Dyanamic Dependencies for build.zig

build.zig

pub fn build(b: *Builder) !void {
    if (b.option(bool, "android", "build an android APK")) {
        if (@tryImport("androidbuild")) |androidbuild| {
            androidbuild.createManifest(.{ ... });
            androidbuild.setTarget(...);
            ...
        } else {
            b.needPackage("androidbuild");
        }
    }
}

zig-packages.json

{
    "git_repositories": {
        "android_sdk": {
            "url": "https://github.com/zig-community/android-zig-sdk",
            "branch": "1.0",
            "sha": "56c433bda1ccf726efcb9923d5537dc41fc738bc"
        }
    }

    "build_zig_dependnecies": [
        {
            "name": "androidbuild",
            "COMMENT": "NOTE: setting optional to true means this dependency will not be downloaded unless build.zig needs it",
            "optional": true,
            "source": {
                "kind": "git_repository",
                "name": "android_sdk",
                "file": "androidbuild.zig"
            }
        }
    ]
}

ZigBuildFlow.md

• Run zig build -Dandroid
• 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
• The package manager will look at zig-packages.json. It will see that build.zig has a dependency on the "androidbuild" package. However, it's marked as "optional" so it isn't downloaed yet.
• 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 importing "androidbuild" fails, 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 "androidbuild" package