feat: add stablePatchmarks option

README.md

@@ -133,6 +133,8 @@ expect(valueA: any).toMatchDiffSnapshot(valueB: any, options?: Options, testName
 - `expand: boolean` (default: `false`) – expand the diff, so the whole information is preserved
 - `colors: boolean` (default: `false`) – preserve color information from Jest diff
 - `contextLines: number` (default: 5) - number of context lines to be shown at the beginning and at the end of a snapshot
+- `stablePatchmarks: boolean` (default: `false`) - prevent line number patch marks from appearing in
+diffs. This can be helpful when diffs are breaking only because of the patch marks. Changes `@@ -1,1 +1,2 @@` to `@@ --- --- @@`.
 - `aAnnotation: string` (default: `'First Value'`) - the annotation indicating from which serialization the `-` lines are
 - `bAnnotation: string` (default: `'Second Value'`) - the annotation indicating from which serialization the `+` lines are
 

__tests__/__snapshots__/snapshotDiff.test.js.snap

@@ -64,6 +64,37 @@ exports[`can use contextLines with React components 1`] = `
 +     my name"
 `;
 
+exports[`can use stablePatchmarks on diff 1`] = `
+"Snapshot Diff:
+- First value
++ Second value
+
+@@ --- --- @@
+  @some
+  @some
+  @some
+  @some
+  @some
+- @foo
++ @bar
+  @some
+  @some
+  @some
+  @some
+  @some
+@@ --- --- @@
+  @some
+  @some
+  @some
+  @some
+  @not
++ @so
+  @very
+  @long
+  @script
+  "
+`;
+
 exports[`collapses diffs and strips ansi by default 1`] = `
 "Snapshot Diff:
 - First value

__tests__/snapshotDiff.test.js

@@ -30,6 +30,51 @@ const b = `
     long
     script
 `;
+const noIndentA = `
+@some
+@some
+@some
+@some
+@some
+@foo
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@not
+@very
+@long
+@script
+`;
+const noIndentB = `
+@some
+@some
+@some
+@some
+@some
+@bar
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@some
+@not
+@so
+@very
+@long
+@script
+`;
 
 type Props = {
   test: string,
@@ -154,6 +199,10 @@ test('can use contextLines with React components', () => {
   ).toMatchSnapshot();
 });
 
+test('can use stablePatchmarks on diff', () => {
+  expect(snapshotDiff(noIndentA, noIndentB, { stablePatchmarks: true })).toMatchSnapshot();
+});
+
 describe('failed optional deps', () => {
   beforeEach(() => {
     jest.mock('react-test-renderer', () => {

src/index.js

@@ -21,6 +21,7 @@ const defaultOptions = {
   expand: false,
   colors: false,
   contextLines: -1, // Forces to use default from Jest
+  stablePatchmarks: false,
   aAnnotation: 'First value',
   bAnnotation: 'Second value',
 };
@@ -43,6 +44,10 @@ const snapshotDiff = (valueA: any, valueB: any, options?: Options): string => {
     difference = stripAnsi(difference);
   }
 
+  if (mergedOptions.stablePatchmarks && !mergedOptions.expand) {
+    difference = difference.replace(/^@@ -[0-9]+,[0-9]+ \+[0-9]+,[0-9]+ @@$/gm, '@@ --- --- @@')
+  }
+
   return SNAPSHOT_TITLE + difference;
 };