Introduce class completion_tracker & rewrite completion<->readline interaction

This patch reworks the whole completion machinery, and prepares it
for later enhancements.

Adds a new "completion_tracker" class that is meant to hold everything
about the state of the current completion operation.

This class now has the responsibility of tracking the list of
completion matches, and checking whether the max completions limit has
been reached.  You can look at this as this patch starting out by
C++fying the existing "completion_tracker" in symtab.c (it's just an
htab_t typedef currently), moving it to completer.h/c, and then making
it a class/generalizing/enhancing it.

Unlike with the current tracking, completion_tracker now checks
whether the limit has been reached on each completion match list
insertion.  This both simplifies the max-completions handling code
(maybe_add_completion_enum is gone, for example), and is a
prerequisite for follow up patches.

The current completion_tracker is only used for symbol completions,
and the symbol code gets at the current instance via globals.  This
patch cleans that up by adding a completion_tracker reference to the
signature of the completion functions, and passing the tracker around
everywhere necessary.

Then, the patch changes how the completion match list is handed over
to readline.  Currently, we're using the rl_completion_entry_function
readline entry point, and the patch switches to
rl_attempted_completion_function.  A following patch will want to let
GDB itself decide the common completion prefix between all matches
(what readline calls the "lowest common denominator"), instead of
having readline compute it, and that's not possible with the
rl_completion_entry_function entry point.  Also,
rl_attempted_completion_function lets GDB hand over the match list to
readline as an array in one go instead of passing down matches one by
one, so from that angle it's a nicer entry point anyway.

Lastly, the patch catches exceptions around the readline entry points,
because we can't let C++ exceptions cross readline.  We handle that in
the readline input entry point, but the completion entry point isn't
guarded, so GDB can abort if completion throws.  E.g., in current
master:

 (gdb) b -function "fun<tab>
 terminate called after throwing an instance of 'gdb_exception_RETURN_MASK_ERROR'
 Aborted (core dumped)

This patch fixes that.  This will be exercised in the new tests added
later on in the series.

gdb/ChangeLog:
2017-07-17  Pedro Alves  <palves@redhat.com>

	* ada-lang.c (symbol_completion_match): Adjust comments.
	(symbol_completion_add): Replace vector parameter with
	completion_tracker parameter.  Use it.
	(ada_make_symbol_completion_list): Rename to...
	(ada_collect_symbol_completion_matches): ... this.  Add
	completion_tracker parameter and use it.
	(ada_language_defn): Adjust.
	* break-catch-syscall.c (catch_syscall_completer): Adjust
	prototype and work with completion_tracker instead of VEC.
	* breakpoint.c (condition_completer): Adjust prototype and work
	with completion_tracker instead of VEC.
	* c-lang.c (c_language_defn, cplus_language_defn)
	(asm_language_defn, minimal_language_defn): Adjust to renames.
	* cli/cli-cmds.c (complete_command): Rework using
	completion_tracker.  Catch exceptions when completing.
	* cli/cli-decode.c (integer_unlimited_completer)
	(complete_on_cmdlist, complete_on_enum): Adjust prototype and work
	with completion_tracker instead of VEC.
	* command.h (struct completion_tracker): Forward declare.
	(completer_ftype, completer_handle_brkchars_ftype): Change
	types.
	(complete_on_cmdlist, complete_on_enum): Adjust.
	* completer.c: Include <algorithm>.
	(struct gdb_completer_state): New.
	(current_completion): New global.
	(readline_line_completion_function): Delete.
	(noop_completer, filename_completer)
	(filename_completer_handle_brkchars, complete_files_symbols)
	(linespec_location_completer): Adjust to work with a
	completion_tracker instead of a VEC.
	(string_or_empty): New.
	(collect_explicit_location_matches): Adjust to work with a
	completion_tracker instead of a VEC.
	(explicit_location_completer): Rename to ...
	(complete_explicit_location): ... this and adjust to work with a
	completion_tracker instead of a VEC.
	(location_completer): Adjust to work with a completion_tracker
	instead of a VEC.
	(add_struct_fields): Adjust to work with a completion_list instead
	of VEC.
	(expression_completer): Rename to ...
	(complete_expression): ... this and adjust to work with a
	completion_tracker instead of a VEC.  Use complete_files_symbols.
	(expression_completer): Reimplement on top of complete_expression.
	(symbol_completer): Adjust to work with a completion_tracker
	instead of a VEC.
	(enum complete_line_internal_reason): Add describing comments.
	(complete_line_internal_normal_command): Adjust to work with a
	completion_tracker instead of a VEC.
	(complete_line_internal): Rename to ...
	(complete_line_internal_1): ... this and adjust to work with a
	completion_tracker instead of a VEC.  Assert TEXT is NULL in the
	handle_brkchars phase.
	(new_completion_tracker): Delete.
	(complete_line_internal): Reimplement as TRY/CATCH wrapper around
	complete_line_internal_1.
	(free_completion_tracker): Delete.
	(INITIAL_COMPLETION_HTAB_SIZE): New.
	(completion_tracker::completion_tracker)
	(completion_tracker::~completion_tracker): New.
	(maybe_add_completion): Delete.
	(completion_tracker::maybe_add_completion)
	(completion_tracker::add_completion)
	(completion_tracker::add_completions): New.
	(throw_max_completions_reached_error): Delete.
	(complete_line): Adjust to work with a completion_tracker instead
	of a VEC.  Don't create a completion_tracker_t or check for max
	completions here.
	(command_completer, command_completer_handle_brkchars)
	(signal_completer, reg_or_group_completer_1)
	(reg_or_group_completer, default_completer_handle_brkchars):
	Adjust to work with a completion_tracker.
	(gdb_completion_word_break_characters_throw): New.
	(gdb_completion_word_break_characters): Reimplement.
	(line_completion_function): Delete.
	(completion_tracker::recompute_lowest_common_denominator)
	(expand_preserving_ws)
	(completion_tracker::build_completion_result)
	(completion_result::completion_result)
	(completion_result::completion_result)
	(completion_result::~completion_result)
	(completion_result::completion_result)
	(completion_result::release_match_list, compare_cstrings)
	(completion_result::sort_match_list)
	(completion_result::reset_match_list)
	(gdb_rl_attempted_completion_function_throw)
	(gdb_rl_attempted_completion_function): New.
	* completer.h (completion_list, struct completion_result)
	(class completion_tracker): New.
	(complete_line): Add completion_tracker parameter.
	(readline_line_completion_function): Delete.
	(gdb_rl_attempted_completion_function): New.
	(noop_completer, filename_completer, expression_completer)
	(location_completer, symbol_completer, command_completer)
	(signal_completer, reg_or_group_completer): Update prototypes.
	(completion_tracker_t, new_completion_tracker)
	(make_cleanup_free_completion_tracker): Delete.
	(enum maybe_add_completion_enum): Delete.
	(maybe_add_completion): Delete.
	(throw_max_completions_reached_error): Delete.
	* corefile.c (complete_set_gnutarget): Adjust to work with a
	completion_tracker instead of a VEC.
	* cp-abi.c (cp_abi_completer): Adjust to work with a
	completion_tracker instead of a VEC.
	* d-lang.c (d_language_defn): Adjust.
	* disasm.c (disassembler_options_completer): Adjust to work with a
	completion_tracker instead of a VEC.
	* f-lang.c (f_make_symbol_completion_list): Rename to ...
	(f_collect_symbol_completion_matches): ... this.  Adjust to work
	with a completion_tracker instead of a VEC.
	(f_language_defn): Adjust.
	* go-lang.c (go_language_defn): Adjust.
	* guile/scm-cmd.c (cmdscm_add_completion, cmdscm_completer):
	Adjust to work with a completion_tracker instead of a VEC.
	* infrun.c (handle_completer): Likewise.
	* interps.c (interpreter_completer): Likewise.
	* interps.h (interpreter_completer): Likewise.
	* language.c (unknown_language_defn, auto_language_defn)
	(local_language_defn): Adjust.
	* language.h (language_defn::la_make_symbol_completion_list):
	Rename to ...
	(language_defn::la_collect_symbol_completion_matches): ... this
	and adjust to work with a completion_tracker instead of a VEC.
	* m2-lang.c (m2_language_defn): Adjust.
	* objc-lang.c (objc_language_defn): Adjust.
	* opencl-lang.c (opencl_language_defn): Adjust.
	* p-lang.c (pascal_language_defn): Adjust.
	* python/py-cmd.c (cmdpy_completer_helper): Handle NULL word.
	(cmdpy_completer_handle_brkchars, cmdpy_completer): Adjust to work
	with a completion_tracker.
	* rust-lang.c (rust_language_defn): Adjust.
	* symtab.c (free_completion_list, do_free_completion_list)
	(return_val, completion_tracker): Delete.
	(completion_list_add_name, completion_list_add_symbol)
	(completion_list_add_msymbol, completion_list_objc_symbol)
	(completion_list_add_fields, add_symtab_completions): Add
	completion_tracker parameter and use it.
	(default_make_symbol_completion_list_break_on_1): Rename to...
	(default_collect_symbol_completion_matches_break_on): ... this.
	Add completion_tracker parameter and use it instead of allocating
	a completion tracker here.
	(default_make_symbol_completion_list_break_on): Delete old
	implementation.
	(default_make_symbol_completion_list): Delete.
	(default_collect_symbol_completion_matches): New.
	(make_symbol_completion_list): Delete.
	(collect_symbol_completion_matches): New.
	(make_symbol_completion_type): Rename to ...
	(collect_symbol_completion_matches_type): ... this.  Add
	completion_tracker parameter and use it instead of VEC.
	(make_file_symbol_completion_list_1): Rename to...
	(collect_file_symbol_completion_matches): ... this.  Add
	completion_tracker parameter and use it instead of VEC.
	(make_file_symbol_completion_list): Delete.
	(add_filename_to_list): Use completion_list instead of a VEC.
	(add_partial_filename_data::list): Now a completion_list.
	(make_source_files_completion_list): Work with a completion_list
	instead of a VEC.
	* symtab.h: Include "completer.h".
	(default_make_symbol_completion_list_break_on)
	(default_make_symbol_completion_list, make_symbol_completion_list)
	(make_symbol_completion_type, make_file_symbol_completion_list)
	(make_source_files_completion_list): Delete.
	(default_collect_symbol_completion_matches_break_on)
	(default_collect_symbol_completion_matches)
	(collect_symbol_completion_matches)
	(collect_symbol_completion_matches_type)
	(collect_file_symbol_completion_matches)
	(make_source_files_completion_list): New.
	* top.c (init_main): Don't install a rl_completion_entry_function
	hook.  Install a rl_attempted_completion_function hook instead.
	* tui/tui-layout.c (layout_completer): Adjust to work with a
	completion_tracker.
	* tui/tui-regs.c (tui_reggroup_completer):
	* tui/tui-win.c (window_name_completer, focus_completer)
	(winheight_completer): Adjust to work with a completion_tracker.
	* value.c: Include "completer.h".
	(complete_internalvar): Adjust to work with a completion_tracker.
	* value.h (complete_internalvar): Likewise.

1 files changed, 163 insertions, 81 deletions

diff --git a/gdb/completer.h b/gdb/completer.h
index 463a53d4ad..4b3b188210 100644
--- a/gdb/completer.h
+++ b/gdb/completer.h
@@ -63,44 +63,184 @@ struct match_list_displayer
   mld_read_key_ftype *read_key;
 };
 
+/* A list of completion candidates.  Each element is a malloc string,
+   because ownership of the strings is transferred to readline, which
+   calls free on each element.  */
+typedef std::vector<gdb::unique_xmalloc_ptr<char>> completion_list;
+
+/* The final result of a completion that is handed over to either
+   readline or the "completion" command (which pretends to be
+   readline).  Mainly a wrapper for a readline-style match list array,
+   though other bits of info are included too.  */
+
+struct completion_result
+{
+  /* Create an empty result.  */
+  completion_result ();
+
+  /* Create a result.  */
+  completion_result (char **match_list, size_t number_matches,
+		     bool completion_suppress_append);
+
+  /* Destroy a result.  */
+  ~completion_result ();
+
+  /* Disable copying, since we don't need it.  */
+  completion_result (const completion_result &rhs) = delete;
+  void operator= (const completion_result &rhs) = delete;
+
+  /* Move a result.  */
+  completion_result (completion_result &&rhs);
+
+  /* Release ownership of the match list array.  */
+  char **release_match_list ();
+
+  /* Sort the match list.  */
+  void sort_match_list ();
+
+private:
+  /* Destroy the match list array and its contents.  */
+  void reset_match_list ();
+
+public:
+  /* (There's no point in making these fields private, since the whole
+     point of this wrapper is to build data in the layout expected by
+     readline.  Making them private would require adding getters for
+     the "complete" command, which would expose the same
+     implementation details anyway.)  */
+
+  /* The match list array, in the format that readline expects.
+     match_list[0] contains the common prefix.  The real match list
+     starts at index 1.  The list is NULL terminated.  If there's only
+     one match, then match_list[1] is NULL.  If there are no matches,
+     then this is NULL.  */
+  char **match_list;
+  /* The number of matched completions in MATCH_LIST.  Does not
+     include the NULL terminator or the common prefix.  */
+  size_t number_matches;
+
+  /* Whether readline should suppress appending a whitespace, when
+     there's only one possible completion.  */
+  bool completion_suppress_append;
+};
+
+/* Object used by completers to build a completion match list to hand
+   over to readline.  It tracks:
+
+   - How many unique completions have been generated, to terminate
+     completion list generation early if the list has grown to a size
+     so large as to be useless.  This helps avoid GDB seeming to lock
+     up in the event the user requests to complete on something vague
+     that necessitates the time consuming expansion of many symbol
+     tables.
+*/
+class completion_tracker
+{
+public:
+  completion_tracker ();
+  ~completion_tracker ();
+
+  /* Disable copy.  */
+  completion_tracker (const completion_tracker &rhs) = delete;
+  void operator= (const completion_tracker &rhs) = delete;
+
+  /* Add the completion NAME to the list of generated completions if
+     it is not there already.  If too many completions were already
+     found, this throws an error.  */
+  void add_completion (gdb::unique_xmalloc_ptr<char> name);
+
+  /* Add all completions matches in LIST.  Elements are moved out of
+     LIST.  */
+  void add_completions (completion_list &&list);
+
+  /* True if we have any completion match recorded.  */
+  bool have_completions () const
+  { return !m_entries_vec.empty (); }
+
+  /* Build a completion_result containing the list of completion
+     matches to hand over to readline.  The parameters are as in
+     rl_attempted_completion_function.  */
+  completion_result build_completion_result (const char *text,
+					     int start, int end);
+
+private:
+
+  /* Add the completion NAME to the list of generated completions if
+     it is not there already.  If false is returned, too many
+     completions were found.  */
+  bool maybe_add_completion (gdb::unique_xmalloc_ptr<char> name);
+
+  /* Given a new match, recompute the lowest common denominator (LCD)
+     to hand over to readline.  */
+  void recompute_lowest_common_denominator (const char *new_match);
+
+  /* The completion matches found so far, in a vector.  */
+  completion_list m_entries_vec;
+
+  /* The completion matches found so far, in a hash table, for
+     duplicate elimination as entries are added.  Otherwise the user
+     is left scratching his/her head: readline and complete_command
+     will remove duplicates, and if removal of duplicates there brings
+     the total under max_completions the user may think gdb quit
+     searching too early.  */
+  htab_t m_entries_hash;
+
+  /* Our idea of lowest common denominator to hand over to readline.  */
+  char *m_lowest_common_denominator = NULL;
+
+  /* If true, the LCD is unique.  I.e., all completion candidates had
+     the same string.  */
+  bool m_lowest_common_denominator_unique = false;
+};
+
 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);
+extern void complete_line (completion_tracker &tracker,
+			   const char *text,
+			   const char *line_buffer,
+			   int point);
 
-extern char *readline_line_completion_function (const char *text,
-						int matches);
+extern char **gdb_rl_attempted_completion_function (const char *text,
+						    int start, int end);
 
-extern VEC (char_ptr) *noop_completer (struct cmd_list_element *,
-				       const char *, const char *);
+extern void noop_completer (struct cmd_list_element *,
+			    completion_tracker &tracker,
+			    const char *, const char *);
 
-extern VEC (char_ptr) *filename_completer (struct cmd_list_element *,
-					   const char *, const char *);
+extern void filename_completer (struct cmd_list_element *,
+				completion_tracker &tracker,
+				const char *, const char *);
 
-extern VEC (char_ptr) *expression_completer (struct cmd_list_element *,
-					     const char *, const char *);
+extern void expression_completer (struct cmd_list_element *,
+				  completion_tracker &tracker,
+				  const char *, const char *);
 
-extern VEC (char_ptr) *location_completer (struct cmd_list_element *,
-					   const char *, const char *);
+extern void location_completer (struct cmd_list_element *,
+				completion_tracker &tracker,
+				const char *, const char *);
 
-extern VEC (char_ptr) *symbol_completer (struct cmd_list_element *,
-					 const char *, const char *);
+extern void symbol_completer (struct cmd_list_element *,
+			      completion_tracker &tracker,
+			      const char *, const char *);
 
-extern VEC (char_ptr) *command_completer (struct cmd_list_element *,
-					  const char *, const char *);
+extern void command_completer (struct cmd_list_element *,
+			       completion_tracker &tracker,
+			       const char *, const char *);
 
-extern VEC (char_ptr) *signal_completer (struct cmd_list_element *,
-					 const char *, const char *);
+extern void signal_completer (struct cmd_list_element *,
+			      completion_tracker &tracker,
+			      const char *, const char *);
 
-extern VEC (char_ptr) *reg_or_group_completer (struct cmd_list_element *,
-					       const char *, const char *);
+extern void reg_or_group_completer (struct cmd_list_element *,
+				    completion_tracker &tracker,
+				    const char *, const char *);
 
-extern VEC (char_ptr) *reggroup_completer (struct cmd_list_element *,
-					   const char *, const char *);
+extern void reggroup_completer (struct cmd_list_element *,
+				completion_tracker &tracker,
+				const char *, const char *);
 
 extern const char *get_gdb_completer_quote_characters (void);
 
@@ -134,62 +274,4 @@ extern const char *skip_quoted (const char *);
 
 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) */