feat: Support build custom flashinfer

[guyueh1]

What does this PR do ?

Add a script to support build custom flash-infer

Issues

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Usage

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Additional Information

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Summary by CodeRabbit

• New Features
  • Added support for optional custom FlashInfer builds. Users can enable this by setting the BUILD_CUSTOM_FLASHINFER environment variable. The build system automatically handles dependency management and configuration for the custom integration.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds support for building custom FlashInfer integration by introducing a new bash script that automates cloning, validation, and configuration of FlashInfer repositories. The script is integrated into the Docker build process via a conditional BUILD_CUSTOM_FLASHINFER flag, mirroring the existing BUILD_CUSTOM_VLLM mechanism.

Changes

Cohort / File(s)	Summary
Docker Build Integration docker/Dockerfile	Adds 4 lines to copy the build-custom-flashinfer.sh script and conditionally execute it during the hermetic build stage when BUILD_CUSTOM_FLASHINFER is set.
FlashInfer Build Script tools/build-custom-flashinfer.sh	New 89-line Bash script that automates custom FlashInfer integration: clones a specified repository, validates structure, updates pyproject.toml with uv and tomlkit to add local source configuration, installs build dependencies, and refreshes lockfiles.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Test Results For Major Changes	⚠️ Warning	PR introduces major changes but provides no test results, testing information, or validation evidence despite the test checklist being incomplete.	Document comprehensive test results and validation approach in the PR description; resolve all identified issues and mark the test checklist complete.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: Support build custom flashinfer' directly and clearly describes the main change: adding support for building custom FlashInfer, which matches the core purpose of both files modified (Dockerfile additions and new build script).
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing touches

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 4

🤖 Fix all issues with AI agents

In `@docker/Dockerfile`:
- Around line 109-111: The Dockerfile uses the shell variable
BUILD_CUSTOM_FLASHINFER in the conditional block but never declares it as a
build ARG, so add an ARG declaration (e.g., add "ARG BUILD_CUSTOM_FLASHINFER" or
"ARG BUILD_CUSTOM_FLASHINFER=0") above the if-statement to ensure the build-arg
is accepted and propagated; keep the existing conditional that calls
tools/build-custom-flashinfer.sh when BUILD_CUSTOM_FLASHINFER is non-empty so
builds can enable this via --build-arg BUILD_CUSTOM_FLASHINFER=1.

In `@tools/build-custom-flashinfer.sh`:
- Around line 38-41: The script currently forces SSH host key verification off
via GIT_SSH_COMMAND which is insecure; change it to only disable verification
when an explicit opt-in env var is set (e.g. ALLOW_INSECURE_SSH=true or
INTERNAL_BUILD=true) and only for SSH-style URLs (check GIT_URL starts with
"ssh://" or matches an SSH host:path pattern) before setting GIT_SSH_COMMAND;
otherwise run a normal git clone to preserve host key checking. Update the logic
around GIT_SSH_COMMAND, GIT_URL and BUILD_DIR so the insecure options are
conditional on the env var and SSH URL detection.
- Around line 58-79: The script fails because project is never defined and it
blindly appends into vllm causing duplicates; fix by initializing project =
doc.setdefault("project", {}) then opt =
project.setdefault("optional-dependencies", {}) and vllm_list =
opt.setdefault("vllm", []) and only append "flashinfer-python" if it's not
already present; also make the sources addition idempotent by checking
sources.get("flashinfer-python") and only set it when missing or different (use
the existing symbols pyproject_path, doc, project, opt, vllm_list, sources, and
the "flashinfer-python" key).
- Around line 26-30: The script currently runs realpath on a target that may not
exist, causing the script to abort under set -e; update the BUILD_DIR assignment
so it does not call realpath on a non-existent path (either use
BUILD_DIR="$SCRIPT_DIR/../3rdparty/flashinfer" or use realpath -m
"$SCRIPT_DIR/../3rdparty/flashinfer") and keep the subsequent existence check
that echoes the error and exits; modify the line that defines BUILD_DIR (and any
usages relying on its absolute value) to use one of these safer alternatives.