fix(parser): inject params into one-line non-async arrow scenarios

parse-function@5.6.10 decides whether its input is an ES6 object method with
`/^\*?.+\([\S\W]*\)\s*{/`. The greedy `.+` combined with `[\S\W]*` matches any
source containing a `) {` sequence, so a non-async arrow whose body holds an
`if`, `for`, `while` or `switch` gets wrapped in braces as a fake object method
and acorn throws. getParams() then returns undefined and nothing is injected —
`I`, page objects and `current` are all undefined when the test runs.

Async arrows escape through the library's own isAsyncArrow check, and in plain
JavaScript a multi-line arrow escapes as well, because `.` does not cross a
newline so the greedy `.+` cannot reach past the first line. That second escape
does not exist under TypeScript: tsx/esbuild emit every function on one line, so
fn.toString() returns the one-line form however the source was written, and
every non-async scenario with destructured params and a conditional fails.

normalizeArrowFn() asks acorn whether the source really is an
ArrowFunctionExpression and, if so, hands parse-function `async <source>` so it
takes the isAsyncArrow branch. Anything acorn does not confirm as an arrow —
class methods, generators, function expressions, strings, unparseable input — is
returned untouched, so only input that fails today is affected. The prefix cannot
change a parameter list, and default values stay correct because their offsets
are sliced from the same prefixed string.

ecmaVersion becomes a shared const so the parse and the arrow check cannot drift
apart; its value is unchanged, so no syntax gains or loses parseability.

Fixes #5679

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Jaromir Obr

lib/parser.js

@@ -4,7 +4,8 @@ function _interopDefault(ex) {
 import * as acorn from 'acorn'
 import parseFunctionModule from 'parse-function'
 const parseFunction = _interopDefault(parseFunctionModule)
-const parser = parseFunction({ parse: acorn.parse, ecmaVersion: 11, plugins: ['objectRestSpread'] })
+const ecmaVersion = 11
+const parser = parseFunction({ parse: acorn.parse, ecmaVersion, plugins: ['objectRestSpread'] })
 import output from './output.js'
 
 parser.use(destructuredArgs)
@@ -17,7 +18,7 @@ export const getParamsToString = function (fn) {
 function getParams(fn, { warnOnLegacyFormat = false } = {}) {
   if (fn.isSinonProxy) return []
   try {
-    const reflected = parser.parse(fn)
+    const reflected = parser.parse(normalizeArrowFn(fn))
     if (warnOnLegacyFormat && (reflected.args.length > 1 || reflected.args[0] === 'I')) {
       output.error('Error: old CodeceptJS v2 format detected. Upgrade your project to the new format -> https://bit.ly/codecept3Up')
     }
@@ -38,6 +39,17 @@ function getParams(fn, { warnOnLegacyFormat = false } = {}) {
 
 export { getParams }
 
+function normalizeArrowFn(fn) {
+  const code = (typeof fn === 'function' ? fn.toString() : String(fn)).trim()
+  if (!code.includes('=>') || code.startsWith('async')) return fn
+  try {
+    if (acorn.parseExpressionAt(code, 0, { ecmaVersion }).type !== 'ArrowFunctionExpression') return fn
+  } catch {
+    return fn
+  }
+  return `async ${code}`
+}
+
 function destructuredArgs() {
   return (node, result) => {
     result.destructuredArgs = result.destructuredArgs || []

test/unit/parser_test.js

@@ -40,5 +40,19 @@ describe('parser', () => {
     it('should get params for class method with destructured args', () => {
       expect(getParams(obj.method5)).to.eql(['locator', 'sec'])
     })
+
+    // prettier-ignore
+    const fixturesOneLineArrows = [
+      ['destructured args and a condition', ({ locator, sec }) => { if (true) { return locator } }, ['locator', 'sec']],
+      ['a single arg and a condition', locator => { if (true) { return locator } }, ['locator']],
+      ['multiple args and a loop', (locator, sec) => { for (;;) { return locator || sec } }, ['locator', 'sec']],
+      ['a nested arrow function', ({ locator, sec }) => { [locator].forEach((l) => { if (l) { return sec } }) }, ['locator', 'sec']],
+    ]
+
+    fixturesOneLineArrows.forEach(([title, fn, params]) => {
+      it(`should get params for one-line arrow function with ${title}`, () => {
+        expect(getParams(fn)).to.eql(params)
+      })
+    })
   })
 })