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cmd/go2go: generic function type assignment fails to type check correctly #40060

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rogpeppe opened this issue Jul 5, 2020 · 4 comments
Closed

cmd/go2go: generic function type assignment fails to type check correctly #40060

rogpeppe opened this issue Jul 5, 2020 · 4 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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Unreleased

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@rogpeppe
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rogpeppe commented Jul 5, 2020

commit 34f7622

The following program seems like it should compile OK, but it does not:

package main

func main() {
}

type S1(type T) struct {
	x S2(T)
}

type S2(type T) struct {
	y sfunc(T)
}

type sfunc(type T) func(*S1(T))

func (*S1(T)) a() {}

func (i *S1(T)) b(f sfunc(T)) {
	i.x.y = f
}

It produces the error:

prog.go2:19:10: cannot use f (variable of type sfunc(T)) as sfunc(T) value in assignment
@ianlancetaylor ianlancetaylor added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jul 6, 2020
@ianlancetaylor ianlancetaylor added this to the Unreleased milestone Jul 6, 2020
@ianlancetaylor
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This looks like a bug in the type checker.

@griesemer
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griesemer commented Jul 7, 2020 •
edited

One of the functions is not properly instantiated; definitively a type-checker issue.

@rogpeppe
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rogpeppe commented Jul 7, 2020

Note that it works OK if the apparently unrelated method a is removed, which is odd.

@rogpeppe
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This now works correctly on tip.

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@rogpeppe @ianlancetaylor @griesemer @gopherbot