Nondeterministic Zig Build with a Syscall

build.zig

const std = @import("std");

pub fn build(b: *std.Build) void {
    const target = b.standardTargetOptions(.{});

    const optimize = b.standardOptimizeOption(.{});

    var prng = std.Random.DefaultPrng.init(blk: {
        var seed: u64 = undefined;
        std.posix.getrandom(std.mem.asBytes(&seed)) catch @panic("syscall error");
        break :blk seed;
    });
    const rand = prng.random();
    const flip = rand.boolean();
    const options = b.addOptions();
    options.addOption(bool, "coin_flip", flip);

    const exe = b.addExecutable(.{
        .name = "nondeterminism",
        .root_source_file = b.path("src/main.zig"),
        .target = target,
        .optimize = optimize,
    });

    b.installArtifact(exe);
    exe.root_module.addOptions("config", options);

    const run_cmd = b.addRunArtifact(exe);
    // It does indeed... it does indeed
    run_cmd.has_side_effects = true;

    run_cmd.step.dependOn(b.getInstallStep());

    if (b.args) |args| {
        run_cmd.addArgs(args);
    }

    const run_step = b.step("run", "Run the app");
    run_step.dependOn(&run_cmd.step);

    const exe_unit_tests = b.addTest(.{
        .root_source_file = b.path("src/main.zig"),
        .target = target,
        .optimize = optimize,
    });

    const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);
    const test_step = b.step("test", "Run unit tests");
    test_step.dependOn(&run_exe_unit_tests.step);
}

main.zig

//! By convention, main.zig is where your main function lives in the case that
//! you are building an executable. If you are making a library, the convention
//! is to delete this file and start with root.zig instead.
const std = @import("std");
const config = @import("config");

fn testFlip(flip: bool, val: usize) bool {
    if (flip) {
        return val % 2 == 0;
    } else {
        return val % 2 == 1;
    }
}

fn isEvenOrOdd(val: usize) bool {
    return testFlip(config.coin_flip, val);
}

pub fn main() !void {
    if (isEvenOrOdd(5)) {
        std.debug.print("function tests oddness", .{});
    } else {
        std.debug.print("function tests evenness", .{});
    }
}