cmd/go: incompatible module path check doesn't apply for gopkg.in/yaml.v2

[hyangah]

What version of Go are you using (go version)?

$ go version
go version
go version go1.20.1 darwin/amd64

What did you do?

-- go.mod --
module w

go 1.20

require gopkg.in/yaml.v2 v2.4.0

replace gopkg.in/yaml.v2 => gopkg.in/yaml.v3 v3.0.0

-- main.go --
package main

import "gopkg.in/yaml.v2"

func main() {
        var t struct{ A string }
        _, _ = yaml.Marshal(&t)
}

And run go build

Note: the go.mod isn't tidy.

What did you expect to see?

Error related to mismatching module paths. (gopkg.in/yaml.v2 vs gopkg.in/yaml.v3)

What did you see instead?

No error.

go list sees the replacement.

$ go list -f '{{.Module}}' gopkg.in/yaml.v2
gopkg.in/yaml.v2 v2.4.0 => gopkg.in/yaml.v3 v3.0.0

go mod tidy adds gopkg.in/yaml.v3 to indirect require group.
go build was ok as long as go.sum has an entry for v2.

module w

go 1.20

require gopkg.in/yaml.v2 v2.4.0

require gopkg.in/yaml.v3 v3.0.1 // indirect

replace gopkg.in/yaml.v2 => gopkg.in/yaml.v3 v3.0.0

On the other hand,

--- go.mod ---
module e

go 1.20

require (
        github.com/go-logr/logr v1.2.0 // indirect
        k8s.io/klog v1.0.0
)
--- main.go ---
package main

import "k8s.io/klog/v2"

func main() {
        _ = klog.Info
}
--- go.sum ---
github.com/go-logr/logr v1.2.0 h1:QK40JKJyMdUDz+h+xvCsru/bJhvG0UxvePV0ufL/AcE=
github.com/go-logr/logr v1.2.0/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
k8s.io/klog/v2 v2.90.0 h1:VkTxIV/FjRXn1fgNNcKGM8cfmL1Z33ZjXRTVxKCoF5M=
k8s.io/klog/v2 v2.90.0/go.mod h1:y1WjHnz7Dj687irZUWR/WLkLc5N1YHtjLdmgWjndZn0=

go build returns an error (however, not explicitly talks about this path issue)

go build
main.go:3:8: no required module provides package k8s.io/klog/v2; to add it:
        go get k8s.io/klog/v2

go mod tidy update go.mod to the following without error.

module e

go 1.20

require k8s.io/klog/v2 v2.90.0

require github.com/go-logr/logr v1.2.0 // indirect

replace k8s.io/klog => k8s.io/klog/v2 v2.90.0

After that go build succeed. (I don't know why).
But go list -f '{{.Module}}' k8s.io/klog reports an error

$ go list -f '{{.Module}}' k8s.io/klog
module k8s.io/klog provides package k8s.io/klog and is replaced but not required; to add it:
        go get k8s.io/klog
$ go get k8s.io/klog
go: k8s.io/klog/v2@v2.90.0 used for two different module paths (k8s.io/klog and k8s.io/klog/v2)

[thanm]

@golang/tools-team