perf: improvement for webpack@5 (#406)

Sets don't allow duplicates, so checking for `has` is not necessary

webpack 5 makes these Sets lazy, which makes reading more expensive.
So only the watcher should read from these Sets, which is called after the compilation has finished,
so that doesn't contribute to build performance.

LazySets also have a `addAll` method, which allows to add an Iterable lazily (only iterated when LazySet is read)

src/index.js

@@ -98,28 +98,20 @@ class CopyPlugin {
     compiler.hooks.afterEmit.tapAsync(plugin, (compilation, callback) => {
       logger.debug('starting after-emit');
 
-      // Add file dependencies if they're not already tracked
-      for (const fileDependency of fileDependencies) {
-        if (compilation.fileDependencies.has(fileDependency)) {
-          logger.debug(
-            `not adding '${fileDependency}' to change tracking, because it's already tracked`
-          );
-        } else {
-          logger.debug(`adding '${fileDependency}' to change tracking`);
-
+      // Add file dependencies
+      if ("addAll" in compilation.fileDependencies) {
+        compilation.fileDependencies.addAll(fileDependencies);
+      } else {
+        for (const fileDependency of fileDependencies) {
           compilation.fileDependencies.add(fileDependency);
         }
       }
 
-      // Add context dependencies if they're not already tracked
-      for (const contextDependency of contextDependencies) {
-        if (compilation.contextDependencies.has(contextDependency)) {
-          logger.debug(
-            `not adding '${contextDependency}' to change tracking, because it's already tracked`
-          );
-        } else {
-          logger.debug(`adding '${contextDependency}' to change tracking`);
-
+      // Add context dependencies
+      if ("addAll" in compilation.contextDependencies) {
+        compilation.contextDependencies.addAll(contextDependencies);
+      } else {
+        for (const contextDependency of contextDependencies) {
           compilation.contextDependencies.add(contextDependency);
         }
       }