C++: warn about implicit declarations of built-in functions

[Zack Weinberg <zack at wolery dot cumb dot org>]

The C++ compiler currently does not issue implicit declaration
warnings for functions that are recognized specially, such as strcpy.
This patch corrects the problem.

It will cause a large number of regressions in the C++ test suite,
which is crawling with implicit declarations of builtins.  I will send
a separate patch for that.

This is analogous to the patch I sent last week to fix the same
problem in the C and ObjC front ends, but completely independent.

zw

	* cp-tree.h (DECL_ANTICIPATED): New macro.
	Document new use of DECL_LANG_FLAG_7.
	* decl.c (builtin_function): Set DECL_ANTICIPATED on builtins
	in the user namespace.
	* lex.c (do_identifier): If the identifier's declaration has
	DECL_ANTICIPATED on, it has not yet been declared.  But do not
	replace it with an ordinary implicit declaration.

	* tinfo2.cc: Include stdlib.h.

===================================================================
Index: cp/cp-tree.h
--- cp/cp-tree.h	2000/05/26 21:05:04	1.463
+++ cp/cp-tree.h	2000/05/28 04:26:01
@@ -101,6 +101,7 @@ Boston, MA 02111-1307, USA.  */
    5: DECL_INTERFACE_KNOWN.
    6: DECL_THIS_STATIC (in VAR_DECL or FUNCTION_DECL).
    7: DECL_DEAD_FOR_LOCAL (in VAR_DECL).
+      DECL_ANTICIPATED (in FUNCTION_DECL).
 
    Usage of language-independent fields in a language-dependent manner:
    
@@ -2461,6 +2462,10 @@ extern int flag_new_for_scope;
    scope) declared in a local scope.  */
 #define DECL_LOCAL_FUNCTION_P(NODE) \
   DECL_LANG_FLAG_0 (FUNCTION_DECL_CHECK (NODE))
+
+/* Nonzero if NODE is a FUNCTION_DECL for a built-in function, and we have
+   not yet seen a prototype for that function.  */
+#define DECL_ANTICIPATED(NODE) DECL_LANG_FLAG_7 (FUNCTION_DECL_CHECK (NODE))
 
 /* This _DECL represents a compiler-generated entity.  */
 #define SET_DECL_ARTIFICIAL(NODE) (DECL_ARTIFICIAL (NODE) = 1)
===================================================================
Index: cp/decl.c
--- cp/decl.c	2000/05/26 21:05:05	1.614
+++ cp/decl.c	2000/05/28 04:26:04
@@ -6769,6 +6769,12 @@ builtin_function (name, type, code, clas
   if (libname)
     DECL_ASSEMBLER_NAME (decl) = get_identifier (libname);
   make_function_rtl (decl);
+
+  /* Warn if a function in the namespace for users
+     is used without an occasion to consider it declared.  */
+  if (name[0] != '_' || name[1] != '_')
+    DECL_ANTICIPATED (decl) = 1;
+
   return decl;
 }
 
===================================================================
Index: cp/lex.c
--- cp/lex.c	2000/05/14 08:44:48	1.197
+++ cp/lex.c	2000/05/28 04:26:05
@@ -3315,8 +3315,9 @@ do_identifier (token, parsing, args)
       id = lookup_name (token, 0);
       return error_mark_node;
     }
-      
-  if (!id)
+
+  if (!id || (TREE_CODE (id) == FUNCTION_DECL
+	      && DECL_ANTICIPATED (id)))
     {
       if (current_template_parms)
 	return build_min_nt (LOOKUP_EXPR, token);
@@ -3328,7 +3329,16 @@ do_identifier (token, parsing, args)
 	}
       else if (in_call && ! flag_strict_prototype)
 	{
-	  id = implicitly_declare (token);
+	  if (!id)
+	    id = implicitly_declare (token);
+	  else
+	    {
+	      /* Implicit declaration of built-in function.  Don't
+		 change the built-in declaration, but don't let this
+		 go by silently, either.  */
+	      cp_pedwarn ("implicit declaration of function `%D'", token);
+	      DECL_ANTICIPATED (id) = 0;  /* only issue this warning once */
+	    }
 	}
       else if (current_function_decl == 0)
 	{
===================================================================
Index: cp/tinfo2.cc
--- cp/tinfo2.cc	2000/05/25 11:49:33	1.24
+++ cp/tinfo2.cc	2000/05/28 04:26:05
@@ -28,6 +28,7 @@
 // the GNU General Public License.
 
 #include <stddef.h>
+#include <stdlib.h>		// for abort
 #include "tinfo.h"
 #include "new"			// for placement new