Improve --debugmode behavior.

* m4/m4module.h (m4_debug_decode): Simplify interface.
* m4/debug.c (m4_debug_decode): Remove parameter, and handle
setting the new value.
* modules/gnu.c (debugmode): Adjust caller.
* src/freeze.c (reload_frozen_state): Likewise.
* src/main.c (main): Likewise.
(usage): Fix default for --debug.
* doc/m4.texinfo (Debugging options): Add an example.

Signed-off-by: Eric Blake <ebb9@byu.net>

7 files changed, 55 insertions, 52 deletions

diff --git a/ChangeLog b/ChangeLog
index 9bb9f605..f21cbd8c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2008-08-22  Eric Blake  <ebb9@byu.net>
+
+	Improve --debugmode behavior.
+	* m4/m4module.h (m4_debug_decode): Simplify interface.
+	* m4/debug.c (m4_debug_decode): Remove parameter, and handle
+	setting the new value.
+	* modules/gnu.c (debugmode): Adjust caller.
+	* src/freeze.c (reload_frozen_state): Likewise.
+	* src/main.c (main): Likewise.
+	(usage): Fix default for --debug.
+	* doc/m4.texinfo (Debugging options): Add an example.
+
 2008-08-21  Eric Blake  <ebb9@byu.net>
 
 	Avoid regression in defn(undef).
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index 06b2ab0a..0b84d089 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -937,23 +937,34 @@ Finally, there are several options for aiding in debugging @code{m4}
 scripts.
 
 @table @code
-@item -d@r{[}@var{FLAGS}@r{]}
-@itemx --debug@r{[}=@var{FLAGS}@r{]}
-@itemx --debugmode@r{[}=@var{FLAGS}@r{]}
+@item -d@r{[}@r{[}-@r{|}+@r{]}@var{FLAGS}@r{]}
+@itemx --debug@r{[}=@r{[}-@r{|}+@r{]}@var{FLAGS}@r{]}
+@itemx --debugmode@r{[}=@r{[}-@r{|}+@r{]}@var{FLAGS}@r{]}
 Set the debug-level according to the flags @var{FLAGS}.  The debug-level
 controls the format and amount of information presented by the debugging
 functions.  @xref{Debugmode}, for more details on the format and
 meaning of @var{FLAGS}.  If omitted, @var{FLAGS} defaults to
-@samp{+aeq}.  When the option is presented multiple times, if later
-@var{FLAGS} starts with @samp{-} or @samp{+}, they are cumulative,
-otherwise the later flags override all earlier occurrences.  Therefore,
-to disable all previously set flags, specify an explicit @var{FLAGS} of
-@samp{-V}.  The
+@samp{+aeq}.  If the option occurs multiple times, @var{FLAGS} starting
+with @samp{-} or @samp{+} are cumulative, while @var{FLAGS} starting
+with a letter override all earlier settings.  Therefore, to disable all
+previously set flags, specify an explicit @var{FLAGS} of @samp{-V}.  The
 spelling @option{--debug} is recognized as an unambiguous option for
 compatibility with earlier versions of @acronym{GNU} M4, but for
 consistency with the builtin name, you can also use the spelling
-@option{--debugmode}.  Order is significant with respect to
-file names.
+@option{--debugmode}.  Order is significant with respect to file names.
+
+The cumulative effect of the various options in this example is
+equivalent to a single invocation of @code{debugmode(alqx)}:
+
+@comment options: -d-V -d+lx --debug --debugmode=-e
+@example
+$ @kbd{m4 -d+lx --debug --debugmode=-e}
+traceon(`len')
+@result{}
+len(`123')
+@error{}m4trace:2: -1- id 2: len(`123')
+@result{}3
+@end example
 
 @item --debugfile=@var{FILE}
 @itemx -o @var{FILE}
diff --git a/m4/debug.c b/m4/debug.c
index d7e7e834..d9efc8b8 100644
--- a/m4/debug.c
+++ b/m4/debug.c
@@ -33,8 +33,9 @@ static void set_debug_file (m4 *, const m4_call_info *, FILE *);
 /* Function to decode the debugging flags OPTS.  Used by main while
    processing option -d, and by the builtin debugmode ().  */
 int
-m4_debug_decode (m4 *context, int previous, const char *opts)
+m4_debug_decode (m4 *context, const char *opts)
 {
+  int previous = context->debug_level;
   int level;
   char mode = '\0';
 
@@ -123,9 +124,9 @@ m4_debug_decode (m4 *context, int previous, const char *opts)
       break;
 
     default:
-      assert (!"INTERNAL ERROR: impossible mode from flags");
+      assert (!"m4_debug_decode");
     }
-
+  context->debug_level = level;
   return level;
 }
 
diff --git a/m4/m4module.h b/m4/m4module.h
index c17c98ab..6c0587b9 100644
--- a/m4/m4module.h
+++ b/m4/m4module.h
@@ -413,7 +413,7 @@ enum {
 
 #define m4_is_debug_bit(C,B)	((m4_get_debug_level_opt (C) & (B)) != 0)
 
-extern int	m4_debug_decode		(m4 *, int, const char *);
+extern int	m4_debug_decode		(m4 *, const char *);
 extern bool	m4_debug_set_output	(m4 *, const m4_call_info *,
 					 const char *);
 extern void	m4_debug_message_prefix (m4 *);
diff --git a/modules/gnu.c b/modules/gnu.c
index 75e53634..2e960305 100644
--- a/modules/gnu.c
+++ b/modules/gnu.c
@@ -599,20 +599,11 @@ M4BUILTIN_HANDLER (debuglen)
  **/
 M4BUILTIN_HANDLER (debugmode)
 {
-  int debug_level = m4_get_debug_level_opt (context);
-  int new_debug_level;
-
   if (argc == 1)
     m4_set_debug_level_opt (context, 0);
-  else
-    {
-      new_debug_level = m4_debug_decode (context, debug_level, M4ARG (1));
-      if (new_debug_level < 0)
-	m4_error (context, 0, 0, m4_arg_info (argv),
-		  _("bad debug flags: `%s'"), M4ARG (1));
-      else
-	m4_set_debug_level_opt (context, new_debug_level);
-    }
+  else if (m4_debug_decode (context, M4ARG (1)) < 0)
+    m4_error (context, 0, 0, m4_arg_info (argv),
+	      _("bad debug flags: `%s'"), M4ARG (1));
 }
 
 
diff --git a/src/freeze.c b/src/freeze.c
index d61a8df3..4d3a2b0f 100644
--- a/src/freeze.c
+++ b/src/freeze.c
@@ -627,9 +627,11 @@ ill-formed frozen file, version 2 directive `%c' encountered"), 'd');
 	  GET_STRING (file, string[0], allocated[0], number[0], false);
 	  VALIDATE ('\n');
 
-	  m4_set_debug_level_opt (context, m4_debug_decode (context, 0,
-							    string[0]));
-
+	  if (m4_debug_decode (context, string[0]) < 0)
+	    m4_error (context, EXIT_FAILURE, 0, NULL,
+		      _("unknown debug mode `%s'"),
+		      quotearg_style_mem (locale_quoting_style, string[0],
+					  number[0]));
 	  break;
 
 	case 'F':
@@ -747,7 +749,9 @@ ill-formed frozen file, version 2 directive `%c' encountered"), 'R');
 	  if (m4_get_regexp_syntax_opt (context) < 0)
 	    {
 	      m4_error (context, EXIT_FAILURE, 0, NULL,
-			_("unknown regexp syntax code `%s'"), string[0]);
+			_("unknown regexp syntax code `%s'"),
+			quotearg_style_mem (locale_quoting_style, string[0],
+					    number[0]));
 	    }
 
 	  break;
diff --git a/src/main.c b/src/main.c
index c5997b16..341a9e81 100644
--- a/src/main.c
+++ b/src/main.c
@@ -148,8 +148,8 @@ Frozen state files:\n\
       puts ("");
       fputs (_("\
 Debugging:\n\
-  -d, --debug[=FLAGS], --debugmode[=FLAGS]\n\
-                               set debug level (no FLAGS implies `aeq')\n\
+  -d, --debug[=[-|+]FLAGS], --debugmode[=[-|+]FLAGS]\n\
+                               set debug level (no FLAGS implies `+aeq')\n\
       --debugfile=FILE         redirect debug and trace output\n\
   -l, --debuglen=NUM           restrict macro tracing size\n\
   -t, --trace=NAME, --traceon=NAME\n\
@@ -532,16 +532,8 @@ main (int argc, char *const *argv, char *const *envp)
              have effect between files.  */
 	  if (seen_file || frozen_file_to_read)
 	    goto defer;
-	  {
-	    int old = m4_get_debug_level_opt (context);
-	    m4_set_debug_level_opt (context, m4_debug_decode (context, old,
-							      optarg));
-	  }
-	  if (m4_get_debug_level_opt (context) < 0)
-	    {
-	      error (0, 0, _("bad debug flags: `%s'"), optarg);
-	      m4_set_debug_level_opt (context, 0);
-	    }
+	  if (m4_debug_decode (context, optarg) < 0)
+	    error (0, 0, _("bad debug flags: `%s'"), optarg);
 	  break;
 
 	case 'e':
@@ -689,16 +681,8 @@ main (int argc, char *const *argv, char *const *envp)
 	  break;
 
 	case 'd':
-	  {
-	    int old = m4_get_debug_level_opt (context);
-	    m4_set_debug_level_opt (context, m4_debug_decode (context, old,
-							      arg));
-	  }
-	  if (m4_get_debug_level_opt (context) < 0)
-	    {
-	      error (0, 0, _("bad debug flags: `%s'"), arg);
-	      m4_set_debug_level_opt (context, 0);
-	    }
+	  if (m4_debug_decode (context, arg) < 0)
+	    error (0, 0, _("bad debug flags: `%s'"), arg);
 	  break;
 
 	case 'm':