Prevent drifting inline snapshots jestjs#8424

Fixes jestjs#8424 by avoiding indenting inline snapshot if second
line of inline snapshot already has been indented.

packages/jest-snapshot/src/__tests__/inline_snapshots.test.ts

@@ -236,6 +236,37 @@ test('saveInlineSnapshots() indents multi-line snapshots with spaces', () => {
   );
 });
 
+test('saveInlineSnapshots() does not re-indent already indented snapshots', () => {
+  const filename = path.join(__dirname, 'my.test.js');
+  (fs.readFileSync as jest.Mock).mockImplementation(
+    () =>
+      "it('is a test', () => {\n" +
+      "  expect({a: 'a'}).toMatchInlineSnapshot(`\n" +
+      '    Object {\n' +
+      "      a: 'a'\n" +
+      '    }\n' +
+      '  `);\n' +
+      '});\n',
+  );
+  (prettier.resolveConfig.sync as jest.Mock).mockReturnValue({
+    bracketSpacing: false,
+    singleQuote: true,
+  });
+
+  saveInlineSnapshots(
+    [
+      {
+        frame: {column: 20, file: filename, line: 2} as Frame,
+        snapshot: `\n    Object {\n      a: 'a'\n    }\n`,
+      },
+    ],
+    prettier,
+    babelTraverse,
+  );
+
+  expect(fs.writeFileSync).not.toHaveBeenCalled();
+});
+
 test('saveInlineSnapshots() indents multi-line snapshots with tabs', () => {
   const filename = path.join(__dirname, 'my.test.js');
   (fs.readFileSync as jest.Mock).mockImplementation(

packages/jest-snapshot/src/inline_snapshots.ts

@@ -120,14 +120,17 @@ const groupSnapshotsByFile = groupSnapshotsBy(({frame: {file}}) => file);
 
 const indent = (snapshot: string, numIndents: number, indentation: string) => {
   const lines = snapshot.split('\n');
+  const secondAlreadyLineIndented =
+    lines.length > 2 && lines[1].startsWith(indentation.repeat(numIndents + 1));
+
   return lines
     .map((line, index) => {
       if (index === 0) {
         // First line is either a 1-line snapshot or a blank line.
         return line;
       } else if (index !== lines.length - 1) {
         // Do not indent empty lines.
-        if (line === '') {
+        if (line === '' || secondAlreadyLineIndented) {
           return line;
         }