cmd/doc: constructor sometimes not associated with type

[dsnet]

Using go1.17.1

When I run:

$ go doc net/http.Request

I see (with some irrelevant details removed):

package http // import "net/http"

type Request struct {
    ...
}

func (r *Request) AddCookie(c *Cookie)
func (r *Request) BasicAuth() (username, password string, ok bool)
func (r *Request) Clone(ctx context.Context) *Request
func (r *Request) Context() context.Context
func (r *Request) Cookie(name string) (*Cookie, error)
func (r *Request) Cookies() []*Cookie
func (r *Request) FormFile(key string) (multipart.File, *multipart.FileHeader, error)
func (r *Request) FormValue(key string) string
func (r *Request) MultipartReader() (*multipart.Reader, error)
func (r *Request) ParseForm() error
func (r *Request) ParseMultipartForm(maxMemory int64) error
func (r *Request) PostFormValue(key string) string
func (r *Request) ProtoAtLeast(major, minor int) bool
func (r *Request) Referer() string
func (r *Request) SetBasicAuth(username, password string)
func (r *Request) UserAgent() string
func (r *Request) WithContext(ctx context.Context) *Request
func (r *Request) Write(w io.Writer) error
func (r *Request) WriteProxy(w io.Writer) error

This only lists the methods of Request, but does not show any of the constructor functions:

• NewRequest
• NewRequestWithContext
• ReadRequest

I would expect it to list the constructors as well, since it does so for other types (e.g., go doc compress/gzip.Reader).

Also, the fact that it does not list the constructors is inconsistent with go.pkg.dev, which does group those three functions with the type.