Reject wrapper types built over unsupported nested types

clickhouse/columns/factory.cpp

@@ -150,16 +150,17 @@ static ColumnRef CreateTerminalColumn(const TypeAst& ast) {
 static ColumnRef CreateColumnFromAst(const TypeAst& ast, CreateColumnByTypeSettings settings) {
     switch (ast.meta) {
         case TypeAst::Array: {
-            return std::make_shared<ColumnArray>(
-                CreateColumnFromAst(GetASTChildElement(ast, 0), settings)
-            );
+            if (auto nested = CreateColumnFromAst(GetASTChildElement(ast, 0), settings)) {
+                return std::make_shared<ColumnArray>(nested);
+            }
+            return nullptr;
         }
 
         case TypeAst::Nullable: {
-            return std::make_shared<ColumnNullable>(
-                CreateColumnFromAst(GetASTChildElement(ast, 0), settings),
-                std::make_shared<ColumnUInt8>()
-            );
+            if (auto nested = CreateColumnFromAst(GetASTChildElement(ast, 0), settings)) {
+                return std::make_shared<ColumnNullable>(nested, std::make_shared<ColumnUInt8>());
+            }
+            return nullptr;
         }
 
         case TypeAst::Terminal: {
@@ -252,12 +253,11 @@ static ColumnRef CreateColumnFromAst(const TypeAst& ast, CreateColumnByTypeSetti
                         //      item and would omit the null item, producing an incorrect nullable
                         //      dictionary.
                         //   2. It lets us construct the ColumnNullable with an explicit UInt8 null-map.
-                        return std::make_shared<ColumnLowCardinality>(
-                            std::make_shared<ColumnNullable>(
-                                CreateColumnFromAst(GetASTChildElement(nested, 0), settings),
-                                std::make_shared<ColumnUInt8>()
-                            )
-                        );
+                        if (auto inner = CreateColumnFromAst(GetASTChildElement(nested, 0), settings)) {
+                            return std::make_shared<ColumnLowCardinality>(
+                                std::make_shared<ColumnNullable>(inner, std::make_shared<ColumnUInt8>()));
+                        }
+                        throw UnimplementedError("LowCardinality(Nullable(" + GetASTChildElement(nested, 0).name + ")) is not supported");
                     default: {
                         // Generic LowCardinality(T): build the inner column and
                         // wrap it. Works for any fixed-size dictionary type that

ut/CreateColumnByType_ut.cpp

@@ -64,6 +64,35 @@ TEST(CreateColumnByType, UnmatchedBrackets) {
     ASSERT_EQ(nullptr, CreateColumnByType("Array(LowCardinality(Nullable(FixedString(10000)))"));
 }
 
+TEST(CreateColumnByType, UnsupportedNestedType) {
+    // A wrapper over a type the factory cannot create must not be built around a null nested column.
+    for (const char* type_name : {
+             "Nullable(5)",
+             "Nullable(DateTime64)",
+             "Array(Nullable(5))",
+             "Array(Null)",
+             "Array(DateTime64)",
+             "Array(5)",
+             "Array(Time64)",
+         }) {
+        EXPECT_EQ(nullptr, CreateColumnByType(type_name)) << type_name;
+    }
+
+    EXPECT_THROW(CreateColumnByType("LowCardinality(Nullable(5))"), UnimplementedError);
+    EXPECT_THROW(CreateColumnByType("LowCardinality(Nullable(DateTime64))"), UnimplementedError);
+
+    for (const char* type_name : {
+             "Nullable(UInt8)",
+             "Array(String)",
+             "LowCardinality(Nullable(String))",
+             "Array(Nullable(DateTime64(3)))",
+         }) {
+        const auto col = CreateColumnByType(type_name);
+        ASSERT_NE(nullptr, col) << type_name;
+        EXPECT_EQ(type_name, col->GetType().GetName());
+    }
+}
+
 TEST(CreateColumnByType, LowCardinalityAsWrappedColumn) {
     CreateColumnByTypeSettings create_column_settings;
     create_column_settings.low_cardinality_as_wrapped_column = true;