feat(go): Unions include runtime validation

generators/go/cmd/fern-go-model/main_test.go

@@ -249,12 +249,6 @@ func TestTime(t *testing.T) {
 	})
 
 	t.Run("union (optional)", func(t *testing.T) {
-		empty := union.NewUnionWithOptionalTimeFromDate(nil)
-
-		emptyBytes, err := json.Marshal(empty)
-		require.NoError(t, err)
-		assert.Equal(t, `{"type":"date"}`, string(emptyBytes))
-
 		value := union.NewUnionWithOptionalTimeFromDate(&date)
 
 		bytes, err := json.Marshal(value)

generators/go/internal/generator/generator.go

@@ -1703,7 +1703,7 @@ func zeroValueForPrimitive(primitive fernir.PrimitiveTypeV1) string {
 	case fernir.PrimitiveTypeV1DateTime, fernir.PrimitiveTypeV1Date:
 		return "time.Time{}"
 	case fernir.PrimitiveTypeV1Uuid:
-		return "uuid.UUID{}"
+		return "uuid.Nil"
 	case fernir.PrimitiveTypeV1Base64:
 		return "nil"
 	}

generators/go/internal/generator/model.go

@@ -474,6 +474,9 @@ func (t *typeVisitor) VisitUnion(union *ir.UnionTypeDeclaration) error {
 
 	// Implement the json.Marshaler interface.
 	t.writer.P("func (", receiver, " ", t.typeName, ") MarshalJSON() ([]byte, error) {")
+	t.writer.P("if err := ", receiver, ".validate(); err != nil {")
+	t.writer.P("return nil, err")
+	t.writer.P("}")
 	if t.unionVersion != UnionVersionV1 {
 		t.writer.P("switch ", receiver, ".", discriminantName, " {")
 	}
@@ -659,6 +662,63 @@ func (t *typeVisitor) VisitUnion(union *ir.UnionTypeDeclaration) error {
 	t.writer.P("}")
 	t.writer.P()
 
+	// Generate the validate method.
+	t.writer.P("func (", receiver, " *", t.typeName, ") validate() error {")
+	t.writer.P("if ", receiver, " == nil {")
+	t.writer.P(`return fmt.Errorf("type %T is nil", `, receiver, ")")
+	t.writer.P("}")
+	t.writer.P("var fields []string")
+	for _, unionType := range union.Types {
+		var (
+			isLiteral  bool
+			isOptional bool
+			date       *date
+		)
+		if unionType.Shape.SingleProperty != nil {
+			isLiteral = isLiteralType(unionType.Shape.SingleProperty.Type, t.writer.types)
+			isOptional = isOptionalType(unionType.Shape.SingleProperty.Type, t.writer.types)
+			date = maybeDate(unionType.Shape.SingleProperty.Type, isOptional)
+		}
+		zeroValue := "nil"
+		if unionType.Shape.PropertiesType == "singleProperty" {
+			zeroValue = zeroValueForTypeReference(unionType.Shape.SingleProperty.Type, t.writer.types)
+		}
+		unionTypeValue := receiver + "." + unionType.DiscriminantValue.Name.PascalCase.UnsafeName
+		if isLiteral {
+			unionTypeValue = receiver + "." + unionType.DiscriminantValue.Name.CamelCase.SafeName
+		}
+		if date != nil && !isOptional {
+			t.writer.P("if !", unionTypeValue, ".IsZero() {")
+		} else {
+			t.writer.P("if ", unionTypeValue, " != ", zeroValue, " {")
+		}
+		t.writer.P(`fields = append(fields, "`, unionType.DiscriminantValue.WireValue, `")`)
+		t.writer.P("}")
+	}
+	t.writer.P("if len(fields) == 0 {")
+	t.writer.P("if ", receiver, ".", discriminantName, ` != "" {`)
+	t.writer.P(`return fmt.Errorf("type %T defines a discriminant set to %q but the field is not set", `, receiver, ", ", receiver, ".", discriminantName, ")")
+	t.writer.P("}")
+	t.writer.P(`return fmt.Errorf("type %T is empty", `, receiver, ")")
+	t.writer.P("}")
+	t.writer.P("if len(fields) > 1 {")
+	t.writer.P(`return fmt.Errorf("type %T defines values for %s, but only one value is allowed", `, receiver, ", fields)")
+	t.writer.P("}")
+	t.writer.P("if ", receiver, ".", discriminantName, ` != "" {`)
+	t.writer.P("field := fields[0]")
+	t.writer.P("if ", receiver, ".", discriminantName, " != field {")
+	t.writer.P("return fmt.Errorf(")
+	t.writer.P(`"type %T defines a discriminant set to %q, but it does not match the %T field; either remove or update the discriminant to match",`)
+	t.writer.P(receiver, ", ")
+	t.writer.P(receiver, ".", discriminantName, ", ")
+	t.writer.P(receiver, ", ")
+	t.writer.P(")")
+	t.writer.P("}")
+	t.writer.P("}")
+	t.writer.P("return nil")
+	t.writer.P("}")
+	t.writer.P()
+
 	return nil
 }
 

generators/go/internal/testdata/model/alias/fixtures/imdb.go

@@ -73,7 +73,7 @@ type Foo struct {
 
 func (f *Foo) GetId() uuid.UUID {
 	if f == nil {
-		return uuid.UUID{}
+		return uuid.Nil
 	}
 	return f.Id
 }
@@ -224,6 +224,9 @@ func (u *Union) UnmarshalJSON(data []byte) error {
 }
 
 func (u Union) MarshalJSON() ([]byte, error) {
+	if err := u.validate(); err != nil {
+		return nil, err
+	}
 	switch u.Type {
 	default:
 		return nil, fmt.Errorf("invalid type %s in %T", u.Type, u)
@@ -269,6 +272,43 @@ func (u *Union) Accept(visitor UnionVisitor) error {
 	}
 }
 
+func (u *Union) validate() error {
+	if u == nil {
+		return fmt.Errorf("type %T is nil", u)
+	}
+	var fields []string
+	if u.FooAlias != nil {
+		fields = append(fields, "fooAlias")
+	}
+	if u.BarAlias != nil {
+		fields = append(fields, "barAlias")
+	}
+	if u.DoubleAlias != 0 {
+		fields = append(fields, "doubleAlias")
+	}
+	if len(fields) == 0 {
+		if u.Type != "" {
+			return fmt.Errorf("type %T defines a discriminant set to %q but the field is not set", u, u.Type)
+		}
+		return fmt.Errorf("type %T is empty", u)
+	}
+	if len(fields) > 1 {
+		return fmt.Errorf("type %T defines values for %s, but only one value is allowed", u, fields)
+	}
+	if u.Type != "" {
+		field := fields[0]
+		if u.Type != field {
+			return fmt.Errorf(
+				"type %T defines a discriminant set to %q, but it does not match the %T field; either remove or update the discriminant to match",
+				u,
+				u.Type,
+				u,
+			)
+		}
+	}
+	return nil
+}
+
 type Unknown = interface{}
 
 type Uuid = uuid.UUID

generators/go/internal/testdata/model/builtin/fixtures/imdb.go

@@ -86,7 +86,7 @@ func (t *Type) GetSeven() time.Time {
 
 func (t *Type) GetEight() uuid.UUID {
 	if t == nil {
-		return uuid.UUID{}
+		return uuid.Nil
 	}
 	return t.Eight
 }

generators/go/internal/testdata/model/custom/fixtures/imdb.go

@@ -59,7 +59,7 @@ type Foo struct {
 
 func (f *Foo) GetId() uuid.UUID {
 	if f == nil {
-		return uuid.UUID{}
+		return uuid.Nil
 	}
 	return f.Id
 }

generators/go/internal/testdata/model/extends/fixtures/imdb.go

@@ -262,6 +262,9 @@ func (n *NestedUnion) UnmarshalJSON(data []byte) error {
 }
 
 func (n NestedUnion) MarshalJSON() ([]byte, error) {
+	if err := n.validate(); err != nil {
+		return nil, err
+	}
 	switch n.Type {
 	default:
 		return nil, fmt.Errorf("invalid type %s in %T", n.Type, n)
@@ -283,6 +286,37 @@ func (n *NestedUnion) Accept(visitor NestedUnionVisitor) error {
 	}
 }
 
+func (n *NestedUnion) validate() error {
+	if n == nil {
+		return fmt.Errorf("type %T is nil", n)
+	}
+	var fields []string
+	if n.One != nil {
+		fields = append(fields, "one")
+	}
+	if len(fields) == 0 {
+		if n.Type != "" {
+			return fmt.Errorf("type %T defines a discriminant set to %q but the field is not set", n, n.Type)
+		}
+		return fmt.Errorf("type %T is empty", n)
+	}
+	if len(fields) > 1 {
+		return fmt.Errorf("type %T defines values for %s, but only one value is allowed", n, fields)
+	}
+	if n.Type != "" {
+		field := fields[0]
+		if n.Type != field {
+			return fmt.Errorf(
+				"type %T defines a discriminant set to %q, but it does not match the %T field; either remove or update the discriminant to match",
+				n,
+				n.Type,
+				n,
+			)
+		}
+	}
+	return nil
+}
+
 type Union struct {
 	Type string
 	Docs string
@@ -339,6 +373,9 @@ func (u *Union) UnmarshalJSON(data []byte) error {
 }
 
 func (u Union) MarshalJSON() ([]byte, error) {
+	if err := u.validate(); err != nil {
+		return nil, err
+	}
 	switch u.Type {
 	default:
 		return nil, fmt.Errorf("invalid type %s in %T", u.Type, u)
@@ -359,3 +396,34 @@ func (u *Union) Accept(visitor UnionVisitor) error {
 		return visitor.VisitOne(u.One)
 	}
 }
+
+func (u *Union) validate() error {
+	if u == nil {
+		return fmt.Errorf("type %T is nil", u)
+	}
+	var fields []string
+	if u.One != nil {
+		fields = append(fields, "one")
+	}
+	if len(fields) == 0 {
+		if u.Type != "" {
+			return fmt.Errorf("type %T defines a discriminant set to %q but the field is not set", u, u.Type)
+		}
+		return fmt.Errorf("type %T is empty", u)
+	}
+	if len(fields) > 1 {
+		return fmt.Errorf("type %T defines values for %s, but only one value is allowed", u, fields)
+	}
+	if u.Type != "" {
+		field := fields[0]
+		if u.Type != field {
+			return fmt.Errorf(
+				"type %T defines a discriminant set to %q, but it does not match the %T field; either remove or update the discriminant to match",
+				u,
+				u.Type,
+				u,
+			)
+		}
+	}
+	return nil
+}

generators/go/internal/testdata/model/github/fixtures/foo.go

@@ -34,7 +34,7 @@ func (f *Foo) GetBar() *bar.Bar {
 
 func (f *Foo) GetUuid() uuid.UUID {
 	if f == nil {
-		return uuid.UUID{}
+		return uuid.Nil
 	}
 	return f.Uuid
 }

generators/go/internal/testdata/model/ir/fixtures/auth.go

@@ -145,6 +145,9 @@ func (a *AuthScheme) UnmarshalJSON(data []byte) error {
 }
 
 func (a AuthScheme) MarshalJSON() ([]byte, error) {
+	if err := a.validate(); err != nil {
+		return nil, err
+	}
 	switch a.Type {
 	default:
 		return nil, fmt.Errorf("invalid type %s in %T", a.Type, a)
@@ -176,6 +179,43 @@ func (a *AuthScheme) Accept(visitor AuthSchemeVisitor) error {
 	}
 }
 
+func (a *AuthScheme) validate() error {
+	if a == nil {
+		return fmt.Errorf("type %T is nil", a)
+	}
+	var fields []string
+	if a.Bearer != nil {
+		fields = append(fields, "bearer")
+	}
+	if a.Basic != nil {
+		fields = append(fields, "basic")
+	}
+	if a.Header != nil {
+		fields = append(fields, "header")
+	}
+	if len(fields) == 0 {
+		if a.Type != "" {
+			return fmt.Errorf("type %T defines a discriminant set to %q but the field is not set", a, a.Type)
+		}
+		return fmt.Errorf("type %T is empty", a)
+	}
+	if len(fields) > 1 {
+		return fmt.Errorf("type %T defines values for %s, but only one value is allowed", a, fields)
+	}
+	if a.Type != "" {
+		field := fields[0]
+		if a.Type != field {
+			return fmt.Errorf(
+				"type %T defines a discriminant set to %q, but it does not match the %T field; either remove or update the discriminant to match",
+				a,
+				a.Type,
+				a,
+			)
+		}
+	}
+	return nil
+}
+
 type AuthSchemesRequirement string
 
 const (

generators/go/internal/testdata/model/ir/fixtures/environment.go

@@ -125,6 +125,9 @@ func (e *Environments) UnmarshalJSON(data []byte) error {
 }
 
 func (e Environments) MarshalJSON() ([]byte, error) {
+	if err := e.validate(); err != nil {
+		return nil, err
+	}
 	switch e.Type {
 	default:
 		return nil, fmt.Errorf("invalid type %s in %T", e.Type, e)
@@ -151,6 +154,40 @@ func (e *Environments) Accept(visitor EnvironmentsVisitor) error {
 	}
 }
 
+func (e *Environments) validate() error {
+	if e == nil {
+		return fmt.Errorf("type %T is nil", e)
+	}
+	var fields []string
+	if e.SingleBaseUrl != nil {
+		fields = append(fields, "singleBaseUrl")
+	}
+	if e.MultipleBaseUrls != nil {
+		fields = append(fields, "multipleBaseUrls")
+	}
+	if len(fields) == 0 {
+		if e.Type != "" {
+			return fmt.Errorf("type %T defines a discriminant set to %q but the field is not set", e, e.Type)
+		}
+		return fmt.Errorf("type %T is empty", e)
+	}
+	if len(fields) > 1 {
+		return fmt.Errorf("type %T defines values for %s, but only one value is allowed", e, fields)
+	}
+	if e.Type != "" {
+		field := fields[0]
+		if e.Type != field {
+			return fmt.Errorf(
+				"type %T defines a discriminant set to %q, but it does not match the %T field; either remove or update the discriminant to match",
+				e,
+				e.Type,
+				e,
+			)
+		}
+	}
+	return nil
+}
+
 type EnvironmentsConfig struct {
 	DefaultEnvironment *EnvironmentId `json:"defaultEnvironment,omitempty" url:"defaultEnvironment,omitempty"`
 	Environments       *Environments  `json:"environments,omitempty" url:"environments,omitempty"`