Ignore additional top-level directories (#241)

* Ignore additional top-level directories

* Incorporate @Lukas-Stuehrk's feedback from review

Author: mattt

Sources/SwiftDoc/Module.swift

@@ -22,27 +22,31 @@ public final class Module {
         let fileManager = FileManager.default
         for path in paths {
             let directory = URL(fileURLWithPath: path)
-            guard let directoryEnumerator = fileManager.enumerator(at: directory, includingPropertiesForKeys: [.isDirectoryKey], options: [.skipsHiddenFiles, .skipsPackageDescendants]) else { continue }
+            guard let directoryEnumerator = fileManager.enumerator(at: directory,
+                                                                   includingPropertiesForKeys: [.isDirectoryKey],
+                                                                   options: [.skipsHiddenFiles, .skipsPackageDescendants])
+            else { continue }
+
+            let ignoredDirectories: Set<URL> = Set([
+                "node_modules",
+                "Packages",
+                "Pods",
+                "Resources",
+                "Tests"
+            ].map { directory.appendingPathComponent($0) })
+
             for case let url as URL in directoryEnumerator {
-                var isDirectory: ObjCBool = false
                 guard url.pathExtension == "swift",
-                    fileManager.isReadableFile(atPath: url.path),
-                    fileManager.fileExists(atPath: url.path, isDirectory: &isDirectory)
+                      fileManager.isReadableFile(atPath: url.path)
                 else {
-                    // Skip top-level Tests directory
-                    if isDirectory.boolValue == true,
-                       url.lastPathComponent == "Tests",
-                       directory.appendingPathComponent("Tests").path == url.path
-                    {
+                    if ignoredDirectories.contains(url) {
                         directoryEnumerator.skipDescendants()
                     }
 
                     continue
                 }
 
-                if isDirectory.boolValue == false {
-                    sources.append((url, directory))
-                }
+                sources.append((url, directory))
             }
         }