Bug 162013 – test262: Should be a SyntaxError for duplicate parameter names in function with default parameters

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Joseph Pecoraro]

Summary:
Should be a SyntaxError for duplicate parameter names in function with default parameters

Currently we only issue a SyntaxError if their is a duplicate name and it or later there is default parameter value:

    jsc> function f(x, x = 0) {}
    Duplicate parameter 'x' not allowed in function with default parameter values.:1

We should, but aren't, issuing the same SyntaxError if there is a duplicate name and there was an earlier default parameter values.

    jsc> function f(x = 0, x) {}
    undefined

We should be issuing a SyntaxError if there is a duplicate name if there are any default parameters.

Spec:
https://tc39.github.io/ecma262/#sec-function-definitions-static-semantics-early-errors

> FormalParameters : FormalParameterList
> 
>     It is a Syntax Error if IsSimpleParameterList of FormalParameterList is
>     false and BoundNames of FormalParameterList contains any duplicate elements.

https://tc39.github.io/ecma262/#sec-destructuring-binding-patterns-static-semantics-issimpleparameterlist

IsSimpleParameterList is false if the parameter list contains
things like any RestParameters, BindingPatterns (destructuring),
or BindingIdentifiers with Initialization (default parameters).

Notes:
- Covered in a bunch of test262 tests, like:
test262/test/language/expressions/function/params-dflt-duplicates.js

[Joseph Pecoraro]

Created attachment 288944 [details]
[PATCH] Proposed Fix

[WebKit Commit Bot]

Comment on attachment 288944 [details]
[PATCH] Proposed Fix

Clearing flags on attachment: 288944

Committed r205969: <http://trac.webkit.org/changeset/205969>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.