[Jiaxu-Li]

• Explanation:
  Prototype implementation of #if deploymentTargetAtLeast(...) for [Proposal] Deployment target conditional compilation swift-evolution#3478. This draft PR allows test toolchains to be built for the proposal review.

• Scope:
  Adds the experimental feature flag and implements the condition in the legacy parser and ASTGen paths. Includes platform and version checks, diagnostics, and tests. Companion SwiftSyntax prototype: Prototype: deployment target conditional compilation in SwiftSyntax swift-syntax#3450.

• Issues:
  Related proposal: [Proposal] Deployment target conditional compilation swift-evolution#3478

• Risk:
  The feature is opt-in. Platform-specific behavior needs validation with test toolchains.

• Testing:
  swift-frontend builds successfully. All three targeted deployment-target conditional-compilation tests pass.

[xwu]

swiftlang/swift-syntax#3450

@swift-ci Please build toolchain

[Jiaxu-Li]

Thanks for starting the toolchain builds. I’ve fixed the two Windows test failures in the latest commit. Could you rerun the toolchain builds on the updated branch?

[xwu]

swiftlang/swift-syntax#3450

@swift-ci Please build toolchain Windows platform

[xwu]

swiftlang/swift-syntax#3450

@swift-ci Please build toolchain Linux platform

[Jiaxu-Li]

Thanks for rerunning the builds. Linux is still failing on a network timeout. I’ve fixed the remaining Windows test issue. could you rerun the Windows build on the latest commit?

[xwu]

swiftlang/swift-syntax#3450

@swift-ci Please build toolchain Linux platform

[xwu]

Looks like the test failure isn't getting in the way of having a build artifact, so I think we can stop repeating the Windows build. Will run the Linux toolchain build again one more time.

[Jiaxu-Li]

The latest Linux build hit the same GitHub connection timeout. The macOS build passed, and Windows produced an artifact. Please let me know if you need anything else from me before the proposal moves to review. Thanks 😊.

[xwu]

Thanks, I think we've got as much as we're going to get. I'll get things ready to go soon from my end.