Added a command line option to specify a path to lint

[larslockefeer]

This pull request adds a command-line option to specify an (absolute or relative) path to a file or directory to lint.

This enables use cases such as:

• Linting only the file that you are currently working on
• Linting only modified files in an Xcode Run Script build phase
• Linting modified files as a pre-commit hook

Usage examples:

• swiftlint lint --path Source/swiftlint/LintCommand.swift
• swiftlint lint --path Source/SwiftLintFramework

This PR relates to issues #6, #16 and #20

[jpsim]

Thanks for the PR, @larslockefeer! This is definitely on the right track, but needs a bit of work:

1. Please run SwiftLint on LintCommand.swift itself, as a number of your additions are causing violations. I'll be sure to add this to our CONTRIBUTING.md document once we add one :).
2. Please add a single newline at the end of the file. We have a SwiftLint rule for this, but it's not working at the moment (see TrailingNewlineRule.swift doesn't seem to work #43).
3. I'd rather you used NSString.absolutePathRepresentation(rootDirectory:) which is already available in SourceKittenFramework, or at least NSString.absolutePath rather than combining path to currentDirectoryPath

Otherwise, I have a few minor comments that I'll add inline to your PR now.

Again, thanks for doing this!

[jpsim]

theff should be the

[larslockefeer]

Thanks for the feedback @jpsim!

I have processed your comments and synced with the upstream again.

I have discovered one additional issue after syncing with the upstream: files are now linted twice. I suspect that it is due to fileManager.allFilesRecursively yielding both contentsOfDirectoryAtPath and subpathsOfDirectoryAtPath but I haven't looked into that in detail yet.

Also, I see that the tests failed. On my machine, they ran fine so this could be an issue with Travis. I see the following error in their console output:

The command "script/cibuild" exited with 2.

[segiddins]

Failure looks unrelated, I restarted the build.

[jpsim]

Seems like this function could be simplified:

func filesToLintAtPath(path: String) -> [String] {
    let absolutePath = path.absolutePathRepresentation()
    var isDirectory: ObjCBool = false
    if fileManager.fileExistsAtPath(absolutePath, isDirectory: &isDirectory) {
        if isDirectory {
            return fileManager.allFilesRecursively(directory: absolutePath).filter {
                $0.isSwiftFile()
            }
        } else if standardizedPath.isSwiftFile() {
            return [standardizedPath]
        }
    }
    return []
 }

[jpsim]

This is great, @larslockefeer. My final comment is about perhaps simplifying filesToLintAtPath(_:). It would also be great if you could add an entry to CHANGELOG.md. Thanks for this.

[larslockefeer]

Thanks again @jpsim, I have processed your feedback.

[jpsim]

Hurray! Great work.