Detect more forms of snapshot file corruption

lib/reporters/improper-usage-messages.js

@@ -20,7 +20,7 @@ Visit the following URL for more details:
 	if (assertion === 'snapshot') {
 		const {name, snapPath} = error.improperUsage;
 
-		if (name === 'ChecksumError') {
+		if (name === 'ChecksumError' || name === 'InvalidSnapshotError') {
 			return `The snapshot file is corrupted.
 
 File path: ${chalk.yellow(snapPath)}

lib/snapshot-manager.js

@@ -52,6 +52,13 @@ export class VersionMismatchError extends SnapshotError {
 	}
 }
 
+export class InvalidSnapshotError extends SnapshotError {
+	constructor(snapPath) {
+		super('Invalid snapshot file', snapPath);
+		this.name = 'InvalidSnapshotError';
+	}
+}
+
 const LEGACY_SNAPSHOT_HEADER = Buffer.from('// Jest Snapshot v1');
 function isLegacySnapshot(buffer) {
 	return LEGACY_SNAPSHOT_HEADER.equals(buffer.slice(0, LEGACY_SNAPSHOT_HEADER.byteLength));
@@ -194,7 +201,12 @@ function decodeSnapshots(buffer, snapPath) {
 
 	// The version starts after the readable prefix, which is ended by a newline
 	// byte (0x0A).
-	const versionOffset = buffer.indexOf(0x0A) + 1;
+	const newline = buffer.indexOf(0x0A);
+	if (newline === -1) {
+		throw new InvalidSnapshotError(snapPath);
+	}
+
+	const versionOffset = newline + 1;
 	const version = buffer.readUInt16LE(versionOffset);
 	if (version !== VERSION) {
 		throw new VersionMismatchError(snapPath, version);
@@ -469,11 +481,9 @@ export function load({file, fixedLocation, projectDir, recordNewSnapshots, updat
 		blocksByTitle = new Map();
 
 		if (!updating) { // Discard all decoding errors when updating snapshots
-			if (error instanceof SnapshotError) {
-				snapshotError = error;
-			} else {
-				throw error;
-			}
+			snapshotError = error instanceof SnapshotError ?
+				error :
+				new InvalidSnapshotError(paths.snapPath);
 		}
 	}
 

test/snapshot-tests/corrupt.js

@@ -0,0 +1,59 @@
+import {promises as fs} from 'fs';
+import path from 'path';
+
+import test from '@ava/test';
+
+import {cwd, fixture} from '../helpers/exec.js';
+import {withTemporaryFixture} from '../helpers/with-temporary-fixture.js';
+
+function countMatches(string, regex) {
+	return [...string.matchAll(regex)].length;
+}
+
+function countStringMatches(string, patternString) {
+	if (patternString.length === 0) {
+		throw new RangeError('Pattern must be non-empty');
+	}
+
+	let index = string.indexOf(patternString);
+	let matches = 0;
+	while (index !== -1 && index < string.length) {
+		matches++;
+		index = string.indexOf(patternString, index + patternString.length);
+	}
+
+	return matches;
+}
+
+test('snapshot corruption is reported to the console', async t => {
+	await withTemporaryFixture(cwd('corrupt'), async cwd => {
+		const snapPath = path.join(cwd, 'test.js.snap');
+		await fs.writeFile(snapPath, Uint8Array.of(0x00));
+		const result = await t.throwsAsync(fixture([], {cwd}));
+		t.snapshot(result.stats.failed, 'failed tests');
+		t.is(countMatches(result.stdout, /The snapshot file is corrupted./g), 2);
+		t.is(countMatches(result.stdout, /File path:/g), 2);
+		t.is(
+			countMatches(
+				result.stdout,
+				/Please run AVA again with the .*--update-snapshots.* flag to recreate it\./g
+			),
+			2
+		);
+		t.is(countStringMatches(result.stdout, snapPath), 2);
+	});
+});
+
+test('with --update-snapshots, corrupt snapshot files are overwritten', async t => {
+	await withTemporaryFixture(cwd('corrupt'), async cwd => {
+		const snapPath = path.join(cwd, 'test.js.snap');
+		const env = {
+			AVA_FORCE_CI: 'not-ci'
+		};
+		await fs.writeFile(snapPath, Uint8Array.of(0x00));
+		await fixture(['--update-snapshots'], {cwd, env});
+
+		const snapContents = await fs.readFile(snapPath);
+		t.not(snapContents.length, 1);
+	});
+});

test/snapshot-tests/fixtures/corrupt/package.json

@@ -0,0 +1 @@
+{}

test/snapshot-tests/fixtures/corrupt/test.js

@@ -0,0 +1,9 @@
+const test = require(process.env.TEST_AVA_IMPORT_FROM);
+
+test('a snapshot', t => {
+	t.snapshot('foo');
+});
+
+test('a snapshot with a message', t => {
+	t.snapshot('foo', 'a message');
+});

test/snapshot-tests/snapshots/corrupt.js.md

@@ -0,0 +1,20 @@
+# Snapshot report for `test/snapshot-tests/corrupt.js`
+
+The actual snapshot is saved in `corrupt.js.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## snapshot corruption is reported to the console
+
+> failed tests
+
+    [
+      {
+        file: 'test.js',
+        title: 'a snapshot',
+      },
+      {
+        file: 'test.js',
+        title: 'a snapshot with a message',
+      },
+    ]