x/pkgsite: show a page for an empty directory that is above a nested module

[julieqiu]

https://pkg.go.dev/google.golang.org/grpc@v1.35.0/cmd currently returns a 404, because it is a directory in the module google.golang.org/grpc that does not contain any packages.

https://pkg.go.dev/google.golang.org/grpc/cmd/protoc-gen-go-grpc however is a nested module in the parent module, https://pkg.go.dev/google.golang.org/grpc.

It would be useful to show a directory page containing the nested module at https://pkg.go.dev/google.golang.org/grpc@v1.35.0/cmd.

[ya5u]

@julieqiu I'd like to take this issue

[julieqiu]

Sounds great - thanks!

[gopherbot]

Change https://golang.org/cl/290049 mentions this issue: internal/frontend: show a page for an empty directory