Dealing with “var x” – Part 2 #1663

This is an unresolved thread from #873. Review in conjunction with #1665.

Dealing with “var x” – Part 2

There is an ambiguity in patterns, the input “var x” could be recognised as a declaration_pattern or as a var_pattern. As is this PR only deals with the latter, on line 191 below, and says nothing about the former.

I think the intended semantics are:

• In declaration_pattern the type cannot be the identifier var; i.e. if it starts with var then var_pattern is considered.
• A var_pattern is invalid (not considered as a valid parse) if a type called var is in scope.

This is tackled with two suggestions:

1. One on line 83 covering declaration_pattern (Part 1)
2. Reword the original statement on line 191

A *var_pattern* cannot be used when a type named `var` is in scope.

Note: I would have moved line 191 to the start of this clause but GitHub will not allow that, that would give:

11.2.4 Var pattern

A var_pattern matches every value. That is, a pattern-matching operation with a var_pattern always succeeds.

A var_pattern is applicable to every type.

A var_pattern cannot be used when a type named var is in scope.

This seems to me to flow better, take your pick.

Originally posted by @Nigel-Ecma in #873 (comment)