Fix hash calculation based on proto.Struct

[krhubert]

close #1315

[NicolasMahe]

Another problem, the following is returning {a:{b:1}}:

Suggested change

	{
	{
	struct {
	a interface{}
	}{
	struct {
	b interface{}
	}{
	b: 1,
	},
	},
	"{a:{}}",
	},
	{

[NicolasMahe]

Solution, replace in structhash.go line 105 by:

- if to.name == "" && reflect.Zero(sf.Type).Kind() == reflect.Interface {
+ if to.name == "" && v.Field(i).Kind() == reflect.Interface && v.Field(i).Elem().Kind() == reflect.Struct {

It will only continue if the field is defined as type interface and has as "real" type Struct.

[krhubert]

This is how it interface works. It's not a bug, it done design.
So let's break it down:

a struct is passed with a interface{] fileds which has no tag.

A struct is serialized and a field is serialized because it's an interface.

Then interface{} has struct inside. That struct is serialized because it's not a field of any struct, but rather the object (interface value). The struct contains b fields which is an interface so it's serialized and interface value contains an integer. So the final output should be {a:{b:1}}

[NicolasMahe]

Test line 60 is wrong:

		{
			struct {
				a int `hash:"omitempty"`
			}{1},
			"{}",
		},

it should returns {a:1}

Solution:
Replace hash:"omitempty" by hash:"name:a,omitempty"

So any field without an explicit hash name is discarded?

[krhubert]

Test line 60 is wrong:

It's not. Field a has no name in the tag, only omitempty and a is not an interface so serialize should return an empty struct.