Bug 106176 – Non-helpful SyntaxError message for duplicate parameters in strict mode

• Component: JavaScriptCore
• Status: UNCONFIRMED

[André Bargull]

The current SyntaxError message isn't really that helpful. 

test cases:
---
> function f(a,a){'use strict'}
Exception: SyntaxError: Unexpected token '}'
> function f(a,a){'use strict'; ''} 
Exception: SyntaxError: Unexpected string ''
> function f(a,a){'use strict'; return a}
Exception: SyntaxError: Return statements are only valid inside functions
---

[Joseph Pecoraro]

Things are slightly better now. It would still be nice if it said duplicate parameters though. Current state of things (r207235):

js> function f(a,a){'use strict'}
Invalid parameters or function name in strict mode.:1
js> function f(a,a){'use strict'; ''} 
Invalid parameters or function name in strict mode.:1
js> function f(a,a){'use strict'; return a}
Invalid parameters or function name in strict mode.:1

[Joseph Pecoraro]

Compare to our error message for classes and arrow functions which force the stricter parsing, these are more helpful because they even note the duplicate parameter:

js> (class { f(a,a){} })
Cannot declare a parameter named 'a' in strict mode as it has already been declared.:1
js> (class { f(a,a){''} })
Cannot declare a parameter named 'a' in strict mode as it has already been declared.:1
js> (class { f(a,a){return a} })
Cannot declare a parameter named 'a' in strict mode as it has already been declared.:1
js> (a,a) => {}
Duplicate parameter 'a' not allowed in an arrow function.:1
js> (a,a) => {''}
Duplicate parameter 'a' not allowed in an arrow function.:1
js> (a,a) => {return a}
Duplicate parameter 'a' not allowed in an arrow function.:1

[Saam Barati]

 Weird I thought we had code that said it's invalid because of duplicate parameters when we parse "use strict". I'll look into it