Make display_gdb_prompt CLI-only.

Enabling target-async by default will require implementing sync
execution on top of an async target, much like foreground command are
implemented on the CLI in async mode.

In order to do that, we will need better control of when to print the
MI prompt.  Currently the interp->display_prompt_p hook is all we
have, and MI just always returns false, meaning, make
display_gdb_prompt a no-op.  We'll need to be able to know to print
the MI prompt in some of the conditions that display_gdb_prompt is
called from the core, but not all.

This is all a litte twisted currently.  As we can see,
display_gdb_prompt is really CLI specific, so make the console
interpreters (console/tui) themselves call it.  To be able to do that,
and add a few different observers that the interpreters can use to
distinguish when or why the the prompt is being printed:

#1 - one called whenever a command is cancelled due to an error.
#2 - another for when a foreground command just finished.

In both cases, CLI wants to print the prompt, while MI doesn't.

MI will want to print the prompt in the second case when in a special
MI mode.

The display_gdb_prompt call in interp_set made me pause.  The comment
there reads:

  /* Finally, put up the new prompt to show that we are indeed here.
     Also, display_gdb_prompt for the console does some readline magic
     which is needed for the console interpreter, at least...  */

But, that looks very much like a no-op to me currently:

 - the MI interpreter always return false in the prompt hook, meaning
   actually display no prompt.

 - the interpreter used at that point is still quiet.  And the
   console/tui interpreters return false in the prompt hook if they're
   quiet, meaning actually display no prompt.

The only remaining possible use would then be the readline magic.  But
whatever that might have been, it's not reacheable today either,
because display_gdb_prompt returns early, before touching readline if
the interpreter returns false in the display_prompt_p hook.

Tested on x86_64 Fedora 20, sync and async modes.

gdb/
2014-05-29  Pedro Alves  <palves@redhat.com>

	* cli/cli-interp.c (cli_interpreter_display_prompt_p): Delete.
	(_initialize_cli_interp): Adjust.
	* event-loop.c: Include "observer.h".
	(start_event_loop): Notify 'command_error' observers instead of
	calling display_gdb_prompt.  Remove FIXME comment.
	* event-top.c (display_gdb_prompt): Remove call into the
	interpreters.
	* inf-loop.c: Include "observer.h".
	(inferior_event_handler): Notify 'command_error' observers instead
	of calling display_gdb_prompt.
	* infrun.c (fetch_inferior_event): Notify 'sync_execution_done'
	observers instead of calling display_gdb_prompt.
	* interps.c (interp_set): Don't call display_gdb_prompt.
	(current_interp_display_prompt_p): Delete.
	* interps.h (interp_prompt_p): Delete declaration.
	(interp_prompt_p_ftype): Delete.
	(struct interp_procs) <prompt_proc_p>: Delete field.
	(current_interp_display_prompt_p): Delete declaration.
	* mi-interp.c (mi_interpreter_prompt_p): Delete.
	(_initialize_mi_interp): Adjust.
	* tui-interp.c (tui_init): Install 'sync_execution_done' and
	'command_error' observers.
	(tui_on_sync_execution_done, tui_on_command_error): New
	functions.
	(tui_display_prompt_p): Delete.
	(_initialize_tui_interp): Adjust.

gdb/doc/
2014-05-29  Pedro Alves  <palves@redhat.com>

	* observer.texi (sync_execution_done, command_error): New
	subjects.
enable target async by default; separate MI and target notions of async

This finally makes background execution commands possible by default.

However, in order to do that, there's one last thing we need to do --
we need to separate the MI and target notions of "async".  Unlike the
CLI, where the user explicitly requests foreground vs background
execution in the execution command itself (c vs c&), MI chose to treat
"set target-async" specially -- setting it changes the default
behavior of execution commands.

So, we can't simply "set target-async" default to on, as that would
affect MI frontends.  Instead we have to make the setting MI-specific,
and teach MI about sync commands on top of an async target.

Because the "target" word in "set target-async" ends up as a potential
source of confusion, the patch adds a "set mi-async" option, and makes
"set target-async" a deprecated alias.

Rather than make the targets always async, this patch introduces a new
"maint set target-async" option so that the GDB developer can control
whether the target is async.  This makes it simpler to debug issues
arising only in the synchronous mode; important because sync mode
seems unlikely to go away.

Unlike in previous revisions, "set target-async" does not affect this
new maint parameter.  The rationale for this is that then one can
easily run the test suite in the "maint set target-async off" mode and
have tests that enable mi-async fail just like they fail on
non-async-capable targets.  This emulation is exactly the point of the
maint option.

I had asked Tom in a previous iteration to split the actual change of
the target async default to a separate patch, but it turns out that
that is quite awkward in this version of the patch, because with MI
async and target async decoupled (unlike in previous versions), if we
don't flip the default at the same time, then just "set target-async
on" alone never actually manages to do anything.  It's best to not
have that transitory state in the tree.

Given "set target-async on" now only has effect for MI, the patch goes
through the testsuite removing it from non-MI tests.  MI tests are
adjusted to use the new and less confusing "mi-async" spelling.

2014-05-29  Pedro Alves  <palves@redhat.com>
	    Tom Tromey  <tromey@redhat.com>

	* NEWS: Mention "maint set target-async", "set mi-async", and that
	background execution commands are now always available.
	* target.h (target_async_permitted): Update comment.
	* target.c (target_async_permitted, target_async_permitted_1):
	Default to 1.
	(set_target_async_command): Rename to ...
	(maint_set_target_async_command): ... this.
	(show_target_async_command): Rename to ...
	(maint_show_target_async_command): ... this.
	(_initialize_target): Adjust.
	* infcmd.c (prepare_execution_command): Make extern.
	* inferior.h (prepare_execution_command): Declare.
	* infrun.c (set_observer_mode): Leave target async alone.
	* mi/mi-interp.c (mi_interpreter_init): Install
	mi_on_sync_execution_done as sync_execution_done observer.
	(mi_on_sync_execution_done): New function.
	(mi_execute_command_input_handler): Don't print the prompt if we
	just started a synchronous command with an async target.
	(mi_on_resume): Check sync_execution before printing prompt.
	* mi/mi-main.h (mi_async_p): Declare.
	* mi/mi-main.c: Include gdbcmd.h.
	(mi_async_p): New function.
	(mi_async, mi_async_1): New globals.
	(set_mi_async_command, show_mi_async_command, mi_async): New
	functions.
	(exec_continue): Call prepare_execution_command.
	(run_one_inferior, mi_cmd_exec_run, mi_cmd_list_target_features)
	(mi_execute_async_cli_command): Use mi_async_p.
	(_initialize_mi_main): Install "set mi-async".  Make
	"target-async" a deprecated alias.

2014-05-29  Pedro Alves  <palves@redhat.com>
	    Tom Tromey  <tromey@redhat.com>

	* gdb.texinfo (Non-Stop Mode): Remove "set target-async 1"
	from example.
	(Asynchronous and non-stop modes): Document '-gdb-set mi-async'.
	Mention that target-async is now deprecated.
	(Maintenance Commands): Document maint set/show target-async.

2014-05-29  Pedro Alves  <palves@redhat.com>
	    Tom Tromey  <tromey@redhat.com>

	* gdb.base/async-shell.exp: Don't enable target-async.
	* gdb.base/async.exp
	* gdb.base/corefile.exp (corefile_test_attach): Remove 'async'
	parameter.  Adjust.
	(top level): Don't test with "target-async".
	* gdb.base/dprintf-non-stop.exp: Don't enable target-async.
	* gdb.base/gdb-sigterm.exp: Don't test with "target-async".
	* gdb.base/inferior-died.exp: Don't enable target-async.
	* gdb.base/interrupt-noterm.exp: Likewise.
	* gdb.mi/mi-async.exp: Use "mi-async" instead of "target-async".
	* gdb.mi/mi-nonstop-exit.exp: Likewise.
	* gdb.mi/mi-nonstop.exp: Likewise.
	* gdb.mi/mi-ns-stale-regcache.exp: Likewise.
	* gdb.mi/mi-nsintrall.exp: Likewise.
	* gdb.mi/mi-nsmoribund.exp: Likewise.
	* gdb.mi/mi-nsthrexec.exp: Likewise.
	* gdb.mi/mi-watch-nonstop.exp: Likewise.
	* gdb.multi/watchpoint-multi.exp: Adjust comment.
	* gdb.python/py-evsignal.exp: Don't enable target-async.
	* gdb.python/py-evthreads.exp: Likewise.
	* gdb.python/py-prompt.exp: Likewise.
	* gdb.reverse/break-precsave.exp: Don't test with "target-async".
	* gdb.server/solib-list.exp: Don't enable target-async.
	* gdb.threads/thread-specific-bp.exp: Likewise.
	* lib/mi-support.exp: Adjust to use mi-async.