[Bug preprocessor/33305] We should warn about empty macro arguments

["manu at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from manu at gcc dot gnu dot org  2007-11-09 02:09 -------
(In reply to comment #3)
> Anyone know where in the preprocessor this should be done?  I.e. which function
> in libcpp?
> 
> If someone would let me know, I'll write a patch.
> 

This is the patch I was playing with before giving up. I don't know how to get
the correct line numbers so I tried 3 possibilities.

Index: libcpp/macro.c
===================================================================
--- libcpp/macro.c      (revision 129897)
+++ libcpp/macro.c      (working copy)
@@ -681,9 +681,39 @@ collect_args (cpp_reader *pfile, const c
     }
   else
     {
+      unsigned int i;
+
       /* A single empty argument is counted as no argument.  */
       if (argc == 1 && macro->paramc == 0 && args[0].count == 0)
        argc = 0;
+
+      for (i = 0; i < argc; i++)
+        {
+          if (args[i].count == 0
+              && CPP_OPTION (pfile, pedantic)
+              && CPP_OPTION (pfile, lang) == CLK_GNUC89)
+            {
+              if (pfile->context->prev && pfile->context->prev->macro)
+                cpp_error_with_line (pfile, CPP_DL_PEDWARN,
+                    pfile->context->prev->macro->value.macro->line, 0,
+                    "invoking  macro \"%s\" "
+                    "with empty arguments is undefined in ISO C90",
+                    NODE_NAME (node));
+              else if (pfile->context->prev || pfile->state.in_directive)
+                cpp_error_with_line (pfile, CPP_DL_PEDWARN,
+                                     node->value.macro->line, 0,
+                                     "invoking  macro \"%s\" "
+                    "with empty arguments is undefined in ISO C90",
+                    NODE_NAME (node));
+              else
+                cpp_error (pfile, CPP_DL_PEDWARN,
+                           "invoking  macro \"%s\" "
+                           "with empty arguments is undefined in ISO C90",
+                           NODE_NAME (node));
+
+          }
+        }
+
       if (_cpp_arguments_ok (pfile, macro, node, argc))
        {
          /* GCC has special semantics for , ## b where b is a varargs

And this is the testcase I am using:

/* { dg-do compile } */
/* { dg-options "-std=c90 -pedantic-errors" } */

#define f2(a,b,c) a; b; c;
#define f(a,b)   f2(a,,b) /* { dg-warning "macro "f2" with empty arguments } */
#define f3(a)    a

#define g()   0

void foo(void)
{
    f(0,0);
    f2(0,,0); /* { dg-warning "macro "f2" with empty arguments } */
    f3(); /* { dg-warning "macro "f3" with empty arguments } */
    g();
}


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33305