module required error when get module in multi module repo mode

[chengjingtao]

Hi, I have a module mode repo like this:

// repo: https://git.mycompany.com/dev/pkg.git

├── README.md
├── go.mod    // go.mycompany.com/pkg
├── util
│   ├── go.mod   // go.mycompany.com/pkg/util
│   ├── go.sum
│   ├── xx.go
├── log
│   ├── go.mod    // go.mycompany.com/pkg/log
│   ├── go.sum
│   └── xx.go

I have add config in vanity.yaml

paths:
  /pkg/util:
    repo: https://git.mycompany.com/dev/pkg

but When execute command go get -v go.company.com/pkg/util , I got error

get "go.company.com/pkg": found meta tag get.metaImport{Prefix:"go.company.com/pkg", VCS:"git", RepoRoot:"https://git.mycompany.com/dev/pkg"} at //git.mycompany.com/pkg?go-get=1
get "go.company.com/pkg/util": found meta tag get.metaImport{Prefix:"go.company.com/pkg/util", VCS:"git", RepoRoot:"https://git.mycompany.com/dev/pkg"} at //git.mycompany.com/pkg/util?go-get=1
go: go.mycompany.com/pkg/util master => v0.1.2-0.20210120054534-86b99a469841
go get: go.mycompany.com/pkg/util@v0.1.2-0.20210120054534-86b99a469841: parsing go.mod:
	module declares its path as: go.mycompany.com/pkg
	        but was required as: go.mycompany.com/pkg/util

Is there any idea to resolve it ?

[danielorbach]

The toolchain supports Module directories within a repository.

Recall that a module path consists of three parts: a repository root path (corresponding to the repository root directory), a module subdirectory, and a major version suffix (only for modules released at v2 or higher).
Modules are sometimes defined in repository subdirectories. Such a module is expected to be found in a subdirectory that matches the part of the module’s path after the repository root path.
For example, suppose the module example.com/monorepo/foo/bar is in the repository with root path example.com/monorepo. Its go.mod file must be in the foo/bar subdirectory.

The following vanity.yaml should work:

host: go.mycompany.com
paths:
  /pkg:
    repo: https://git.mycompany.com/dev/pkg

For troubleshooting, when running go get -v go.company.com/pkg/util expect to see the following:

...
get "go.company.com/pkg/util": found meta tag vcs.metaImport{Prefix:"go.company.com/pkg", VCS:"git", RepoRoot:"https://git.mycompany.com/dev/pkg"} at //git.mycompany.com/pkg/util?go-get=1
...

[danielorbach]

Also note that the current latest version of this repository (2171d0d) fails to handle the path / correctly.
Here's a possible fix:

diff --git a/tools/vanity-urls/handler.go b/tools/vanity-urls/handler.go
@@ -70,6 +70,10 @@ func newHandler(config []byte) (*handler, error) {
                        display: e.Display,
                        vcs:     e.VCS,
                }
+               // A path may be "/", which is trimmed to "" above.
+               if pc.path == "" {
+                       pc.path = "/"
+               }
                switch {
                case e.Display != "":
                        // Already filled in.