Editorial: Narrow integer into non-negative integer in return type of ExpectedArgumentCount

[tmdghks]

I carefully assume that the return type of ExpectedArgumentCount can be narrowed into non-negative integer, which is integer in current specification.
The reason why I suggest this PR is that the return type of the ExpectedArgumentCount is integer makes type mismatching in OrdinaryFunctionCreate and SetFunctionLength.

[tmdghks]

The following is the additional reason why I think it is possible to narrow.

First, the following cases are all the cases where ExpectedArgumentCount returns value.

1. FormalParameters: [empty] FunctionRestParameter
   • Returns 0
2. FormalParameters: FormalParameterList, FunctionRestParameter
   • Return non-negative integer
3. FormalParameterList: FormalParameter:
   • Return 0 or Return 1
4. FormalParameterList: FormalParameterList, FormalParameter
   • Return count or count + 1, and count should be non-negative.
5. ArrowParameters: BindingIdentifier
   • Return 1
6. ArrowParameters : CoverParenthesizedExpresionAndArrowParameterList
   • Return a non-negative integer
7. PropertySetParameterList: FormalParameter
   • Return 0 or 1
8. AsyncArrowBindingIdentifier: BindingIdentifier
   • Return 0 or 1

In addition, the following is the reason why the type mismatching occurs

In the step 21 of 10.2.3 OrdinaryFunctionCreate, len should have the type integer. However, in the step 22 of 10.2.3 OrdinaryFunctionCreate, SetFunctionLength get len argument as a second argument, and the type of this argument should be either non-negative integer or +∞. Therefore, if the return type of the 15.1.5 Static Semantics ExpectedArgumentCount is integer then type mismatch can occur. However, if the return type is changed into non-negative integer then we can prevent the type mismatch regarding these functions.

[jmdyck]

Looks correct to me.

[michaelficarra]

Thanks!

[tmdghks]

Thank you very much for your review!