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fix(go): include Type property in seen struct types #4216

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fix(go): include Type property in seen struct types #4216

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926ec84
fix(go): include type property in seen struct types
hugoaguirre Jan 21, 2026
8aaaa56
update test comments
hugoaguirre Jan 21, 2026
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1 change: 1 addition & 0 deletions go/internal/base/json.go
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Original file line number Diff line number Diff line change
Expand Up @@ -103,6 +103,7 @@ func InferJSONSchema(x any) (s *jsonschema.Schema) {
if baseType.Kind() == reflect.Struct {
if seen[baseType] {
return &jsonschema.Schema{
Type: "object",
AdditionalProperties: jsonschema.TrueSchema,
}
Comment on lines 105 to 108
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@gemini-code-assist gemini-code-assist bot Jan 21, 2026

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high

This change correctly adds Type: "object" for seen structs, making the schema more specific. However, this introduces an issue for struct types that implement json.Marshaler to produce a non-object JSON representation (e.g., a string or number).

For such types, this logic will incorrectly claim the type is object. For example:

type MyStringer struct { Value string }
func (s MyStringer) MarshalJSON() ([]byte, error) { return json.Marshal(s.Value) }

type Container struct {
    A MyStringer
    B MyStringer
}

When inferring the schema for Container, the schema for the second occurrence of MyStringer (field B) will be incorrectly marked as type: "object".

To fix this, we should check if the struct implements json.Marshaler and, if so, fall back to a more generic schema that doesn't specify the type, which is consistent with how jsonschema handles marshalers.

          var marshalerType = reflect.TypeOf((*json.Marshaler)(nil)).Elem()
          if baseType.Implements(marshalerType) || reflect.PtrTo(baseType).Implements(marshalerType) {
            return &jsonschema.Schema{
              AdditionalProperties: jsonschema.TrueSchema,
            }
          }
          return &jsonschema.Schema{
            Type:                 "object",
            AdditionalProperties: jsonschema.TrueSchema,
          }

}
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32 changes: 32 additions & 0 deletions go/internal/base/json_test.go
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Expand Up @@ -196,7 +196,39 @@ 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"])
}
}
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