En, it looks the implementation is correct, it is consistent with reflection:

package main

import (
	"fmt"
	"reflect"
)

type S struct{}

func (*S) F() {}

type T struct {
	*T
	*S
}

func (*T) M() {}


func main(){
	T{}.F()   // no problem
	T{}.S.F() // no problem
	//T{}.M()   // cannot take the address of T literal
	T{}.T.M() // no problem
	
	_ = T{}.F   // no problem
	//_ = T{}.M // cannot take the address of T literal
	
	// <invalid reflect.Value>
	fmt.Println(reflect.ValueOf(T{}).MethodByName("M"))
	// {  <nil> <invalid Value> 0} false
	fmt.Println(reflect.TypeOf(T{}).MethodByName("M"))
	// 1
	fmt.Println(reflect.TypeOf(T{}).NumMethod())
	// {F  func(main.T) <func(main.T) Value> 0}
	fmt.Println(reflect.TypeOf(T{}).Method(0))
	
	_, ok := (interface{}(T{})).(interface{M()})
	fmt.Println(ok) // false
}

Maybe, a small adjustment is needed in spec?

If S contains an embedded field T, the method sets of S and *S both include promoted methods with receiver T. The method set of *S also includes promoted methods with receiver *T.

A simpler example with names used in spec:

package main

import (
	"fmt"
	"reflect"
)

type S struct {
	T
}

func (*S) M() {}

type T struct{}

func (T) M() {}

func main(){
	//S{}.M() // cannot take the address of T literal
	
	//_ = S{}.M // cannot take the address of T literal

	fmt.Println(reflect.TypeOf(S{}).NumMethod())  // 0
	fmt.Println(reflect.TypeOf(&S{}).NumMethod()) // 1
}

In the final example I think you are suggesting that S should inherit the method M from the embedded field T, even though there is a method M on *S. I think it's clear that the language is not intended to permit that. It's possible that the spec does not clearly state that. I think the place to state it would be https://golang.org/ref/spec#Selectors.

CC @griesemer

@ianlancetaylor Yes, I agree.

It looks the current design views S{}.M as a legal but invalid selector. However I haven't found how the spec distinguishes "legal" from "valid" for selectors.

I think this is a dup of #15708. In particular, I think this is my first example here.

I agree this is a dup of #15708, so close it.

Maybe it is good to add a complement in the https://golang.org/ref/spec#Selectors section

For a primary expression x (always assume it is addressable) that is not a package name, the selector expression ....