Making this change at this point is sure to break some existing tests, and the benefit seems quite small.

Agree.

Another interesting find is the string representation of a zero reflect.Value may be different:

package main

import "reflect"
import "fmt"

func main() {
	var z reflect.Value // a zero Value value
	var v = reflect.ValueOf(&z).Elem()
	fmt.Println(v) // <invalid Value>
	fmt.Println(z) // <invalid reflect.Value>
}

It looks the docs of reflect.Value clearly states

The zero Value represents no value. Its IsValid method returns false, its Kind method returns Invalid, its String method returns "<invalid Value>"

Ah, in the last code example, the v and z really represent different values. The v is reflect.Value value which represents another reflect.Value value, whereas z represents no value.

However, I think the docs may really need to be corrected.

[edit]: sorry, my old understanding for the string representations was wrong.
It looks the string representation of a valid reflect.Value is like
the form [the-type-of-the-value-represented-by-the-Value-represented-by-the-Value Value] if the value represented by a reflect.Value value is also a reflect.Value value.

I also think the string representation of v is wrong. It should be <reflect.Value Value>, same as the string representation of y in the following example:

package main

import "reflect"
import "fmt"

func main() {
	var z reflect.Value // a zero Value value
	var v = reflect.ValueOf(&z).Elem()
	fmt.Println(v) // <invalid Value>
	fmt.Println(z) // <invalid reflect.Value>
	fmt.Println(v.IsValid()) // true
	
	var y = reflect.ValueOf(&v).Elem()
	fmt.Println(y) // <reflect.Value Value>
}

More:

package main

import "reflect"
import "fmt"

func main() {
	var z reflect.Value // a zero Value value
	var w = reflect.ValueOf(&z)
	
	var y = reflect.ValueOf(&w).Elem()
	fmt.Println(y.Kind()) // struct
	
	var v = w.Elem()
	fmt.Println(v.Kind()) // struct
	fmt.Println(v) // <invalid Value>
	fmt.Println(v.IsValid()) // true
	
	// The two lines should be both panic or both not.
	v.Set(v) // ok
	v.Set(z) // panic: reflect: call of reflect.Value.Set on zero Value
}

[edit]: sorry, the behavior of the program is okay. But the error message is misleading. argument of reflect.Value.Set should be valid would be better, for on zero Value makes people think the receiver argument is zero.

Sorry, updated my last two comments.

closed for some misunderstanding on printing reflect.Value values.