ability to declare package development dependencies

[dweiller]

This is a competing proposal to #14597.

Currently in a build.zig.zon file you can declare dependencies for a project, which will be fetched transitively by dependees. Various projects might have dependencies that are only required by developers of the project itself and not for any exported artifacts (modules, executables, libraries, ...); an example could be benchmarking or testing tools. In this case dependees of the package have no need to fetch these development dependencies and they should be declare separately or have an extra flag indicating this.

For example build.zig.zon file of a package could look like:

.{
    .name = "optimised-package",
    .version = "1.0.0",

    .dependencies = .{
        .some_pkg = .{
            .url = "https://some.forge/some_pkg.tar.gz",
            .hash = "asdfasdf0",
        },
    },
    .dev_dependencies = .{
        .benchmarking = .{
            .url = "https://some.forge/benchmarking.tar.gz",
            .hash = "asdfasdf1",
        },
        .fuzz_tools = .{
            .url = "https://some.forge/fuzz_tools.tar.gz",
            .hash = "asdfasdf2",
    },
}

Alternately, this could be expressed as:

.{
    .name = "optimised-package",
    .version = "1.0.0",

    .dependencies = .{
        .some_pkg = .{
            .url = "https://some.forge/some_pkg.tar.gz",
            .hash = "asdfasdf0",
        },
        .benchmarking = .{
            .url = "https://some.forge/benchmarking.tar.gz",
            .hash = "asdfasdf1",
            .devel_only = true,
        },
        .fuzz_tools = .{
            .url = "https://some.forge/fuzz_tools.tar.gz",
            .hash = "asdfasdf2",
            .devel_only = true,
    },
}

Then these development dependencies can be skipped by the build runner of a dependee.

[star-tek-mb]

If it's all about download size, we could lazily fetch packages, if they are used. But i'm not sure..

const some_dep = b.dependency("foobar", .{}); // not fetched yet
some_dep.artifact("lib"); // fetched
some_dep.module("mod"); // also fetched

As far as I know, golang (go mod) doesn't have dev dependencies support, but is doing well.

[TUSF]

Lazily fetching packages would also be useful in cases where you only use a package for certain OS targets, or with certain build flags.

[andrewrk]

I opened a competing proposal: #14597

[dweiller]

I think I agree that lazy fetching would be a good way to handle things - it would require less work on the part of package developers and dependees. Either lazy fetching or the original proposal here could also support the --fetch flag from #14597.

[praschke]

i think hardcoding two modes is overly limiting and inflexible. using an inexpressive mechanism like this complicates the logic and splits what you need to see (conditions under which dependencies are required) across two files. "it won't preclude using arbitrary logic" means that you have to read build.zig anyway.

for the simple cases you say would benefit from this, the build.zig without this proposal would also be correspondingly simpler.

[dweiller]

"it won't preclude using arbitrary logic" means that you have to read build.zig anyway.

Nothing can every get around this - the build runner runs an arbitrary function. The goal of the original idea (lazy fetching which I think is probably nice way to handle this) is to simplify this process and remove complexity from dependees don't need various optional/development dependencies by making a standard way to handle this.