fix: surface fatal errors from eslint

src/lintResultSerializer.test.ts

@@ -4,11 +4,29 @@ import { VariableDeclarator } from 'estree'
 
 const processCwd = jest.spyOn(process, 'cwd')
 const sourceCode = `\nconst foo = 'something';`
+let consoleSpy: jest.SpyInstance
 
 beforeEach(() => {
+	consoleSpy?.mockRestore()
 	processCwd.mockReturnValue('/cwd')
 })
 
+it('should surface fatal errors from eslint', () => {
+	consoleSpy = jest.spyOn(console, 'error').mockImplementation(() => {})
+
+	expect(() => {
+		lint(sourceCode, { parser: 'this-parser-does-not-exist' })
+	}).toThrowErrorMatchingInlineSnapshot(
+		`"Encountered fatal error during lint execution: Configured parser 'this-parser-does-not-exist' was not found."`
+	)
+
+	expect(consoleSpy.mock.calls[0][0]).toMatchObject({
+		ruleId: null,
+		severity: 2,
+		message: "Configured parser 'this-parser-does-not-exist' was not found.",
+	})
+})
+
 describe('serializeLintResult supports per-test setup and mocking for lint rules', () => {
 	test('should not have errors', () => {
 		processCwd.mockReturnValue('/foo')
@@ -21,10 +39,11 @@ describe('serializeLintResult supports per-test setup and mocking for lint rules
 	})
 })
 
-function lint(source: string) {
+function lint(source: string, config: Linter.Config = {}) {
 	const linter = new Linter({})
 	linter.defineRule('my-rule-name', testRule)
 	const lintMessages = linter.verify(source, {
+		...config,
 		rules: { ['my-rule-name']: 'error' },
 		parserOptions: {
 			ecmaVersion: 2020,

src/lintResultSerializer.ts

@@ -41,6 +41,8 @@ export function serializeLintResult({ lintedSource, lintMessages }: SerializeOpt
 	const uniqueMessages: string[] = []
 
 	lintMessages.forEach((lintMessage) => {
+		checkFatalError(lintMessage)
+
 		// ESLint line & column are 1-indexed for better IDE integration, but 0 works
 		// better for us here
 		const startLine = lintMessage.line - 1
@@ -103,6 +105,16 @@ export function serializeLintResult({ lintedSource, lintMessages }: SerializeOpt
 	return interleaved.join('\n')
 }
 
+function checkFatalError(lintMessage: Linter.LintMessage) {
+	// Allow parsing errors (indicated by non-zero coordinates) to show in the snapshot
+	// instead of throwing a hard error, but something like a misconfigured parser or
+	// missing rule should throw
+	if (lintMessage.fatal && lintMessage.line === 0 && lintMessage.column === 0) {
+		console.error(lintMessage)
+		throw new Error(`Encountered fatal error during lint execution: ${lintMessage.message}`)
+	}
+}
+
 function collapseErrorLines(allErrorLines: string[][]) {
 	let [mainLine, ...rest] = allErrorLines
 	const collidedErrorLines: string[][] = []