Make command line editing (use of readline) be per UI

Due to the way that readline's API works (based on globals), we can
only have one instance of readline in a process.  So the goal of this
patch is to only allow editing in the main UI, and make sure that only
one UI calls into readline.  Some MI paths touch readline variables
currently, which is bad as that is changing variables that matter for
the main console UI.  This patch fixes those.

This actually fixes a nasty bug -- starting gdb in MI mode ("gdb
-i=mi"), and then doing "set editing on" crashes GDB, because MI is
not prepared to use readline:

 set editing on
 &"set editing on\n"
 =cmd-param-changed,param="editing",value="on"
 ^done
 (gdb)
 p 1
 readline: readline_callback_read_char() called with no handler!
 Aborted (core dumped)

The fix for that was to add an interp_proc method to query the
interpreter whether it actually supports editing.  New test included.

gdb/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	PR mi/20034
	* cli/cli-interp.c: Include cli-interp.h and event-top.h.
	(cli_interpreter_resume): Pass 1 to gdb_setup_readline.  Set the
	UI's input_handler here.
	(cli_interpreter_supports_command_editing): New function.
	(cli_interp_procs): Install it.
	* cli/cli-interp.h: New file.
	* event-top.c (async_command_editing_p): Rename to ...
	(set_editing_cmd_var): ... this.
	(change_line_handler): Add parameter 'editing', and use it.  Bail
	early if the interpreter doesn't support editing.  Don't touch
	readline state if editing is off.
	(gdb_rl_callback_handler_remove, gdb_rl_callback_handler_install)
	(gdb_rl_callback_handler_reinstall): Assert the current UI is the
	main UI.
	(display_gdb_prompt): Don't call gdb_rl_callback_handler_remove if
	not using readline.  Check whether the current UI is using command
	editing instead of checking the async_command_editing_p global.
	(set_async_editing_command): Delete.
	(gdb_setup_readline): Add 'editing' parameter.  Only allow editing
	on the main UI.  Don't touch readline state if editing is off.
	(gdb_disable_readline): Don't touch readline state if editing is
	off.
	* event-top.h (gdb_setup_readline): Add 'int' parameter.
	(set_async_editing_command): Delete declaration.
	(change_line_handler, command_line_handler): Declare.
	(async_command_editing_p): Rename to ...
	(set_editing_cmd_var): ... this.
	* infrun.c (reinstall_readline_callback_handler_cleanup): Check
	whether the current UI has editing enabled rather than checking
	the async_command_editing_p global.
	* interps.c (interp_supports_command_editing): New function.
	* interps.h (interp_supports_command_editing_ftype): New typedef.
	(struct interp_procs) <supports_command_editing_proc>: New field.
	(interp_supports_command_editing): Declare.
	* mi/mi-interp.c (mi_interpreter_resume): Pass 0 to
	gdb_setup_readline.  Don't clear the async_command_editing_p
	global.  Update comments.
	* top.c (gdb_readline_wrapper_line, gdb_readline_wrapper): Check
	whether the current UI has editing enabled rather than checking
	the async_command_editing_p global.  Don't touch readline state if
	editing is off.
	(undo_terminal_modifications_before_exit): Switch to the main UI.
	Unconditionally call gdb_disable_readline.
	(set_editing): New function.
	(show_async_command_editing_p): Rename to ...
	(show_editing): ... this.  Show the state of the current UI.
	(_initialize_top): Adjust.
	* top.h (struct ui) <command_editing>: New field.
	* tui/tui-interp.c: Include cli/cli-interp.h.
	(tui_resume): Pass 1 to gdb_setup_readline.  Set the UI's
	input_handler.
	(tui_interp_procs): Install
	cli_interpreter_supports_command_editing.
	* tui/tui-io.c (tui_getc): Check whether the current UI has
	editing enabled rather than checking the async_command_editing_p
	global.

gdb/testsuite/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	PR mi/20034
	* gdb.mi/mi-editing.exp: New file.

1 files changed, 5 insertions, 5 deletions

diff --git a/gdb/event-top.h b/gdb/event-top.h
index 4fe7737..dd0b4bc 100644
--- a/gdb/event-top.h
+++ b/gdb/event-top.h
@@ -28,12 +28,12 @@ struct cmd_list_element;
    FIXME: these should really go into top.h.  */
 
 extern void display_gdb_prompt (const char *new_prompt);
-void gdb_setup_readline (void);
-void gdb_disable_readline (void);
+extern void gdb_setup_readline (int);
+extern void gdb_disable_readline (void);
 extern void async_init_signals (void);
-extern void set_async_editing_command (char *args, int from_tty,
-				       struct cmd_list_element *c);
+extern void change_line_handler (int);
 
+extern void command_line_handler (char *rl);
 extern void command_handler (char *command);
 
 /* Signal to catch ^Z typed while reading a command: SIGTSTP or SIGCONT.  */
@@ -54,7 +54,7 @@ extern void async_enable_stdin (void);
 /* Exported variables from event-top.c.
    FIXME: these should really go into top.h.  */
 
-extern int async_command_editing_p;
+extern int set_editing_cmd_var;
 extern int exec_done_display_p;
 extern struct prompts the_prompts;
 extern void (*after_char_processing_hook) (void);