Build error with Swift 4.2.1

What did you do?

Building 4.3.0 with Carthage

swift --version
Apple Swift version 4.2.1 (swiftlang-1000.11.42 clang-1000.11.45.1)

What did you expect to happen?

Successful build

What actually happened instead?

Build failed with

Build settings from command line:
    CARTHAGE = YES
    CLANG_ENABLE_CODE_COVERAGE = NO
    CODE_SIGN_IDENTITY = 
    CODE_SIGNING_REQUIRED = NO
    GCC_INSTRUMENT_PROGRAM_FLOW_ARCS = NO
    ONLY_ACTIVE_ARCH = NO
    SDKROOT = iphoneos12.1
    SKIP_INSTALL = YES
    STRIP_INSTALLED_PRODUCT = NO

note: Using new build system
note: Planning build
note: Constructing build description
Build system information
error: SWIFT_VERSION '5.0' is unsupported, supported versions are: 3.0, 4.0, 4.2. (in target 'SwiftyJSON iOS')

Build system information
error: SWIFT_VERSION '5.0' is unsupported, supported versions are: 3.0, 4.0, 4.2. (in target 'SwiftyJSON iOS')

Environment

• Carthage: 0.32

Project that demonstrates the issue

Any, Add Cartfile and try to build

Reproduce the failure by building version 4.3.0 with Carthage using Apple Swift 4.2.1 and the shown iOS SDK settings. Inspect the project’s build configuration for the SwiftyJSON iOS target; done means the Carthage build completes with a Swift version supported by the installed toolchain.