[arrow-rs] branch master updated: Document safety justification of some uses of `from_trusted_len_iter` (#1148)

[alamb]

This is an automated email from the ASF dual-hosted git repository.

alamb pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/arrow-rs.git


The following commit(s) were added to refs/heads/master by this push:
     new f085647  Document safety justification of some uses of 
`from_trusted_len_iter` (#1148)
f085647 is described below

commit f0856473937ca1526b7f2bd140c865f00973fcdb
Author: Andrew Lamb <and...@nerdnetworks.org>
AuthorDate: Tue Jan 11 14:10:01 2022 -0500

    Document safety justification of some uses of `from_trusted_len_iter` 
(#1148)
---
 arrow/src/array/array_primitive.rs      | 2 +-
 arrow/src/buffer/ops.rs                 | 3 ++-
 arrow/src/compute/kernels/arithmetic.rs | 6 +++++-
 arrow/src/compute/kernels/length.rs     | 2 +-
 4 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arrow/src/array/array_primitive.rs 
b/arrow/src/array/array_primitive.rs
index a9e1ba8..e2272ed 100644
--- a/arrow/src/array/array_primitive.rs
+++ b/arrow/src/array/array_primitive.rs
@@ -140,7 +140,7 @@ impl<T: ArrowPrimitiveType> PrimitiveArray<T> {
 
     /// Creates a PrimitiveArray based on a constant value with `count` 
elements
     pub fn from_value(value: T::Native, count: usize) -> Self {
-        // # Safety: length is known
+        // # Safety: iterator (0..count) correctly reports its length
         let val_buf = unsafe { 
Buffer::from_trusted_len_iter((0..count).map(|_| value)) };
         let data = unsafe {
             ArrayData::new_unchecked(
diff --git a/arrow/src/buffer/ops.rs b/arrow/src/buffer/ops.rs
index 14d3811..279c85e 100644
--- a/arrow/src/buffer/ops.rs
+++ b/arrow/src/buffer/ops.rs
@@ -140,7 +140,8 @@ where
         .iter()
         .zip(right_chunks.iter())
         .map(|(left, right)| op(left, right));
-    // Soundness: `BitChunks` is a trusted len iterator
+    // Soundness: `BitChunks` is a `BitChunks` iterator which
+    // correctly reports its upper bound
     let mut buffer = unsafe { MutableBuffer::from_trusted_len_iter(chunks) };
 
     let remainder_bytes = ceil(left_chunks.remainder_len(), 8);
diff --git a/arrow/src/compute/kernels/arithmetic.rs 
b/arrow/src/compute/kernels/arithmetic.rs
index 267c40f..0ee0608 100644
--- a/arrow/src/compute/kernels/arithmetic.rs
+++ b/arrow/src/compute/kernels/arithmetic.rs
@@ -185,7 +185,7 @@ where
     //  Benefit
     //      ~60% speedup
     //  Soundness
-    //      `values` is an iterator with a known size.
+    //      `values` is an iterator with a known size from a PrimitiveArray
     let buffer = unsafe { Buffer::from_trusted_len_iter(values) };
 
     let data = unsafe {
@@ -241,6 +241,7 @@ where
                 }
             },
         );
+        // Safety: Iterator comes from a PrimitiveArray which reports its size 
correctly
         unsafe { Buffer::try_from_trusted_len_iter(values) }
     } else {
         // no value is null
@@ -255,6 +256,7 @@ where
                     Ok(*left % *right)
                 }
             });
+        // Safety: Iterator comes from a PrimitiveArray which reports its size 
correctly
         unsafe { Buffer::try_from_trusted_len_iter(values) }
     }?;
 
@@ -311,6 +313,7 @@ where
                 }
             },
         );
+        // Safety: Iterator comes from a PrimitiveArray which reports its size 
correctly
         unsafe { Buffer::try_from_trusted_len_iter(values) }
     } else {
         // no value is null
@@ -325,6 +328,7 @@ where
                     Ok(*left / *right)
                 }
             });
+        // Safety: Iterator comes from a PrimitiveArray which reports its size 
correctly
         unsafe { Buffer::try_from_trusted_len_iter(values) }
     }?;
 
diff --git a/arrow/src/compute/kernels/length.rs 
b/arrow/src/compute/kernels/length.rs
index b0f3d9a..d6d554f 100644
--- a/arrow/src/compute/kernels/length.rs
+++ b/arrow/src/compute/kernels/length.rs
@@ -48,7 +48,7 @@ where
     //  Benefit
     //      ~60% speedup
     //  Soundness
-    //      `values` is an iterator with a known size.
+    //      `values` come from a slice iterator with a known size.
     let buffer = unsafe { Buffer::from_trusted_len_iter(lengths) };
 
     let null_bit_buffer = array