fix(@angular/build): perform incremental background file updates with component updates

When HMR is enabled, a change to a lazy route component template may alter the
names of lazy chunks. These lazy chunks must be updated within the development
server so that any later non-HMR based update will have access to these chunks.
To support this, the incremental results from the build process can now emit
background file updates that will provide output file changes without triggering
client updates.

Author: clydin

packages/angular/build/src/builders/application/build-action.ts

@@ -264,6 +264,8 @@ function* emitOutputResults(
     const incrementalResult: IncrementalResult = {
       kind: ResultKind.Incremental,
       warnings: warnings as ResultMessage[],
+      // These files need to be updated in the dev server but should not signal any updates
+      background: hasTemplateUpdates,
       added: [],
       removed: [],
       modified: [],
@@ -281,13 +283,6 @@ function* emitOutputResults(
     for (const file of outputFiles) {
       removedOutputFiles.delete(file.path);
 
-      // Temporarily ignore JS files until Angular compiler plugin refactor to allow
-      // bypassing application code bundling for template affecting only changes.
-      // TODO: Remove once refactor is complete.
-      if (hasTemplateUpdates && /\.js(?:\.map)?$/.test(file.path)) {
-        continue;
-      }
-
       const previousHash = previousOutputInfo.get(file.path)?.hash;
       let needFile = false;
       if (previousHash === undefined) {

packages/angular/build/src/builders/application/results.ts

@@ -36,6 +36,7 @@ export interface FullResult extends BaseResult {
 
 export interface IncrementalResult extends BaseResult {
   kind: ResultKind.Incremental;
+  background?: boolean;
   added: string[];
   removed: { path: string; type: BuildOutputFileType }[];
   modified: string[];

packages/angular/build/src/builders/dev-server/vite-server.ts

@@ -217,6 +217,7 @@ export async function* serveWithVite(
       });
     }
 
+    let needClientUpdate = true;
     switch (result.kind) {
       case ResultKind.Full:
         if (result.detail?.['htmlIndexPath']) {
@@ -261,6 +262,9 @@ export async function* serveWithVite(
       case ResultKind.Incremental:
         assert(server, 'Builder must provide an initial full build before incremental results.');
 
+        // Background updates should only update server files/options
+        needClientUpdate = !result.background;
+
         for (const removed of result.removed) {
           const filePath = '/' + normalizePath(removed.path);
           generatedFiles.delete(filePath);
@@ -363,15 +367,17 @@ export async function* serveWithVite(
         ]),
       ];
 
-      await handleUpdate(
-        normalizePath,
-        generatedFiles,
-        assetFiles,
-        server,
-        serverOptions,
-        context.logger,
-        componentStyles,
-      );
+      if (needClientUpdate) {
+        await handleUpdate(
+          normalizePath,
+          generatedFiles,
+          assetFiles,
+          server,
+          serverOptions,
+          context.logger,
+          componentStyles,
+        );
+      }
     } else {
       const projectName = context.target?.project;
       if (!projectName) {