Add support for suspend and resume.

[willmcgugan]

Textual swallows ctrl+Z which would normally allow the user to suspend the app. We should restore this behaviour.

There many be another issue for this somewhere, and some initial work.

This may require a little work on the driver code. Bear in mind there are several concrete implementations and we want to avoid breaking them. Suggest talking this through with @willmcgugan once you have a plan for this.

2d

[davep]

Previous issue is #1582 and related PR is #1655 which, at the time, was working but stalled when it came to testing via the pilot.

[davep]

While the bulk of this is now in place, I have run into one problem when it comes to SIGTSTP background of the app. With this PR in place, if you Ctrl+Z the app then fg it from the resulting shell it works fine. On the other hand if you first bg (which doesn't make sense for a full-screen application, of course, but it's something the user could attempt) and then fg you get the following:

╭─────────────────────────────────────────────────── Traceback (most recent call last) ───────────────────────────────────────────────────╮
│ /Users/davep/develop/python/textual/src/textual/app.py:3375 in action_suspend_process                                                   │
│                                                                                                                                         │
│   3372 │   │   """                                                                                                                      │
│   3373 │   │   if not WINDOWS:                                                                                                          │
│   3374 │   │   │   try:                                                                                                                 │
│ ❱ 3375 │   │   │   │   with self.suspend():                                                                                             │
│   3376 │   │   │   │   │   os.kill(os.getpid(), signal.SIGTSTP)                                                                         │
│   3377 │   │   │   except SuspendNotSupported:                                                                                          │
│   3378 │   │   │   │   pass                                                                                                             │
│                                                                                                                                         │
│ ╭────────────────────────── locals ───────────────────────────╮                                                                         │
│ │ self = SplashApp(title='SplashApp', classes={'-dark-mode'}) │                                                                         │
│ ╰─────────────────────────────────────────────────────────────╯                                                                         │
│                                                                                                                                         │
│ /Users/davep/.pyenv/versions/3.11.6/lib/python3.11/contextlib.py:144 in __exit__                                                        │
│                                                                                                                                         │
│   141 │   def __exit__(self, typ, value, traceback):                                                                                    │
│   142 │   │   if typ is None:                                                                                                           │
│   143 │   │   │   try:                                                                                                                  │
│ ❱ 144 │   │   │   │   next(self.gen)                                                                                                    │
│   145 │   │   │   except StopIteration:                                                                                                 │
│   146 │   │   │   │   return False                                                                                                      │
│   147 │   │   │   else:                                                                                                                 │
│                                                                                                                                         │
│ ╭──────────────────────────────── locals ─────────────────────────────────╮                                                             │
│ │      self = <contextlib._GeneratorContextManager object at 0x106af29d0> │                                                             │
│ │ traceback = None                                                        │                                                             │
│ │       typ = None                                                        │                                                             │
│ │     value = None                                                        │                                                             │
│ ╰─────────────────────────────────────────────────────────────────────────╯                                                             │
│                                                                                                                                         │
│ /Users/davep/develop/python/textual/src/textual/app.py:3358 in suspend                                                                  │
│                                                                                                                                         │
│   3355 │   │   │   self._driver.close()                                                                                                 │
│   3356 │   │   │   with redirect_stdout(sys.__stdout__), redirect_stderr(sys.__stderr__):                                               │
│   3357 │   │   │   │   yield                                                                                                            │
│ ❱ 3358 │   │   │   self._driver.start_application_mode()                                                                                │
│   3359 │   │   │   self.app_resume_signal.publish()                                                                                     │
│   3360 │   │   else:                                                                                                                    │
│   3361 │   │   │   raise SuspendNotSupported(                                                                                           │
│                                                                                                                                         │
│ ╭────────────────────────── locals ───────────────────────────╮                                                                         │
│ │ self = SplashApp(title='SplashApp', classes={'-dark-mode'}) │                                                                         │
│ ╰─────────────────────────────────────────────────────────────╯                                                                         │
│                                                                                                                                         │
│ /Users/davep/develop/python/textual/src/textual/drivers/linux_driver.py:167 in start_application_mode                                   │
│                                                                                                                                         │
│   164 │   │   │   # defaults to ASCII EOT = Ctrl-D = 4.)                                                                                │
│   165 │   │   │   newattr[tty.CC][termios.VMIN] = 1                                                                                     │
│   166 │   │   │                                                                                                                         │
│ ❱ 167 │   │   │   termios.tcsetattr(self.fileno, termios.TCSANOW, newattr)                                                              │
│   168 │   │                                                                                                                             │
│   169 │   │   self.write("\x1b[?25l")  # Hide cursor                                                                                    │
│   170 │   │   self.write("\033[?1003h\n")                                                                                               │
│                                                                                                                                         │
│ ╭─────────────────────────────────────────────────────────── locals ───────────────────────────────────────────────────────────╮        │
│ │               loop = <_UnixSelectorEventLoop running=True closed=False debug=False>                                          │        │
│ │            newattr = [                                                                                                       │        │
│ │                      │   26626,                                                                                              │        │
│ │                      │   3,                                                                                                  │        │
│ │                      │   19200,                                                                                              │        │
│ │                      │   67,                                                                                                 │        │
│ │                      │   9600,                                                                                               │        │
│ │                      │   9600,                                                                                               │        │
│ │                      │   [                                                                                                   │        │
│ │                      │   │   b'\x04',                                                                                        │        │
│ │                      │   │   b'\xff',                                                                                        │        │
│ │                      │   │   b'\xff',                                                                                        │        │
│ │                      │   │   b'\x7f',                                                                                        │        │
│ │                      │   │   b'\x17',                                                                                        │        │
│ │                      │   │   b'\x15',                                                                                        │        │
│ │                      │   │   b'\x12',                                                                                        │        │
│ │                      │   │   b'\xff',                                                                                        │        │
│ │                      │   │   b'\x03',                                                                                        │        │
│ │                      │   │   b'\xff',                                                                                        │        │
│ │                      │   │   ... +10                                                                                         │        │
│ │                      │   ]                                                                                                   │        │
│ │                      ]                                                                                                       │        │
│ │ on_terminal_resize = <function LinuxDriver.start_application_mode.<locals>.on_terminal_resize at 0x106a5fc40>                │        │
│ │               self = <LinuxDriver SplashApp(title='SplashApp', classes={'-dark-mode'})>                                      │        │
│ │    send_size_event = <function LinuxDriver.start_application_mode.<locals>.send_size_event at 0x106a5c220>                   │        │
│ ╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯        │
╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
error: (4, 'Interrupted system call')

Attempting something similar with vim (for example), works just fine; the process stays in a stopped state and resumes without a problem. I'll use a bit more time to dig into how the Linux driver works and/or the method used to SIGTSTP the application as I sense the issue will be around there.

It's also worth noting that this mostly works fine with Midnight Commander (as another example app to test), although I have managed to get it into a state where it's failing to properly process non-alphanumeric keys or mouse input.

[davep]

+1d

[github-actions]

Don't forget to star the repository!

Follow @textualizeio for Textual updates.