Adopt MemberImportVisibility

[plemarquand]

Adopt the experimental feature MemberImportVisibility.

Motivation:

Due to a weakness in the existing Swift language implementation, a public extension declared in a library module can be accessible to source code that doesn’t directly import that module.

Modifications:

Adopt MemberImportVisibility on all targets and adjust imports to be explicit. There were a few places where ambiguities were exposed. The most apparent one is the ambiguity between Basics.AbsolutePath and TSCBasics.AbsolutePath. In this case they're functionally equivalent since the Basics version just type aliases the TSCBasics version. There were a few others where identically named methods were defined in both a SwiftPM module and an imported dependency.

Result:

SwiftPM compiles with no code included without a corresponding explicit import.

[plemarquand]

@swift-ci test

[jakepetroules]

Thanks!

Can I ask you to factor the enableExperimentalFeature("MemberImportVisibility") statements into a common swiftSettings array at the top of the package, though, as in Swift Build?

We'll want to add more of these over time, and it's much easier if we can apply to the whole package at once without having to copy-paste 20 times.

[plemarquand]

Looks like there is a compile failure on macOS when adopting this feature on 6.0.3. Bisected it down to adding MemberImportVisibility to the Basics target. Going to have to dig deeper to see if this is something we can work around.

[plemarquand]

@swift-ci please test windows platform

[cmcgee1024]

The changes look good to me, and this change can make unexpected usages much more apparent moving forward.

I've added a question and one other comment, nothing blocking.

[plemarquand]

@swift-ci please test windows

[plemarquand]

@swift-ci test windows

[bkhouri]

I very much favour this change to make import more explicit.

My primary concern is posted as a comment in Package.swift.

[bkhouri]

question: should we be using swift6CompatibleExperimentalFeatures instead of commonExperimentalFeatures in the event a developer is using Swift 6.0.x to build the project?

[plemarquand]

We want these to apply to any toolchain. The swift6CompatibleExperimentalFeatures var only exists for targets that currently fail to build with MemberImportVisibility on in 6.0.3.

[bkhouri]

Do we understand why those targets fail to build on 6.0.3? Can we raise an issue to ensure we get this addressed?

[plemarquand]

They don't fail on 6.1, so my assumption is it's already fixed.