[GitHub] [arrow] pitrou commented on a change in pull request #10969: ARROW-13676: [C++][Parquet] Avoid potential invalid access.

[GitBox <gi...@apache.org>]

pitrou commented on a change in pull request #10969:
URL: https://github.com/apache/arrow/pull/10969#discussion_r693934168



##########
File path: cpp/src/parquet/arrow/path_internal_test.cc
##########
@@ -170,6 +170,24 @@ TEST_F(MultipathLevelBuilderTest, NullableSingleListWithAllNullsLists) {
                      /*rep_levels=*/std::vector<int16_t>(4, 0));
 }
 
+TEST_F(MultipathLevelBuilderTest, EmptyLists) {
+  // ARROW-13676 - ensure no out of bounds list memory accesses.
+  auto entries = field("Entries", ::arrow::int64());
+  auto list_type = list(entries);

Review comment:
       Can you add a "translates to parquet schema" comment as above?

##########
File path: cpp/src/parquet/arrow/path_internal.cc
##########
@@ -342,7 +341,9 @@ class ListPathNode {
     *child_range = selector_.GetRange(range->start);
     while (child_range->Empty() && !range->Empty()) {
       ++range->start;
-      *child_range = selector_.GetRange(range->start);
+      if (!range->Empty()) {
+        *child_range = selector_.GetRange(range->start);
+      }
     }

Review comment:
       Would be nice to clean up the repetition of conditionals here, for example:
   ```c++
   int64_t empty_elements = 0;
   do {
     *child_range = selector_.GetRange(range->start++);
     if (!child_range->Empty()) {
       break;
     }
     ++empty_elements;
   } while (!range->Empty());
   ```




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