fix(go): include Type property in seen struct types

go/internal/base/json.go

@@ -102,7 +102,15 @@ func InferJSONSchema(x any) (s *jsonschema.Schema) {
 			}
 			if baseType.Kind() == reflect.Struct {
 				if seen[baseType] {
+					// check if the type implements json.Marshaler since it might serialize to a non-object
+					marshalerType := reflect.TypeOf((*json.Marshaler)(nil)).Elem()
+					if baseType.Implements(marshalerType) || reflect.PointerTo(baseType).Implements(marshalerType) {
+						return &jsonschema.Schema{
+							AdditionalProperties: jsonschema.TrueSchema,
+						}
+					}
 					return &jsonschema.Schema{
+						Type:                 "object",
 						AdditionalProperties: jsonschema.TrueSchema,
 					}
 				}

go/internal/base/json_test.go

@@ -17,6 +17,7 @@
 package base
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -196,7 +197,75 @@ func TestSchemaAsMapRecursive(t *testing.T) {
 		t.Fatal("expected children to have items")
 	}
 	// The recursive Node reference should have become an "any" schema
+	// including "type" property to prevent recursion errors for schemas for the same type
+	if items["type"] != "object" {
+		t.Errorf("expected children.items.type to be 'object', got %v", items["type"])
+	}
 	if items["additionalProperties"] != true {
 		t.Errorf("expected children.items to be 'any' schema (additionalProperties: true), got %v", items)
 	}
 }
+
+func TestInferJSONSchema_SharedType(t *testing.T) {
+	type Shared struct {
+		Amount float64 `json:"amount"`
+	}
+	type Prizes struct {
+		First  Shared `json:"first"`
+		Second Shared `json:"second"`
+	}
+
+	schema := SchemaAsMap(InferJSONSchema(Prizes{}))
+	properties, ok := schema["properties"].(map[string]any)
+	if !ok {
+		t.Fatal("expected properties in schema")
+	}
+
+	second, ok := properties["second"].(map[string]any)
+	if !ok {
+		t.Fatal("expected 'second' property in schema")
+	}
+
+	if second["type"] != "object" {
+		t.Errorf("expected type: object for shared type occurrence, got %v", second["type"])
+	}
+	if second["additionalProperties"] != true {
+		t.Errorf("expected additionalProperties: true for shared type occurrence, got %v", second["additionalProperties"])
+	}
+}
+
+type testStringer struct {
+	Value string
+}
+
+func (s testStringer) MarshalJSON() ([]byte, error) {
+	return json.Marshal(s.Value)
+}
+
+func TestInferJSONSchema_SharedTypeWithMarshaler(t *testing.T) {
+	type Container struct {
+		A testStringer
+		B testStringer
+	}
+	schema := SchemaAsMap(InferJSONSchema(Container{}))
+	properties, ok := schema["properties"].(map[string]any)
+	if !ok {
+		t.Fatal("expected properties in schema")
+	}
+
+	second, ok := properties["B"].(map[string]any)
+	if !ok {
+		t.Fatal("expected 'B' property in schema")
+	}
+
+	// type should be non-object because it implements json.Marshaler
+	if typ, hasType := second["type"]; hasType {
+		if typ == "object" {
+			t.Errorf("expected type to NOT be object for shared type with marshaler, got %v", typ)
+		}
+	}
+
+	if val, ok := second["additionalProperties"]; !ok || val != true {
+		t.Errorf("expected additionalProperties: true, got %v", val)
+	}
+}