Support forcing colors

[grant0417]

If deno is not running in a tty there is currently no way to override it so that colors are shown

https://github.com/denoland/deno/blob/98bbf87742969802b392130c536454aa61a20395/runtime/js/99_main.js#L250

Some options are:

• FORCE_COLOR env var - this would ignore the other values and never set noColor
• --color flag - similar to ls and other CLI utils
  • auto -> current behavior
  • never -> same behavior as NO_COLOR
  • always -> force color on

[grant0417]

Also open to making the actual change if this is something wanted, just don't know which behavior is preferred.

[bartlomieju]

If we were to support it, it should be via env var. Is there a prior art for FORCE_COLOR env variable?

[grant0417]

Prior art for FORCE_COLOR

• Node supports FORCE_COLOR albeit it in a slightly different way than a simple boolean: https://nodejs.org/api/tty.html#writestreamgetcolordepthenv

More approaches:

• An environment variable that controls always, never, auto would be similar to cargo, i.e. DENO_TERM_COLOR: https://doc.rust-lang.org/cargo/reference/config.html#termcolor

• There is also the CLICOLOR and CLICOLOR_FORCE env vars, but I figured this would not work as well with NO_COLOR: https://bixense.com/clicolors/

I do not have any strong preference on the approach here

[bartlomieju]

@dsherret thoughts on this one?

[dsherret]

We should probably do exactly what Node does, so go with FORCE_COLOR. It defaults to 2 when non-empty and not 0-3:

https://github.com/nodejs/node/blob/9eb363a3e00dbba572756c7ed314273f17ea8e2e/lib/internal/tty.js#L123

Environment variable sounds much better than a flag.

[grant0417]

Seems like the lib termcolor only supports forcing color, no color or auto, but has no concept of color depth support: https://docs.rs/termcolor/latest/termcolor/enum.ColorChoice.html

Would replicating the logic of what is "enabled" for the flags be enough or should the it support the concept of color depth as well?

[dsherret]

I think for compatibility with Node we should get it to work the same way, so maybe that means using a different crate or implementing this ourselves. As a stepping stone, we could maybe implement this broken for now with the same API as Node then fix it up later.

[jcbhmr]

this would be beneficial to allow forcing color to be enabled in ci like github actions which arent tty but still can show colors

^{related: https://github.com/pypa/pip/issues/10909 https://github.com/Textualize/rich/issues/2425 https://github.com/wntrblm/nox/issues/502 https://github.com/python-poetry/cleo/issues/341 https://github.com/astral-sh/ruff/issues/5499 https://github.com/dotnet/command-line-api/issues/1710 https://github.com/pre-commit/pre-commit/issues/2918 https://github.com/pytest-dev/pytest/issues/7443 https://github.com/python/mypy/issues/13806}

[mdekstrand]

Also the extremely useful case of piping to less.