cmd/go: diagnose packages listed in lexically-impossible modules in vendor/modules.txt

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

Does this issue reproduce with the latest release?

Yes

What did you do?

Moved from https://groups.google.com/u/1/g/golang-nuts/c/04MtZ96TPWo

I checked out the kubernetes project at tag v1.20.4. Then run "go list -deps -json ./... > json.txt" in the project root. In the produced json.txt file, I noticed that the module path for two packages look not right. The path of a package should be prefixed with its module path. But the two aren't. Bug?

The first:

{
    "Dir": "/home/myname/opensource/it-infrastructure/kubernetes/vendor/github.com/Azure/go-autorest/autorest/azure",
    "ImportPath": "github.com/Azure/go-autorest/autorest/azure",
    "Name": "azure",
    "Doc": "Package azure provides Azure-specific implementations used with AutoRest.",
    "Module": {
        "Path": "github.com/Azure/go-autorest/autorest/adal",
        "Replace": {
            "Path": "github.com/Azure/go-autorest/autorest/adal",
            "Version": "v0.9.5"
        }
    },
    ...

The second:

{
    "Dir": "/home/myname/opensource/it-infrastructure/kubernetes/vendor/cloud.google.com/go/compute/metadata",
    "ImportPath": "cloud.google.com/go/compute/metadata",
    "Name": "metadata",
    "Doc": "Package metadata provides access to Google Compute Engine (GCE) metadata and API service accounts.",
    "Module": {
        "Path": "cloud.google.com/go/bigquery",
        "Replace": {
            "Path": "cloud.google.com/go/bigquery",
            "Version": "v1.4.0"
        },
        "Indirect": true
    },
    ...

What did you expect to see?

The path of a package should be prefixed with the path of its containing module.

What did you see instead?

The paths of two 2 packages are not prefixed with their module paths.