Respect TERM=dumb and emit no colour escape codes

[andreastt]

Certain shells are not particularly happy with colour escape codes. To make them happy, clap should respect TERM=dumb and refrain from emitting colour escape codes.

Rust Version

rustc 1.15.0 (10893a9a3 2017-01-19)

Affected Version of clap

% grep clap Cargo.toml
clap = "2.19.0"

Expected Behavior Summary

For a program using clap to respect TERM=dumb and emit no colour escape codes.

Actual Behavior Summary

Program using clap emits colour escape codes as shown in BurntSushi/ripgrep#353.

Steps to Reproduce the issue

Compile any program using clap as a dependency and use an unrecognised flag:

% rg --color never -asd
�[1;31merror:�[0m Found argument '�[33m-d�[0m' which wasn't expected, or isn't valid in this context

USAGE:
    
    rg [OPTIONS] <pattern> [<path> ...]
    rg [OPTIONS] [-e PATTERN | -f FILE ]... [<path> ...]
    rg [OPTIONS] --files [<path> ...]
    rg [OPTIONS] --type-list

For more information try �[32m--help�[0m

[kbknapp]

Thanks!

Relates to #836

[nateozem]

I wonder if someone can reference TERM=dumb is standardize across applications. Is there any documentation that explains how it should behave?

[BurntSushi]

@nateozem This is the best I could find: https://linux.die.net/man/7/term --- TL;DR the TERM=dumb convention is quite old. The behavior today is to treat TERM=dumb as "don't emit escape sequences because the terminal being used won't know how to use them."

[nateozem]

@BurntSushi, interesting.
Seem like the behavior would depend on each individual machine. In most probability, everyone has the same capability for dumb, but there can be an instance where someone can change how the terminal type behaves by using the tic command.
On my system, I can do this to check the definition: $ infocmp -L dumb

$ infocmp -L dumb
#       Reconstructed via infocmp from file: /usr/share/terminfo/64/dumb
dumb|80-column dumb tty,
		auto_right_margin,
		columns#80,
		bell=^G, carriage_return=^M, cursor_down=^J,
		scroll_forward=^J,

My expectation of moving forward is by calling "curses interfaces to terminfo database" ($ man curs_terminfo(3X)). What do you guys think?

When I discover anything more, I'll report back.

[BurntSushi]

@nateozem Consulting terminfo is certainly one path. It's a complex one, but it's valid. On the other hand, just respecting TERM=dumb will solve a good number of problems. Perhaps not all of them, but some of them. :-)

An example of a popular piece of software that generally gets colors correct is GNU grep, but they don't consult terminfo at all. This sacrifices compatibility on some very obscure terminal environments, but standard ANSI escapes pretty much work everywhere. (And GNU grep supports TERM=dumb explicitly.)