Fix launch_kernel handling of restricted and partially specified kernel arguments

[dantegd]

Fix downstream compilation failures introduced by the raft::launch_kernel migration.

Some sparse symmetrization launches combine:

• partially specified kernel templates,
• implicit argument conversions such as T* to const T*, and
• __restrict__-qualified pointer parameters.

The dispatcher preserved __restrict__ in its explicit parameter packs and later attempted to convert addresses of those parameter copies to void const*, which NVCC rejects. In addition, the conversion overload cannot resolve a partially specified kernel template.

This change:

• lets dispatch deduce its by-value parameter types so outermost extended qualifiers such as __restrict__ are dropped before arguments are staged for cudaLaunchKernelExC;
• performs required conversions before that deduction in the converting overload;
• fully specializes the affected COO/from-KNN symmetrization kernels; and
• adds regression coverage for restricted pointers, restricted pointers requiring conversion, the legacy COO API, and from_knn_symmetrize_matrix.

This fixes the UMAP and t-SNE compilation failures observed when building cuML against current RAFT.

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[coderabbitai]

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ℹ️ Recent review info

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Run ID: 6b5803ca-b3ce-4bb8-9952-a73c449f4baf

📥 Commits

Reviewing files that changed from the base of the PR and between f633a16 and 479aea4.

📒 Files selected for processing (4)

• cpp/include/raft/sparse/linalg/detail/symmetrize.cuh
• cpp/include/raft/util/kernel_launch.hpp
• cpp/tests/sparse/symmetrize.cu
• cpp/tests/util/kernel_launch.cu

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes

  • Improved sparse matrix symmetrization reliability when using restricted device-memory pointers.
  • Improved kernel execution compatibility by handling qualified pointer arguments correctly during launches.
  • Preserved existing behavior and public interfaces.

• Tests

  • Added coverage for legacy COO symmetrization, KNN symmetrization, and restricted-pointer kernel operations.

Walkthrough

Changes

Kernel launch and symmetrization updates

Layer / File(s)	Summary
Dispatch qualifier handling cpp/include/raft/util/kernel_launch.hpp, cpp/tests/util/kernel_launch.cu	Typed launch overloads convert arguments before dispatch. Tests cover restricted input and output pointers.
Symmetrization kernel instantiation cpp/include/raft/sparse/linalg/detail/symmetrize.cuh, cpp/tests/sparse/symmetrize.cu	Symmetrization launches now specify kernel template arguments. Tests cover legacy COO output and restricted-pointer KNN input.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Mergeability Score: ⚪ Minimal · up to 479ae

The PR fixes kernel argument handling for restricted and partially specified arguments and adds regression coverage; no actionable merge-blocking risk remains.

Possibly related PRs

• NVIDIA/raft#3104: Both PRs update symmetrize.cuh and kernel_launch.hpp; this PR refines related typed dispatch and kernel instantiation changes.

Suggested reviewers: achirkin, divyegala

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change to launch_kernel handling of restricted and partially specified kernel arguments.
Description check	✅ Passed	The description directly explains the compilation fix, affected kernels, and added regression tests.
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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[divyegala]

/merge

[achirkin]

Thanks Dante for handling this!