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faq.md

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Frequently Asked Questions (FAQ)

Table of Contents

Does this replace [rules_spm]?

Yes. There are some limitations with the rules_spm implementation. After receiving feedback and suggestions from the community, we opted to create a clean sheet implementation which includes new features and improvements:

  • Bazel build file generation for the primary workspace.
  • Build the external dependencies with rules_swift.
  • Pin the exact versions for the direct and transitive dependencies.

Where is the Swift gazelle plugin?

It has moved to https://github.com/cgrindel/swift_gazelle_plugin.

After running //:swift_update_pkgs, I see a .build directory. What is it? Do I need it?

The //:swift_update_pkgs target runs the Gazelle plugin in update-repos mode. This mode resolves the external dependencies listed in your Package.swift by running Swift package manager commands. These commands result in a .build directory being created. The directory is a side effect of running the Swift package manager commands. It can be ignored and should not be checked into source control. It is not used by the Gazelle plugin or the Starlark repository rules.

Can I store the Swift dependency files in a sub-package (i.e., not in the root of the workspace)?

Yes. The vapor example demonstrates storing the Swift dependency files in a sub-package called swift.

How do I handle the error Unable to resolve byName reference XXX in @swiftpkg_yyy.?

tl;dr A transitive dependency uses a by-name product reference format that was deprecated in Swift 5.2. You need to patch the Swift package to use a more explicit product reference.

How do I fix this issue?

Patch the Swift package to use a fully-qualified product reference.

Let's look at an example. At the time of this writing, the pusher-websocket-swift Package.swift refers to the TweetNacl product in the tweetnacl-swiftwrap package using just the name of the product.

// Parts of the definition have been omitted for brevity.
let package = Package(
    name: "PusherSwift",
    dependencies: [
        .package(url: "https://github.com/pusher/NWWebSocket.git", .upToNextMajor(from: "0.5.4")),
        .package(url: "https://github.com/bitmark-inc/tweetnacl-swiftwrap", .upToNextMajor(from: "1.0.0")),
    ],
    targets: [
        .target(
            name: "PusherSwift",
            dependencies: [
                "NWWebSocket",
                "TweetNacl",   // <=== byName reference to product in tweetnacl-swiftwrap
            ],
            path: "Sources"
        ),
    ],
)

To make this work with rules_swift_package_manager, you need to patch this file so that the reference is the following:

        .target(
            name: "PusherSwift",
            dependencies: [
                "NWWebSocket",
                .product(name: "TweetNacl", package: "tweetnacl-swiftwrap"),  // <=== Explicit ref
            ],
            path: "Sources"
        ),

What is the cause of the error? Why can't rules_swift_package_manager handle this situation?

This specific case is the reason that previous versions of rules_swift_package_manager pre-processed the transitive Swift dependencies using the Gazelle plugin’s update-repos action and stored the results in a JSON file that was checked into source control.

Here is a quick explainer of why rules_swift_package_manager cannot resolve this dependency with the new architecture:

  • Each Swift package is declared as an external Bazel repository.
  • During the loading phase, there is no mechanism for one external repository to peek into another external repository. In other words, a Swift package cannot query another Swift package to determine all of the available products.
  • So, when rules_swift_package_manager generates a BUILD.bazel file for a Swift package external repo, it only has the information that is returned by calling swift package description and swift package dump-package. The output from these calls only provides the identity and the type of the Swift package (e.g., remote, file system).
  • As a result, byName lookups can only be resolved to the targets/products in the current package and to products in Swift packages where the identity exactly matches the product name.