method.go

package defaults

import (
	"reflect"
	"runtime"
)

// isPromotedMethod reports whether the method called name is promoted from an embedded field rather
// than declared by t itself.
//
// reflect lists the two alike, under the same name and signature in the same method set, so this asks
// where the method's code comes from instead. For a promoted method the compiler generates a wrapper
// that calls through to the field, and positions it in "<autogenerated>"; a declared method is
// positioned in the file that declares it.
//
// The value's method set is read before the pointer's, because a method declared on a value receiver
// is in the pointer's set too, as exactly such a generated wrapper.
//
// t, or a pointer to t, must have the method. With neither there is no code to ask about, and
// isPromotedMethod panics rather than answer for a method that is not there.
//
// Which method the walk cares about is not this file's business: the caller names it.
func isPromotedMethod(t reflect.Type, name string) bool {
	m, ok := t.MethodByName(name)
	if !ok {
		m, _ = reflect.PointerTo(t).MethodByName(name)
	}

	pc := m.Func.Pointer()
	file, _ := runtime.FuncForPC(pc).FileLine(pc)
	return file == "<autogenerated>"
}