refactor(@angular/build): extract shared breadth-first initial file analysis

Previously, both `BundlerContext` and `optimizeChunks` maintained separate implementations for
discovering transitive initial files and calculating their import depths from the esbuild
metafile. Both implementations used a depth-first stack traversal via `Array.prototype.pop()`,
which visited deeper branches in reverse import order and failed to propagate updated minimum
depths to the transitive dependencies of already-visited chunks in diamond dependency graphs.

This commit extracts a shared `findTransitiveInitialFiles` helper that uses a breadth-first
queue traversal over direct static imports. Processing chunks in breadth-first order guarantees
that each file is discovered at its true shortest import depth on first visit, preserves the
natural declaration order of imports at each depth level, and eliminates the duplicated
metafile traversal logic across initial bundling and chunk optimization.

Author: clydin

packages/angular/build/src/builders/application/chunk-optimizer.ts

@@ -24,8 +24,8 @@ import { BundleMergedContextResult } from '../../tools/esbuild/bundler-context';
 import {
   type BuildOutputFile,
   BuildOutputFileType,
-  type InitialFileRecord,
   createOutputFile,
+  findTransitiveInitialFiles,
 } from '../../tools/esbuild/bundler-files';
 import { useRolldownChunks } from '../../utils/environment-options';
 import { assertIsError } from '../../utils/error';
@@ -166,21 +166,6 @@ function bundleOutputToEsbuildMetafile(
   return newMetafile;
 }
 
-/**
- * Creates an InitialFileRecord object with a specified depth.
- * @param depth The depth of the file in the dependency graph.
- * @returns An InitialFileRecord object.
- */
-function createInitialFileRecord(depth: number): InitialFileRecord {
-  return {
-    type: 'script',
-    entrypoint: false,
-    external: false,
-    serverFile: false,
-    depth,
-  };
-}
-
 /**
  * Creates an esbuild message object for a chunk optimization failure.
  * @param message The error message detailing the cause of the failure.
@@ -369,14 +354,11 @@ export async function optimizeChunks(
   );
 
   // Add new optimized chunks
-  const importsPerFile: Record<string, string[]> = {};
   for (const optimizedFile of optimizedOutput) {
     if (optimizedFile.type !== 'chunk') {
       continue;
     }
 
-    importsPerFile[optimizedFile.fileName] = optimizedFile.imports;
-
     original.outputFiles.push(
       createOutputFile(optimizedFile.fileName, optimizedFile.code, BuildOutputFileType.Browser),
     );
@@ -392,41 +374,17 @@ export async function optimizeChunks(
   }
 
   // Update initial files to reflect optimized chunks
-  const entriesToAnalyze: [string, InitialFileRecord][] = [];
   for (const usedFile of usedChunks) {
     // Leave the main file since its information did not change
-    if (usedFile === mainFile) {
-      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-      entriesToAnalyze.push([mainFile, original.initialFiles.get(mainFile)!]);
-      continue;
+    if (usedFile !== mainFile) {
+      original.initialFiles.delete(usedFile);
     }
-
-    // Remove all other used chunks
-    original.initialFiles.delete(usedFile);
   }
 
   // Analyze for transitive initial files
-  let currentEntry;
-  while ((currentEntry = entriesToAnalyze.pop())) {
-    const [entryPath, entryRecord] = currentEntry;
-
-    for (const importPath of importsPerFile[entryPath]) {
-      const existingRecord = original.initialFiles.get(importPath);
-      if (existingRecord) {
-        // Store the smallest value depth
-        if (existingRecord.depth > entryRecord.depth + 1) {
-          existingRecord.depth = entryRecord.depth + 1;
-        }
-
-        continue;
-      }
-
-      const record = createInitialFileRecord(entryRecord.depth + 1);
-
-      original.initialFiles.set(importPath, record);
-      entriesToAnalyze.push([importPath, record]);
-    }
-  }
+  const mainRecord = original.initialFiles.get(mainFile);
+  assert(mainRecord, `Main file record should always be present in initialFiles [${mainFile}].`);
+  findTransitiveInitialFiles(newMetafile, original.initialFiles, [[mainFile, mainRecord]]);
 
   return original;
 }

packages/angular/build/src/tools/esbuild/bundler-context.ts

@@ -24,6 +24,7 @@ import {
   BuildOutputFileType,
   type InitialFileRecord,
   convertOutputFile,
+  findTransitiveInitialFiles,
 } from './bundler-files';
 import { LoadResultCache, MemoryLoadResultCache } from './load-result-cache';
 
@@ -363,41 +364,7 @@ export class BundlerContext {
     }
 
     // Analyze for transitive initial files
-    const entriesToAnalyze = [...initialFiles];
-    let currentEntry;
-    while ((currentEntry = entriesToAnalyze.pop())) {
-      const [entryPath, entryRecord] = currentEntry;
-
-      for (const initialImport of result.metafile.outputs[entryPath].imports) {
-        const existingRecord = initialFiles.get(initialImport.path);
-        if (existingRecord) {
-          // Store the smallest value depth
-          if (existingRecord.depth > entryRecord.depth + 1) {
-            existingRecord.depth = entryRecord.depth + 1;
-          }
-
-          continue;
-        }
-
-        if (initialImport.kind === 'import-statement' || initialImport.kind === 'import-rule') {
-          const record: InitialFileRecord = {
-            type: initialImport.kind === 'import-rule' ? 'style' : 'script',
-            entrypoint: false,
-            external: initialImport.external,
-            serverFile: isPlatformServer,
-            depth: entryRecord.depth + 1,
-          };
-
-          if (!this.initialFilter || this.initialFilter(record)) {
-            initialFiles.set(initialImport.path, record);
-          }
-
-          if (!initialImport.external) {
-            entriesToAnalyze.push([initialImport.path, record]);
-          }
-        }
-      }
-    }
+    findTransitiveInitialFiles(result.metafile, initialFiles, undefined, this.initialFilter);
 
     // Collect all external package names
     const externalImports = new Set<string>();

packages/angular/build/src/tools/esbuild/bundler-files.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import type { OutputFile } from 'esbuild';
+import type { Metafile, OutputFile } from 'esbuild';
 import { calculateHash } from '../../utils/hash';
 
 export interface InitialFileRecord {
@@ -18,6 +18,54 @@ export interface InitialFileRecord {
   depth: number;
 }
 
+/**
+ * Analyzes a metafile to find and record all transitive initial files starting from the given
+ * initial entries using breadth-first traversal so each file is recorded at its minimum depth.
+ *
+ * @param metafile The esbuild metafile containing output import relationships.
+ * @param initialFiles The map of initial files to populate.
+ * @param entriesToAnalyze Optional starting entries to traverse; defaults to all current `initialFiles`.
+ * @param initialFilter Optional filter predicate to determine whether a discovered record should be added.
+ */
+export function findTransitiveInitialFiles(
+  metafile: Metafile,
+  initialFiles: Map<string, InitialFileRecord>,
+  entriesToAnalyze: Iterable<[string, InitialFileRecord]> = initialFiles,
+  initialFilter?: (initial: Readonly<InitialFileRecord>) => boolean,
+): void {
+  const queue = [...entriesToAnalyze];
+  for (const [entryPath, entryRecord] of queue) {
+    const entryOutput = metafile.outputs[entryPath];
+    if (!entryOutput) {
+      continue;
+    }
+
+    for (const initialImport of entryOutput.imports) {
+      if (initialFiles.has(initialImport.path)) {
+        continue;
+      }
+
+      if (initialImport.kind === 'import-statement' || initialImport.kind === 'import-rule') {
+        const record: InitialFileRecord = {
+          type: initialImport.kind === 'import-rule' ? 'style' : 'script',
+          entrypoint: false,
+          external: initialImport.external,
+          serverFile: entryRecord.serverFile,
+          depth: entryRecord.depth + 1,
+        };
+
+        if (!initialFilter || initialFilter(record)) {
+          initialFiles.set(initialImport.path, record);
+
+          if (!initialImport.external) {
+            queue.push([initialImport.path, record]);
+          }
+        }
+      }
+    }
+  }
+}
+
 export enum BuildOutputFileType {
   Browser,
   Media,