The documentation "Equal is called even if x or y is nil" seems incorrect.

[your-diary]

The documentation of Equal() (introduced in #63) seems incorrect (emphasis mine):

If the values have an Equal method of the form "(T) Equal(T) bool" or "(T) Equal(I) bool" where T is assignable to I, then use the result of x.Equal(y) even if x or y is nil. Otherwise, no such method exists and evaluation proceeds to the next rule.

As far as I tested, x.Equal(y) is NOT called if x == nil or/and y == nil.

playground

package main

import (
	"fmt"

	"github.com/google/go-cmp/cmp"
)

type S struct {
	V *T
}

type T struct {
}

func (t1 T) Equal(t2 T) bool {
	fmt.Println("hello")
	return true
}

func main() {
	{
		s1 := S{
			V: &T{},
		}
		s2 := S{
			V: &T{},
		}
		fmt.Println(cmp.Equal(s1, s2)) //=> hello, hello, true (as expected)
	}

	{
		s1 := S{
			V: nil,
		}
		s2 := S{
			V: &T{},
		}
		// s1.V.Equal(*s2.V) //panics
		fmt.Println(cmp.Equal(s1, s2)) //=> false (doesn't panic)
	}
}