Rationalize "backtrace" command line parsing

The backtrace command has peculiar command-line parsing.  In
particular, it splits the command line, then loops over the arguments.
If it sees a word it recognizes, like "full", it effectively drops
this word from the argument vector.  Then, it pastes together the
remaining arguments, passing them on to backtrace_command_1, which in
turn passes the resulting string to parse_and_eval_long.

The documentation doesn't mention the parse_and_eval_long at all, so
it is a bit of a hidden feature that you can "bt 3*2".  The strange
algorithm above also means you can "bt 3 * no-filters 2" and get 6
frames...

This patch changes backtrace's command line parsing to be a bit more
rational.  Now, special words like "full" are only recognized at the
start of the command.

This also updates the documentation to describe the various bt options
individually.

gdb/ChangeLog
2018-03-26  Tom Tromey  <tom@tromey.com>

	* stack.c (backtrace_command): Rewrite command line parsing.

gdb/doc/ChangeLog
2018-03-26  Tom Tromey  <tom@tromey.com>

	* gdb.texinfo (Backtrace): Describe options individually.

1 files changed, 20 insertions, 42 deletions

diff --git a/gdb/stack.c b/gdb/stack.c
index aad8fcd..13af659 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -1850,61 +1850,39 @@ backtrace_command_1 (const char *count_exp, int show_locals, int no_filters,
 static void
 backtrace_command (const char *arg, int from_tty)
 {
-  int fulltrace_arg = -1, arglen = 0, argc = 0, no_filters  = -1;
-  int user_arg = 0;
+  bool fulltrace = false;
+  bool filters = true;
 
-  std::string reconstructed_arg;
   if (arg)
     {
-      char **argv;
-      int i;
+      bool done = false;
 
-      gdb_argv built_argv (arg);
-      argv = built_argv.get ();
-      argc = 0;
-      for (i = 0; argv[i]; i++)
+      while (!done)
 	{
-	  unsigned int j;
+	  const char *save_arg = arg;
+	  std::string this_arg = extract_arg (&arg);
 
-	  for (j = 0; j < strlen (argv[i]); j++)
-	    argv[i][j] = TOLOWER (argv[i][j]);
+	  if (this_arg.empty ())
+	    break;
 
-	  if (no_filters < 0 && subset_compare (argv[i], "no-filters"))
-	    no_filters = argc;
+	  if (subset_compare (this_arg.c_str (), "no-filters"))
+	    filters = false;
+	  else if (subset_compare (this_arg.c_str (), "full"))
+	    fulltrace = true;
 	  else
 	    {
-	      if (fulltrace_arg < 0 && subset_compare (argv[i], "full"))
-		fulltrace_arg = argc;
-	      else
-		{
-		  user_arg++;
-		  arglen += strlen (argv[i]);
-		}
-	    }
-	  argc++;
-	}
-      arglen += user_arg;
-      if (fulltrace_arg >= 0 || no_filters >= 0)
-	{
-	  if (arglen > 0)
-	    {
-	      for (i = 0; i < argc; i++)
-		{
-		  if (i != fulltrace_arg && i != no_filters)
-		    {
-		      reconstructed_arg += argv[i];
-		      reconstructed_arg += " ";
-		    }
-		}
-	      arg = reconstructed_arg.c_str ();
+	      /* Not a recognized argument, so stop.  */
+	      arg = save_arg;
+	      done = true;
 	    }
-	  else
-	    arg = NULL;
 	}
+
+      if (*arg == '\0')
+	arg = NULL;
     }
 
-  backtrace_command_1 (arg, fulltrace_arg >= 0 /* show_locals */,
-		       no_filters >= 0 /* no frame-filters */, from_tty);
+  backtrace_command_1 (arg, fulltrace /* show_locals */,
+		       !filters /* no frame-filters */, from_tty);
 }
 
 /* Iterate over the local variables of a block B, calling CB with