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cmd/compile: puzzling "does not satisfy comparable" error message #49112

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ALTree opened this issue Oct 22, 2021 · 5 comments
Closed

cmd/compile: puzzling "does not satisfy comparable" error message #49112

ALTree opened this issue Oct 22, 2021 · 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. release-blocker
Milestone
Go1.18

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@ALTree
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ALTree commented Oct 22, 2021 

$ gotip version
go version devel go1.18-9ff91b9098 Fri Oct 22 00:57:18 2021 +0000 windows/amd64

package main

type I interface {
	int
}

func f[G I](g G) {
	println(g)
}

func main() {
	var v1 float64
	var v2 []int
	f(v1)
	f(v2)
}

Building prints:

$ gotip build test.go
# command-line-arguments
.\test.go:14:3: float64 does not satisfy I
.\test.go:15:3: []int does not satisfy comparable

The error message for f(v1) makes sense:

float64 does not satisfy I

but the one for f(v2) is puzzling:

[]int does not satisfy comparable

It mentions the predeclared constraint comparable, but comparable has nothing to do with I. Why?

cc @griesemer @findleyr
@ALTree ALTree added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Oct 22, 2021
@ALTree ALTree added this to the Go1.18 milestone Oct 22, 2021
@DiscoRiver
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DiscoRiver commented Oct 22, 2021 •
edited

Error message needs updating?

go/src/cmd/compile/internal/types2/instantiate.go

Line 165 in 9ff91b9

return errorf("%s does not satisfy comparable", targ)

@findleyr
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@DiscoRiver yes, that looks right. We're checking comparable as a precondition (since the type set {int} is comparable), but the error message is misleading.

Thanks for the report.

@findleyr findleyr added okay-after-beta1 Used by release team to mark a release-blocker issue as okay to resolve either before or after beta1 release-blocker labels Oct 22, 2021
@griesemer griesemer self-assigned this Oct 22, 2021
@cherrymui cherrymui removed the okay-after-beta1 Used by release team to mark a release-blocker issue as okay to resolve either before or after beta1 label Dec 14, 2021
@cherrymui
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Any update on this? Thanks. (checking in as this is a release blocker.)

@griesemer
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I will start looking at this later today.

@gopherbot
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Change https://golang.org/cl/372594 mentions this issue: cmd/compile/internal/types2: delay "does not satisfy comparable" error until needed

@golang golang locked and limited conversation to collaborators Jun 23, 2023
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