fixup! perf(@angular/build): cache transformed configuration in TypeScript compilation

Author: alan-agius4

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

@@ -53,6 +53,7 @@ export abstract class TypeScriptCompilation extends AngularCompilation {
       return this.#cachedConfiguration;
     }
 
+    // TODO(alanagius): remove casting when @angular/compiler-cli exports the correct typings.
     const { readConfiguration } = (await TypeScriptCompilation.loadCompilerCli()) as typeof ng & {
       readConfiguration(
         project: string,
@@ -119,7 +120,7 @@ export abstract class TypeScriptCompilation extends AngularCompilation {
       extendedConfigFiles: [...this.#extendedConfigCache.keys()],
     };
 
-    if (currentRootFiles?.length) {
+    if (config.extendedConfigFiles?.length && currentRootFiles?.length) {
       this.#cachedConfiguration = config;
       this.#cachedRootFiles = currentRootFiles;
     }
@@ -133,15 +134,25 @@ export abstract class TypeScriptCompilation extends AngularCompilation {
     for (const file of files) {
       const posixFile = toPosixPath(file);
       this.sourceFiles.delete(posixFile);
-      if (
-        /\.json$/i.test(posixFile) ||
-        this.#extendedConfigCache.has(posixFile) ||
-        this.#extendedConfigCache.has(canonicalizePath(posixFile))
-      ) {
-        // If a tsconfig changes, we need to re-read the configuration.
-        this.#cachedConfiguration = undefined;
-        this.#cachedRootFiles = undefined;
-        this.#extendedConfigCache.clear();
+
+      if (this.#extendedConfigCache.size) {
+        let cacheKey: string | undefined;
+        if (this.#extendedConfigCache.has(posixFile)) {
+          cacheKey = posixFile;
+        } else {
+          // TypeScript lowercases the keys of the extended config cache on case-insensitive operating systems.
+          const lowerCasedPosixFile = posixFile.toLowerCase();
+          if (this.#extendedConfigCache.has(lowerCasedPosixFile)) {
+            cacheKey = lowerCasedPosixFile;
+          }
+        }
+
+        if (cacheKey) {
+          // If a tsconfig changes, we need to re-read the configuration.
+          this.#cachedConfiguration = undefined;
+          this.#cachedRootFiles = undefined;
+          this.#extendedConfigCache.delete(cacheKey);
+        }
       }
     }
   }