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cmd/go2go: error when a type parameter name and an interface name are same #39659

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hajimehoshi opened this issue Jun 17, 2020 · 1 comment
Closed

cmd/go2go: error when a type parameter name and an interface name are same #39659

hajimehoshi opened this issue Jun 17, 2020 · 1 comment
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@hajimehoshi
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What version of Go are you using (go version)?

n/a

Does this issue reproduce with the latest release?

n/a

What operating system and processor architecture are you using (go env)?

n/a

What did you do?

https://go2goplay.golang.org/p/6CjvnnMekvf

package main

type Foo interface{}

func F(type Foo Foo)() {
}

func main() {
}

What did you expect to see?

Compilation succeeds, or a better error message?

What did you see instead?

type checking failed for main
prog.go2:5:17: Foo is not an interface
@ianlancetaylor
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This is expected behavior. It's a consequence of the fact that within a type parameter list, all type parameters are visible throughout the list (https://go.googlesource.com/proposal/+/refs/heads/master/design/go2draft-type-parameters.md#mutually-referencing-type-parameters). In (type Foo Foo) the second Foo refers to the first Foo, so it is indeed not an interface type.

CC @griesemer in case he sees a way to get a better error message.

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@hajimehoshi @ianlancetaylor @gopherbot