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.

2 files changed, 47 insertions, 42 deletions

diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index 0930342..fa5dd4c 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -238,6 +238,7 @@ help_command (char *command, int from_tty)
   help_cmd (command, gdb_stdout);
 }
 
+
 /* Note: The "complete" command is used by Emacs to implement completion.
    [Is that why this function writes output with *_unfiltered?]  */
 
@@ -246,8 +247,6 @@ complete_command (char *arg_entry, int from_tty)
 {
   const char *arg = arg_entry;
   int argpoint;
-  char *arg_prefix;
-  VEC (char_ptr) *completions;
 
   dont_repeat ();
 
@@ -279,43 +278,46 @@ complete_command (char *arg_entry, int from_tty)
       point--;
     }
 
-  arg_prefix = (char *) alloca (point - arg + 1);
-  memcpy (arg_prefix, arg, point - arg);
-  arg_prefix[point - arg] = 0;
-
-  completions = complete_line (point, arg, argpoint);
+  completion_tracker tracker_handle_completions;
 
-  if (completions)
+  TRY
+    {
+      complete_line (tracker_handle_completions, point, arg, strlen (arg));
+    }
+  CATCH (ex, RETURN_MASK_ALL)
     {
-      int ix, size = VEC_length (char_ptr, completions);
-      char *item, *prev = NULL;
+      return;
+    }
 
-      qsort (VEC_address (char_ptr, completions), size,
-	     sizeof (char *), compare_strings);
+  std::string arg_prefix (arg, point - arg);
 
-      /* We do extra processing here since we only want to print each
-	 unique item once.  */
-      for (ix = 0; VEC_iterate (char_ptr, completions, ix, item); ++ix)
+  completion_result result
+    = (tracker_handle_completions.build_completion_result
+       (point, point - arg, strlen (arg)));
+
+  if (result.number_matches != 0)
+    {
+      if (result.number_matches == 1)
+	printf_unfiltered ("%s%s\n", arg_prefix.c_str (), result.match_list[0]);
+      else
 	{
-	  if (prev == NULL || strcmp (item, prev) != 0)
+	  result.sort_match_list ();
+
+	  for (size_t i = 0; i < result.number_matches; i++)
 	    {
-	      printf_unfiltered ("%s%s\n", arg_prefix, item);
-	      xfree (prev);
-	      prev = item;
+	      printf_unfiltered ("%s%s",
+				 arg_prefix.c_str (),
+				 result.match_list[i + 1]);
+	      printf_unfiltered ("\n");
 	    }
-	  else
-	    xfree (item);
 	}
 
-      xfree (prev);
-      VEC_free (char_ptr, completions);
-
-      if (size == max_completions)
+      if (result.number_matches == 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,
+			     arg_prefix.c_str (), point,
 			     get_max_completions_reached_message ());
 	}
     }
diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index 064b481..1bbbe46 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -657,8 +657,9 @@ add_setshow_optional_filename_cmd (const char *name, enum command_class theclass
 /* Completes on literal "unlimited".  Used by integer commands that
    support a special "unlimited" value.  */
 
-static VEC (char_ptr) *
+static void
 integer_unlimited_completer (struct cmd_list_element *ignore,
+			     completion_tracker &tracker,
 			     const char *text, const char *word)
 {
   static const char * const keywords[] =
@@ -667,7 +668,7 @@ integer_unlimited_completer (struct cmd_list_element *ignore,
       NULL,
     };
 
-  return complete_on_enum (keywords, text, word);
+  complete_on_enum (tracker, keywords, text, word);
 }
 
 /* Add element named NAME to both the set and show command LISTs (the
@@ -1771,13 +1772,13 @@ lookup_cmd_composition (const char *text,
    "foo" and we want to complete to "foobar".  If WORD is "oo", return
    "oobar"; if WORD is "baz/foo", return "baz/foobar".  */
 
-VEC (char_ptr) *
+void
 complete_on_cmdlist (struct cmd_list_element *list,
+		     completion_tracker &tracker,
 		     const char *text, const char *word,
 		     int ignore_help_classes)
 {
   struct cmd_list_element *ptr;
-  VEC (char_ptr) *matchlist = NULL;
   int textlen = strlen (text);
   int pass;
   int saw_deprecated_match = 0;
@@ -1786,8 +1787,10 @@ complete_on_cmdlist (struct cmd_list_element *list,
      commands.  If we see no matching commands in the first pass, and
      if we did happen to see a matching deprecated command, we do
      another loop to collect those.  */
-  for (pass = 0; matchlist == 0 && pass < 2; ++pass)
+  for (pass = 0; pass < 2; ++pass)
     {
+      bool got_matches = false;
+
       for (ptr = list; ptr; ptr = ptr->next)
 	if (!strncmp (ptr->name, text, textlen)
 	    && !ptr->abbrev_flag
@@ -1820,32 +1823,34 @@ complete_on_cmdlist (struct cmd_list_element *list,
 		match[text - word] = '\0';
 		strcat (match, ptr->name);
 	      }
-	    VEC_safe_push (char_ptr, matchlist, match);
+	    tracker.add_completion (gdb::unique_xmalloc_ptr<char> (match));
+	    got_matches = true;
 	  }
+
+      if (got_matches)
+	break;
+
       /* If we saw no matching deprecated commands in the first pass,
 	 just bail out.  */
       if (!saw_deprecated_match)
 	break;
     }
-
-  return matchlist;
 }
 
 /* Helper function for SYMBOL_COMPLETION_FUNCTION.  */
 
-/* Return a vector of char pointers which point to the different
-   possible completions in CMD of TEXT.
+/* Add the different possible completions in ENUMLIST of TEXT.
 
    WORD points in the same buffer as TEXT, and completions should be
    returned relative to this position.  For example, suppose TEXT is "foo"
    and we want to complete to "foobar".  If WORD is "oo", return
    "oobar"; if WORD is "baz/foo", return "baz/foobar".  */
 
-VEC (char_ptr) *
-complete_on_enum (const char *const *enumlist,
+void
+complete_on_enum (completion_tracker &tracker,
+		  const char *const *enumlist,
 		  const char *text, const char *word)
 {
-  VEC (char_ptr) *matchlist = NULL;
   int textlen = strlen (text);
   int i;
   const char *name;
@@ -1870,10 +1875,8 @@ complete_on_enum (const char *const *enumlist,
 	    match[text - word] = '\0';
 	    strcat (match, name);
 	  }
-	VEC_safe_push (char_ptr, matchlist, match);
+	tracker.add_completion (gdb::unique_xmalloc_ptr<char> (match));
       }
-
-  return matchlist;
 }