cmd/compile: syntax error for valid type parameter list

[zigo101]

What version of Go are you using (go version)?

$ go version
go version go1.18rc1 linux/amd64

What did you do?

type foo[T *string,] struct{x T}      // okay
type bar[T *string|bool,] struct{x T} // syntax error: unexpected comma; expecting ]
type tik[T *string|bool, X int] struct{x T} // syntax error: unexpected comma; expecting ]

What did you expect to see?

compiles okay

What did you see instead?

fails to compile

[ianlancetaylor]

CC @griesemer

[ianlancetaylor]

Thanks, we can address this for 1.19.

[zigo101]

more forms:

type bar[T *string|bool] struct{x T}
type bar[T *[]int|bool] struct{x T}

[griesemer]

We're aware of them, thanks. See #49482.

[zigo101]

So this is covered in spec?

package main

const T, int, bool = 1, 1, 2

type bar[T *int|bool] struct{}

func main() {
	var _ bar
}

But it looks this one is not covered in spec.
*string is also a type literal, but this line fails to compile.
Maybe it should always compile? Because *string may not be a constant,

type bar[T **string] struct{} // *string (type) is not an expression

[zigo101]

sorry, remove one , from the last comment.

[zigo101]

Is it worth considering this case: #6386 (comment) ?

[edit]: maybe it is not worth it. If array could be declared as const, array index expressions should be banned in the length expressions of array declarations.

[zigo101]

Not sure whether or not this is intended:

type C4[T ([]int)] struct{}      // compiles okay
type C5[T ([]int)|bool] struct{} // fails to compile

[zigo101]

Luckily, aConstString[aConstInteger] is not a constant.

const S = "abcde"
const int = 2
const N = S[2]*int // error

type _ [S[2]*int] struct{} // error

[griesemer]

Closing as duplicate of #49482.