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, 66 insertions, 0 deletions

diff --git a/gdb/completer.h b/gdb/completer.h
index dbb1cfb441..56e1a2b5d1 100644
--- a/gdb/completer.h
+++ b/gdb/completer.h
@@ -66,6 +66,8 @@ struct match_list_displayer
 extern void gdb_display_match_list (char **matches, int len, int max,
 				    const struct match_list_displayer *);
 
+extern const char *get_max_completions_reached_message (void);
+
 extern VEC (char_ptr) *complete_line (const char *text,
 				      const char *line_buffer,
 				      int point);
@@ -112,4 +114,68 @@ extern const char *skip_quoted_chars (const char *, const char *,
 
 extern const char *skip_quoted (const char *);
 
+/* Maximum number of candidates to consider before the completer
+   bails by throwing MAX_COMPLETIONS_REACHED_ERROR.  Negative values
+   disable limiting.  */
+
+extern int max_completions;
+
+/* Object to track how many unique completions have been generated.
+   Used to limit the size of generated completion lists.  */
+
+typedef htab_t completion_tracker_t;
+
+/* Create a new completion tracker.
+   The result is a hash table to track added completions, or NULL
+   if max_completions <= 0.  If max_completions < 0, tracking is disabled.
+   If max_completions == 0, the max is indeed zero.  */
+
+extern completion_tracker_t new_completion_tracker (void);
+
+/* Make a cleanup to free a completion tracker, and reset its pointer
+   to NULL.  */
+
+extern struct cleanup *make_cleanup_free_completion_tracker
+		      (completion_tracker_t *tracker_ptr);
+
+/* Return values for maybe_add_completion.  */
+
+enum maybe_add_completion_enum
+{
+  /* NAME has been recorded and max_completions has not been reached,
+     or completion tracking is disabled (max_completions < 0).  */
+  MAYBE_ADD_COMPLETION_OK,
+
+  /* NAME has been recorded and max_completions has been reached
+     (thus the caller can stop searching).  */
+  MAYBE_ADD_COMPLETION_OK_MAX_REACHED,
+
+  /* max-completions entries has been reached.
+     Whether NAME is a duplicate or not is not determined.  */
+  MAYBE_ADD_COMPLETION_MAX_REACHED,
+
+  /* NAME has already been recorded.
+     Note that this is never returned if completion tracking is disabled
+     (max_completions < 0).  */
+  MAYBE_ADD_COMPLETION_DUPLICATE
+};
+
+/* Add the completion NAME to the list of generated completions if
+   it is not there already.
+   If max_completions is negative, nothing is done, not even watching
+   for duplicates, and MAYBE_ADD_COMPLETION_OK is always returned.
+
+   If MAYBE_ADD_COMPLETION_MAX_REACHED is returned, callers are required to
+   record at least one more completion.  The final list will be pruned to
+   max_completions, but recording at least one more than max_completions is
+   the signal to the completion machinery that too many completions were
+   found.  */
+
+extern enum maybe_add_completion_enum
+  maybe_add_completion (completion_tracker_t tracker, char *name);
+
+/* Wrapper to throw MAX_COMPLETIONS_REACHED_ERROR.  */ 
+
+extern void throw_max_completions_reached_error (void);
+
 #endif /* defined (COMPLETER_H) */