gdb patch to suppress empty lines

[Per Bothner <bothner@cygnus.com>]

Here is a simple patch which improves the command line interface of gdb.
If you repeat a command, by submitting an empty line, then normally
will show a lot of useless lines containing only the command prompt.
After an x/i followed by two empty lines, we get:

(gdb) x/i $pc
0xe1038 <main+8>:       call  0x138818 <get_run_time>
(gdb) 
0xe103c <main+12>:      st  %i1, [ %fp + 0x48 ]
(gdb) 
0xe1040 <main+16>:      st  %o0, [ %fp + -464 ]
(gdb) 

This wastes a lot of screen real estate, and is harder to read.
*With* my patches, we instead get:

(gdb) x/i $pc
0xe1038 <main+8>:       call  0x138818 <get_run_time>
0xe103c <main+12>:      st  %i1, [ %fp + 0x48 ]
0xe1040 <main+16>:      st  %o0, [ %fp + -464 ]
(gdb)

If you type another empty line (<Enter> only), then the "(gdb) " prompt
is erased, and replaced by the dis-assembled following line.

Index: top.c
===================================================================
RCS file: /cvs/cvsfiles/devo/gdb/top.c,v
retrieving revision 2.109
diff -u -p -r2.109 top.c
--- top.c	1999/05/06 16:42:34	2.109
+++ top.c	1999/05/13 20:30:59
@@ -2122,7 +2122,12 @@ command_line_input (prrompt, repeat, ann
 	}
       else if (command_editing_p && instream == stdin && ISATTY (instream))
 	{
+	  int can_repeat = *line != 0;
+	  if (can_repeat)
+	    rl_erase_empty_line++;
 	  rl = readline (local_prompt);
+	  if (can_repeat)
+	    rl_erase_empty_line--;
 	}
       else
 	{

The patches does require that reeadline be updated.  Either update
to the current version, or apply the following patch.

Index: display.c
===================================================================
RCS file: /cvs/cvsfiles/devo/readline/display.c,v
retrieving revision 1.15
diff -u -p -r1.15 display.c
--- display.c	1999/03/23 15:57:41	1.15
+++ display.c	1999/05/13 20:30:08
@@ -1564,3 +1564,12 @@ _rl_clean_up_for_exit ()
       rl_restart_output ();
     }
 }
+
+void
+_rl_erase_entire_line ()
+{
+  cr ();
+  _rl_clear_to_eol (0);
+  cr ();
+  fflush (rl_outstream);
+}
Index: readline.c
===================================================================
RCS file: /cvs/cvsfiles/devo/readline/readline.c,v
retrieving revision 1.47
diff -u -p -r1.47 readline.c
--- readline.c	1998/12/22 21:53:32	1.47
+++ readline.c	1999/05/13 20:30:09
@@ -286,6 +286,9 @@ char *_rl_comment_begin;
 /* Keymap holding the function currently being executed. */
 Keymap rl_executing_keymap;
 
+/* Non-zero means to erase entire line, including prompt, on empty input lines. */
+int rl_erase_empty_line = 0;
+
 /* Line buffer and maintenence. */
 char *rl_line_buffer = (char *)NULL;
 int rl_line_buffer_len = 0;
@@ -488,6 +491,12 @@ readline_internal_charloop ()
       if (rl_done == 0)
 	(*rl_redisplay_function) ();
 
+      /* If the application writer has told us to erase the entire line if
+	  the only character typed was something bound to rl_newline, do so. */
+      if (rl_erase_empty_line && rl_done && rl_last_func == rl_newline &&
+	  rl_point == 0 && rl_end == 0)
+	_rl_erase_entire_line ();
+
 #if defined (READLINE_CALLBACKS)
       return 0;
 #else
@@ -1427,6 +1436,11 @@ rl_newline (count, key)
       _rl_vi_reset_last ();
     }
 #endif /* VI_MODE */
+
+  /* If we've been asked to erase empty lines, suppress the final update,
+     since _rl_update_final calls crlf(). */
+  if (rl_erase_empty_line && rl_point == 0 && rl_end == 0)
+    return 0;
 
   if (readline_echoing_p)
     _rl_update_final ();
Index: readline.h
===================================================================
RCS file: /cvs/cvsfiles/devo/readline/readline.h,v
retrieving revision 1.12
diff -u -p -r1.12 readline.h
--- readline.h	1998/12/22 21:53:33	1.12
+++ readline.h	1999/05/13 20:30:09
@@ -288,6 +288,12 @@ extern VFunction *rl_deprep_term_functio
 extern Keymap rl_executing_keymap;
 extern Keymap rl_binding_keymap;
 
+/* Display variables. */
+/* If non-zero, readline will erase the entire line, including any prompt,
+   if the only thing typed on an otherwise-blank line is something bound to
+   rl_newline. */
+extern int rl_erase_empty_line;
+
 /* Completion variables. */
 /* Pointer to the generator function for completion_matches ().
    NULL means to use filename_entry_function (), the default filename

I can install these, if there are no objections.

	--Per Bothner
bothner@cygnus.com     http://www.cygnus.com/~bothner