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cmd/go2go: instantiate generic redeclared in this block #39653

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kylelemons opened this issue Jun 17, 2020 · 5 comments
Closed

cmd/go2go: instantiate generic redeclared in this block #39653

kylelemons opened this issue Jun 17, 2020 · 5 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@kylelemons
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What version of Go are you using (go version)?

go2goplay.golang.org

What did you do?

https://go2goplay.golang.org/p/s37l9l0m7Du

type End struct{}

type Dimension(type P) struct {
	Name   string
	Parent P
}

func Dim(type Parent)(name string, p Parent) Dimension(Parent) {
	return Dimension(Parent){
		Name:   name,
		Parent: p,
	}
}

func main() {
	d := Dim("a", Dim("b", Dim("c", End{})))
	fmt.Printf("%T", d)
}

What did you expect to see?

Something like Dim(Dim(Dim(End))) except mangled as successful output

What did you see instead?

The following error:

./prog.go2:23: instantiate୦୦Dimension୦main୮aEnd redeclared in this block
	previous declaration at ./prog.go2:28
./prog.go2:21: cannot use p (type instantiate୦୦Dimension୦main୮aEnd) as type instantiate୦୦Dimension୦main୮aEnd in field value

This is either an incorrect error (if the code should be fine) or an error message that I am unable to interpret to be able to figure out what I did wrong.
@kylelemons
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It seems to work fine with one and two levels of nesting, but not three.

@andybons
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@griesemer @ianlancetaylor

@andybons andybons added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jun 17, 2020
@andybons andybons added this to the Unplanned milestone Jun 17, 2020
@griesemer
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This looks like a bug in the translator part (type checking is fine).

@griesemer griesemer modified the milestones: Unplanned, Unreleased Jun 17, 2020
@gopherbot
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Change https://golang.org/cl/238618 mentions this issue: [dev.go2go] go/go2go: make uses of typeInstantiations consistent

@ianlancetaylor
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Thanks, this should be fixed now.

gopherbot pushed a commit that referenced this issue Jun 17, 2020
@ianlancetaylor
[dev.go2go] go/go2go: make uses of typeInstantiations consistent
e0d5d9f 
Fixes #39653

Change-Id: I98fd1bd4f0deccb5b4c2ed0d67d508c7f0117839
Reviewed-on: https://go-review.googlesource.com/c/go/+/238618
Reviewed-by: Ian Lance Taylor <iant@golang.org>
@mewmew mewmew mentioned this issue Feb 8, 2021
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@golang golang locked and limited conversation to collaborators Jun 17, 2021
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