[libcudacxx] Add debugger pretty-printers for cuda::std::optional by theo-bermudez · Pull Request #10843 · NVIDIA/cccl

theo-bermudez · 2026-08-16T06:30:32Z

Description

What

Adds GDB and LLDB pretty-printers for cuda::std::optional, following the pattern
established by the existing array (#10528), tuple (#10534), and span (#10699)
printers. New printers live at libcudacxx/share/libcudacxx/{gdb,lldb}/optional.py,
registered in each __init__.py, with a test scenario under
libcudacxx/test/debugging/optional/.

Correctness note

The disengaged state is rendered without dereferencing the payload storage: both
printers read only the engaged flag (__engaged_) before deciding whether to expose
the contained value. The optional<T&> specialization stores a pointer instead, so it
is detected via its __value_ member and reported disengaged when the pointer is null.
Coverage includes engaged, disengaged, nested optional (engaged and disengaged inner),
a non-trivially-destructible payload, an alias, both engaged and disengaged
optional<int&>, and re-inspection after reset().

Verification

The .expected fixtures were generated by running the real debuggers through the test
harness (run_pretty_printer_test.py --update-expected). Environment: aarch64 Linux
container, CUDA Toolkit 13.3, gdb 15.1, lldb 18.1.3 (no GPU; these scenarios are
host-only).

$ ctest -R 'debugging.*optional' --output-on-failure
Test project /work/build/spike/libcudacxx-cpp17
    Start 139: libcudacxx.test.debugging.optional.lldb
1/2 Test #139: libcudacxx.test.debugging.optional.lldb ...   Passed    0.57 sec
    Start 140: libcudacxx.test.debugging.optional.gdb
2/2 Test #140: libcudacxx.test.debugging.optional.gdb ....   Passed    0.14 sec

100% tests passed, 0 tests failed out of 2

The pre-existing array scenario still passes unchanged (ctest -R 'debugging.*array',
2/2).
pre-commit passes on all changed files.
The optional.update.before/optional.update.after cases lock the reset() edge in
regression: after reset() leaves stale payload bytes in __val_, both debuggers
render the optional as empty rather than surfacing the stale value.

Checklist

New or existing tests cover these changes.
The documentation is up to date with these changes.

Adds GDB and LLDB pretty-printers for cuda::std::optional, following the pattern of the existing array, tuple, and span printers (NVIDIA#10528, NVIDIA#10534, NVIDIA#10699), plus a test scenario under test/debugging/optional. The disengaged state is rendered without dereferencing the payload storage; optional<T&> is handled through its pointer member. Closes NVIDIA#10093.

copy-pr-bot · 2026-08-16T06:30:35Z

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coderabbitai · 2026-08-16T06:32:46Z

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between 4803298 and 958dcd2.

📒 Files selected for processing (1)

libcudacxx/share/libcudacxx/gdb/optional.py

🚧 Files skipped from review as they are similar to previous changes (1)

libcudacxx/share/libcudacxx/gdb/optional.py

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📝 Walkthrough

Summary by CodeRabbit

New Features
- Added GDB and LLDB pretty-printing support for cuda::std::optional.
- Debuggers now show whether an optional contains a value and display that value when available.
- Added support for nested, reference, aliased, non-trivial, and state-updated optionals.
Tests
- Added comprehensive debugging coverage for engaged, disengaged, nested, reference, alias, reset, and non-trivial optional values across GDB and LLDB.

Walkthrough

Changes

Debugger optional support

Layer / File(s)	Summary
GDB optional printer `libcudacxx/share/libcudacxx/gdb/optional.py`, `libcudacxx/share/libcudacxx/gdb/__init__.py`	GDB recognizes `cuda::std::optional`, reports engagement, exposes engaged payloads, and registers the printer.
LLDB optional formatter `libcudacxx/share/libcudacxx/lldb/optional.py`, `libcudacxx/share/libcudacxx/lldb/__init__.py`	LLDB summarizes optional state, exposes engaged payloads, handles reference and union-backed storage, and registers the formatter.
Optional debugger tests `libcudacxx/test/debugging/optional/*`, `libcudacxx/test/debugging/CMakeLists.txt`	The test target covers engaged, disengaged, nested, aliased, reference, non-trivial, and reset-state optionals for GDB and LLDB.

Assessment against linked issues

Objective	Addressed	Explanation
Create GDB and LLDB pretty printers under the specified paths [`#10093`]	✅
Add exhaustive tests under `libcudacxx/test/debugging/optional` [`#10093`]	✅

Suggested reviewers: griwes

Merge Risk: ⚪ Minimal · up to 958dc

This change adds debugger display support for cuda::std::optional without changing runtime behavior; no actionable merge-blocking risk remains after normal checks and review.

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miscco

Looks good, just one nit regarding detection with our inline ABI namespaces

miscco · 2026-08-17T11:47:23Z

+def _is_cuda_optional(value_type: gdb.Type) -> bool:
+    value_type = cccl_common.canonical_type(value_type)
+    template_name = cccl_common.template_name(cccl_common.public_type_name(value_type))
+    return template_name == "cuda::std::optional"


I am not sure whether this works with our inline namespaces

Suggested change

return template_name == "cuda::std::optional"

return (

public_name.startswith("cuda::std::")

and template_name.rsplit("::", 1)[-1] == "optional"

)

Good catch — applied in 958dcd2, mirroring the array/tuple detection pattern. ctest -R 'debugging.*optional' still passes 2/2 and the .expected goldens are unchanged.

Match the array/tuple detection pattern: check the ABI-stripped name prefix and the last template-name component instead of an exact match, so detection survives namespace forms the strip pattern doesn't know.

theo-bermudez · 2026-09-04T20:02:24Z

Superseded by #10847, which merged the same GDB/LLDB optional pretty-printer support and debugger test coverage. Closing this older duplicate to keep the review queue clear. Thanks for the review here.

theo-bermudez requested review from a team as code owners August 16, 2026 06:30

theo-bermudez requested a review from griwes August 16, 2026 06:30

github-project-automation Bot added this to CCCL Aug 16, 2026

github-project-automation Bot moved this to Todo in CCCL Aug 16, 2026

cccl-authenticator-app Bot moved this from Todo to In Review in CCCL Aug 16, 2026

miscco reviewed Aug 17, 2026

View reviewed changes

Make GDB optional detection robust to inline ABI namespaces

958dcd2

Match the array/tuple detection pattern: check the ABI-stripped name prefix and the last template-name component instead of an exact match, so detection survives namespace forms the strip pattern doesn't know.

coderabbitai Bot mentioned this pull request Aug 17, 2026

[libcudacxx] Add GDB and LLDB pretty-printers for cuda::std::optional #10847

Merged

2 tasks done

theo-bermudez closed this Sep 4, 2026

github-project-automation Bot moved this from In Review to Done in CCCL Sep 4, 2026

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[libcudacxx] Add debugger pretty-printers for cuda::std::optional - #10843

[libcudacxx] Add debugger pretty-printers for cuda::std::optional#10843
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-    return template_name == "cuda::std::optional"
+    return (
+        public_name.startswith("cuda::std::")
+        and template_name.rsplit("::", 1)[-1] == "optional"
+    )

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theo-bermudez commented Aug 16, 2026

Description

What

Correctness note

Verification

Checklist

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coderabbitai Bot commented Aug 16, 2026 •

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