rebuild

Name: rebuild
Author: ray-project/ray

$npx mdskill add ray-project/ray/rebuild

Rebuilds Ray from source based on file changes

Solves the problem of rebuilding Ray after code changes
Uses git and Python environment from CLAUDE.local.md
Analyzes changed files to determine build mode
Executes appropriate build command for Python, C++, or dashboard changes

SKILL.md

.github/skills/rebuildView on GitHub ↗

---
name: rebuild
description: Rebuild Ray from source — determines the right build mode based on what changed
---

# Rebuild Ray

Canonical build docs: doc/source/ray-contribute/development.md
Use the user's configured Python from CLAUDE.local.md, or fall back to `which python`.
Update this skill if any changes are detected in development.rst.

## Determine what to rebuild

1. Check what files changed: `git diff --name-only HEAD` (or ask the user)
2. Pick the appropriate build mode:
   - **Only .py files changed** (no .h, .cc, .pyx, .pxd) → Python-only rebuild (not required if installed with `pip install -e .` — editable mode auto-picks up Python changes)
   - **.h, .cc, .pyx, .pxd files changed** → C++/Cython rebuild
   - **Dashboard files changed** (python/ray/dashboard/client/) → Dashboard rebuild first
   - **First time / clean build** → Full source build

**Running Python tests that exercise C++ changes:** When a Python test depends on
C++ or Cython code (raylet, GCS, core_worker, etc.), run the C++/Cython rebuild
below before running the test. Editable Python installs do not rebuild the compiled
extensions, so stale binaries will run otherwise.

## Python-only rebuild

For changes to Tune, RLlib, Autoscaler, and most Python files.
Two approaches depending on how Ray was installed:

### If installed with `pip install -e .` (editable/full source build)
No rebuild needed — Python changes are picked up automatically.

### If installed from nightly wheel + setup-dev.py
1. Ensure a nightly wheel is installed (see doc/source/ray-contribute/development.md
   for the correct wheel URL for the user's platform and Python version)
2. Link local files: `python python/ray/setup-dev.py`
3. Can skip specific dirs: `python python/ray/setup-dev.py -y --skip _private dashboard`

**Warning:** With setup-dev.py, don't run `pip uninstall ray` or `pip install -U`.
Instead: `rm -rf <site-packages>/ray`, reinstall wheel, re-run setup-dev.py.

## C++/Cython rebuild (after initial full build)

### Full package rebuild
```bash
bazel run //:gen_ray_pkg
```

### Build individual modules (faster)
```bash
bazel build //src/ray/raylet:raylet          # Raylet only
bazel build //src/ray/gcs:gcs_server         # GCS server only
bazel build //src/ray/core_worker:core_worker # Core worker only
bazel build //:ray_pkg                       # All C++ and Cython
```

### Build variants
- `bazel run -c fastbuild //:gen_ray_pkg` — fast build (less optimization)
- `bazel run -c dbg //:gen_ray_pkg` — debug build with symbols (for gdb)
- `bazel run -c opt //:gen_ray_pkg` — optimized build

Make permanent in `~/.bazelrc`: `build --compilation_mode=fastbuild`

## Full source build (first time)

1. If dashboard changed: `cd python/ray/dashboard/client && npm ci && npm run build && cd -`
2. Install deps: `cd python/ && pip install -r requirements.txt`
3. Build: `pip install -e . --verbose`

## Resource-constrained builds
Add to `~/.bazelrc` if machine runs out of memory:
```
build --local_ram_resources=HOST_RAM*.5 --local_cpu_resources=4
build --disk_cache=~/bazel-cache
```

## Worktree notes
- Verify build paths: `bazel info execution_root`
- If build fails, check .bazelversion matches installed Bazel
- Each worktree may need its own `pip install -e .`
- If in a worktree and bazel targets fail, ensure symlinks are correct

More from ray-project/ray

Skill	Description
backport-docs	Cherry-pick documentation changes from master onto a release branch so they appear on the docs.ray.io /latest build
bazel-visibility	Rules for setting Bazel target visibility in Ray BUILD files — keep every target as private as possible, grant the minimal visibility needed, and lay out tests in a subdir. Applies when adding or editing any BUILD.bazel target.
fetch-buildkite-logs	Fetch Buildkite CI job logs, and a job's artifacts when the logs are not enough, from a Buildkite build URL or build number, then summarize the failures
lint	Run linting and formatting checks on Ray code
ray-dependencies	Manage Python dependencies in Ray — add/remove/upgrade packages, work with raydepsets lock files, debug dependency conflicts, and regenerate compiled requirements. Covers `python/requirements`, `python/requirements/`, `python/deplocks/`, and `ci/raydepsets/configs/.depsets.yaml`.
ray-soft-wrap	Soft-wrap (unwrap) hard-wrapped prose in Markdown/MyST files in the ray-project/ray repo so each paragraph and list item is one line, with deterministic content-invariant, render-equality, and idempotency checks. Use when asked to soft-wrap, unwrap, or reflow Ray docs (.md/.markdown), or to normalize line wrapping before style and grammar edits. Markdown only — rST files are converted to MyST first by a separate effort.
rst-to-myst	Convert Ray documentation pages from reStructuredText (.rst) to MyST Markdown (.md). Use when migrating existing files under doc/source/ to MyST, finishing a partial MyST migration of a directory, or when asked to convert/migrate a doc page to markdown. Covers the RST-to-MyST directive mapping, label and cross-reference preservation, sphinx-design tabs/dropdowns/card grids, doctest/testcode handling, the doc/BUILD.bazel doctest exclusions, and the build and doctest verification needed to land a clean docs PR.
sphinx-fix	Diagnose a failing Ray Sphinx / Read the Docs documentation build. Parses the Sphinx warning stream (an RtD build log, a local build, or pasted text), classifies each warning against a rules table, and proposes the canonical fix in severity-tier order. Detects a hard-broken build, segregates known-benign suppressed classes, and lists every unclassified warning. Use when a `docs/readthedocs.com:anyscale-ray` check fails, when asked "why is the docs build failing?" or "what warning is breaking this PR?", or to turn a Sphinx warning dump into an ordered fix list.