Error: libSyntax(UnknownDecl)

[eXhausted]

I've cloned this repo and tried to use prettier swift plugin but but I ran into the error. Here is some info:

$ echo $TOOLCHAIN
swift-4.1-DEVELOPMENT-SNAPSHOT-2018-03-20-a.xctoolchain

$ echo $PRETTIER_SWIFT_SWIFTC
/Users/username/Library/Developer/Toolchains/swift-4.1-DEVELOPMENT-SNAPSHOT-2018-03-20-a.xctoolchain/usr/bin/swiftc

$ echo $PATH
/Users/username/Library/Developer/Toolchains/swift-4.1-DEVELOPMENT-SNAPSHOT-2018-03-20-a.xctoolchain/usr/bin/:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Applications/Wireshark.app/Contents/MacOS:/Users/username/Library/Android/sdk/platform-tools/:/Users/username/Library/Android/sdk/tools/

$ swift --version
Apple Swift version 4.1-dev (LLVM 260a172ffb, Clang cd84be6c42, Swift 04baf31321)
Target: x86_64-apple-darwin17.5.0

$ swiftc --version
Apple Swift version 4.1-dev (LLVM 260a172ffb, Clang cd84be6c42, Swift 04baf31321)
Target: x86_64-apple-darwin17.5.0

$ less accessors.swift
class A {
    func a() {
        return
    }
}
accessors.swift (END)

$ yarn prettier accessors.swift
yarn run v1.5.1
$ prettier --plugin=. --parser=swift accessors.swift

[error] accessors.swift: Error: libSyntax(UnknownDecl):⏎funca()⏎retur⏎⏎
[error]     at genericPrint (/Users/username/Development/Quest/plugin-swift/src/printer/generic.js:834:15)
[error]     at comments.printComments (/Users/username/Development/Quest/plugin-swift/src/printer/index.js:33:13)
[error]     at Object.printComments (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/main/comments.js:1051:19)
[error]     at Object.module.exports [as print] (/Users/username/Development/Quest/plugin-swift/src/printer/index.js:31:14)
[error]     at genericPrint (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/main/ast-to-doc.js:97:18)
[error]     at printGenerically (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/main/ast-to-doc.js:34:13)
[error]     at FastPath.map (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/common/fast-path.js:124:19)
[error]     at genericPrint (/Users/username/Development/Quest/plugin-swift/src/printer/generic.js:140:29)
[error]     at comments.printComments (/Users/username/Development/Quest/plugin-swift/src/printer/index.js:33:13)
[error]     at Object.printComments (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/main/comments.js:1051:19)
[error]     at Object.module.exports [as print] (/Users/username/Development/Quest/plugin-swift/src/printer/index.js:31:14)
[error]     at genericPrint (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/main/ast-to-doc.js:97:18)
[error]     at printGenerically (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/main/ast-to-doc.js:34:13)
[error]     at FastPath.map (/Users/username/Development/Quest/plugin-swift/node_modules/prettier/src/common/fast-path.js:124:19)
[error]     at genericPrint (/Users/username/Development/Quest/plugin-swift/src/printer/generic.js:341:21)
[error]     at comments.printComments (/Users/username/Development/Quest/plugin-swift/src/printer/index.js:33:13)
error An unexpected error occurred: "Command failed.
Exit code: 2
Command: sh
Arguments: -c prettier --plugin=. --parser=swift accessors.swift
Directory: /Users/username/Development/Quest/plugin-swift
Output:
".
info If you think this is a bug, please open a bug report with the information provided in "/Users/username/Development/Quest/plugin-swift/yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.