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

[kobarity <kobarity@gmail.com>]

Eli Zaretskii wrote:
> 
> > 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.

I confirmed that the patch resolves the issue.  Also, Evgenii's survey
seems sufficient.  So I agree with this patch.