perf(@ngtools/webpack): reduce source file and Webpack module iteration

During a build, the number of iterations over both the TypeScript program's source files and Webpack's modules has been reduced. Both of these collections can contain a significant number of elements especially in larger applications.

Author: clydin

packages/ngtools/webpack/src/ivy/plugin.ts

@@ -258,14 +258,23 @@ export class AngularWebpackPlugin {
             resourceLoader,
           );
 
-      const allProgramFiles = builder
-        .getSourceFiles()
-        .filter((sourceFile) => !internalFiles?.has(sourceFile));
+      // Set of files used during the unused TypeScript file analysis
+      const currentUnused = new Set<string>();
 
-      // Ensure all program files are considered part of the compilation and will be watched
-      allProgramFiles.forEach((sourceFile) =>
-        compilation.fileDependencies.add(sourceFile.fileName),
-      );
+      for (const sourceFile of builder.getSourceFiles()) {
+        if (internalFiles?.has(sourceFile)) {
+          continue;
+        }
+
+        // Ensure all program files are considered part of the compilation and will be watched
+        compilation.fileDependencies.add(sourceFile.fileName);
+
+        // Add all non-declaration files to the initial set of unused files. The set will be
+        // analyzed and pruned after all Webpack modules are finished building.
+        if (!sourceFile.isDeclarationFile) {
+          currentUnused.add(normalizePath(sourceFile.fileName));
+        }
+      }
 
       compilation.hooks.finishModules.tapPromise(PLUGIN_NAME, async (modules) => {
         // Rebuild any remaining AOT required modules
@@ -279,16 +288,13 @@ export class AngularWebpackPlugin {
           return;
         }
 
-        const currentUnused = new Set(
-          allProgramFiles
-            .filter((sourceFile) => !sourceFile.isDeclarationFile)
-            .map((sourceFile) => normalizePath(sourceFile.fileName)),
-        );
-        Array.from(modules).forEach(({ resource }: Module & { resource?: string }) => {
+        for (const webpackModule of modules) {
+          const resource = (webpackModule as NormalModule).resource;
           if (resource) {
             this.markResourceUsed(normalizePath(resource), currentUnused);
           }
-        });
+        }
+
         for (const unused of currentUnused) {
           if (previousUnused && previousUnused.has(unused)) {
             continue;