build.zig

const buildpkgs = @import("buildpkgs");

pub fn build(b: *Builder) !void {
    if (b.option(bool, "android", "build an android APK")) {
        // note: this hasImport function is comptime
        if (buildpkgs.hasPackage("androidbuild")) {
            const androidbuild = @import("androidbuild");
            androidbuild.createManifest(.{ ... });
            androidbuild.setTarget(...);
            ...
        } else {
            b.needPackage("androidbuild");
        }
    }
}

ZigBuildFlow.md

• Run zig build -Dandroid
• Zig generates the "buildpkgs" module with a list of the packages that are available

buildpkgs.zig

pub fn hasPackage(comptime name: []const u8) bool {
    return false;
}

• build.zig gets compiled
• the resulting build executable is executed
• build_runner.zig detects that there is a "needPackage" configured so it prints this error:

$ zig build -Dandroid
error: build.zig is missing needed package "androidbuild"

ZigPackageManagerFlow.md

• Run the package manager with the "android" build option enabled
• Zig generates the "buildpkgs" module with a list of the packages that are available

buildpkgs.zig

pub fn hasPackage(comptime name: []const u8) bool {
    return false;
}

• build.zig gets compiled
• the resulting build executable gets executed with the option "--get-needed-packages"
• the build.zig executable sees that "android" is enabled, but hasPackage("androidbuild") returns false, so it lists "androidbuild" as a needed package
• the package manager now downloads the android_sdk repository to retrieve the androidbuild package for build.zig
• build.zig gets compiled a second time, this time with the following buildpkgs module:

buildpkgs.zig

pub fn hasPackage(comptime name: []const u8) bool {
    if (std.mem.eql(u8, name, "androidbuild") return true;
    return false;
}