Remove "show" command completers, "set" command completers for string commands

The default command completer is symbol_completer, but it makes no
sense for a "show" command to complete on symbols, or anything else,
really.

I wonder whether we should instead make the default be no completer.
That seems like a much larger/complicated audit/change, so I'd like to
move forward with this version, as it'll be covered by tests.  I
noticed this because a following patch will add a new
gdb.base/settings.exp testcase that exercises all sorts of details of
settings commands, including completing the show commands, using new
representative "maint test-settings <type or settings command>"
commands.

Also remove the completer for var_string and var_string_noescape
commands.  No point in completing symbols when GDB is expecting a
string.

gdb/ChangeLog:
2019-06-13  Pedro Alves  <palves@redhat.com>

	* cli/cli-decode.c (add_setshow_cmd_full): Remove "show"
	completer.
	(add_setshow_string_cmd, add_setshow_string_noescape_cmd): Remove
	"set" completers.

1 files changed, 13 insertions, 1 deletions

diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index e59e0c7..30f79b5 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -509,6 +509,9 @@ add_setshow_cmd_full (const char *name,
 			      full_show_doc, show_list);
   show->doc_allocated = 1;
   show->show_value_func = show_func;
+  /* Disable the default symbol completer.  Doesn't make much sense
+     for the "show" command to complete on anything.  */
+  set_cmd_completer (show, nullptr);
 
   if (set_result != NULL)
     *set_result = set;
@@ -633,11 +636,16 @@ add_setshow_string_cmd (const char *name, enum command_class theclass,
 			struct cmd_list_element **set_list,
 			struct cmd_list_element **show_list)
 {
+  cmd_list_element *set_cmd;
+
   add_setshow_cmd_full (name, theclass, var_string, var,
 			set_doc, show_doc, help_doc,
 			set_func, show_func,
 			set_list, show_list,
-			NULL, NULL);
+			&set_cmd, NULL);
+
+  /* Disable the default symbol completer.  */
+  set_cmd_completer (set_cmd, nullptr);
 }
 
 /* Add element named NAME to both the set and show command LISTs (the
@@ -659,6 +667,10 @@ add_setshow_string_noescape_cmd (const char *name, enum command_class theclass,
 			set_func, show_func,
 			set_list, show_list,
 			&set_cmd, NULL);
+
+  /* Disable the default symbol completer.  */
+  set_cmd_completer (set_cmd, nullptr);
+
   return set_cmd;
 }