Add max-completions parameter, and implement tab-completion limiting.

This commit adds a new exception, MAX_COMPLETIONS_REACHED_ERROR, to be
thrown whenever the completer has generated too many candidates to
be useful.  A new user-settable variable, "max_completions", is added
to control this behaviour.  A top-level completion limit is added to
complete_line_internal, as the final check to ensure the user never
sees too many completions.  An additional limit is added to
default_make_symbol_completion_list_break_on, to halt time-consuming
symbol table expansions.

gdb/ChangeLog:

	PR cli/9007
	PR cli/11920
	PR cli/15548
	* cli/cli-cmds.c (complete_command): Notify user if max-completions
	reached.
	* common/common-exceptions.h (enum errors)
	<MAX_COMPLETIONS_REACHED_ERROR>: New value.
	* completer.h (get_max_completions_reached_message): New declaration.
	(max_completions): Likewise.
	(completion_tracker_t): New typedef.
	(new_completion_tracker): New declaration.
	(make_cleanup_free_completion_tracker): Likewise.
	(maybe_add_completion_enum): New enum.
	(maybe_add_completion): New declaration.
	(throw_max_completions_reached_error): Likewise.
	* completer.c (max_completions): New global variable.
	(new_completion_tracker): New function.
	(free_completion_tracker): Likewise.
	(make_cleanup_free_completion_tracker): Likewise.
	(maybe_add_completions): Likewise.
	(throw_max_completions_reached_error): Likewise.
	(complete_line): Remove duplicates and limit result to max_completions
	entries.
	(get_max_completions_reached_message): New function.
	(gdb_display_match_list): Handle max_completions.
	(_initialize_completer): New declaration and function.
	* symtab.c: Include completer.h.
	(completion_tracker): New static variable.
	(completion_list_add_name): Call maybe_add_completion.
	(default_make_symbol_completion_list_break_on_1): Renamed from
	default_make_symbol_completion_list_break_on.  Maintain
	completion_tracker across calls to completion_list_add_name.
	(default_make_symbol_completion_list_break_on): New function.
	* top.c (init_main): Set rl_completion_display_matches_hook.
	* tui/tui-io.c: Include completer.h.
	(tui_old_rl_display_matches_hook): New static global.
	(tui_rl_display_match_list): Notify user if max-completions reached.
	(tui_setup_io): Save/restore rl_completion_display_matches_hook.
	* NEWS (New Options): Mention set/show max-completions.

gdb/doc/ChangeLog:

	* gdb.texinfo (Command Completion): Document new
	"set/show max-completions" option.

gdb/testsuite/ChangeLog:

	* gdb.base/completion.exp: Disable completion limiting for
	existing tests.  Add new tests to check completion limiting.
	* gdb.linespec/ls-errs.exp: Disable completion limiting.

1 files changed, 23 insertions, 1 deletions

diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index e20d8dd..e46f036 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -236,7 +236,8 @@ help_command (char *command, int from_tty)
   help_cmd (command, gdb_stdout);
 }
 
-/* The "complete" command is used by Emacs to implement completion.  */
+/* Note: The "complete" command is used by Emacs to implement completion.
+   [Is that why this function writes output with *_unfiltered?]  */
 
 static void
 complete_command (char *arg, int from_tty)
@@ -247,6 +248,18 @@ complete_command (char *arg, int from_tty)
 
   dont_repeat ();
 
+  if (max_completions == 0)
+    {
+      /* Only print this for non-mi frontends.  An MI frontend may not
+	 be able to handle this.  */
+      if (!ui_out_is_mi_like_p (current_uiout))
+	{
+	  printf_unfiltered (_("max-completions is zero,"
+			       " completion is disabled.\n"));
+	}
+      return;
+    }
+
   if (arg == NULL)
     arg = "";
   argpoint = strlen (arg);
@@ -293,6 +306,15 @@ complete_command (char *arg, int from_tty)
 
       xfree (prev);
       VEC_free (char_ptr, completions);
+
+      if (size == max_completions)
+	{
+	  /* ARG_PREFIX and POINT are included in the output so that emacs
+	     will include the message in the output.  */
+	  printf_unfiltered (_("%s%s %s\n"),
+			     arg_prefix, point,
+			     get_max_completions_reached_message ());
+	}
     }
 }