(fix): eliminate Core.Box allocation in @inline @with_pool functions

[mgyoo86]

Problem

@inline @with_pool pool function caused heap allocations (32–48 bytes per scope) due to Core.Box boxing. When the compiler inlined the _dispatch_pool_scope closure into outer callers crossing try/finally boundaries, it lost type tracking and boxed closure-captured variables.

This was a regression from v0.2.2, where AdaptiveArrayPool was non-parametric and didn't need union splitting.

Fix

Replace the closure-based _dispatch_pool_scope(pool -> body, getter) with a closureless let/if isa chain directly in the macro expansion:

let _raw = get_task_local_pool()
    if _raw isa AdaptiveArrayPool{0}
        let pool = _raw::AdaptiveArrayPool{0}; body end
    elseif _raw isa AdaptiveArrayPool{1}
        ...
    end
end

No closure → no boxing → zero allocation.

Allocation comparison (per @with_pool scope, fixed cost)

Version	v0.2.2	v0.2.3 (closure)	This PR
Julia 1.12	0B	32B	0B
Julia 1.10/1.11	16B	48B	16B

• Cost is fixed per scope, not per acquire! (1 acquire = 8 acquires = same)
• Hot loops inside functions: 0B on all versions (compiler eliminates let scope)

Test changes

• _ZERO_ALLOC_THRESHOLD: 0 on Julia ≥1.12, 16 on <1.12
• Hot loop tests wrapped in function barriers for consistent 0B measurement
• All 23 zero-allocation tests pass on 1.10, 1.11, and 1.12

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.97%. Comparing base (a3da1a3) to head (85d5175).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #30      +/-   ##
==========================================
+ Coverage   96.54%   96.97%   +0.43%     
==========================================
  Files          14       14              
  Lines        2632     2645      +13     
==========================================
+ Hits         2541     2565      +24     
+ Misses         91       80      -11     

Files with missing lines	Coverage Δ
src/macros.jl	98.90% <100.00%> (-0.10%)	⬇️

... and 5 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

Eliminates heap allocations caused by Core.Box when @with_pool-wrapped functions are inlined, by replacing a closure-based dispatch with closureless union-splitting in the macro expansion.

Changes:

• Reworked @with_pool macro expansion to avoid _dispatch_pool_scope closures and prevent boxing across try/finally.
• Added/adjusted allocation regression tests for @inline @with_pool and version-dependent thresholds / function barriers.
• Expanded CI matrix to include Julia 1.11 explicitly.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
src/macros.jl	Replaces closure-based pool dispatch with a closureless let + isa chain to avoid boxing/allocations.
test/test_zero_allocation.jl	Adds regression tests for @inline @with_pool and version-specific allocation thresholds/function barriers.
test/test_reshape.jl	Adds a function barrier for stable @allocated measurement.
.github/workflows/CI.yml	Adds Julia 1.11 to CI matrix for coverage of the affected behavior.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.