[GitHub] [arrow-rs] alamb commented on a change in pull request #1444: Add Full UnionArray validation

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

alamb commented on a change in pull request #1444:
URL: https://github.com/apache/arrow-rs/pull/1444#discussion_r826658448



##########
File path: arrow/src/array/data.rs
##########
@@ -1117,6 +1119,44 @@ impl ArrayData {
         )
     }
 
+    /// Ensures that for each union element, the offset is correct for
+    /// the corresponding child array
+    fn validate_dense_union_full(&self) -> Result<()> {
+        // safety justification is that the size of the buffers was validated in self.validate()
+        let type_ids = self.typed_offsets::<i8>(&self.buffers[0])?;
+        let offsets = self.typed_offsets::<i32>(&self.buffers[1])?;
+
+        type_ids.iter().enumerate().try_for_each(|(i, &type_id)| {
+            // this will panic if out of bounds. Could make a nicer error message
+            let type_id: usize = type_id
+                .try_into()
+                .map_err(|_| {
+                    ArrowError::InvalidArgumentError(format!(
+                        "Offset invariant failure: Could not convert type id {} to usize in slot {}",
+                        type_id, i))
+                })?;
+
+            let num_children = self.child_data[type_id].len();
+            let child_offset: usize = offsets[i]
+                .try_into()
+                .map_err(|_| {
+                    ArrowError::InvalidArgumentError(format!(
+                        "Offset invariant failure: Could not convert offset {} at position {} to usize",
+                        offsets[i], i))
+                })?;
+
+
+            if child_offset >= num_children {
+                Err(ArrowError::InvalidArgumentError(format!(
+                    "Value at position {} out of bounds: {} (child array {} length is {})",

Review comment:
       ```suggestion
                       "Offset at position {} out of bounds: {} (child array {} length is {})",
   ```




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