FR: Add \x01 and \x02 to the color formats to support $PS1

[yjyao]

Is your feature request related to a problem? Please describe.
i was trying to use jj --ignore-working-copy log --no-graph -l1 -r @ -T '...' to build a $PS1 prompt. however, the coloring confuses the readline length calculation because of lack of \x01/\x02 (or \[/\]) control characters.

Describe the solution you'd like
always wrap color control codes with \x01/\x02 --- unless that would cause any problem?

Describe alternatives you've considered
create a dedicated $PS1-generator like how Git has __git_ps1.

[martinvonz]

I'm not familiar with \x01/\x02. Do you mean that we should just print those two bytes before/after color codes? How is the terminal supposed to treat them? Can you link to the spec? Is it well supported?

[yjyao]

sorry i should have shared more info.

yes, i'm suggesting printing \x01/x02 (or \001/002) before and after color codes. they are non-printable characters so the displayed output should look the same.

they help readline count the characters. this is useful for setting up prompt line for a shell environment, the $PS1, especially on the same line where the user enters the command. if readline counts the color control characters, it will think the line is longer than what the user sees. this can cause problems if you enter a long command that spans multiple lines on the terminal. \x01\e[32m\x02 effectively tells readline to exclude itself when counting characters.

https://superuser.com/a/301355 provides a quote and links to a wikipedia page which links to a (very old) message format manual.

it looks like this is not supported everywhere: i found this issue for MS Terminal and it looks like dash doesn't support this because it doesn't support line editting...? i haven't used any shell other than bash and zsh.

[yuja]

Appears that less visualizes these control chars, so it's not an option to change the default --color behavior.

% printf '\x01' | less -FRX
^A

Another way around is to make templater parse \x<hex> escapes and let user insert \x01\x1b[m, etc. manually.

[yjyao]

actually this is a non-issue. i wasn't thinking straight. apparently i can just generate the '\x01' and '\e' strings in the template and then evaluate them in PS1...

1. use jj log -l1--color never -T '"\\e[32m" ++ "hey" ++ "\\e[0m"' to create the string \e[32mhey\e[0m.
2. use printf '%b' (or echo -e) to print it.

and with jj's support on custom functions, creating these templates is very neat:

echo -e "$(jj --ignore-working-copy --color never log -l1 -r @ --no-graph --config-toml "
[template-aliases]
'colored(color, txt)' = '''
  surround('\x01\e[' ++ color ++ 'm\x02', '\x01\e[0m\x02', txt)
'''
'red(txt)'     = '''colored('31', txt)'''
'green(txt)'   = '''colored('32', txt)'''
'yellow(txt)'  = '''colored('33', txt)'''
'blue(txt)'    = '''colored('34', txt)'''
'magenta(txt)' = '''colored('35', txt)'''
'cyan(txt)'    = '''colored('36', txt)'''
'white(txt)'   = '''colored('37', txt)'''
" -T '
green(change_id.shortest())
'

sorry for the noise and feel free to close this ticket.