Add ImplicitGetterRule

[marcelofabri]

Partially fixes #57

It seems that SourceKit doesn't provide information on subscript, which is weird because there is a FunctionSubscript case on SyntaxKind.

struct Thing {

    subscript(index: Int) -> Int {
      return 2
    }
}

sourcekitten structure --file file.swift

{
  "key.substructure" : [
    {
      "key.kind" : "source.lang.swift.decl.struct",
      "key.offset" : 0,
      "key.nameoffset" : 7,
      "key.namelength" : 5,
      "key.bodyoffset" : 14,
      "key.bodylength" : 58,
      "key.accessibility" : "source.lang.swift.accessibility.internal",
      "key.substructure" : [
        {
          "key.kind" : "source.lang.swift.decl.var.parameter",
          "key.offset" : 30,
          "key.nameoffset" : 0,
          "key.namelength" : 0,
          "key.length" : 10,
          "key.typename" : "Int",
          "key.name" : "index"
        }
      ],
      "key.name" : "Thing",
      "key.length" : 73
    }
  ],
  "key.offset" : 0,
  "key.diagnostic_stage" : "source.diagnostic.stage.swift.parse",
  "key.length" : 74
}

[codecov-io]

Current coverage is 85.84% (diff: 97.18%)

No coverage report found for master at 1b82909.

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[norio-nomura]

False positive pattern with local scoped type:

class Foo {
  var foo: Int {
    struct Bar {
      var bar: Int {
        get { return 1 } // violation produced on this line
        set { _ = newValue }
      }
    }
    return Bar().bar
  }
}

[marcelofabri]

Nice catch! Do you have any tips on how to deal with this?

[norio-nomura]

If I need to write this rule, I guess I would do:

1. Search keyword get from SyntaxMap
2. Search deepest structure containing the get, like as Structure.kindsFor(_:)
3. Check condition of the structure for violation

The key of avoiding false positive is 2.
I guess 1 would be faster than using ASTRule.

[marcelofabri]

I'm not a fan of breaking line here, but I couldn't think of other ways to respect the 100 length limit 😬

[marcelofabri]

Sorry for taking to take a look at this, but I've implemented your suggestion on 772e702, @norio-nomura. Thanks again 🙌

[jpsim]

Awesome work! 🎉

[frank61003]

My project can run in my old Macbook Pro but show the error in my new Mac mini. I check my Xcode(11.4.1) and swift version(4.2) are all the same. how to solve this issue? I use cocoa pod to install swiftlint and the version is 0.27. (pod 'SwiftLint', '0.27'). I check the document many times but still can't find the answer.

https://stackoverflow.com/questions/61947496/how-to-slove-implicit-getter-violation-computed-read-only-subscripts-should-avo