bug#45938: [PATCH] Avoid ANSI escape characters (bug#45938)

[Eli Zaretskii <eliz@gnu.org>]

> From: Evgenii Klimov <eugene.dev@lipklim.org>
> Cc: kobarity@gmail.com,  45938@debbugs.gnu.org
> Date: Wed, 28 Aug 2024 21:39:27 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Evgenii Klimov <eugene.dev@lipklim.org>
> >> Cc: kobarity <kobarity@gmail.com>,  45938@debbugs.gnu.org
> >> Date: Wed, 28 Aug 2024 17:28:30 +0100
> >> 
> >> Eli Zaretskii <eliz@gnu.org> writes:
> >> [...]
> >> >> diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
> >> >> index a00289d6de9..7193cc19425 100644
> >> >> --- a/lisp/progmodes/python.el
> >> >> +++ b/lisp/progmodes/python.el
> >> >> @@ -4549,6 +4549,9 @@ (defun python-shell-completion-native-setup ()
> >> >>              readline.parse_and_bind('tab: complete')
> >> >>              # Require just one tab to send output.
> >> >>              readline.parse_and_bind('set show-all-if-ambiguous on')
> >> >> +            # Avoid ANSI escape characters in the output
> >> >> +            readline.parse_and_bind('set colored-completion-prefix off')
> >> >> +            readline.parse_and_bind('set colored-stats off')
> >> >>              # Avoid replacing common prefix with ellipsis.
> >> >>              readline.parse_and_bind('set completion-prefix-display-length 0')
> >> >>  
> >> >
> >> > Are these commands available in every version of Python?
> >> 
> >> These commands are from GNU Readline, not from Python
> >
> > Yes, I know.  But not every Python is built with GNU Readline, right?
> 
> If Python is not built with GNU Readline, then this function
> (python-shell-completion-native-setup) will not set up native completion
> in any case:
> 
>     ;; Shell completion: hitting tab will try to complete the current
>     ;; word.  The two built-in mechanisms depend on Python's readline
>     ;; module [1]
> 
>     (defun python-shell-completion-native-setup ()
>       "Try to setup native completion, return non-nil on success."
>       (let* ((process (python-shell-get-process))
>              (output (python-shell-send-string-no-output "
>     def __PYTHON_EL_native_completion_setup():
>         try:
>             import readline
>             ...
>         except:
>             import sys
>             print ('python.el: native completion setup failed, %s: %s'
>                    % sys.exc_info()[:2])
> 
> [...]
> > Which versions of Python or GNU/Linux are likely to have older
> > versions of Readline?  And what happens in an older Readline when
> > these commands are sent?
> 
> I tested what happens if we pass nonexistent variable - it prints to
> stdout:
> 
>     In [15]: readline.parse_and_bind("set nonexistent-variable off")
>     readline: nonexistent-variable: unknown variable name
> 
> In the context of `python-shell-completion-native-setup' such output
> doesn't hurt, because output string still matches with expected one.
> E.g. let's say that I added nonexistent-variable:
> 
>     (defun python-shell-completion-native-setup ()
>       "Try to setup native completion, return non-nil on success."
>       (let* ((process (python-shell-get-process))
>              (output (python-shell-send-string-no-output "
>     def __PYTHON_EL_native_completion_setup():
>             ...
>             if readline.__doc__ and 'libedit' in readline.__doc__:
>                 raise Exception('''libedit based readline is known not to work,
>           see etc/PROBLEMS under \"In Inferior Python mode, input is echoed\".''')
>                 readline.parse_and_bind('bind ^I rl_complete')
>             else:
>                 readline.parse_and_bind('tab: complete')
>                 # Require just one tab to send output.
>                 readline.parse_and_bind('set show-all-if-ambiguous on')
> ->              readline.parse_and_bind('set nonexistent-variable off')
>                 # Avoid replacing common prefix with ellipsis.
>                 readline.parse_and_bind('set completion-prefix-display-length 0')
> 
>             print ('python.el: native completion setup loaded')
>         except:
>             import sys
>             print ('python.el: native completion setup failed, %s: %s'
>                    % sys.exc_info()[:2])
> 
>     __PYTHON_EL_native_completion_setup()" process)))
>         (when (string-match-p "python\\.el: native completion setup loaded"
>                               output)
>           (python-shell-completion-native-try))))
> 
> Then the `output' would be:
> 
>      "readline: nonexistent-variable: unknown variable name\npython.el: native completion setup loaded\n"
> 
> and
> 
>     (string-match-p "python\\.el: native completion setup loaded"
>                               output)
> 
> finds the match.
> 
> I tried that in CPython and IPython.
> 
> Actually, I also tried python built with readline-6.2
> (`python-shell-completion-native-setup' already uses
> "show-all-if-ambiguous", first appeared in that version) and found out
> that that version doesn't even print anything when nonexistent variable
> is passed.
> 
>     eugene@gx:~/git (gx)
>     $ guix shell --with-input=readline=readline@6.2 python 
>     eugene@gx:~/git (gx) [env]
>     $ which python3
>     /gnu/store/hhcay3d42k3k7avahrmlqv3qnjk2l6wp-profile/bin/python3
>     eugene@gx:~/git (gx) [env]
>     $ echo $GUIX_ENVIRONMENT 
>     /gnu/store/hhcay3d42k3k7avahrmlqv3qnjk2l6wp-profile
>     eugene@gx:~/git (gx) [env]
>     $ python3
>     Python 3.10.7 (main, Jan  1 1970, 00:00:01) [GCC 11.3.0] on linux
>     Type "help", "copyright", "credits" or "license" for more information.
>     >>> import readline
>     >>> readline.parse_and_bind("set nonexistent-variable off")
>     >>> 

Thanks, this all sounds good.  Let's see what kobarity has to say
about this.