Include directory suffixed with .swift causes doc command to fail

[1ec5]

The Mapbox Navigation SDK for iOS runs jazzy passing in this podspec as --podspec. Among the errors we’re working through in mapbox/mapbox-navigation-ios#1795 is this one caused by the dependency on the MapboxDirections.swift pod:

Could not read contents of `/var/folders/cl/8cgpg37n5cl78pjkbpgml94w0000gn/T/jazzy20190128-87912-1r7txvvMapboxNavigation-Documentation/build/Release-iphoneos/MapboxDirections.swift`
Could not parse `MapboxDirections.swift`. Please open an issue at https://github.com/jpsim/SourceKitten/issues with the file contents.

CocoaPods places the pod’s downloaded framework inside a MapboxDirections.swift directory. jazzy passes the framework root’s path to xcodebuild as an include directory (-I). But the “.swift” suffix in the directory name causes SourceKitten to detect the folder as a Swift file:

SourceKitten/Source/SourceKittenFramework/String+SourceKitten.swift

Lines 453 to 455 in 4a0f386

	public func isSwiftFile() -> Bool {
	return pathExtension == "swift"
	}

So then sourcekitten doc fails because Module.docs thinks it needs to parse a “MapboxDirections.swift” file for documentation:

SourceKitten/Source/SourceKittenFramework/Module.swift

Line 81 in 4a0f386

self.init(name: moduleName, compilerArguments: arguments)

SourceKitten/Source/SourceKittenFramework/File.swift

Lines 64 to 69 in 4a0f386

	do {
	_contents = try String(contentsOfFile: path, encoding: .utf8)
	} catch {
	fputs("Could not read contents of `\(path)`\n", stderr)
	return nil
	}

/cc @JThramer

[jpsim]

I think isSwiftFile is a red herring, since the only place where it's used in SourceKitten is here: https://github.com/jpsim/SourceKitten/blob/0.22.0/Source/SourceKittenFramework/Module.swift#L120

And that also validates that it's a file and not a directory.

sourceFiles = compilerArguments.filter({
    $0.bridge().isSwiftFile() && $0.isFile
}).map {
    return URL(fileURLWithPath: $0).resolvingSymlinksInPath().path
}

[jpsim]

Oops, you were right, the isFile helper is incorrect and also returns true for directories. Your fix at #575 looks good at a glance, we just have to figure out why it's failing CI.