feat: expand allocator support in specialization.rs (#710) by Ankit-cs · Pull Request #759 · servo/rust-smallvec

Ankit-cs · 2026-10-09T17:41:50Z

Description

This PR addresses the allocator expansion task for specialization.rs (#710).

The following specialization traits have been updated to be generic over Heap: Allocator rather than being hardcoded to the Global allocator:

SpecFromElem (for both Clone and Copy item implementations)
SpecFromSlice (for both Clone and Copy item implementations)

Note on SpecFromIterator:
As discussed in the main allocator tracking issue by @bolshoytoster and @alejandro-vaz, expanding FromIterator to custom allocators would awkwardly require A: Allocator + Default. To stay consistent with standard library patterns, SpecFromIterator was intentionally left untouched and remains bound to Global.

Related Issue

Fixes #710

Ankit-cs · 2026-10-09T17:42:54Z

lookin for feedback for the above pr @alejandro-vaz

alejandro-vaz · 2026-10-09T17:43:46Z

 const SPILLED_SIZE: usize = 100;

-trait Vector<T>: for<'a> From<&'a [T]> + Extend<T> + FromIterator<T> {
+/// A trait defining common vector operations, implemented by vectors taking items from a slice of lifetime 'slice.


remove the doc comment, we really aren't reading them at all

we will figure out in rc what doc comments we really need

alejandro-vaz · 2026-10-09T17:52:02Z

 // Bounded `usize` between `0..=CAP`
-impl<'a, const CAP: usize> Arbitrary<'a> for Bounded<usize, CAP> {
+impl<'data, const CAP: usize> Arbitrary<'data> for Bounded<usize, CAP> {
+    /// Generates an arbitrary bounded usize value using the unstructured fuzzing data of lifetime 'data.


alejandro-vaz · 2026-10-09T17:52:06Z

+where T: Arbitrary<'data>
 {
-    fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
+    /// Generates an arbitrary bounded vector by consuming items from the unstructured data stream of lifetime 'data.


alejandro-vaz · 2026-10-09T18:09:57Z

 fn splice_reserve_panic() {
-    struct CountDrop<'a>(&'a Cell<usize>);
+    /// A helper struct that increments a counter when dropped, bound to the cell's lifetime 'cell.
+    struct CountDrop<'cell>(&'cell Cell<usize>);


change this to 'valid

alejandro-vaz · 2026-10-09T18:10:18Z

+    struct DropCounter<'cell>(&'cell Cell<i32>);

-    impl<'a> Drop for DropCounter<'a> {
+    impl<'cell> Drop for DropCounter<'cell> {


alejandro-vaz · 2026-10-09T18:11:02Z

 #[test]
 fn splice_reserve_panic() {
-    struct CountDrop<'a>(&'a Cell<usize>);
+    /// A helper struct that increments a counter when dropped, bound to the cell's lifetime 'cell.


no doc comment

alejandro-vaz · 2026-10-09T18:11:07Z

 #[test]
 fn into_iter_drop() {
-    struct DropCounter<'a>(&'a Cell<i32>);
+    /// A helper struct that increments a counter when dropped, bound to the cell's lifetime 'cell.


alejandro-vaz · 2026-10-09T18:11:29Z

also half of the checks fail

Ankit-cs · 2026-10-09T18:20:59Z

Ooh sorry for that I will to solve this fully by tomorrow morning and make sure every checks passes

alejandro-vaz · 2026-10-14T13:29:13Z

you there?? no pressure

Ankit-cs · 2026-10-14T14:05:03Z

Yes sir I got a fever for 3 days

alejandro-vaz · 2026-10-14T14:07:56Z

hahahaha fair brother fair

Ankit-cs · 2026-10-15T06:31:26Z

Hi @alejandro-vaz, I am here! I have addressed all your review comments:

Removed the doc comments on Vector, Arbitrary implementations, and test helper structs.
Renamed all remaining lifetimes ('slice, 'data, 'cell) to 'valid.
The changes have just been pushed to this branch. But i am unable to solve this checks any guidance for this ?

alejandro-vaz · 2026-10-15T11:16:12Z

conflicts to be solved now in the base allocator

Ankit-cs · 2026-10-15T11:25:52Z

OK sir just 30 minutes I will solve this ci part

Ankit-cs · 2026-10-16T05:06:07Z

thanks @alejandro-vaz the above suggestion work successfuly

alejandro-vaz

I'm wondering if any of the implementations indeed needs allocator support on specialization at all

alejandro-vaz · 2026-10-16T12:04:25Z

+impl<Item, const INLINE: usize, Heap: Allocator + Default> Default
+    for SmallVec<Item, INLINE, Heap>
+{
    #[inline]
    fn default() -> Self {
-        Self::new()
+        Self::new_in(Heap::default())
    }
 }


this is wrong, no allocator support should be added here

default should always use the global allocator

alejandro-vaz · 2026-10-16T12:04:37Z

 /// a separate implementation block for easy access whenever specialization is
 /// disabled.
-impl<Item, const INLINE: usize> SmallVec<Item, INLINE, Global> {
+impl<Item, const INLINE: usize, Heap: Allocator + Default> SmallVec<Item, INLINE, Heap> {


same as above

alejandro-vaz · 2026-10-16T12:04:43Z

    unsafe fn from_elem_fallback(elem: Item, n: usize) -> Self
    where Item: Clone {
-        let mut result = Self::new();
+        let mut result = Self::new_in(Heap::default());


alejandro-vaz · 2026-10-16T12:04:52Z

    unsafe fn from_slice_fallback(slice: &[Item]) -> Self
    where Item: Clone {
-        let mut v = Self::new();
+        let mut v = Self::new_in(Heap::default());


alejandro-vaz · 2026-10-16T12:06:04Z

 }

-impl<Item: Clone, const INLINE: usize> SpecFromElem<Item> for SmallVec<Item, INLINE, Global> {
+impl<Item: Clone, const INLINE: usize, Heap: Allocator + Default> SpecFromElem<Item>


same as above

alejandro-vaz · 2026-10-16T12:06:10Z

+impl<Item: Copy, const INLINE: usize, Heap: Allocator + Default> SpecFromElem<Item>
+    for SmallVec<Item, INLINE, Heap>
+{


alejandro-vaz · 2026-10-16T12:06:15Z

+{
    unsafe fn spec_from_elem(elem: Item, n: usize) -> Self {
-        let mut result = Self::new();
+        let mut result = Self::new_in(Heap::default());


alejandro-vaz · 2026-10-16T12:06:23Z

+impl<Item: Clone, const INLINE: usize, Heap: Allocator + Default> SpecFromSlice<Item>
+    for SmallVec<Item, INLINE, Heap>
+{


same as above

alejandro-vaz · 2026-10-16T12:06:29Z

+impl<Item: Copy, const INLINE: usize, Heap: Allocator + Default> SpecFromSlice<Item>
+    for SmallVec<Item, INLINE, Heap>
+{


alejandro-vaz · 2026-10-16T12:06:32Z

+{
    unsafe fn spec_from(slice: &[Item]) -> Self {
-        let mut v = Self::new();
+        let mut v = Self::new_in(Heap::default());


Ankit-cs · 2026-10-16T12:09:21Z

Ok sir i will complete all the above feedback by the Eod

…ialization

Ankit-cs · 2026-10-16T13:51:12Z

Updated! Reverted Default, from_elem, and from_slice specializations back to SmallVec<Item, INLINE, Global>. Constructors without an allocator parameter shouldn't assume Heap: Allocator + Default. Pushed in commit 751df21.
Looking for feedback @alejandro-vaz

alejandro-vaz · 2026-10-16T14:54:48Z

well yeah... no files changed

specialization didn't need allocator support now I'm realizing

thanks @Ankit-cs for finding out

Ankit-cs · 2026-10-16T14:57:46Z

OK @alejandro-vaz sir Finally it's completed

alejandro-vaz requested changes Oct 9, 2026

View reviewed changes

alejandro-vaz assigned Ankit-cs Oct 13, 2026

Ankit-cs force-pushed the fix/710-allocator-specialization branch from ff5d79a to e18d381 Compare October 15, 2026 07:43

fix(servo#710): expand allocator support in specialization.rs

4f072ac

Ankit-cs force-pushed the fix/710-allocator-specialization branch from e18d381 to 4f072ac Compare October 16, 2026 05:03

alejandro-vaz requested changes Oct 16, 2026

View reviewed changes

fix(servo#710): address review feedback, revert Global allocator spec…

751df21

…ialization

alejandro-vaz closed this Oct 16, 2026

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Ankit-cs commented Oct 9, 2026

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alejandro-vaz commented Oct 9, 2026

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Ankit-cs commented Oct 16, 2026

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