Make cuBLASLt descriptor wrappers move-safe

[fallintoplace]

Summary

• make the cuBLASLt matrix layout and matmul descriptor wrappers move-safe
• transfer descriptor ownership explicitly on move construction and move assignment
• make moved-from wrappers null-safe on destruction
• add focused tests that verify each wrapper transfers its raw handle and nulls the source on move

Why

These wrappers own raw cublasLt* descriptors and destroy them in their destructors, but their move constructor and move assignment operator were defaulted. That meant moving a wrapper copied the raw handle into the destination without clearing the source, so both objects believed they owned the same descriptor.

Impact

This closes a double-destroy hazard in any path that moves or move-assigns these wrappers, including code that caches or returns compound matmul descriptor objects.

Root cause

The wrapper types were acting like RAII owners while still using raw-pointer default move semantics.

Validation

• git diff --check
• attempted PARALLEL_LEVEL=8 ./build.sh tests -n --limit-tests=LINALG_TEST
• local build is blocked here because nvcc is not installed and CMake cannot resolve CUDAToolkit_ROOT

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 1b39f329-b81e-438b-b803-10495f262fdc

📥 Commits

Reviewing files that changed from the base of the PR and between c515501 and 2b09036.

📒 Files selected for processing (3)

• cpp/include/raft/linalg/detail/cublaslt_wrappers.hpp
• cpp/tests/CMakeLists.txt
• cpp/tests/linalg/cublaslt_wrappers.cpp

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes

  • Improved ownership handling for cuBLASLt wrapper objects during moves, reducing the risk of double-destruction and invalid handle cleanup.
  • Destructors now safely skip cleanup when no handle is present.

• Tests

  • Added unit coverage for move construction and move assignment of the cuBLASLt matrix layout and matmul descriptor wrappers.
  • Included the new test file in the test build configuration.

Walkthrough

Updates cuBLASLt handle-wrapper structs to use explicit noexcept move constructors and move-assignment operators via std::exchange, with destructors that conditionally destroy only when the handle pointer is non-null. Adds a new gtest test file validating this move behavior and registers it in the CMake test build.

Changes

cuBLASLt RAII Move Semantics

Layer / File(s)	Summary
Move semantics and conditional destruction cpp/include/raft/linalg/detail/cublaslt_wrappers.hpp	Replaces defaulted move constructor/assignment with explicit noexcept implementations using std::exchange for cublastlt_matrix_layout and cublastlt_matmul_desc; destructors now only destroy the handle when non-null.
Move behavior tests and build wiring cpp/tests/linalg/cublaslt_wrappers.cpp, cpp/tests/CMakeLists.txt	New test file adds four gtest cases validating move construction and move assignment ownership transfer for both wrapper types; CMake test list updated to build the new file under LINALG_TEST.

Estimated code review effort: 2 (Simple) | ~15 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: making the cuBLASLt wrappers move-safe.
Description check	✅ Passed	The description matches the patch and explains the move-safety fix, tests, and validation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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