GH-49956: [GLib] Add fallback data type for unknown extension data type

Users can define any extension data type. So we may encounter an
unknown extension type. We can't use `GArrowExtensionDataType` for an
unknown extension data type because `GArrowExtensionDataType` is an
abstract class.

This adds `GArrowUnknownExtensionDataType` and uses it for all unknown
extension data types.

Author: kou

c_glib/arrow-glib/basic-data-type.cpp

@@ -131,6 +131,9 @@ G_BEGIN_DECLS
  * #GArrowExtensionDataType is a base class for user-defined extension
  * data types.
  *
+ * #GArrowUnknownExtensionDataType is a class for unknown extension
+ * data types.
+ *
  * #GArrowExtensionDataTypeRegistry is a class to manage extension
  * data types.
  *
@@ -2080,6 +2083,20 @@ namespace garrow {
 
 G_BEGIN_DECLS
 
+G_DEFINE_TYPE(GArrowUnknownExtensionDataType,
+              garrow_unknown_extension_data_type,
+              GARROW_TYPE_EXTENSION_DATA_TYPE)
+
+static void
+garrow_unknown_extension_data_type_init(GArrowUnknownExtensionDataType *object)
+{
+}
+
+static void
+garrow_unknown_extension_data_type_class_init(GArrowUnknownExtensionDataTypeClass *klass)
+{
+}
+
 typedef struct GArrowExtensionDataTypeRegistryPrivate_
 {
   std::shared_ptr<arrow::ExtensionTypeRegistry> registry;
@@ -2720,16 +2737,25 @@ garrow_data_type_new_raw(std::shared_ptr<arrow::DataType> *arrow_data_type)
     type = GARROW_TYPE_DURATION_DATA_TYPE;
     break;
   case arrow::Type::type::EXTENSION:
+    type = GARROW_TYPE_UNKNOWN_EXTENSION_DATA_TYPE;
     {
-      auto g_extension_data_type =
-        std::static_pointer_cast<garrow::GExtensionType>(*arrow_data_type);
-      if (g_extension_data_type) {
-        auto garrow_data_type = g_extension_data_type->garrow_data_type();
-        g_object_ref(garrow_data_type);
-        return GARROW_DATA_TYPE(garrow_data_type);
+      auto arrow_extension_data_type =
+        std::static_pointer_cast<arrow::ExtensionType>(*arrow_data_type);
+      auto name = arrow_extension_data_type->extension_name();
+      if (name == "arrow.fixed_shape_tensor") {
+        type = GARROW_TYPE_FIXED_SHAPE_TENSOR_DATA_TYPE;
+      } else if (name == "arrow.uuid") {
+        type = GARROW_TYPE_UUID_DATA_TYPE;
+      } else {
+        auto g_extension_data_type =
+          std::dynamic_pointer_cast<garrow::GExtensionType>(*arrow_data_type);
+        if (g_extension_data_type) {
+          auto garrow_data_type = g_extension_data_type->garrow_data_type();
+          g_object_ref(garrow_data_type);
+          return GARROW_DATA_TYPE(garrow_data_type);
+        }
       }
     }
-    type = GARROW_TYPE_EXTENSION_DATA_TYPE;
     break;
   case arrow::Type::type::FIXED_SIZE_LIST:
     type = GARROW_TYPE_FIXED_SIZE_LIST_DATA_TYPE;

c_glib/arrow-glib/basic-data-type.h

@@ -758,6 +758,19 @@ GArrowChunkedArray *
 garrow_extension_data_type_wrap_chunked_array(GArrowExtensionDataType *data_type,
                                               GArrowChunkedArray *storage);
 
+#define GARROW_TYPE_UNKNOWN_EXTENSION_DATA_TYPE                                          \
+  (garrow_unknown_extension_data_type_get_type())
+GARROW_AVAILABLE_IN_25_0
+G_DECLARE_DERIVABLE_TYPE(GArrowUnknownExtensionDataType,
+                         garrow_unknown_extension_data_type,
+                         GARROW,
+                         UNKNOWN_EXTENSION_DATA_TYPE,
+                         GArrowExtensionDataType)
+struct _GArrowUnknownExtensionDataTypeClass
+{
+  GArrowExtensionDataTypeClass parent_class;
+};
+
 #define GARROW_TYPE_EXTENSION_DATA_TYPE_REGISTRY                                         \
   (garrow_extension_data_type_registry_get_type())
 GARROW_AVAILABLE_IN_3_0

c_glib/test/test-fixed-shape-tensor-data-type.rb

@@ -104,4 +104,9 @@ def test_mismatch_dim_names_size
     assert_equal(message,
                  error.message.lines.first.chomp)
   end
+
+  def test_converted_from_cpp
+    schema = Arrow::Schema.new([Arrow::Field.new("tensor", @data_type)])
+    assert_equal(@data_type, schema.fields[0].data_type)
+  end
 end

c_glib/test/test-uuid-data-type.rb

@@ -32,4 +32,9 @@ def test_name
   def test_to_s
     assert_equal("extension<arrow.uuid>", @data_type.to_s)
   end
+
+  def test_converted_from_cpp
+    schema = Arrow::Schema.new([Arrow::Field.new("uuid", @data_type)])
+    assert_equal(@data_type, schema.fields[0].data_type)
+  end
 end