Re: [C++17] Implement N3928 - Extending static_assert

[Ed Smith-Rowland <3dw4rd@verizon.net>]

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On 06/17/2015 03:22 PM, Jason Merrill wrote:
> On 06/17/2015 01:53 PM, Ed Smith-Rowland wrote:
>> I tried the obvious: an error message with %qE and got 'false'.
>> constexpr values are evaluated early on.
>>
>> Is there a possibility that late folding could help or is that
>> completely different?
>
> Late folding could help, but I think handling it in libcpp (by 
> actually stringizing the argument) would work better.
>
> Jason
>
>
OK, Doing the bit with libcpp and getting a better message is taking 
longer than I thought it would.
I'm going ahead with what I had back in May.
I'm still working on better - it'll just take a hot minute.

Meanwhile, this takes care of an annoyance for many.

Committed 224903.

Ed


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cp/

2015-06-24  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Implement N3928 - Extending static_assert
	* parser.c (cp_parser_static_assert): Support static_assert with
	no message string.  Supply an empty string in this case.
	* semantics.c (finish_static_assert): Don't try to print a message if
	the message strnig is empty.


testsuite/

2015-06-24  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Implement N3928 - Extending static_assert
	* g++.dg/cpp0x/static_assert8.C: Adjust.
	* g++.dg/cpp0x/static_assert12.C: New.
	* g++.dg/cpp0x/static_assert13.C: New.
	* g++.dg/cpp1y/static_assert1.C: New.
	* g++.dg/cpp1y/static_assert2.C: New.
	* g++.dg/cpp1z/static_assert-nomsg.C: New.


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Index: cp/parser.c
===================================================================
--- cp/parser.c	(revision 224897)
+++ cp/parser.c	(working copy)
@@ -12173,6 +12173,7 @@
 
    static_assert-declaration:
      static_assert ( constant-expression , string-literal ) ; 
+     static_assert ( constant-expression ) ; (C++1Z)
 
    If MEMBER_P, this static_assert is a class member.  */
 
@@ -12210,20 +12211,35 @@
                                    /*allow_non_constant_p=*/true,
                                    /*non_constant_p=*/&dummy);
 
-  /* Parse the separating `,'.  */
-  cp_parser_require (parser, CPP_COMMA, RT_COMMA);
+  if (cp_lexer_peek_token (parser->lexer)->type == CPP_CLOSE_PAREN)
+    {
+      if (cxx_dialect < cxx1z)
+	pedwarn (input_location, OPT_Wpedantic,
+		 "static_assert without a message "
+		 "only available with -std=c++1z or -std=gnu++1z");
+      /* Eat the ')'  */
+      cp_lexer_consume_token (parser->lexer);
+      message = build_string (1, "");
+      TREE_TYPE (message) = char_array_type_node;
+      fix_string_type (message);
+    }
+  else
+    {
+      /* Parse the separating `,'.  */
+      cp_parser_require (parser, CPP_COMMA, RT_COMMA);
 
-  /* Parse the string-literal message.  */
-  message = cp_parser_string_literal (parser, 
-                                      /*translate=*/false,
-                                      /*wide_ok=*/true);
+      /* Parse the string-literal message.  */
+      message = cp_parser_string_literal (parser, 
+                                	  /*translate=*/false,
+                                	  /*wide_ok=*/true);
 
-  /* A `)' completes the static assertion.  */
-  if (!cp_parser_require (parser, CPP_CLOSE_PAREN, RT_CLOSE_PAREN))
-    cp_parser_skip_to_closing_parenthesis (parser, 
-                                           /*recovering=*/true, 
-                                           /*or_comma=*/false,
-					   /*consume_paren=*/true);
+      /* A `)' completes the static assertion.  */
+      if (!cp_parser_require (parser, CPP_CLOSE_PAREN, RT_CLOSE_PAREN))
+	cp_parser_skip_to_closing_parenthesis (parser, 
+                                               /*recovering=*/true, 
+                                               /*or_comma=*/false,
+					       /*consume_paren=*/true);
+    }
 
   /* A semicolon terminates the declaration.  */
   cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
Index: cp/semantics.c
===================================================================
--- cp/semantics.c	(revision 224897)
+++ cp/semantics.c	(working copy)
@@ -7174,8 +7174,17 @@
       input_location = location;
       if (TREE_CODE (condition) == INTEGER_CST 
           && integer_zerop (condition))
-        /* Report the error. */
-        error ("static assertion failed: %s", TREE_STRING_POINTER (message));
+	{
+	  int sz = TREE_INT_CST_LOW (TYPE_SIZE_UNIT
+				     (TREE_TYPE (TREE_TYPE (message))));
+	  int len = TREE_STRING_LENGTH (message) / sz - 1;
+          /* Report the error. */
+	  if (len == 0)
+            error ("static assertion failed");
+	  else
+            error ("static assertion failed: %s",
+		   TREE_STRING_POINTER (message));
+	}
       else if (condition && condition != error_mark_node)
 	{
 	  error ("non-constant condition for static assertion");
Index: testsuite/g++.dg/cpp0x/static_assert12.C
===================================================================
--- testsuite/g++.dg/cpp0x/static_assert12.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/static_assert12.C	(working copy)
@@ -0,0 +1,30 @@
+// { dg-do compile }
+// { dg-options "-std=gnu++11 -pedantic" }
+
+template<typename T>
+  struct is_float
+  {
+    static constexpr bool value = false;
+  };
+
+template<>
+  struct is_float<float>
+  {
+    static constexpr bool value = true;
+  };
+
+template<typename T>
+  T
+  float_thing(T __x)
+  {
+    static_assert(is_float<T>::value, ""); // { dg-error "static assertion failed" }
+    static_assert(is_float<T>::value); // { dg-error "static assertion failed" }
+  }
+
+int
+main()
+{
+  float_thing(1);
+}
+
+// { dg-warning "static_assert without a message only available with " "" { target *-*-* } 21 }
Index: testsuite/g++.dg/cpp0x/static_assert13.C
===================================================================
--- testsuite/g++.dg/cpp0x/static_assert13.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/static_assert13.C	(working copy)
@@ -0,0 +1,28 @@
+// { dg-do compile }
+// { dg-options "-std=gnu++11" }
+
+template<typename T>
+  struct is_float
+  {
+    static constexpr bool value = false;
+  };
+
+template<>
+  struct is_float<float>
+  {
+    static constexpr bool value = true;
+  };
+
+template<typename T>
+  T
+  float_thing(T __x)
+  {
+    static_assert(is_float<T>::value, ""); // { dg-error "static assertion failed" }
+    static_assert(is_float<T>::value); // { dg-error "static assertion failed" }
+  }
+
+int
+main()
+{
+  float_thing(1);
+}
Index: testsuite/g++.dg/cpp0x/static_assert8.C
===================================================================
--- testsuite/g++.dg/cpp0x/static_assert8.C	(revision 224897)
+++ testsuite/g++.dg/cpp0x/static_assert8.C	(working copy)
@@ -1,7 +1,9 @@
 // { dg-do compile { target c++11 } }
 
-static_assert (1 == 0); // { dg-error "expected (string-literal|',') before" }
+static_assert (1 == 0); // { dg-error "static assertion failed" }
 
 static_assert (1 == 0,); // { dg-error "expected string-literal before '\\)'" }
 
 static_assert (1 == 0, "oops"); // { dg-error "static assertion failed" }
+
+// { dg-error "static_assert without a message only available with " "" { target *-*-* } 3 }
Index: testsuite/g++.dg/cpp1y/static_assert1.C
===================================================================
--- testsuite/g++.dg/cpp1y/static_assert1.C	(revision 0)
+++ testsuite/g++.dg/cpp1y/static_assert1.C	(working copy)
@@ -0,0 +1,30 @@
+// { dg-do compile }
+// { dg-options "-std=gnu++14 -pedantic" }
+
+template<typename T>
+  struct is_float
+  {
+    static constexpr bool value = false;
+  };
+
+template<>
+  struct is_float<float>
+  {
+    static constexpr bool value = true;
+  };
+
+template<typename T>
+  T
+  float_thing(T __x)
+  {
+    static_assert(is_float<T>::value, ""); // { dg-error "static assertion failed" }
+    static_assert(is_float<T>::value); // { dg-error "static assertion failed" }
+  }
+
+int
+main()
+{
+  float_thing(1);
+}
+
+// { dg-warning "static_assert without a message only available with " "" { target *-*-* } 21 }
Index: testsuite/g++.dg/cpp1y/static_assert2.C
===================================================================
--- testsuite/g++.dg/cpp1y/static_assert2.C	(revision 0)
+++ testsuite/g++.dg/cpp1y/static_assert2.C	(working copy)
@@ -0,0 +1,28 @@
+// { dg-do compile }
+// { dg-options "-std=gnu++14" }
+
+template<typename T>
+  struct is_float
+  {
+    static constexpr bool value = false;
+  };
+
+template<>
+  struct is_float<float>
+  {
+    static constexpr bool value = true;
+  };
+
+template<typename T>
+  T
+  float_thing(T __x)
+  {
+    static_assert(is_float<T>::value, ""); // { dg-error "static assertion failed" }
+    static_assert(is_float<T>::value); // { dg-error "static assertion failed" }
+  }
+
+int
+main()
+{
+  float_thing(1);
+}
Index: testsuite/g++.dg/cpp1z/static_assert-nomsg.C
===================================================================
--- testsuite/g++.dg/cpp1z/static_assert-nomsg.C	(revision 0)
+++ testsuite/g++.dg/cpp1z/static_assert-nomsg.C	(working copy)
@@ -0,0 +1,27 @@
+// { dg-do compile { target c++1z } }
+
+template<typename T>
+  struct is_float
+  {
+    static constexpr bool value = false;
+  };
+
+template<>
+  struct is_float<float>
+  {
+    static constexpr bool value = true;
+  };
+
+template<typename T>
+  T
+  float_thing(T __x)
+  {
+    static_assert(is_float<T>::value, ""); // { dg-error "static assertion failed" }
+    static_assert(is_float<T>::value); // { dg-error "static assertion failed" }
+  }
+
+int
+main()
+{
+  float_thing(1);
+}