`--color-output` doesn't work

[bluenote10]

Bug Report

Using mypy --color-output does not seem to have any effect.

To Reproduce

$ mypy --color-output . | cat

Expected Behavior

This should produce a colored output, because --color-output suggests that colors are enforced. It should look like this (if I omit the | cat):

Actual Behavior

Output is not colored.

Your Environment

• Mypy version used: 1.15.0
• Mypy command-line flags: --color-output
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.12.3

May have a similar cause as #13817. EDIT: actually, I no longer think so because FORCE_COLOR and MYPY_FORCE_COLOR works under _some_conditions (if the check I've mentioned there passes, which is not the case in e.g. GitHub or Gitlab), but --color-output never seems to have an effect for me.

[ilevkivskyi]

This is expected behavior (similar to many other CLI tools btw). By default --color-output mode is auto, i.e. it will use color if isatty() returns True, which is never the case for pipes.

[bluenote10]

@ilevkivskyi To me the docstring was suggestion something else, but yes it is not very clear:

  --no-color-output         Do not colorize error messages (inverse: --color-
                            output)

To me the inverse of forcing color off would be forcing color on. Also the imperative wording "color output" very much sounds like "force" to me. I'm literally telling mypy to color the output, not --color-output-if-possible.

This raises the question what effect --color-output actually has, because without specifying anything, the logic uses auto-detection anyway, right? So doesn't that mean that --color-output is a command line argument that does nothing?

My expectation was that --color-output is more like the common --color=yes or --color=always, which add meaningful functionality, because they allow turning off the auto-detection, and enforcing colors. This is basically something most other tools offer in one way or another. Here for instance in the example of pytest:

Should I instead open a feature request for that?

[hepcat72]

I agree. Supplying --color-output should mean: I don't care whether I'm in a tty or not: output in color. --no-color-output should mean: I don't care whether I'm in a tty or not: do not output in color. Not supplying either should mean: output in color if this is a tty, otherwise don't output in color. Otherwise supplying --color-output is no different from not supplying either argument.

[studyingegret]

Has someone opened a pull request for this? I agree with @hepcat72, if there is no existing PR, I can try and work on this

I'm on Windows, setting MYPY_FORCE_COLOR works:

[bluenote10]

I agree with @hepcat72, if there is no existing PR, I can try and work on this

I'd definitely welcome a fix for this!

Perhaps it helps to convince @ilevkivskyi -- in particular because the argument "similar to many other CLI tools" doesn't really fit considering that mypy is behaving different then almost any other CLI tool in that regard 😉

[studyingegret]

considering that mypy is behaving different then almost any other CLI tool in that regard 😉

Yes, and it's unknown if it's a bug (@ilevkivskyi's comment only talks about --color-output's default behavior)

[studyingegret]

By the way, can someone re-open this issue?