Support for `blue` as a formatter

[guettli]

Is it possible to use blue instead of black?

blue is a somewhat less uncompromising code formatter than black.

See also:

• many-formatters sub-project

[akaihola]

Thanks for the heads-up @guettli, I've never taken a look at blue before.

Do you know if the internals are at all similar to black's? Darker uses the Python (non-public, see psf/black#779) API of Black instead of calling it as a subprocess.

---

Design

See also #304 for the idea to allow to disable reformatting.

Alternative 1: Separate --black/--blue configuration options for both formatters

Pros: Similar to the --isort option we already have.
Cons: Somewhat tricky to implement, plus the question about --no-black and --no-blue.

pyproject.toml

In absence of formatter related command line options:

[tool.darker]
black = true  # the default, uses Black as the formatter

[tool.darker]
blue = true  # disables Black and uses Blue as the formatter

[tool.darker]
black = false  # disables reformatting, see also #304

[tool.darker]
blue = false  # no effect, Black still enabled

Command line arguments

Examples in absence of pyproject.toml configuration:

$ darker .  # use Black (the default)
$ darker --black .  # no effect, still use Black
$ darker --blue .  # use Blue, disable Black
$ darker --no-black .  # disable reformatting (do we want this? see also #304)
$ darker --no-blue .  # no effect, still use Black (do we want this?)

Alternative 2: One common --formatter option

Pros: Similar to the --lint option we already have; simple to implement.
Cons: More verbose and maybe not so intuitive for the user.

pyproject.toml

In absence of formatter related command line options:

[tool.darker]
formatter = "black"  # the default, uses Black as the formatter

[tool.darker]
formatter = "blue"  # disables Black and uses Blue as the formatter

[tool.darker]
formatter = ""  # disables reformatting, see also #304
formatter = "none"  # alternative syntax, which one is better? (see #304)

Command line arguments

Examples in absence of pyproject.toml configuration:

$ darker .  # use Black (the default)
$ darker --formatter=black .  # no effect, still use Black
$ darker --formatter=blue .  # use Blue, disable Black
$ darker --formatter= .  # disable reformatting (do we want this? see #304)
$ darker --formatter=none .  # disable reformatting (alternative syntax, see #304)

[guettli]

@akaihola sorry. I have not looked at the internals of blue. AFAIK it is black with some small modifications.

[akaihola]

Ok, I'll return to possible blue support after I've made the 1.4.0 release.

One tricky problem to solve is the command line option for this. I've already regretted that --black isn't an option, and running black is the default.

[akaihola]

@guettli & @jedie, I'm now returning to this idea since 1.4.0 has been released.

The first thing I had to ponder is the command line interface and configuration options. I added a design section to my first comment above – what's your take on the two alternative configuration syntaxes, or do you have further ideas?

[guettli]

@akaihola I prefer Alternative2 ("formatter") a bit. Maybe in the long run there is a third formatter (maybe called "green"). I think then Alternative2 makes more sense. But no strong feelings here. A1 is fine, too.

[jedie]

+1 for --formatter

[akaihola]

#309 is a placeholder pull request to start working on this.

[guettli]

I thought about this again. Since Django will use black, I think I will do so, too. Sometimes it is easier to drop the own opinion and go with the flow.

[akaihola]

Thanks for the note, @guettli. I'll still keep this idea around, but deprioritize it and move it to a future milestone.