support omitting empty fields on map encoders

[whyrusleeping]

No description provided.

[Stebalien]

This isn't go's definition of "empty".

The "omitempty" option specifies that the field should be omitted from the encoding if the field has an empty value, defined as false, 0, a nil pointer, a nil interface value, and any empty array, slice, map, or string.

You can:

• Do nothing if you don't care.
• Use reflect.Value.IsZero (some runtime cost).
• Have a bunch of logic to define the "zeros" for different kinds.
• Define per-field zero values as "variables" in codegen (using reflect.Zero).

[Stebalien]

Oh, so, there's an easier way.

var {{.Name}}Zero {{.Type}}
if t.{{.Name}} == {{.Name}}Zero {
    ...
}

[whyrusleeping]

yeah... I was getting kinda lazy since this fix was three layers down the rabbit hole. I'd like to avoid runtime costs so i think generator time type checking is the right thing to do

[Stebalien]

nit: define fieldCount, then subtract one by one for every empty field.

[whyrusleeping]

will fix the zero type stuff at a later time