From dffcd237c32aae6b2ac6ec7d934c1b838a5bd0b8 Mon Sep 17 00:00:00 2001
From: Huaijin <haohuaijin@gmail.com>
Date: Tue, 28 Jul 2026 17:18:39 +0800
Subject: [PATCH] fix(parquet): restore opaque return type for
 `RowSelection::iter`

#10141 changed `RowSelection::iter` from `impl Iterator<Item = &RowSelector>`
to a named type, `RowSelectionIter<'_>`. Restore the opaque return type so we
stay free to change the implementation later.

Both match arms are already `std::slice::Iter<'_, RowSelector>`, so
`RowSelectionIter` is not needed at all and is removed rather than made
private. No behaviour change.
---
 parquet/src/arrow/arrow_reader/mod.rs         |  3 +-
 .../src/arrow/arrow_reader/selection/mod.rs   | 11 ++--
 .../arrow/arrow_reader/selection/selector.rs  | 53 -------------------
 3 files changed, 7 insertions(+), 60 deletions(-)

diff --git a/parquet/src/arrow/arrow_reader/mod.rs b/parquet/src/arrow/arrow_reader/mod.rs
index a9cd82b3a3de..e4a7b3d135f5 100644
--- a/parquet/src/arrow/arrow_reader/mod.rs
+++ b/parquet/src/arrow/arrow_reader/mod.rs
@@ -25,8 +25,7 @@ use arrow_select::filter::filter_record_batch;
 pub use filter::{ArrowPredicate, ArrowPredicateFn, RowFilter};
 use selection::MaskCursor;
 pub use selection::{
-    MaskRunIter, RowSelection, RowSelectionCursor, RowSelectionIter, RowSelectionPolicy,
-    RowSelector,
+    MaskRunIter, RowSelection, RowSelectionCursor, RowSelectionPolicy, RowSelector,
 };
 use std::fmt::{Debug, Formatter};
 use std::sync::Arc;
diff --git a/parquet/src/arrow/arrow_reader/selection/mod.rs b/parquet/src/arrow/arrow_reader/selection/mod.rs
index b8a5bc0f2a74..41a59c048e2b 100644
--- a/parquet/src/arrow/arrow_reader/selection/mod.rs
+++ b/parquet/src/arrow/arrow_reader/selection/mod.rs
@@ -55,7 +55,7 @@ use boolean::{
 pub(crate) use cursor::{LoadedRowRanges, MaskCursor, RowSelectionStrategy};
 pub use cursor::{RowSelectionCursor, RowSelectionPolicy};
 use ranges::{expand_to_batch_boundaries_from_selectors, scan_ranges_from_selectors};
-pub use selector::{RowSelectionIter, RowSelector};
+pub use selector::RowSelector;
 use selector::{limit_selectors, offset_selectors, split_off_selectors};
 
 /// [`RowSelection`] represents selecting a subset of rows
@@ -605,7 +605,8 @@ impl RowSelection {
         }
     }
 
-    /// Returns a borrowed iterator yielding the [`RowSelector`]s for this selection.
+    /// Returns an iterator over the [`RowSelector`]s for this
+    /// [`RowSelection`].
     ///
     /// Mask-backed selections materialize a `Vec<RowSelector>` cache on first
     /// call (one allocation, `O(set_slices)` work) so the iterator can hand out
@@ -613,10 +614,10 @@ impl RowSelection {
     /// over mask-backed selections, prefer streaming directly via
     /// [`Self::as_mask`] + [`MaskRunIter::new`] — that path is allocation-free
     /// and avoids populating the cache.
-    pub fn iter(&self) -> RowSelectionIter<'_> {
+    pub fn iter(&self) -> impl Iterator<Item = &RowSelector> {
         match &self.inner {
-            RowSelectionInner::Selectors(s) => RowSelectionIter::new(s),
-            RowSelectionInner::Mask(m) => RowSelectionIter::new(m.selectors()),
+            RowSelectionInner::Selectors(s) => s.iter(),
+            RowSelectionInner::Mask(m) => m.selectors().iter(),
         }
     }
 
diff --git a/parquet/src/arrow/arrow_reader/selection/selector.rs b/parquet/src/arrow/arrow_reader/selection/selector.rs
index 15261a5c7a89..a7ba939ae49a 100644
--- a/parquet/src/arrow/arrow_reader/selection/selector.rs
+++ b/parquet/src/arrow/arrow_reader/selection/selector.rs
@@ -55,59 +55,6 @@ impl RowSelector {
     }
 }
 
-/// Borrowed iterator over the [`RowSelector`]s of a
-/// [`RowSelection`](crate::arrow::arrow_reader::RowSelection).
-#[derive(Debug)]
-pub struct RowSelectionIter<'a>(std::slice::Iter<'a, RowSelector>);
-
-impl<'a> RowSelectionIter<'a> {
-    pub(super) fn new(selectors: &'a [RowSelector]) -> Self {
-        Self(selectors.iter())
-    }
-}
-
-impl<'a> Iterator for RowSelectionIter<'a> {
-    type Item = &'a RowSelector;
-
-    #[inline]
-    fn next(&mut self) -> Option<Self::Item> {
-        self.0.next()
-    }
-
-    #[inline]
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.0.size_hint()
-    }
-
-    #[inline]
-    fn count(self) -> usize {
-        self.0.count()
-    }
-
-    #[inline]
-    fn nth(&mut self, n: usize) -> Option<Self::Item> {
-        self.0.nth(n)
-    }
-
-    #[inline]
-    fn last(self) -> Option<Self::Item> {
-        self.0.last()
-    }
-
-    #[inline]
-    fn fold<B, F>(self, init: B, f: F) -> B
-    where
-        F: FnMut(B, Self::Item) -> B,
-    {
-        self.0.fold(init, f)
-    }
-}
-
-impl ExactSizeIterator for RowSelectionIter<'_> {}
-
-// once it returns None, it will continue returning None
-impl std::iter::FusedIterator for RowSelectionIter<'_> {}
-
 /// Splits `selectors` at the first `row_count` rows, returning `(head, tail)`.
 pub(super) fn split_off_selectors(
     mut selectors: Vec<RowSelector>,