Disable terminal ANSI escape sequences when the output is a file

[yujinakayama]

The continuation of #497.

[fuadsaud]

I'm not very familiar with rubocop's source code, but I checked it out and it seemed like a good solution to decorate the output used in the base formatter and then check whether it is a tty in order to add ansi escape sequences.

[bbatsov]

@fuadsaud Feel free to send a PR implementing your proposed solution :-) This won't affect paging programs understanding ANSI colors like less, right?

[fuadsaud]

Yes, a simple check for IO#tty? will return false for pipes and such. I'm not sure how to handle this either.

I'm not sure when I'll have time, but I plan to look into it. If anyone has a better idea, please go on.

[jonas054]

I think the problem should be solved in the Rainbow gem. I have opened an issue over there.

[jonas054]

Issue 16 in sickill/rainbow has been closed and version 1.99.0 of that gem has the fix. I have tested manually that color codes are not included when stderr is redirected to a file. A bundle update in the rubocop directory is needed.

[ku1ik]

Copy pasting what I just wrote in #497 :

I have just released a new rainbow 1.99 which has this fixed (checks if any of stdout and stderr is not a tty). rainbow will drop monkey patching of String class in 2.0 and this 1.99 release is a preparation for that. You can now upgrade to 1.99 and convert all "foo".color(:red) to Rainbow("foo").color(:red). When 2.0 is out you'll be prepared.

[yujinakayama]

I don't think this issue is solved.

The rainbow's update solves the @fuadsaud's log that is caused by shell redirection. However, rainbow cannot detect whether a formatter's output is a file (with -o/--out option) or not, and as I wrote it cannot handle multiple formatters, though these are not rainbow's fault.

[ku1ik]

@yujinakayama rubocop can disable rainbow (via Rainbow.enabled = false) when a formatter's output is a file. I understand the case here is that you would want to both print to terminal with colors enabled and at the same time to a file with colors disabled, right?

A solution for that would be something like this:

FileRainbow = Rainbow.get_instance
FileRainbow.enabled = <...your custom condition...>

For example:

# this adds color if the terminal is a TTY
Rainbow("foo").color(:red) # => "\e[31mfoo\e[0m"

# this never adds a color
FileRainbow.enabled = false
FileRainbow("foo").color(:red) # => "foo"

Would that solve this rubocop problem?

[ku1ik]

Basically, each formatter could acquire its own instance of Rainbow and rubocop could disable coloring on the Rainbow instances that are used by formatters that output to files.

[yujinakayama]

@sickill

I understand the case here is that you would want to both print to terminal with colors enabled and at the same time to a file with colors disabled, right?

Yes.

The proposed solution is great. If rainbow provides the feature, we can solve the problem without migrating from rainbow. Although I think Rainbow.new would be more idiomatic than Rainbow.get_instance.

[ku1ik]

👍 on Rainbow.new, I agree that it's better.

I should find some time for this in the coming days, I'll let you know when it gets implemented.

[yujinakayama]

@sickill Thanks!

[ku1ik]

@yujinakayama it's there. I have just released 1.99.1 with a support for multiple rainbow wrapper instances. Check the readme section "Advanced usage".

[yujinakayama]

@sickill Thanks! I'll try later.