# Make a local copy of the substitutions.
config.substitutions = list(config.substitutions)

swift_build_sdk_interfaces = (r'env SWIFT_EXEC=%%swiftc_driver_plain %r '
                              r'%%utils/swift_build_sdk_interfaces.py '
                              r'%%mcp_opt' %
                              (sys.executable,))
config.substitutions.insert(0, ('%swift_build_sdk_interfaces',
                                swift_build_sdk_interfaces))

config.suffixes.add('.py')