Introduction
Adoption tooling for upcoming features pitch proposed to extend the Swift compiler to add an integrated mechanism for producing source-compatible adjustments to code that can be applied to preserve its behavior once a given eligible upcoming feature is enabled.
To enable seemless migration experience for Swift packages, I'd like to propose a new Swift Package Manager command - swift migrate to complement the Swift compiler-side changes.
The command would accept one or more features that have migration mode enabled and optionally a set of targets to migrate, if no targets are specified the whole package is going to be migrated to use new features.
Interface
USAGE: swift migrate [<options>] --to-feature <to-feature> ...
OPTIONS:
--targets <targets> The targets to migrate to specified set of features or a new language mode.
--to-feature <to-feature>
The Swift language upcoming/experimental feature to migrate to.
-h, --help Show help information.
Use case
swift migrate --targets MyTarget,MyTest --to-feature ExistentialAny
This command would attempt to build MyTarget and MyTest targets with ExistentialAny:migrate feature flag, apply any fix-its associated with
the feature produced by the compiler, and update the Package.swift to
enable the feature(s) if both of the previous actions are successful:
.target(
name: "MyTarget",
...
swiftSettings: [
// ... existing settings,
.enableUpcomingFeature("ExistentialAny")
]
)
...
.testTarget(
name: "MyTest",
...
swiftSettings: [
// ... existing settings,
.enableUpcomingFeature("ExistentialAny")
]
)
In the "whole package" mode, every target is going to be updated to include
new feature flag(s). This is supported by the same functionality as swift package add-setting command.
If it's, for some reason, impossible to add the setting the diagnostic message would suggest what to add and where i.e. ...; please add '.enableUpcomingFeature("ExistentialAny")' to MyTarget target manually.
Impact on Interface
This proposal introduces a new command but does that does not interfere with existing commands. It follows the same pattern as swift build and swift test in a consistent manner.