Re: warning: multi-line comment (why?)

[Jamie Lokier <egcs at tantalophile dot demon dot co dot uk>]

Neil Booth wrote:
> // this \
> /\
> / is all one comment.
> 
> I know it's pedantic, but it's valid and we should continue to get it
> right.  I think your loop will terminate the comment at the end of the
> 2nd line.  A call to get_effective_char will handle that (instead of
> buffer->cur++).
> 
> If you do this, would you provide a testcase for the bug above, and
> that ensures the warning about multiline comments in not emitted in
> the case you're talking about?  Don't bother about null character
> testcases; in my experience they really confuse CVS.

Neal, you're right my loop was broken with /\<newline>/.  Please find
attached one patch and one test case.  I don't have Dejagnu installed
but I've formatted the test case that way so you can give it a try.

If you like the patch I'll need to send in the copyright assignment
form.

enjoy,
-- Jamie

2000-09-25  Jamie Lokier  <jamie.lokier@cern.ch>

	* cpplex.c (skip_line_comment): Don't warn about multi-line
	comments if the following line is another "//" comment.

Index: cpplex.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/cpplex.c,v
retrieving revision 1.101
diff -u -w -r1.101 cpplex.c
--- cpplex.c	2000/09/24 10:42:09	1.101
+++ cpplex.c	2000/09/25 19:39:52
@@ -796,15 +796,17 @@
   return c != '/' || prevc != '*';
 }
 
-/* Skip a C++ line comment.  Handles escaped newlines.  Returns
-   non-zero if a multiline comment.  The following new line, if any,
-   is left in buffer->read_ahead.  */
+/* Skip a C++ line comment.  Handles escaped newlines.  Returns non-zero
+   if a multiline comment that we should warn about.  That means there
+   is an escaped newline that is not followed by whitespace then "//".
+   The following new line, if any, is left in buffer->read_ahead.  */
 static int
 skip_line_comment (pfile)
      cpp_reader *pfile;
 {
   cpp_buffer *buffer = pfile->buffer;
   unsigned int orig_lineno = buffer->lineno;
+  int multiline = 0;
   cppchar_t c;
 
   pfile->state.lexing_comment = 1;
@@ -815,14 +817,43 @@
 	break;
 
       c = *buffer->cur++;
-      if (c == '?' || c == '\\')
+      if (c != '?' && c != '\\')
+	continue;
+
 	c = skip_escaped_newlines (buffer, c);
+      if (orig_lineno == buffer->lineno)
+	continue;
+      orig_lineno = buffer->lineno;
+
+      /* If c == EOF there'll be a warning about backslash-newline at
+	 end of the file.  No need for a multi-line warning as well. */
+      if (c == EOF)
+	continue;
+
+      /* Skip only ' ' and \t, on the subsequent comment line. */
+      while (is_hspace (c))
+	{
+	  if (c == '\t')
+	    adjust_column (pfile);
+	  c = EOF;
+	  if (buffer->cur == buffer->rlimit)
+	    break;
+	  c = *buffer->cur++;
+	}
+
+      /* If the next token isn't literally "//", warn about a multi-line
+	 comment.  Take care with "/\<newline>/": do warn about
+	 multi-line in this case, and do continue the comment. */
+      if (c == '/' && buffer->cur < buffer->rlimit && *buffer->cur == '/')
+	buffer->cur++;
+      else
+	multiline = 1;
     }
   while (!is_vspace (c));
 
   pfile->state.lexing_comment = 0;
   buffer->read_ahead = c;	/* Leave any newline for caller.  */
-  return orig_lineno != buffer->lineno;
+  return multiline;
 }
 
 /* pfile->buffer->cur is one beyond the \t character.  Update


---------------------
testsuite/gcc.dg/cpp/multiline.c (how do you make a cvs-style diff
against a file which isn't in the repository?)

/* { dg-do compile } */

/* Warn about multi-line //-style comments, but not when the subsequent
   lines are also //-style comments.  Contributed by Jamie Lokier. */

/* { dg-warning "multi-line comment" 7 } */
// this \
  produces a warning;

// neither \
  // this

// nor \
//   this do, though

/* { dg-warning "multi-line comment" 18 } */
int
// this one \
  compiles
  ok;

/* { dg-warning "multi-line comment" 23 } */
// remember to handle \
/\
/ embedded newlines.