Project result top level columns according to scan spec for non-selec…

…tive readers (#5726)

Summary:
Pull Request resolved: #5726

For non-selective readers, there is no filters in scan spec, but we still need to handle the projections for top level columns specified there.  Add an helper function to achieve that and use it to fix `TextReader` (non-OSS).

Reviewed By: zacw7

Differential Revision: D47597154

fbshipit-source-id: 1aea75c02e6ec1e33db2b148ec0062cc2039042b

velox/dwio/common/CMakeLists.txt

@@ -43,6 +43,7 @@ add_library(
   MetadataFilter.cpp
   Options.cpp
   Range.cpp
+  Reader.cpp
   ReaderFactory.cpp
   ScanSpec.cpp
   ColumnLoader.cpp

velox/dwio/common/Reader.cpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "velox/dwio/common/Reader.h"
+
+namespace facebook::velox::dwio::common {
+
+VectorPtr RowReader::projectColumns(
+    const VectorPtr& input,
+    const velox::common::ScanSpec& spec) {
+  auto* inputRow = input->as<RowVector>();
+  VELOX_CHECK_NOT_NULL(inputRow);
+  auto& inputRowType = input->type()->asRow();
+  column_index_t numColumns = 0;
+  for (auto& childSpec : spec.children()) {
+    numColumns = std::max(numColumns, childSpec->channel() + 1);
+  }
+  std::vector<std::string> names(numColumns);
+  std::vector<TypePtr> types(numColumns);
+  std::vector<VectorPtr> children(numColumns);
+  for (auto& childSpec : spec.children()) {
+    if (!childSpec->projectOut()) {
+      continue;
+    }
+    auto i = childSpec->channel();
+    names[i] = childSpec->fieldName();
+    if (childSpec->isConstant()) {
+      children[i] = BaseVector::wrapInConstant(
+          input->size(), 0, childSpec->constantValue());
+    } else {
+      children[i] =
+          inputRow->childAt(inputRowType.getChildIdx(childSpec->fieldName()));
+    }
+    types[i] = children[i]->type();
+  }
+  return std::make_shared<RowVector>(
+      input->pool(),
+      ROW(std::move(names), std::move(types)),
+      nullptr,
+      input->size(),
+      std::move(children));
+}
+
+} // namespace facebook::velox::dwio::common

velox/dwio/common/Reader.h

@@ -104,6 +104,14 @@ class RowReader {
   virtual bool allPrefetchIssued() const {
     return false;
   }
+
+  /**
+   * Helper function used by non-selective reader to project top level columns
+   * according to the scan spec.
+   */
+  static VectorPtr projectColumns(
+      const VectorPtr& input,
+      const velox::common::ScanSpec&);
 };
 
 /**