Factor out API defaulting from validation logic

Currently, the validation logic validates fields in an object and supply default
values wherever applies. This change factors out defaulting to a set of
defaulting callback functions for decoding (see #1502 for more discussion).

 * This change is based on pull request 2587.

 * Most defaulting has been migrated to defaults.go where the defaulting
   functions are added.

 * validation_test.go and converter_test.go have been adapted to not testing the
   default values.

 * Fixed all tests with that create invalid objects with the absence of
   defaulting logic.

pkg/conversion/deep_equal.go

@@ -233,3 +233,140 @@ func (e Equalities) DeepEqual(a1, a2 interface{}) bool {
 	}
 	return e.deepValueEqual(v1, v2, make(map[visit]bool), 0)
 }
+
+func (e Equalities) deepValueDerive(v1, v2 reflect.Value, visited map[visit]bool, depth int) bool {
+	if !v1.IsValid() || !v2.IsValid() {
+		return v1.IsValid() == v2.IsValid()
+	}
+	if v1.Type() != v2.Type() {
+		return false
+	}
+	if fv, ok := e[v1.Type()]; ok {
+		return fv.Call([]reflect.Value{v1, v2})[0].Bool()
+	}
+
+	hard := func(k reflect.Kind) bool {
+		switch k {
+		case reflect.Array, reflect.Map, reflect.Slice, reflect.Struct:
+			return true
+		}
+		return false
+	}
+
+	if v1.CanAddr() && v2.CanAddr() && hard(v1.Kind()) {
+		addr1 := v1.UnsafeAddr()
+		addr2 := v2.UnsafeAddr()
+		if addr1 > addr2 {
+			// Canonicalize order to reduce number of entries in visited.
+			addr1, addr2 = addr2, addr1
+		}
+
+		// Short circuit if references are identical ...
+		if addr1 == addr2 {
+			return true
+		}
+
+		// ... or already seen
+		typ := v1.Type()
+		v := visit{addr1, addr2, typ}
+		if visited[v] {
+			return true
+		}
+
+		// Remember for later.
+		visited[v] = true
+	}
+
+	switch v1.Kind() {
+	case reflect.Array:
+		for i := 0; i < v1.Len(); i++ {
+			if !e.deepValueDerive(v1.Index(i), v2.Index(i), visited, depth+1) {
+				return false
+			}
+		}
+		return true
+	case reflect.Slice:
+		if (v1.IsNil() || v1.Len() == 0) != (v2.IsNil() || v2.Len() == 0) {
+			return false
+		}
+		if v1.IsNil() || v1.Len() == 0 {
+			return true
+		}
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		for i := 0; i < v1.Len(); i++ {
+			if !e.deepValueDerive(v1.Index(i), v2.Index(i), visited, depth+1) {
+				return false
+			}
+		}
+		return true
+	case reflect.String:
+		if v1.Len() == 0 {
+			return true
+		}
+		return v1.String() == v2.String()
+	case reflect.Interface:
+		if v1.IsNil() {
+			return true
+		}
+		return e.deepValueDerive(v1.Elem(), v2.Elem(), visited, depth+1)
+	case reflect.Ptr:
+		if v1.IsNil() {
+			return true
+		}
+		return e.deepValueDerive(v1.Elem(), v2.Elem(), visited, depth+1)
+	case reflect.Struct:
+		for i, n := 0, v1.NumField(); i < n; i++ {
+			if !e.deepValueDerive(v1.Field(i), v2.Field(i), visited, depth+1) {
+				return false
+			}
+		}
+		return true
+	case reflect.Map:
+		if (v1.IsNil() || v1.Len() == 0) != (v2.IsNil() || v2.Len() == 0) {
+			return false
+		}
+		if v1.IsNil() || v1.Len() == 0 {
+			return true
+		}
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		for _, k := range v1.MapKeys() {
+			if !e.deepValueDerive(v1.MapIndex(k), v2.MapIndex(k), visited, depth+1) {
+				return false
+			}
+		}
+		return true
+	case reflect.Func:
+		if v1.IsNil() && v2.IsNil() {
+			return true
+		}
+		// Can't do better than this:
+		return false
+	default:
+		// Normal equality suffices
+		if v1.CanInterface() && v2.CanInterface() {
+			return v1.Interface() == v2.Interface()
+		}
+		return v1.CanInterface() == v2.CanInterface()
+	}
+}
+
+// DeepDerivative is similar to DeepEqual except that unset fields in a1 are
+// ignored (not compared). This allows we to focus on the fields that matter to
+// the semantic comparison.
+//
+// The unset fields include a nil pointer and an empty string.
+func (e Equalities) DeepDerivative(a1, a2 interface{}) bool {
+	if a1 == nil {
+		return true
+	}
+	v1 := reflect.ValueOf(a1)
+	v2 := reflect.ValueOf(a2)
+	if v1.Type() != v2.Type() {
+		return false
+	}
+	return e.deepValueDerive(v1, v2, make(map[visit]bool), 0)
+}