The package product 'MyLibrary' cannot be used as a dependency of this target because it uses unsafe build flags

Question

I'm trying to add SPM support for my library. I need to define unsafeFlags for one of my library's targets (In order to import Swift code into Objective-C++):

.target(name: "MyLibrary",
        dependencies: ["MyOtherTarget"],
        cSettings: [
            .unsafeFlags(["-fmodules", "-fcxx-modules"]),
            .define("BUILDING_FOR_SPM")
        ]
),

The resulting package builds. But when I import it into a host app, it fails to build because

The package product 'MyLibrary' cannot be used as a dependency of this target because it uses unsafe build flags.

According to this post and the corresponding pull request, the issue was addressed in Swift 4. I'm using Xcode 12.5 and Swift 5.

So what's going on?

Paul Beusterien · Accepted Answer · 2021-06-09 00:06:23Z

9

.unsafeFlags are not allowed for dependencies specified with a version. The workaround is to specify the version with a commit hash.

Detailed discussion and another workaround for monorepos at https://forums.swift.org/t/override-for-unsafeflags-in-swift-package-manager/45273

answered Jun 9, 2021 at 0:06

Paul Beusterien

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OhadM Over a year ago

Worth mentioning that you should clean the project before recompiling again with the commit hash option.

Surpher · Accepted Answer · 2023-08-01 12:46:48Z

2

Just had the same issue where our own package was failing to resolve:

xcodebuild: error: Could not resolve package dependencies:
the target '_a_target_A' in product '_a_product' contains unsafe build flags
the target '_a_target_B' in product '_a_product' contains unsafe build flags

The solution was to define the exact revision of the package to pull in:

.package(
  url: "https://[email protected]/.../OurProject/_git/OurOwnPackageName",
  revision: ".....complete_hash_of_version_commit......"
)

answered Aug 1, 2023 at 12:46

Surpher

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