How do you actually use phases?

[arxanas]

I want to customize the scalafmt phase. I don't understand how to actually customize configuration settings, such as the scalafmt config.

The current definition is this:

ext_scalafmt = {
    "attrs": {
        "config": attr.label(
            allow_single_file = [".conf"],
            default = "@scalafmt_default//:config",
            doc = "The Scalafmt configuration file.",
        ),
        "format": attr.bool(
            default = False,
            doc = "Switch of enabling formatting.",
        ),
        "_fmt": attr.label(
            cfg = "host",
            default = "//scala/scalafmt",
            executable = True,
        ),
        "_runner": attr.label(
            allow_single_file = True,
            default = "//scala/scalafmt:runner",
        ),
        "_testrunner": attr.label(
            allow_single_file = True,
            default = "//scala/scalafmt:testrunner",
        ),
    },
    "outputs": {
        "scalafmt_runner": "%{name}.format",
        "scalafmt_testrunner": "%{name}.format-test",
    },
    "phase_providers": [
        "//scala/scalafmt:phase_scalafmt",
    ],
}

Am I supposed to be able to override the default values somehow? Or is default actually used to set the configuration value, and isn't supposed to be modifiable later? I couldn't find any guidance in the documentation.

Currently, my solution is to make my own version of ext_scalafmt, using different values for default. Is that correct?

my_ext_scalafmt = {
    "attrs": {
        "config": attr.label(
            allow_single_file = [".conf"],
            default = "//my/new/config,
            doc = "The Scalafmt configuration file.",
        ),
       ...
    },
   ...
}

_scala_macro_library = make_scala_macro_library(my_ext_scalafmt)

[liucijus]

You can provide config with a macro in WORKSPACE, like here: https://github.com/bazelbuild/rules_scala/blob/master/WORKSPACE#L64 (accepts path parameter to config file https://github.com/bazelbuild/rules_scala/blob/72c27ef603fc8b771fa80e3398c3fe7701af1515/scala/scalafmt/scalafmt_repositories.bzl#L7)

Is this what you are looking for?

[arxanas]

@liucijus: that probably works for specifically the config attribute, but how can I configure _fmt, etc.? @scalafmt_default can be created as a new_local_repository for my project, but not the same for //scala/scalafmt and so on.

[liucijus]

What is the need behind changing private attributes? They are considered implementation details.
In general phases are meant for rule developer who add new functionality and should not be used for simple configuration. If there's a limitation for generic configuration, I think, we need to address it by modifying existing implementation.

[ittaiz]

+1 to what @liucijus says.
Phases are meant for rule developers or for power users who need very advanced abilities (replacing the type of the compiler). In return these have less of guarantees and we might break APIs as they are not public ones per-se.

Giving more inputs on what you need would indeed help us help you

[arxanas]

Sorry, I didn't realize that the attributes prefixed with _ were meant to be private attributes.

We need a different version of scalafmt. Currently it's set to 2.3.2: https://github.com/bazelbuild/rules_scala/blob/d8f5bd96f8f1719bf24ebab765e5025d037349b1/third_party/repositories/scala_2_12.bzl#L71

It seems that you can set your preferred versions of all the artifacts (I think with scalafmt_repositories), but I'm not sure if there's an easy way to pin all of those. In fact, we have a scalafmt target already in our repository, and I would prefer just to use that one rather than duplicate all of its dependencies, which would add significant operational burden for future maintainers. Thus, it would be easier if I could just set the _fmt target directly.

I was also advised by a coworker (cc @ShaneDelmore) that scalafmt-native was better for long-term memory usage, which is important when formatting our entire repository. We decided to go with that approach instead of the JVM-based scalafmt. In that case, it looks like I should use my own phase provider, and don't need to rely on any guarantees about private attributes? (The current phase provider is incompatible due to reliance on persistent workers.)

[liucijus]

@arxanas, to use different versions of scalafmt deps, the preferred way is to define your own toolchain of type @io_bazel_rules-scala//scala/scalafmt/toolchain:scalafmt_toolchain_type, like here: https://github.com/liucijus/rules_scala/blob/master/scala/scalafmt/BUILD#L49

declare_deps_provider(
    name = "scalafmt_classpath_provider",
    deps_id = "scalafmt_classpath",
    visibility = ["//visibility:public"],
    deps = [
        "@com_geirsson_metaconfig_core",
        "@org_scalameta_parsers",
        "@org_scalameta_scalafmt_core",
    ],
)

scalafmt_toolchain(
    name = "scalafmt_toolchain_impl",
    dep_providers = [
        ":scalafmt_classpath_provider",
    ],
    visibility = ["//visibility:public"],
)

toolchain(
    name = "scalafmt_toolchain",
    toolchain = ":scalafmt_toolchain_impl",
    toolchain_type = "//scala/scalafmt/toolchain:scalafmt_toolchain_type",
    visibility = ["//visibility:public"],
)

It's a new feature, let me know if it does not work for you.