perf(@ngtools/webpack): avoid full compiler lazy route analysis on JIT rebuilds

The deprecated lazy route string form requires code analysis prior to each build to locate any lazy routes and connect them with Webpack.
This change uses the previous fast but less accurate AST based lazy route discovery for JIT rebuilds. The first build will still perform a full Angular compiler analysis to ensure an accurate list of all initial deprecated string form lazy routes.

Author: clydin

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

@@ -16,6 +16,7 @@ import {
   NormalModuleReplacementPlugin,
   compilation,
 } from 'webpack';
+import { findLazyRoutes } from '../lazy_routes';
 import { NgccProcessor } from '../ngcc_processor';
 import { TypeScriptPathsPlugin } from '../paths-plugin';
 import { WebpackResourceLoader } from '../resource_loader';
@@ -229,7 +230,7 @@ export class AngularWebpackPlugin {
 
       // Create the file emitter used by the webpack loader
       const { fileEmitter, builder, internalFiles } = this.pluginOptions.jitMode
-        ? this.updateJitProgram(compilerOptions, rootNames, host, diagnosticsReporter)
+        ? this.updateJitProgram(compilerOptions, rootNames, host, diagnosticsReporter, changedFiles)
         : this.updateAotProgram(
             compilerOptions,
             rootNames,
@@ -523,6 +524,7 @@ export class AngularWebpackPlugin {
     rootNames: readonly string[],
     host: CompilerHost,
     diagnosticsReporter: DiagnosticsReporter,
+    changedFiles: Set<string> | undefined,
   ) {
     const builder = ts.createEmitAndSemanticDiagnosticsBuilderProgram(
       rootNames,
@@ -547,39 +549,61 @@ export class AngularWebpackPlugin {
 
     const transformers = createJitTransformers(builder, this.pluginOptions);
 
-    // Required to support asynchronous resource loading
-    // Must be done before listing lazy routes
-    // NOTE: This can be removed once support for the deprecated lazy route string format is removed
-    const angularProgram = new NgtscProgram(
-      rootNames,
-      compilerOptions,
-      host,
-      this.ngtscNextProgram,
-    );
-    const angularCompiler = angularProgram.compiler;
-    const pendingAnalysis = angularCompiler.analyzeAsync().then(() => {
-      for (const lazyRoute of angularCompiler.listLazyRoutes()) {
-        const [routeKey] = lazyRoute.route.split('#');
-        this.lazyRouteMap[routeKey] = lazyRoute.referencedModule.filePath;
+    // Only do a full, expensive Angular compiler string lazy route analysis on the first build
+    // `changedFiles` will be undefined on a first build
+    if (!changedFiles) {
+      // Required to support asynchronous resource loading
+      // Must be done before listing lazy routes
+      // NOTE: This can be removed once support for the deprecated lazy route string format is removed
+      const angularProgram = new NgtscProgram(
+        rootNames,
+        compilerOptions,
+        host,
+        this.ngtscNextProgram,
+      );
+      const angularCompiler = angularProgram.compiler;
+      const pendingAnalysis = angularCompiler.analyzeAsync().then(() => {
+        for (const lazyRoute of angularCompiler.listLazyRoutes()) {
+          const [routeKey] = lazyRoute.route.split('#');
+          this.lazyRouteMap[routeKey] = lazyRoute.referencedModule.filePath;
+        }
+
+        return this.createFileEmitter(builder, transformers, () => []);
+      });
+      const analyzingFileEmitter: FileEmitter = async (file) => {
+        const innerFileEmitter = await pendingAnalysis;
+
+        return innerFileEmitter(file);
+      };
+
+      if (this.watchMode) {
+        this.ngtscNextProgram = angularProgram;
       }
 
-      return this.createFileEmitter(builder, transformers, () => []);
-    });
-    const analyzingFileEmitter: FileEmitter = async (file) => {
-      const innerFileEmitter = await pendingAnalysis;
+      return {
+        fileEmitter: analyzingFileEmitter,
+        builder,
+        internalFiles: undefined,
+      };
+    } else {
+      // Update lazy route map for changed files using fast but less accurate method
+      for (const changedFile of changedFiles) {
+        if (!builder.getSourceFile(changedFile)) {
+          continue;
+        }
 
-      return innerFileEmitter(file);
-    };
+        const routes = findLazyRoutes(changedFile, host, builder.getProgram());
+        for (const [routeKey, filePath] of Object.entries(routes)) {
+          this.lazyRouteMap[routeKey] = filePath;
+        }
+      }
 
-    if (this.watchMode) {
-      this.ngtscNextProgram = angularProgram;
+      return {
+        fileEmitter: this.createFileEmitter(builder, transformers, () => []),
+        builder,
+        internalFiles: undefined,
+      };
     }
-
-    return {
-      fileEmitter: analyzingFileEmitter,
-      builder,
-      internalFiles: undefined,
-    };
   }
 
   private createFileEmitter(