fix(file): Preserve final line ending when rewriting JSON

Author: seb-cr

src/file.ts

@@ -102,7 +102,10 @@ export async function withJsonFile<T = any>(
 
   // set indentation based on the first indented line
   const indent = /^(\s+)/m.exec(rawContent)?.[1] || 0;
-  const newContent = JSON.stringify(doc, null, indent);
+  // preserve final line ending if present
+  const ending = rawContent.endsWith('\n') ? '\n' : '';
+
+  const newContent = JSON.stringify(doc, null, indent) + ending;
   if (newContent !== rawContent) {
     await writeFile(path, newContent);
   }

tests/file.spec.ts

@@ -102,6 +102,17 @@ describe('withJsonFile', () => {
       expect(newContent).to.equal(JSON.stringify(EXPECTED_DATA, null, indentation));
     });
   });
+
+  it('should preserve final line ending', async () => {
+    await writeFile(TEST_FILE, '{}\n');
+
+    await withJsonFile(TEST_FILE, (f) => {
+      f.key = 'value';
+    });
+
+    const newContent = (await readFile(TEST_FILE)).toString();
+    expect(newContent).to.equal('{"key":"value"}\n');
+  });
 });
 
 describe('withYamlFile', () => {