Unhelpful error messages when adding multi-lingual resources at a custom location

[yakovmanshin]

Description

I’m adding SwiftPM support to a CocoaPods framework. Currently, I have the following layout of the repo, and for backward compatibility, I can’t move files around.

Repo root/
|
|-- Sources/
|   |
|   |-- SourceFile.swift
|
|-- Resources/
|   |
|   |-- Assets.xcassets/
|   |
|   |-- en.lproj/
|   |   |
|   |   |-- Localizable.strings
|   |
|   |-- es.lproj/
|   |   |
|   |   |-- Localizable.strings        

Because of this layout, I have to manually point Package.swift to the resources.

When I use the resources: [.process("../Resources/")] parameter, package resolution seemingly succeeds. However, attempts to access Bundle.module in code result in a build-time error that reads:

Type 'Bundle' has no member 'module'

I also tried to fix this by creating a symbolic link (Sources/Resources → Resources) but this resulted in Xcode hung while resolving the package.

For debugging, I moved the resources to the expected location in Sources and removed the resources parameter from Package.swift. Now package resolution fails—but it tells the real reason Bundle.module was unavailable:

manifest property 'defaultLocalization' not set; it is required in the presence of localized resources

With the resources moved to the original location and the defaultLocalization parameter present in Package.swift, Bundle.module is now available.

Expected behavior

Package resolution fails, pointing to the actual reason resources were not resolved (no defaultLocalization specified). No building should be needed to find out about the error.

Actual behavior

Package resolution succeeds, but building the library doesn’t. The compiler output is confusing because package resolution doesn’t report any issues.

Steps to reproduce

No response

Swift Package Manager version/commit hash

Swift Package Manager - Swift 5.9.0

Swift & OS version (output of swift --version ; uname -a)

swift-driver version: 1.87.3 Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: x86_64-apple-macosx14.0

[MaxDesiatov]

Thank you for reporting this. Is the issue reproducible for you when using SwiftPM CLI tools like swift build or only in Xcode?

[yyvch]

I checked the reported issue.

A bit of background, that localization (l10n) uses bundled resources and rely on them. https://developer.apple.com/documentation/xcode/bundling-resources-with-a-swift-package#Access-a-resource-in-code gives a one-liner "When you build your Swift package, Xcode treats each target as a Swift module. If a target includes resources, Xcode creates a resource bundle and an internal static extension on Bundle to access it for each module.". This is important: if the resources are declared, then Swift Package Manager will generate a bundle accessor, and that bundle accessor will provide Bundle.module. If for any reason the resource bundle isn't recognized then Bundle.module won't exist and there will be a build error on compiling the code which uses Bundle.module, which is most likely a code that consumes translations.

Most of the l10n documentation implies that the resources structure is accurate. IMO, it's non-trivial to check if indeed the resources are defined and declared accurately without writing some kind of client code, and for the reasons above, and illustrated by the issue report, diagnostic messages aren't helpful.

My mitigation recommendation is to run swift package describe and compare what resources it shows vs what is expected path and resources. If the resources aren't shown or the path is not right, then you'll have to check the structure of the resources declaration.

I've prepared two demos which illustrate how it can be done:

• l10n_default_resources.zip a l10n demo with standard location of the l10n resources
• l10n_toplevel_resources.zip a l10n demo with top-level location of the l10n resources

% sh demo.sh 
+ swift package reset
+ swift build
Building for debugging...
[15/15] Applying runhello
Build complete! (39.42s)
+ .build/debug/runhello
Current locale is en
Current localization bundle: …/.build/arm64-apple-macosx/debug/lex_Hello.bundle/en.lproj
Hello, World!
+ LANG=ru_RU.UTF-8
+ .build/debug/runhello
Текущая локаль — ru
Текущий набор ресурсов для локализации — …/.build/arm64-apple-macosx/debug/lex_Hello.bundle/ru.lproj
Привет, мир