Add clang-format to pre-commit hooks

[mdboom]

This adds a pre-commit hook for clang-format, and then updates our C, C++ and CUDA code to follow that convention.

To be familiar for other developers of Python/C extensions, the formatting rules are based on PEP7, but deviating in 2 important ways:

• 120 line limit
• Line wrapping of function calls and declarations follows the black/ruff convention, where it either fits on one line, or it is line wrapped with a single argument per line. IMHO, line wrapping to fit columns is a confusing convention that causes poor diffs. This doesn't contradict PEP7, it merely extends it a little bit.

Follow-on

After this is merged, I plan to continue with clang-tidy as well.

Also after this is merged, we should add the merge commit's hash to .git-blame-ignore-revs so that git blame will skip over it (this is merely reformatting and generally would not be useful to a git blame query).

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 4e9e33d and a86e93a.

📒 Files selected for processing: 13

• .clang-format
• benchmarks/cuda_bindings/benchmarks/cpp/bench_ctx_device.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_event.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_launch.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_memory.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_stream.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_support.hpp
• cuda_core/cuda/core/_cpp/rt/context.cpp
• cuda_core/cuda/core/_cpp/rt/context_scope.hpp
• cuda_core/cuda/core/_cpp/rt/event.cpp
• cuda_core/cuda/core/_cpp/rt/memory.cpp
• cuda_core/cuda/core/_cpp/rt/stream.cpp
• cuda_core/cuda/core/_cpp/rt/texture.cpp

🚧 Files skipped from review as they are similar to previous changes: 12

• benchmarks/cuda_bindings/benchmarks/cpp/bench_memory.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_event.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_ctx_device.cpp
• cuda_core/cuda/core/_cpp/rt/event.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_stream.cpp
• cuda_core/cuda/core/_cpp/rt/texture.cpp
• cuda_core/cuda/core/_cpp/rt/context_scope.hpp
• cuda_core/cuda/core/_cpp/rt/stream.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_launch.cpp
• benchmarks/cuda_bindings/benchmarks/cpp/bench_support.hpp
• cuda_core/cuda/core/_cpp/rt/context.cpp
• cuda_core/cuda/core/_cpp/rt/memory.cpp

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📝 Summary

Summary by CodeRabbit

• Chores
  • Standardized C, C++ and CUDA code formatting across the project.
  • Added contributor guidance and automatic formatting checks for supported source files.

Adds a pinned clang-format hook and repository formatting guidance. The configured style is applied to C++ and CUDA benchmark and runtime sources. The summaries report no changes to behavior, signatures, or benchmark operations.

Changes: C++ and CUDA formatting

Layer / File(s)	Summary
Formatting policy and setup .clang-format, .pre-commit-config.yaml, CONTRIBUTING.md	Adds the repository clang-format configuration, pins the formatter hook to version 23.1.3, and documents formatting instructions for C, C++, and CUDA files.
Benchmark source formatting benchmarks/cuda_bindings/benchmarks/cpp/*	Reformats benchmark implementations and shared helpers. Benchmark operations, arguments, error handling, and output behavior remain unchanged.
Runtime API and shared contracts cuda_core/cuda/core/_cpp/rt/api.hpp, cuda_core/cuda/core/_cpp/rt/{context_scope,driver_api,error,internal,types,versions}.*	Reformats runtime declarations and shared types. Signatures and documented behavior remain unchanged.
Runtime handle and resource implementations cuda_core/cuda/core/_cpp/rt/{context,event,graph,graph_exec,memory,program,stream,texture,virtual_memory}.*	Reformats runtime implementation code. Control flow, ownership, cleanup, and error handling remain unchanged.
Python integration and CUDA helpers cuda_core/cuda/core/_cpp/rt/py*, cuda_core/cuda/core/_include/{layout,utility}.hpp, cuda_core/tests/test_binaries/saxpy.cu	Reformats Python-coupled code, native-handle and layout helpers, and the SAXPY CUDA source. Signatures and behavior remain unchanged.

Suggested reviewers: danielfrg

Priority: ⬇️ Low

Change: Other

Merge Risk: ⚪ Minimal · up to a86e9

The PR adds formatting tooling and reformats C++ and CUDA sources. No actionable behavior or formatting-contract issue is established in the supplied context, so no PR-specific merge risk remains beyond normal checks.

- [ ] Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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[github-actions]

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[rparolin]

This is where the line limit should inform the formatter to break the lambda across multiple lines the way it was before. Take a look at the clang-format settings I proposed in the issue ticket.

[mdboom]

This doesn't exceed the line limit of 120. I think what you may really be asking for is to always break inside of the {}?

[rparolin]

This is another example where the format should break to a new line.

[mdboom]

I think the intention of the rule here is that single-line for loops are on the same line to prevent this kind of confusion:

for (int i = 0; i < 16; ++i) 
    packed_16[i] = &int_ptrs[i];
    packed_16[i] = &int_ptrs[i];

So the fix is to add explicit {}.

[rparolin]

This largely looks fine, but I would fix the lambda's so they are not all slammed onto a single line.