Revised given syntax

[odersky]

Update given syntax to latest discussed variant in the SIP

tests/pos/given-syntax.scala shows a semi-systematic list of possible syntax forms.

[odersky]

A good way to judge the merits or problems of the change to optional names is to look at the diff of tests/pos/typeclasses-arrow0.scala in https://github.com/scala/scala3/pull/21208/files. In my opinion, the double : looks not too bad now, so that I don't think replacing it with with is justified anymore. I believe the change that if there is an optional name, the colon always appears at the same point (after the identifier) helps. That way it becomes easy to see what is what. Previously, : could appear at various places which made it more confusing.

[hamzaremmal]

These changes should be reverted

[hamzaremmal]

This a new neg test, it should have it's own .check file

[kitbellew]

is this really DefTermParamClause, or can it be FunParamClause instead? as far as i can tell, the difference is in modifiers (inline, erased) and default value.

[odersky]

It s a DefTypeParamClause. Modifiers and default values are allowed.

[kitbellew]

how do we resolve ambiguity between DefTermParamClause and '(' FunArgTypes ')', especially since a simple type can look like a parameter?

[odersky]

You mean, if the given actually implements a function? In that case the function has to come in parentheses.