apacheGH-41667: [C++][Parquet] Refuse writing non-nullable column that contains nulls

A non-nullable column that contains nulls would result in an invalid Parquet file.

Author: pitrou

cpp/src/parquet/arrow/arrow_reader_writer_test.cc

@@ -3349,6 +3349,27 @@ TEST(TestArrowWrite, CheckChunkSize) {
                 WriteTable(*table, ::arrow::default_memory_pool(), sink, chunk_size));
 }
 
+void CheckWritingNonNullableColumnWithNulls(std::shared_ptr<::arrow::Field> field,
+                                            std::string json_batch) {
+  ARROW_SCOPED_TRACE("field = ", field, ", json_batch = ", json_batch);
+  auto schema = ::arrow::schema({field});
+  auto table = ::arrow::TableFromJSON(schema, {json_batch});
+  auto sink = CreateOutputStream();
+  EXPECT_RAISES_WITH_MESSAGE_THAT(
+      Invalid, ::testing::HasSubstr("is declared non-nullable but contains nulls"),
+      WriteTable(*table, ::arrow::default_memory_pool(), sink));
+}
+
+TEST(TestArrowWrite, InvalidSchema) {
+  // GH-41667: nulls in non-nullable column
+  CheckWritingNonNullableColumnWithNulls(
+      ::arrow::field("a", ::arrow::int32(), /*nullable=*/false),
+      R"([{"a": 456}, {"a": null}])");
+  CheckWritingNonNullableColumnWithNulls(
+      ::arrow::field("a", ::arrow::utf8(), /*nullable=*/false),
+      R"([{"a": "foo"}, {"a": null}])");
+}
+
 void DoNestedValidate(const std::shared_ptr<::arrow::DataType>& inner_type,
                       const std::shared_ptr<::arrow::Field>& outer_field,
                       const std::shared_ptr<Buffer>& buffer,

cpp/src/parquet/column_writer.cc

@@ -1301,6 +1301,10 @@ class TypedColumnWriterImpl : public ColumnWriterImpl, public TypedColumnWriter<
     bool single_nullable_element =
         (level_info_.def_level == level_info_.repeated_ancestor_def_level + 1) &&
         leaf_field_nullable;
+    if (!leaf_field_nullable && leaf_array.null_count() != 0) {
+      return Status::Invalid("Column '", descr_->name(),
+                             "' is declared non-nullable but contains nulls");
+    }
     bool maybe_parent_nulls = level_info_.HasNullableValues() && !single_nullable_element;
     if (maybe_parent_nulls) {
       ARROW_ASSIGN_OR_RAISE(