all: statically enforce json/v2 interface satisfaction (#15154)

The json/v2 prototype is still in flux and the API can/will change.

Statically enforce that types implementing the v2 methods
satisfy the correct interface so that changes to the signature
can be statically detected by the compiler.

Updates tailscale/corp#791

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

types/opt/value_test.go

@@ -13,6 +13,11 @@ import (
 	"tailscale.com/util/must"
 )
 
+var (
+	_ jsonv2.MarshalerTo     = (*Value[bool])(nil)
+	_ jsonv2.UnmarshalerFrom = (*Value[bool])(nil)
+)
+
 type testStruct struct {
 	Int int    `json:",omitempty,omitzero"`
 	Str string `json:",omitempty"`

types/prefs/list.go

@@ -157,6 +157,11 @@ func (lv ListView[T]) Equal(lv2 ListView[T]) bool {
 	return lv.ж.Equal(*lv2.ж)
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*ListView[bool])(nil)
+	_ jsonv2.UnmarshalerFrom = (*ListView[bool])(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (lv ListView[T]) MarshalJSONTo(out *jsontext.Encoder) error {
 	return lv.ж.MarshalJSONTo(out)

types/prefs/prefs.go

@@ -158,6 +158,11 @@ func (p *preference[T]) SetReadOnly(readonly bool) {
 	p.s.Metadata.ReadOnly = readonly
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*preference[struct{}])(nil)
+	_ jsonv2.UnmarshalerFrom = (*preference[struct{}])(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (p preference[T]) MarshalJSONTo(out *jsontext.Encoder) error {
 	return jsonv2.MarshalEncode(out, &p.s)

types/prefs/prefs_example/prefs_types.go

@@ -128,6 +128,11 @@ type AppConnectorPrefs struct {
 	Advertise prefs.Item[bool] `json:",omitzero"`
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*Prefs)(nil)
+	_ jsonv2.UnmarshalerFrom = (*Prefs)(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 // It is implemented as a performance improvement and to enable omission of
 // unconfigured preferences from the JSON output. See the [Prefs] doc for details.

types/prefs/prefs_test.go

@@ -19,6 +19,20 @@ import (
 
 //go:generate go run tailscale.com/cmd/viewer --tags=test --type=TestPrefs,TestBundle,TestValueStruct,TestGenericStruct,TestPrefsGroup
 
+var (
+	_ jsonv2.MarshalerTo     = (*ItemView[*TestBundle, TestBundleView])(nil)
+	_ jsonv2.UnmarshalerFrom = (*ItemView[*TestBundle, TestBundleView])(nil)
+
+	_ jsonv2.MarshalerTo     = (*MapView[string, string])(nil)
+	_ jsonv2.UnmarshalerFrom = (*MapView[string, string])(nil)
+
+	_ jsonv2.MarshalerTo     = (*StructListView[*TestBundle, TestBundleView])(nil)
+	_ jsonv2.UnmarshalerFrom = (*StructListView[*TestBundle, TestBundleView])(nil)
+
+	_ jsonv2.MarshalerTo     = (*StructMapView[string, *TestBundle, TestBundleView])(nil)
+	_ jsonv2.UnmarshalerFrom = (*StructMapView[string, *TestBundle, TestBundleView])(nil)
+)
+
 type TestPrefs struct {
 	Int32Item   Item[int32]  `json:",omitzero"`
 	UInt64Item  Item[uint64] `json:",omitzero"`
@@ -53,6 +67,11 @@ type TestPrefs struct {
 	Group TestPrefsGroup `json:",omitzero"`
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*TestPrefs)(nil)
+	_ jsonv2.UnmarshalerFrom = (*TestPrefs)(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (p TestPrefs) MarshalJSONTo(out *jsontext.Encoder) error {
 	// The testPrefs type shadows the TestPrefs's method set,

util/syspolicy/setting/origin.go

@@ -50,6 +50,11 @@ func (s Origin) String() string {
 	return s.Scope().String()
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*Origin)(nil)
+	_ jsonv2.UnmarshalerFrom = (*Origin)(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (s Origin) MarshalJSONTo(out *jsontext.Encoder) error {
 	return jsonv2.MarshalEncode(out, &s.data)

util/syspolicy/setting/raw_item.go

@@ -75,6 +75,11 @@ func (i RawItem) String() string {
 	return fmt.Sprintf("%v%s", i.data.Value.Value, suffix)
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*RawItem)(nil)
+	_ jsonv2.UnmarshalerFrom = (*RawItem)(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (i RawItem) MarshalJSONTo(out *jsontext.Encoder) error {
 	return jsonv2.MarshalEncode(out, &i.data)
@@ -114,6 +119,11 @@ func RawValueOf[T RawValueType](v T) RawValue {
 	return RawValue{opt.ValueOf[any](v)}
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*RawValue)(nil)
+	_ jsonv2.UnmarshalerFrom = (*RawValue)(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (v RawValue) MarshalJSONTo(out *jsontext.Encoder) error {
 	return jsonv2.MarshalEncode(out, v.Value)

util/syspolicy/setting/snapshot.go

@@ -147,6 +147,11 @@ type snapshotJSON struct {
 	Settings map[Key]RawItem `json:",omitempty"`
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*Snapshot)(nil)
+	_ jsonv2.UnmarshalerFrom = (*Snapshot)(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (s *Snapshot) MarshalJSONTo(out *jsontext.Encoder) error {
 	data := &snapshotJSON{}

util/syspolicy/setting/summary.go

@@ -54,6 +54,11 @@ func (s Summary) String() string {
 	return s.data.Scope.String()
 }
 
+var (
+	_ jsonv2.MarshalerTo     = (*Summary)(nil)
+	_ jsonv2.UnmarshalerFrom = (*Summary)(nil)
+)
+
 // MarshalJSONTo implements [jsonv2.MarshalerTo].
 func (s Summary) MarshalJSONTo(out *jsontext.Encoder) error {
 	return jsonv2.MarshalEncode(out, &s.data)