Slightly confusing error with type parameters

[Brian Candler]

I don't know if there's much that can be done about this, but thought I'd mention it anyway.

Suppose you're trying to make a parameterised type, like

type Elem[T any] blah...

ex: https://go.dev/play/p/1tS1SCxTFP-

but you forget the "any", and just write

type Elem[T] blah...

ex: https://go.dev/play/p/uig7iXsgZeU

The error message, and the automatic reformatting you get, is a bit confusing:

type Elem [T]blah...

undeclared name T for array length

I guess this is a fundamental ambiguity in the language.  However, if an array length expression comes directly after a type name, and the array length itself consists of a single undeclared name, I wonder if the error message could give more of a hint?

undeclared name T for array length, or missing constraint for type parameter (e.g. "T any")

When there are multiple type parameters, it's fine:

https://go.dev/play/p/_gmrdPzoWCD