[swift2objc] Support closures

[liamappelbe]

Support functions and methods that accept and return closures:

class Foo {
  func bar(callback: (Int) -> Int) {
    // ...
  }
}

[nikeokoronkwo]

Closure parsing via swiftc doesn't work or isn't as clear as it is for other types in Swift. Same goes for tuples (which makes picking out closures much more difficult)

For the given variables:

// tuple
public var myTuple = (9)

// closure
public var myClosure = { (o: Int) -> Int in return 9 }

swiftc generates the following symbol graph for them

{
  "kind": {
      "identifier": "swift.var",
      "displayName": "Global Variable"
  },
  "identifier": {
      "precise": "s:28primitive_symbolgraph_module7myTupleSivp",
      "interfaceLanguage": "swift"
  },
  "pathComponents": [
      "myTuple"
  ],
  "names": {
      "title": "myTuple",
      "subHeading": [
          {
              "kind": "keyword",
              "spelling": "var"
          },
          {
              "kind": "text",
              "spelling": " "
          },
          {
              "kind": "identifier",
              "spelling": "myTuple"
          },
          {
              "kind": "text",
              "spelling": ": ("
          },
          {
              "kind": "typeIdentifier",
              "spelling": "Int",
              "preciseIdentifier": "s:Si"
          },
          {
              "kind": "text",
              "spelling": ")"
          }
      ]
  },
  "declarationFragments": [
      {
          "kind": "keyword",
          "spelling": "var"
      },
      {
          "kind": "text",
          "spelling": " "
      },
      {
          "kind": "identifier",
          "spelling": "myTuple"
      },
      {
          "kind": "text",
          "spelling": ": ("
      },
      {
          "kind": "typeIdentifier",
          "spelling": "Int",
          "preciseIdentifier": "s:Si"
      },
      {
          "kind": "text",
          "spelling": ")"
      }
  ],
  "accessLevel": "public",
  "location": {
      "uri": "file://types.swift",
      "position": {
          "line": 23,
          "character": 11
      }
  }
},
{
  "kind": {
      "identifier": "swift.var",
      "displayName": "Global Variable"
  },
  "identifier": {
      "precise": "s:28primitive_symbolgraph_module9myClosureyS2icvp",
      "interfaceLanguage": "swift"
  },
  "pathComponents": [
      "myClosure"
  ],
  "names": {
      "title": "myClosure",
      "subHeading": [
          {
              "kind": "keyword",
              "spelling": "var"
          },
          {
              "kind": "text",
              "spelling": " "
          },
          {
              "kind": "identifier",
              "spelling": "myClosure"
          },
          {
              "kind": "text",
              "spelling": ": ("
          },
          {
              "kind": "typeIdentifier",
              "spelling": "Int",
              "preciseIdentifier": "s:Si"
          },
          {
              "kind": "text",
              "spelling": ") -> "
          },
          {
              "kind": "typeIdentifier",
              "spelling": "Int",
              "preciseIdentifier": "s:Si"
          }
      ]
  },
  "declarationFragments": [
      {
          "kind": "keyword",
          "spelling": "var"
      },
      {
          "kind": "text",
          "spelling": " "
      },
      {
          "kind": "identifier",
          "spelling": "myClosure"
      },
      {
          "kind": "text",
          "spelling": ": ("
      },
      {
          "kind": "typeIdentifier",
          "spelling": "Int",
          "preciseIdentifier": "s:Si"
      },
      {
          "kind": "text",
          "spelling": ") -> "
      },
      {
          "kind": "typeIdentifier",
          "spelling": "Int",
          "preciseIdentifier": "s:Si"
      }
  ],
  "accessLevel": "public",
  "location": {
      "uri": "file://types.swift",
      "position": {
          "line": 26,
          "character": 11
      }
  }
}

Apparently, it doesn't play so well with types containing characters other than literal characters (i.e symbols).

[liamappelbe]

Ok. Looks like we'll have to write a bit of custom parsing logic for this.