Fix compilation error: add missing <optional> header by he-yufeng · Pull Request #2772 · flashinfer-ai/flashinfer

he-yufeng · 2026-03-12T18:13:20Z

trtllm_allreduce_fusion.cuh and trtllm_moe_allreduce_fusion.cuh use std::optional and std::nullopt but only include <cuda/std/optional>, which conditionally includes the standard <optional> header based on __cpp_lib_optional. When that macro is not defined (varies by CUDA toolkit version and compiler), std::optional is undefined and compilation fails.

Add the standard <optional> include directly.

Fixes #2767

Summary by CodeRabbit

Chores
- Small internal compatibility update: added standard optional header usage alongside existing platform-specific optional support in a couple of communication modules. Improves build robustness and maintainability with no changes to public APIs or runtime behavior. Low-risk change aimed at smoothing compilation across environments.

gemini-code-assist · 2026-03-12T18:13:33Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a compilation issue by ensuring the necessary <optional> header is always included in specific CUDA utility files. This prevents build failures that could occur when std::optional is not implicitly brought in by <cuda/std/optional> under certain compiler configurations, thereby improving the robustness and portability of the codebase.

Highlights

Compilation Fix: Addressed a compilation error in trtllm_allreduce_fusion.cuh and trtllm_moe_allreduce_fusion.cuh where std::optional was undefined due to conditional inclusion of the standard <optional> header.
Header Inclusion: Explicitly included the standard <optional> header in the affected files to ensure std::optional and std::nullopt are always properly defined, regardless of CUDA toolkit version or compiler settings.

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Changelog

include/flashinfer/comm/trtllm_allreduce_fusion.cuh
- Added direct inclusion of <optional> to resolve std::optional definition issues.
include/flashinfer/comm/trtllm_moe_allreduce_fusion.cuh
- Added direct inclusion of <optional> to resolve std::optional definition issues.

Activity

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coderabbitai · 2026-03-12T18:13:41Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: a7fcba1f-f0f9-4d2f-8857-46d74a9b307b

📥 Commits

Reviewing files that changed from the base of the PR and between 19a5fa9 and 58008c2.

📒 Files selected for processing (1)

include/flashinfer/comm/trtllm_moe_allreduce_fusion.cuh

✅ Files skipped from review due to trivial changes (1)

include/flashinfer/comm/trtllm_moe_allreduce_fusion.cuh

📝 Walkthrough

Walkthrough

This PR adds the C++ standard header <optional> to two CUDA header files in include/flashinfer/comm/ (trtllm_allreduce_fusion.cuh and trtllm_moe_allreduce_fusion.cuh) by inserting #include <optional> alongside the existing #include <cuda/std/optional>; no other code changes.

Changes

Cohort / File(s)	Summary
Header Include Fixes `include/flashinfer/comm/trtllm_allreduce_fusion.cuh`, `include/flashinfer/comm/trtllm_moe_allreduce_fusion.cuh`	Added `#include <optional>` in each file to ensure the C++ `<optional>` header is available when `cuda/std/optional` does not itself include it. No other edits.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐰 I hopped through headers, found a tiny spot,
A missing optional that mattered a lot.
One gentle include, stitched up the seam,
Now compiles hum softly — a coder's dream. 🥕✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely summarizes the main change: adding a missing header to fix compilation errors.
Description check	✅ Passed	The PR description clearly explains the issue, root cause, and solution, though the author did not fill out the structured template sections.
Linked Issues check	✅ Passed	The changes directly address issue `#2767` by adding the standard header to both affected files, resolving the compilation error.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the compilation error described in issue `#2767`; no out-of-scope modifications are present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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gemini-code-assist

Code Review

This pull request correctly fixes a compilation error by adding the missing <optional> header in two files. My review includes a minor suggestion to improve the organization of the include statements for better readability and adherence to common C++ style guidelines.

gemini-code-assist · 2026-03-12T18:23:12Z

+#include <optional>
+
 #include <cuda/std/optional>
 #include <tuple>
 #include <type_traits>


For better readability and to follow common C++ style guides, it's good practice to group standard library headers together and sort them alphabetically. This makes it easier to see which standard headers are included.

#include <optional> #include <tuple> #include <type_traits> #include <cuda/std/optional>

gemini-code-assist · 2026-03-12T18:23:12Z

+#include <optional>
+
 #include <cuda/std/optional>
 #include <tuple>
 #include <type_traits>


To improve code organization and follow standard C++ conventions, it's recommended to group standard library headers together. This change also sorts them alphabetically for better readability.

#include <optional> #include <tuple> #include <type_traits> #include <cuda/std/optional>

Move `#include <optional>` after `#include <cuda/std/optional>` to satisfy the include-order linter, and remove the stray blank line between them.

he-yufeng · 2026-03-24T02:47:58Z

@yzh119 this one's approved and ready — just a missing <optional> header. Mind merging?

aleozlx · 2026-04-13T03:58:09Z

/bot run

flashinfer-bot · 2026-04-13T03:59:52Z

GitLab MR !534 has been created, and the CI pipeline #48369395 is currently running. I'll report back once the pipeline job completes.

… regression

## 📌 Description  ## 🔍 Related Issues #2772 ## 🚀 Pull Request Checklist Thank you for contributing to FlashInfer! Before we review your pull request, please make sure the following items are complete. ### ✅ Pre-commit Checks - [ ] I have installed `pre-commit` by running `pip install pre-commit` (or used your preferred method). - [ ] I have installed the hooks with `pre-commit install`. - [ ] I have run the hooks manually with `pre-commit run --all-files` and fixed any reported issues. > If you are unsure about how to set up `pre-commit`, see [the pre-commit documentation](https://pre-commit.com/). ## 🧪 Tests - [ ] Tests have been added or updated as needed. - [ ] All tests are passing (`unittest`, etc.). ## Reviewer Notes   ## Summary by CodeRabbit * **Refactor** * Updated internal CUDA device code for improved compatibility and consistency in quantization and memory computation kernels used in AllReduce fusion operations.

Fix compilation error: add missing <optional> header for std::optional

b4356f5

gemini-code-assist Bot reviewed Mar 12, 2026

View reviewed changes

aleozlx added the op: comm label Mar 19, 2026

aleozlx approved these changes Mar 19, 2026

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aleozlx enabled auto-merge (squash) March 19, 2026 21:06

Fix include ordering to pass pre-commit hooks

19a5fa9

Move `#include <optional>` after `#include <cuda/std/optional>` to satisfy the include-order linter, and remove the stray blank line between them.

auto-merge was automatically disabled March 21, 2026 01:03
Head branch was pushed to by a user without write access

he-yufeng requested review from bkryu, jimmyzho, nv-yunzheq and yzh119 as code owners March 21, 2026 01:03

Merge branch 'main' into fix/missing-optional-header

58008c2

aleozlx added the run-ci label Apr 13, 2026

aleozlx enabled auto-merge (squash) April 13, 2026 03:58

aleozlx merged commit 5678471 into flashinfer-ai:main Apr 13, 2026
32 of 34 checks passed

aleozlx added a commit to aleozlx/flashinfer that referenced this pull request Apr 14, 2026

PR flashinfer-ai#2772 might have introduced a device side compilation…

383f4c6

… regression

coderabbitai Bot mentioned this pull request Apr 14, 2026

PR #2772 might have introduced a device side compilation regression #3056

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Fix compilation error: add missing <optional> header#2772

Fix compilation error: add missing <optional> header#2772
aleozlx merged 3 commits intoflashinfer-ai:mainfrom
he-yufeng:fix/missing-optional-header

he-yufeng commented Mar 12, 2026 •

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