () const { return 4; }
+    constexpr const char *data () const { return "test"; } };
+  template <typename T>
+  struct F {
+    static_assert (false, T{});        // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+  };                           // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+  template <typename T>
+  struct G {
+    static_assert (false, T{});        // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+  };                           // { dg-error "'static_assert' message must be a string literal or object with 'size' and 'data' members" "" { target *-*-* } .-1 }
+                               // { dg-error "request for member 'size' in '0', which is of non-class type 'long int'" "" { target *-*-* } .-2 }
+  F<E> fe;
+  G<long> gl;
+  constexpr E operator ""_myd (const char *, size_t) { return E{}; }
+  static_assert (false, "foo"_myd);    // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+  constexpr E operator + (const char *, const E &) { return E{}; }
+  static_assert (false, "foo" + E{});  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "static assertion failed: test" "" { target *-*-* } .-1 }
+  struct H {
+    static constexpr int size () { return 7; }
+    static constexpr const char *data () { return "message"; } };
+  static_assert (true, H{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+  static_assert (false, H{});          // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "static assertion failed: message" "" { target *-*-* } .-1 }
+  struct I {
+    static constexpr int size () { return 0; }
+    static constexpr const char *data () { return nullptr; } };
+  static_assert (true, I{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+  static_assert (false, I{});          // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                                       // { dg-error "static assertion failed" "" { target *-*-* } .-1 }
+#if __cplusplus >= 201402L
+  struct J {
+    static constexpr int size () { return 0; }
+    static constexpr const char *data (int x = 0) { if (x) return nullptr; else throw 1; } }; // { dg-error "expression '<throw-expression>' is not a constant expression" "" { target c++14 } }
+  static_assert (true, J{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++14 && c++23_down } } }
+  static_assert (false, J{});          // { dg-warning "'static_assert' with non-string message only available with" "" { target { c++14 && c++23_down } } }
+                                       // { dg-error "'static_assert' message 'data\\\(\\\)' must be a core constant expression" "" { target c++14 } .-1 }
+#endif
+#if __cpp_if_consteval >= 202106L
+  struct K {
+    static constexpr int size () { if consteval { return 4; } else { throw 1; } }
+    static constexpr const char *data () { return "test"; }
+  };
+  static_assert (true, K{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+  static_assert (false, K{});          // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+                                       // { dg-error "static assertion failed: test" "" { target c++23 } .-1 }
+  struct L {
+    static constexpr int size () { return 4; }
+    static constexpr const char *data () { if consteval { return "test"; } else { throw 1; } }
+  };
+  static_assert (true, L{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+  static_assert (false, L{});          // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+                                       // { dg-error "static assertion failed: test" "" { target c++23 } .-1 }
+  struct M {
+    static constexpr int size () { if consteval { throw 1; } else { return 4; } } // { dg-error "expression '<throw-expression>' is not a constant expression" "" { target c++23 } }
+    static constexpr const char *data () { return "test"; }
+  };
+  static_assert (true, M{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+  static_assert (false, M{});          // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+                                       // { dg-error "'static_assert' message 'size\\\(\\\)' must be a constant expression" "" { target c++23 } .-1 }
+  struct N {
+    static constexpr int size () { return 4; }
+    static constexpr const char *data () { if consteval { throw 1; } else { return "test"; } } // { dg-error "expression '<throw-expression>' is not a constant expression" "" { target c++23 } }
+  };
+  static_assert (true, N{});           // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+  static_assert (false, N{});          // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_only } }
+                                       // { dg-error "'static_assert' message 'data\\\(\\\)\\\[0\\\]' must be a constant expression" "" { target c++23 } .-1 }
+#endif
+  struct O { constexpr int operator () () const { return 12; } };
+  struct P { constexpr const char *operator () () const { return "another test"; } };
+  struct Q { O size; P data; };
+  static_assert (true, Q ());  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+  static_assert (false, Q {}); // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: another test" "" { target *-*-* } .-1 }
+  constexpr int get_size () { return 16; }
+  constexpr const char *get_data () { return "yet another test"; }
+  struct R { int (*size) () = NN::get_size;
+            const char *(*data) () = NN::get_data; };
+  static_assert (true, R ());  // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+  static_assert (false, R {}); // { dg-warning "'static_assert' with non-string message only available with" "" { target c++23_down } }
+                               // { dg-error "static assertion failed: yet another test" "" { target *-*-* } .-1 }
+}