fix(@schematics/angular): preserve blank lines in jasmine-to-vitest schematic

The TypeScript printer, by design, does not retain blank lines. This caused the jasmine-to-vitest refactoring schematic to produce code that lost the original file's vertical spacing, harming readability.

This commit introduces a pre- and post-processing step within the main transformation function. Before parsing, blank lines are converted into unique placeholder comments. After the TypeScript printer generates the new code, these placeholders are converted back into blank lines, ensuring that the vertical formatting of the original file is preserved in the transformed output.

Author: clydin

packages/schematics/angular/refactor/jasmine-vitest/test-file-transformer.integration_spec.ts

@@ -16,9 +16,7 @@ async function expectTransformation(input: string, expected: string): Promise<vo
   const reporter = new RefactorReporter(logger);
   const transformed = transformJasmineToVitest('spec.ts', input, reporter);
   const formattedTransformed = await format(transformed, { parser: 'typescript' });
-  let formattedExpected = await format(expected, { parser: 'typescript' });
-  // Strip blank lines to avoid test failures due to cosmetic differences.
-  formattedExpected = formattedExpected.replace(/\n\s*\n/g, '\n');
+  const formattedExpected = await format(expected, { parser: 'typescript' });
 
   expect(formattedTransformed).toBe(formattedExpected);
 }

packages/schematics/angular/refactor/jasmine-vitest/test-file-transformer.ts

@@ -41,6 +41,21 @@ import {
 import { RefactorContext } from './utils/refactor-context';
 import { RefactorReporter } from './utils/refactor-reporter';
 
+const BLANK_LINE_PLACEHOLDER = '// __PRESERVE_BLANK_LINE__';
+
+function preserveBlankLines(content: string): string {
+  return content
+    .split('\n')
+    .map((line) => (line.trim() === '' ? BLANK_LINE_PLACEHOLDER : line))
+    .join('\n');
+}
+
+function restoreBlankLines(content: string): string {
+  const regex = new RegExp(`^\\s*${BLANK_LINE_PLACEHOLDER.replace(/\//g, '\\/')}\\s*$`, 'gm');
+
+  return content.replace(regex, '');
+}
+
 /**
  * Transforms a string of Jasmine test code to Vitest test code.
  * This is the main entry point for the transformation.
@@ -53,9 +68,11 @@ export function transformJasmineToVitest(
   content: string,
   reporter: RefactorReporter,
 ): string {
+  const contentWithPlaceholders = preserveBlankLines(content);
+
   const sourceFile = ts.createSourceFile(
     filePath,
-    content,
+    contentWithPlaceholders,
     ts.ScriptTarget.Latest,
     true,
     ts.ScriptKind.TS,
@@ -151,6 +168,7 @@ export function transformJasmineToVitest(
   }
 
   const printer = ts.createPrinter();
+  const transformedContentWithPlaceholders = printer.printFile(result.transformed[0]);
 
-  return printer.printFile(result.transformed[0]);
+  return restoreBlankLines(transformedContentWithPlaceholders);
 }