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

[ALTree]

$ 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

[DiscoRiver]

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]

@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.

[cherrymui]

Any update on this? Thanks. (checking in as this is a release blocker.)

[griesemer]

I will start looking at this later today.

[gopherbot]

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