cppinit.c (cpp_create_reader, [...]): Warn about trigraphs unless explicity set or -trigraphs.

	* cppinit.c (cpp_create_reader, post_options): Warn about
	trigraphs unless explicity set or -trigraphs.
	* cpplex.c (warn_in_comment): New.
	(_cpp_process_line_notes): Better handling of -Wtrigraphs.
	(_cpp_skip_block_comment): Add call to _cpp_process_line_notes.
	* doc/cppopts.texi, doc/cpp.texi: Update.
testsuite:
	* gcc.dg/cpp/Wtrigraphs.c: Update.
	* gcc.dg/cpp/Wtrigraphs-2.c: New tests.

From-SVN: r66459

gcc/cppinit.c

@@ -149,6 +149,7 @@ cpp_create_reader (lang, table)
   CPP_OPTION (pfile, show_column) = 1;
   CPP_OPTION (pfile, tabstop) = 8;
   CPP_OPTION (pfile, operator_names) = 1;
+  CPP_OPTION (pfile, warn_trigraphs) = 2;
   CPP_OPTION (pfile, warn_endif_labels) = 1;
   CPP_OPTION (pfile, warn_deprecated) = 1;
   CPP_OPTION (pfile, warn_long_long) = !CPP_OPTION (pfile, c99);
@@ -554,6 +555,9 @@ post_options (pfile)
       CPP_OPTION (pfile, traditional) = 0;
     }
 
+  if (CPP_OPTION (pfile, warn_trigraphs) == 2)
+    CPP_OPTION (pfile, warn_trigraphs) = !CPP_OPTION (pfile, trigraphs);
+
   if (CPP_OPTION (pfile, traditional))
     {
       /* Traditional CPP does not accurately track column information.  */

gcc/cpplex.c

@@ -63,6 +63,7 @@ static void save_comment PARAMS ((cpp_reader *, cpp_token *, const uchar *,
 				  cppchar_t));
 static void create_literal PARAMS ((cpp_reader *, cpp_token *, const uchar *,
 				    unsigned int, enum cpp_ttype));
+static bool warn_in_comment PARAMS ((cpp_reader *, _cpp_line_note *));
 static int name_p PARAMS ((cpp_reader *, const cpp_string *));
 static cppchar_t maybe_read_ucn PARAMS ((cpp_reader *, const uchar **));
 static tokenrun *next_tokenrun PARAMS ((tokenrun *));
@@ -180,6 +181,36 @@ _cpp_clean_line (pfile)
   buffer->next_line = s + 1;
 }
 
+/* Return true if the trigraph indicated by NOTE should be warned
+   about in a comment.  */
+static bool
+warn_in_comment (pfile, note)
+     cpp_reader *pfile;
+     _cpp_line_note *note;
+{
+  const uchar *p;
+
+  /* Within comments we don't warn about trigraphs, unless the
+     trigraph forms an escaped newline, as that may change
+     behaviour.  */
+  if (note->type != '/')
+    return false;
+
+  /* If -trigraphs, then this was an escaped newline iff the next note
+     is coincident.  */
+  if (CPP_OPTION (pfile, trigraphs))
+    return note[1].pos == note->pos;
+
+  /* Otherwise, see if this forms an escaped newline.  */
+  p = note->pos + 3;
+  while (is_nvspace (*p))
+    p++;
+
+  /* There might have been escaped newlines between the trigraph and the
+     newline we found.  Hence the position test.  */
+  return (*p == '\n' && p < note[1].pos);
+}
+
 /* Process the notes created by add_line_note as far as the current
    location.  */
 void
@@ -219,7 +250,8 @@ _cpp_process_line_notes (pfile, in_comment)
 	}
       else if (_cpp_trigraph_map[note->type])
 	{
-	  if (!in_comment && CPP_OPTION (pfile, warn_trigraphs))
+	  if (CPP_OPTION (pfile, warn_trigraphs)
+	      && (!in_comment || warn_in_comment (pfile, note)))
 	    {
 	      if (CPP_OPTION (pfile, trigraphs))
 		cpp_error_with_line (pfile, DL_WARNING, pfile->line, col,
@@ -284,6 +316,7 @@ _cpp_skip_block_comment (pfile)
 	}
     }
 
+  _cpp_process_line_notes (pfile, true);
   return false;
 }
 

gcc/doc/cpp.texi

@@ -293,16 +293,18 @@ obsolete systems that lack some of C's punctuation to use C@.  For
 example, @samp{??/} stands for @samp{\}, so @t{'??/n'} is a character
 constant for a newline.
 
-Trigraphs are not popular and many compilers implement them incorrectly.
-Portable code should not rely on trigraphs being either converted or
-ignored.  If you use the @option{-Wall} or @option{-Wtrigraphs} options,
-GCC will warn you when a trigraph would change the meaning of your
-program if it were converted.
-
-In a string constant, you can prevent a sequence of question marks from
-being confused with a trigraph by inserting a backslash between the
-question marks.  @t{"(??\?)"} is the string @samp{(???)}, not
-@samp{(?]}.  Traditional C compilers do not recognize this idiom.
+Trigraphs are not popular and many compilers implement them
+incorrectly.  Portable code should not rely on trigraphs being either
+converted or ignored.  With @option{-Wtrigraphs} GCC will warn you
+when a trigraph may change the meaning of your program if it were
+converted.  @xref{Wtrigraphs}.
+
+In a string constant, you can prevent a sequence of question marks
+from being confused with a trigraph by inserting a backslash between
+the question marks, or by separating the string literal at the
+trigraph and making use of string literal concatenation.  @t{"(??\?)"}
+is the string @samp{(???)}, not @samp{(?]}.  Traditional C compilers
+do not recognize these idioms.
 
 The nine trigraphs and their replacements are
 

gcc/doc/cppopts.texi

@@ -69,10 +69,12 @@ use @option{-o} to specify the output file.
 
 @item -Wall
 @opindex Wall
-Turns on all optional warnings which are desirable for normal code.  At
-present this is @option{-Wcomment} and @option{-Wtrigraphs}.  Note that
-many of the preprocessor's warnings are on by default and have no
-options to control them.
+Turns on all optional warnings which are desirable for normal code.
+At present this is @option{-Wcomment}, @option{-Wtrigraphs},
+@option{-Wmultichar} and a warning about integer promotion causing a
+change of sign in @code{#if} expressions.  Note that many of the
+preprocessor's warnings are on by default and have no options to
+control them.
 
 @item -Wcomment
 @itemx -Wcomments
@@ -84,10 +86,13 @@ comment, or whenever a backslash-newline appears in a @samp{//} comment.
 
 @item -Wtrigraphs
 @opindex Wtrigraphs
-Warn if any trigraphs are encountered.  This option used to take effect
-only if @option{-trigraphs} was also specified, but now works
-independently.  Warnings are not given for trigraphs within comments, as
-they do not affect the meaning of the program.
+@anchor{Wtrigraphs}
+Warn if any trigraphs that may change the meaning of a program are
+encountered.  This option is in effect unless trigraphs are turned on,
+and is implied by @option{-Wall}.  With the exception of a trigraph
+that would form an escaped newline, warnings are not given for
+trigraphs within comments as they do not affect the meaning of the
+program.
 
 @item -Wtraditional
 @opindex Wtraditional

gcc/testsuite/gcc.dg/cpp/Wtrigraphs-2.c

+/* { dg-do preprocess } */
+/* { dg-options "-std=c99 -Wtrigraphs -fno-show-column" } */
+
+/* Test we don't double warn for trigraphs immediately after preceding
+   text.  Source Neil Booth.  4 May 2003.  */
+
+/* { dg-bogus "ignored" } Test ??< ??= a few ??/ random things in
+   { dg-warning "converted" } some ??/
+   { dg-bogus "ignored" } ??< comments.  */
+
+// { dg-bogus "ignored" } More ??/ comment ??> tests.
+
+// { dg-warning "converted" } Another ??/
+   Test
+
+// { dg-warning "converted" } And another with space after ??/  
+   the escape
+
+// { dg-bogus "ignored" } A tricky one ??/\
+

gcc/testsuite/gcc.dg/cpp/Wtrigraphs.c

 /* { dg-do preprocess } */
-/* { dg-options "-Wtrigraphs -fno-show-column" } */
+/* { dg-options "-std=gnu99 -Wtrigraphs -fno-show-column" } */
 
 /* Test we don't double warn for trigraphs immediately after preceding
    text.  Source Neil Booth.  22 Nov 2000.  */
@@ -7,3 +7,21 @@
 abcdef??<			/* { dg-warning "ignored" } */
 123456??>			/* { dg-warning "ignored" } */
 +??=				/* { dg-warning "ignored" } */
+
+/* Test we warn of escaped newlines only in comments.  Source Neil
+   Booth.  4 May 2003.  */
+
+/* { dg-bogus "ignored" } Test ??< ??= a few ??/ random things in
+   { dg-warning "ignored" } some ??/
+   { dg-bogus "ignored" } ??< comments.  */
+
+// { dg-bogus "ignored" } More ??/ comment ??> tests.
+
+// { dg-warning "ignored" } Another ??/
+   Test
+
+// { dg-warning "ignored" } And another with space after ??/  
+   the escape
+
+// { dg-bogus "ignored" } A tricky one ??/\
+