Go模块：go / types conf.Check return err：无法导入github.com/xxx/yyy/sub

I have a project using Go module, and the content of go.mod is

module github.com/xxx/yyy

Then, I create a sub directory log and a source file log.go, the project structure looks like this:

yyy
- go.mod
- main.go
- log
  - log.go

Then I write the code in main.go

import (
    "github.com/xxx/yyy/log"
    "go/ast"
    "go/build"
    "go/importer"
    "go/parser"
    "go/token"
    "go/types"
)

var fileSet  = token.NewFileSet()
func main() {
    file, err := parser.ParseFile(fileSet, "main", nil, parser.ParseComments)
    conf := types.Config{Importer: importer.Default()}
    pkg, err := conf.Check(".", fileSet, []*ast.File{file}, nil)
    if err != nil {
        log.Log.Fatal(err.Error()) // type error
    }
}

Then I build it successfully, but when I run it, it crashes and logs could not import github.com/xxx/yyy/log. The err comes from conf.Check definitely, but why does it crash? Does go/types not support go module?