Move SpareBufferWriter back into vortex-array

The writer only exists to serve the PiecewiseSequence gather loops, so
keep it pub(crate) in arrays::piecewise_sequence as its own submodule
rather than growing vortex-buffer's public API. It only uses BufferMut's
public surface, so nothing in vortex-buffer changes behavior.

Signed-off-by: "Robert" <robert@spiraldb.com>
Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GUSY34eRKq9du5zQK1FuZq

Author: claude

vortex-array/src/arrays/decimal/compute/take.rs

@@ -4,7 +4,6 @@
 use itertools::Itertools as _;
 use vortex_buffer::Buffer;
 use vortex_buffer::BufferMut;
-use vortex_buffer::SpareBufferWriter;
 use vortex_error::VortexResult;
 use vortex_error::vortex_ensure;
 use vortex_error::vortex_err;
@@ -18,6 +17,7 @@ use crate::arrays::DecimalArray;
 use crate::arrays::PiecewiseSequence;
 use crate::arrays::PrimitiveArray;
 use crate::arrays::dict::TakeExecute;
+use crate::arrays::piecewise_sequence::SpareBufferWriter;
 use crate::arrays::piecewise_sequence::constant_unsigned_usize;
 use crate::arrays::piecewise_sequence::maybe_contiguous_slices;
 use crate::dtype::IntegerPType;

vortex-array/src/arrays/piecewise_sequence/mod.rs

@@ -28,12 +28,14 @@ use crate::executor::ExecutionCtx;
 use crate::scalar::PValue;
 
 pub mod array;
+mod spare_buffer_writer;
 mod vtable;
 
 #[cfg(test)]
 mod tests;
 
 pub use array::PiecewiseSequenceArrayExt;
+pub(crate) use spare_buffer_writer::SpareBufferWriter;
 pub use vtable::*;
 
 pub(crate) fn check_index_arrays(

vortex-buffer/src/spare_buffer_writer.rs …iecewise_sequence/spare_buffer_writer.rsvortex-buffer/src/spare_buffer_writer.rs renamed to vortex-array/src/arrays/piecewise_sequence/spare_buffer_writer.rs vortex-buffer/src/spare_buffer_writer.rs renamed to vortex-array/src/arrays/piecewise_sequence/spare_buffer_writer.rs

@@ -3,11 +3,10 @@
 
 use std::ptr;
 
+use vortex_buffer::BufferMut;
 use vortex_error::VortexResult;
 use vortex_error::vortex_ensure;
 
-use crate::BufferMut;
-
 /// Writes slices sequentially into the spare capacity of an empty [`BufferMut`].
 ///
 /// This is useful when the caller knows the final output length up front and wants to avoid
@@ -22,7 +21,7 @@ use crate::BufferMut;
 /// [`set_len`]: BufferMut::set_len
 /// [`finish`]: SpareBufferWriter::finish
 #[must_use = "call `finish` to set the buffer length after writing"]
-pub struct SpareBufferWriter<'a, T> {
+pub(crate) struct SpareBufferWriter<'a, T> {
     buffer: &'a mut BufferMut<T>,
     written: usize,
     output_len: usize,
@@ -32,7 +31,7 @@ impl<'a, T: Copy> SpareBufferWriter<'a, T> {
     /// Creates a writer for `output_len` values in `buffer`'s spare capacity.
     ///
     /// The target buffer must be empty and have capacity for at least `output_len` values.
-    pub fn new(buffer: &'a mut BufferMut<T>, output_len: usize) -> VortexResult<Self> {
+    pub(crate) fn new(buffer: &'a mut BufferMut<T>, output_len: usize) -> VortexResult<Self> {
         vortex_ensure!(
             buffer.is_empty(),
             "slice copy buffer already has {} initialized values",
@@ -53,7 +52,7 @@ impl<'a, T: Copy> SpareBufferWriter<'a, T> {
 
     /// Copies `source` into the next output slots.
     #[inline]
-    pub fn copy_slice(&mut self, source: &[T]) -> VortexResult<()> {
+    pub(crate) fn copy_slice(&mut self, source: &[T]) -> VortexResult<()> {
         vortex_ensure!(
             source.len() <= self.output_len - self.written,
             "slice copy length {} exceeds remaining output length {}",
@@ -73,7 +72,7 @@ impl<'a, T: Copy> SpareBufferWriter<'a, T> {
     }
 
     /// Sets the target buffer length after exactly `output_len` values have been written.
-    pub fn finish(self) -> VortexResult<()> {
+    pub(crate) fn finish(self) -> VortexResult<()> {
         vortex_ensure!(
             self.written == self.output_len,
             "slice copy length {} does not match declared output length {}",
@@ -91,10 +90,10 @@ impl<'a, T: Copy> SpareBufferWriter<'a, T> {
 
 #[cfg(test)]
 mod tests {
+    use vortex_buffer::BufferMut;
     use vortex_error::VortexResult;
 
     use super::SpareBufferWriter;
-    use crate::BufferMut;
 
     #[test]
     fn writes_slices_into_spare_capacity() -> VortexResult<()> {

vortex-array/src/arrays/primitive/compute/take/mod.rs

@@ -9,7 +9,6 @@ use std::sync::LazyLock;
 use itertools::Itertools as _;
 use vortex_buffer::Buffer;
 use vortex_buffer::BufferMut;
-use vortex_buffer::SpareBufferWriter;
 use vortex_error::VortexResult;
 use vortex_error::vortex_bail;
 use vortex_error::vortex_ensure;
@@ -25,6 +24,7 @@ use crate::arrays::PiecewiseSequence;
 use crate::arrays::Primitive;
 use crate::arrays::PrimitiveArray;
 use crate::arrays::dict::TakeExecute;
+use crate::arrays::piecewise_sequence::SpareBufferWriter;
 use crate::arrays::piecewise_sequence::constant_unsigned_usize;
 use crate::arrays::piecewise_sequence::maybe_contiguous_slices;
 use crate::builtins::ArrayBuiltins;

vortex-array/src/arrays/varbin/compute/take.rs

@@ -5,7 +5,6 @@ use itertools::Itertools as _;
 use vortex_buffer::BitBufferMut;
 use vortex_buffer::BufferMut;
 use vortex_buffer::ByteBufferMut;
-use vortex_buffer::SpareBufferWriter;
 use vortex_error::VortexExpect;
 use vortex_error::VortexResult;
 use vortex_error::vortex_ensure;
@@ -22,6 +21,7 @@ use crate::arrays::PrimitiveArray;
 use crate::arrays::VarBin;
 use crate::arrays::VarBinArray;
 use crate::arrays::dict::TakeExecute;
+use crate::arrays::piecewise_sequence::SpareBufferWriter;
 use crate::arrays::piecewise_sequence::constant_unsigned_usize;
 use crate::arrays::piecewise_sequence::maybe_contiguous_slices;
 use crate::arrays::primitive::PrimitiveArrayExt;

vortex-array/src/arrays/varbinview/compute/take.rs

@@ -8,7 +8,6 @@ use itertools::Itertools as _;
 use num_traits::AsPrimitive;
 use vortex_buffer::Buffer;
 use vortex_buffer::BufferMut;
-use vortex_buffer::SpareBufferWriter;
 use vortex_error::VortexResult;
 use vortex_error::vortex_ensure;
 use vortex_error::vortex_err;
@@ -24,6 +23,7 @@ use crate::arrays::PrimitiveArray;
 use crate::arrays::VarBinView;
 use crate::arrays::VarBinViewArray;
 use crate::arrays::dict::TakeExecute;
+use crate::arrays::piecewise_sequence::SpareBufferWriter;
 use crate::arrays::piecewise_sequence::constant_unsigned_usize;
 use crate::arrays::piecewise_sequence::maybe_contiguous_slices;
 use crate::arrays::varbinview::BinaryView;

vortex-buffer/src/lib.rs

@@ -53,7 +53,6 @@ pub use buffer_mut::*;
 pub use bytes::*;
 pub use r#const::*;
 pub use dispatch::*;
-pub use spare_buffer_writer::*;
 pub use string::*;
 mod alignment;
 #[cfg(feature = "arrow")]
@@ -70,7 +69,6 @@ mod macros;
 mod memmap2;
 #[cfg(feature = "serde")]
 mod serde;
-mod spare_buffer_writer;
 mod string;
 /// Trusted-length iterator trait and adapters for safe pre-allocation.
 pub mod trusted_len;