dbms: Server: Adding nullable type support to functions manipulating arrays. [#METR-19266]

dbms/src/Functions/FunctionsArray.cpp

@@ -2536,34 +2536,29 @@ bool FunctionArrayReverse::executeFixedString(
 	const ColumnNullable * nullable_col,
 	ColumnNullable * nullable_res_col)
 {
-	auto do_reverse = [](const auto & src_data, const auto & src_offsets, auto & res_data)
-	{
-		size_t size = src_offsets.size();
-		ColumnArray::Offset_t src_prev_offset = 0;
-
-		for (size_t i = 0; i < size; ++i)
-		{
-			const auto * src = &src_data[src_prev_offset];
-			const auto * src_end = &src_data[src_offsets[i]];
-
-			if (src == src_end)
-				continue;
-
-			auto dst = &res_data[src_offsets[i] - 1];
-
-			while (src < src_end)
-			{
-				*dst = *src;
-				++src;
-				--dst;
-			}
-
-			src_prev_offset = src_offsets[i];
-		}
-	};
-
 	if (const ColumnFixedString * src_data_concrete = typeid_cast<const ColumnFixedString *>(&src_data))
 	{
+		/// XXX The original implementation, i.e. everything but the new code
+		/// XXX for nullable support is buggy. Example with a table with one column
+		/// XXX whose type is Array(FixedString(3))):
+		/// │ ['a\0\0','bc\0','def'] │
+		/// │ ['a\0\0','bc\0','def'] │
+		/// │ ['a\0\0','bc\0','def'] │
+		/// │ ['a\0\0','bc\0','def'] │
+		/// │ ['a\0\0','bc\0','def'] │
+		/// │ ['a\0\0','bc\0','def'] │
+		/// │ ['a\0\0','bc\0','def'] │
+		///
+		/// XXX SELECT reverse(col) FROM table gives the following output:
+		///
+		/// │ ['def','a\0\0','bc\0']    │
+		/// │ ['def','a\0\0','bc\0']    │
+		/// │ ['def','a\0\0','bc\0']    │
+		/// │ ['def','a\0\0','bc\0']    │
+		/// │ ['def','a\0\0','bc\0']    │
+		/// │ ['def','a\0\0','bc\0']    │
+		/// │ ['def','\0\0\0','\0\0\0'] │
+
 		const size_t n = src_data_concrete->getN();
 		const ColumnFixedString::Chars_t & src_data = src_data_concrete->getChars();
 		ColumnFixedString::Chars_t & res_data = typeid_cast<ColumnFixedString &>(res_data_col).getChars();
@@ -2597,8 +2592,29 @@ bool FunctionArrayReverse::executeFixedString(
 			/// Make a reverted null map.
 			const auto & src_null_map = static_cast<const ColumnUInt8 &>(*nullable_col->getNullValuesByteMap()).getData();
 			auto & res_null_map = static_cast<ColumnUInt8 &>(*nullable_res_col->getNullValuesByteMap()).getData();
-			res_null_map.resize(src_data.size());
+			res_null_map.resize(src_null_map.size());
-			do_reverse(src_null_map, src_offsets, res_null_map);
+
+			ColumnArray::Offset_t src_prev_offset = 0;
+
+			for (size_t i = 0; i < size; ++i)
+			{
+				const UInt8 * src = &src_null_map[src_prev_offset];
+				const UInt8 * src_end = &src_null_map[src_offsets[i]];
+
+				if (src == src_end)
+					continue;
+
+				UInt8 * dst = &res_null_map[src_offsets[i] - 1];
+
+				while (src < src_end)
+				{
+					*dst = *src;
+					++src;
+					--dst;
+				}
+
+				src_prev_offset = src_offsets[i];
+			}
 		}
 
 		return true;