refactor(@angular/build): add initial infrastructure to support inline template HMR

The Angular AOT compilation logic for a rebuild has been updated to include
infrastructure for additional checks of stale TypeScript files against updated
files. The actual comparison aspects have not yet been implement and no behavior
changes are yet present for template HMR.

Author: clydin

packages/angular/build/src/tools/angular/compilation/aot-compilation.ts

@@ -66,6 +66,18 @@ export class AotCompilation extends AngularCompilation {
       hostOptions.externalStylesheets ??= new Map();
     }
 
+    // Collect stale source files for HMR analysis of inline component resources
+    let staleSourceFiles;
+    if (compilerOptions['_enableHmr'] && hostOptions.modifiedFiles && this.#state) {
+      for (const modifiedFile of hostOptions.modifiedFiles) {
+        const sourceFile = this.#state.typeScriptProgram.getSourceFile(modifiedFile);
+        if (sourceFile) {
+          staleSourceFiles ??= new Map<string, ts.SourceFile>();
+          staleSourceFiles.set(modifiedFile, sourceFile);
+        }
+      }
+    }
+
     // Create Angular compiler host
     const host = createAngularCompilerHost(ts, compilerOptions, hostOptions);
 
@@ -95,14 +107,12 @@ export class AotCompilation extends AngularCompilation {
     await profileAsync('NG_ANALYZE_PROGRAM', () => angularCompiler.analyzeAsync());
 
     let templateUpdates;
-    if (
-      compilerOptions['_enableHmr'] &&
-      hostOptions.modifiedFiles &&
-      hasOnlyTemplates(hostOptions.modifiedFiles)
-    ) {
-      const componentNodes = [...hostOptions.modifiedFiles].flatMap((file) => [
-        ...angularCompiler.getComponentsWithTemplateFile(file),
-      ]);
+    if (compilerOptions['_enableHmr'] && hostOptions.modifiedFiles && this.#state) {
+      const componentNodes = collectHmrCandidates(
+        hostOptions.modifiedFiles,
+        angularProgram,
+        staleSourceFiles,
+      );
 
       for (const node of componentNodes) {
         if (!ts.isClassDeclaration(node)) {
@@ -423,15 +433,46 @@ function findAffectedFiles(
   return affectedFiles;
 }
 
-function hasOnlyTemplates(modifiedFiles: Set<string>): boolean {
+function collectHmrCandidates(
+  modifiedFiles: Set<string>,
+  { compiler }: ng.NgtscProgram,
+  staleSourceFiles: Map<string, ts.SourceFile> | undefined,
+): Set<ts.ClassDeclaration> {
+  const candidates = new Set<ts.ClassDeclaration>();
+
   for (const file of modifiedFiles) {
-    const lowerFile = file.toLowerCase();
-    if (lowerFile.endsWith('.html') || lowerFile.endsWith('.svg')) {
+    const templateFileNodes = compiler.getComponentsWithTemplateFile(file);
+    if (templateFileNodes.size) {
+      templateFileNodes.forEach((node) => candidates.add(node as ts.ClassDeclaration));
+      continue;
+    }
+
+    const styleFileNodes = compiler.getComponentsWithStyleFile(file);
+    if (styleFileNodes.size) {
+      styleFileNodes.forEach((node) => candidates.add(node as ts.ClassDeclaration));
       continue;
     }
 
-    return false;
+    const staleSource = staleSourceFiles?.get(file);
+    if (staleSource === undefined) {
+      // Unknown file requires a rebuild so clear out the candidates and stop collecting
+      candidates.clear();
+      break;
+    }
+
+    const updatedSource = compiler.getCurrentProgram().getSourceFile(file);
+    if (updatedSource === undefined) {
+      // No longer existing program file requires a rebuild so clear out the candidates and stop collecting
+      candidates.clear();
+      break;
+    }
+
+    // Compare the stale and updated file for changes
+
+    // TODO: Implement -- for now assume a rebuild is needed
+    candidates.clear();
+    break;
   }
 
-  return true;
+  return candidates;
 }