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cmd/go2go: incorrect redeclaration error in very specific circumstance with multiple files #39739

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DeedleFake opened this issue Jun 21, 2020 · 1 comment

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@DeedleFake
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@DeedleFake DeedleFake commented Jun 21, 2020

This doesn't work in the playground because it requires a second file.

File one:

package main

func main() {
	Do().Func(Wrap(struct{})())
}

File two:

package main

type Struct(type T) struct {
	v T
}

func Do() Struct(struct{}) {
	return Struct(struct{}){}
}

func (s Struct(T)) Func(f Func(T)) Struct(T) {
	return Struct(T){
		v: f(s.v),
	}
}

type Func(type T) func(T) T

func Wrap(type T)() Func(T) {
	return func(v T) T {
		return v
	}
}

Output:

$ go tool go2go run *.go2# command-line-arguments
./test.go2:4: cannot use instantiate୦୦Wrap୦struct୮4୮5() (type instantiate୦୦Func୦struct୮4୮5) as type instantiate୦୦Func୦struct୮4୮5 in argument to Do().Func
./second.go2:23: instantiate୦୦Func୦struct୮4୮5 redeclared in this block
	previous declaration at ./second.go2:15
/home/deedles/devel/build/go/bin/go [run second.go test.go] failed: exit status 2

Moving the definition of Do() into the first file fixes it. Using a named empty struct type, such as type None struct {}, doesn't fix it.

@DeedleFake DeedleFake changed the title cmd/go2go: returning a generic anonymous function type from a function declared in a second file with an empty struct parameter incorrectly claims a redeclaration cmd/go2go: incorrect redeclaration claim in very specific circumstance with two files Jun 21, 2020
@DeedleFake DeedleFake changed the title cmd/go2go: incorrect redeclaration claim in very specific circumstance with two files cmd/go2go: incorrect redeclaration error in very specific circumstance with multiple files Jun 21, 2020
@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jun 22, 2020

Also reported as #39749. Fixed on dev.go2go branch.

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