Add color keyword argument

[kimikage]

This is a change intended for Documenter's ANSI color support (cf. JuliaDocs/Documenter.jl#1441)

This adds color keyword argument to iocapture(). Currently, this argument does not work on Julia v1.5 or earlier, but to avoid version-based conditional branching on the user side, it does not throw an error.

Of course, it is a reasonable option to set color to false by default. However, I chose true for the following reasons.

• It is intuitive that the raw stdout output matches the capture result.
• The ANSI escape codes are easy to detect and remove, but impossible to add later.
• Since Julia v1.6 is still in development, this breaking change has little problem.
  • However, we need to bump a minor version as it is not compatible with v0.1.

[mortenpi]

Sorry for the delay. The implementation and tests look great, thanks a lot!

1. I wonder if the default to color should be false though. My argument would be that the most common use case of iocapture is probably where you want to do some post-processing on the output (e.g. to regex out some information). At that point, you probably prefer not having the color escapes in the output. To counter the intuitiveness point, I think for me it would be slightly more intuitive if the captured output (by default) only contains the characters that I can see in the terminal.

   It would also make the default behavior consistent across Julia versions, with the ability to capture color, that must be explicitly enabled, only having an effect in 1.6+.

   Do these arguments sway you, or do you think true is still the better option?

2. Currently, if I read the tests right, we test slightly different code paths depending on settings (e.g. depending on --color or Julia version)? I wonder if we could have cases where we force-enable and force-disable color on stdout/err somehow, to make sure we test all the cases every time? It's not too important though, i.e. not worth investing too much time into this I think.

[mortenpi]

Should this be get(stderr, ...)?

[MichaelHatherly]

It would also make the default behavior consistent across Julia versions, with the ability to capture color, that must be explicitly enabled, only having an effect in 1.6+.

Agreed, if we can have consistent behavior across versions that would be less surprising.

[MichaelHatherly]

Worth sticking a @static in here to avoid the runtime branch?

[kimikage]

I'm skeptical that there is a runtime branch, but I'll stick the @static to be clear.

[MichaelHatherly]

Yeah, looks like it's smart enough these days:

julia> function f(x, y)
           if VERSION >= v"1.4.0"
               x + y
           else
               x - y
           end
       end

julia> @code_typed f(1, 2)
CodeInfo(
1 ─ %1 = Base.add_int(x, y)::Int64
└──      return %1
) => Int64

No point adding @static then.

[kimikage]

Thanks for the reviews!
I changed the default value to false.

[mortenpi]

Thanks again! Will tag this shortly, so that the Documenter PR could make use of this without having to jump through hoops.