SyntaxError not thrown for duplicate parameters in arrow functions

[theauk]

ff487e0

Test Case

(a, a) => {  }

Expected Behavior
I would expect to see a syntax error about duplicated parameters not being allowed in this context. Running the test case on other JavaScript engines (Node, Hermes, QuickJS, Deno, Ecargot), I get some version of a duplicated parameter SyntaxError.

[gfwilliams]

Thanks for these reports! I'll take a look at them when I get a bit of free time.

In the mean time if you or anyone else wants to contribute fixes that'd be awesome!