fix(migrations): migration host incorrectly reading empty files (#48849)

crisbeto · thePunderWoman · commit af31f98b00a5 · 2023-01-26T15:54:14.000Z
Fixes that the migration host was doing a basic falsy check if the content was read correctly which meant that a component with an empty template would be considered as having a missing template file. Fixes #48846. PR Close #48849
diff --git a/packages/core/schematics/utils/typescript/compiler_host.ts b/packages/core/schematics/utils/typescript/compiler_host.ts
@@ -50,7 +50,7 @@ export function createMigrationCompilerHost(
     const treeRelativePath = relative(basePath, fileName);
     let result: string|undefined = fakeRead?.(treeRelativePath);
 
-    if (result === undefined) {
+    if (typeof result !== 'string') {
       // If the relative path resolved to somewhere outside of the tree, fall back to
       // TypeScript's default file reading function since the `tree` will throw an error.
       result = treeRelativePath.startsWith('..') ? defaultReadFile.call(host, fileName) :
@@ -60,7 +60,7 @@ export function createMigrationCompilerHost(
     // Strip BOM as otherwise TSC methods (Ex: getWidth) will return an offset,
     // which breaks the CLI UpdateRecorder.
     // See: https://github.com/angular/angular/pull/30719
-    return result ? result.replace(/^\uFEFF/, '') : undefined;
+    return typeof result === 'string' ? result.replace(/^\uFEFF/, '') : undefined;
   };
 
   return host;
