Custom step in build.zig

build.zig

const std = @import("std");
const Builder = std.build.Builder;
const Step = std.build.Step;

pub fn build(b: *Builder) void {
    const target = b.standardTargetOptions(.{});
    const mode = b.standardReleaseOptions();

    const exe = b.addExecutable("hw", "hw.zig");
    exe.setTarget(target);
    exe.setBuildMode(mode);
    exe.install();

    var my_build = b.allocator.create(MyBuildStep) catch unreachable;
    my_build.* = MyBuildStep.init(b.allocator, 15);
    my_build.step.dependOn(&exe.step);
    
    b.default_step.dependOn(&my_build.step);
}

const MyBuildStep = struct {
    step: Step,
    some_variable: i32,

    pub fn init(allocator: *std.mem.Allocator, some_variable: i32) MyBuildStep {
        return .{
            .step = Step.init("my build", allocator, MyBuildStep.doStep),
            .some_variable = some_variable,
        };
    }
    
    pub fn doStep(step: *Step) anyerror!void {
        const self = @fieldParentPtr(MyBuildStep, "step", step);

        // self is a MyBuildStep.
        // Do something with self.some_variable.
    }
};