.readthedocs.yaml

# .readthedocs.yaml
# Read the Docs configuration file
# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details

# Required
version: 2

# Set the version of Python and other tools you might need
build:
  os: ubuntu-24.04
  tools:
    python: "3.11"
  jobs:
    # On PR builds, skip the Sphinx build when the PR doesn't touch any
    # files that affect documentation output. Reduces queue pressure on
    # the shared RTD build slots when several PRs are open at once.
    # Tag/branch builds (master, stable, etc.) always run.
    # The guard matches doc/ but excludes doc/.claude/ (Claude Code skills
    # and agent files), which never participate in the Sphinx build, so a
    # PR that changes only those paths skips the build instead of running one.
    # Code sources (python/ray/, rllib/) are intentionally not matched, so a
    # code-only PR skips this PR preview. The RTD PR check is not a required
    # merge gate, and the post-merge master build and the Buildkite doc_build
    # still render docstring-driven API-reference changes. This trades a
    # non-gating premerge preview for less pressure on the shared RTD slots.
    # See https://docs.readthedocs.com/platform/stable/guides/build/skip-build.html
    #
    # Some constructs are avoided deliberately because RTD's job runner
    # silently drops scripts that contain them: use echo (not printf
    # with a backslash-escape format string), avoid backslash escapes
    # in general, and keep shell comments out of this block so that
    # backticks/$() inside comments don't confuse the preprocessor.
    # The runner also strips the surrounding single quotes from arguments,
    # so use git's :! exclude shorthand rather than :(exclude): unquoted
    # parentheses reach /bin/sh (dash) and abort the script with a syntax error.
    post_checkout:
      - |
        if [ "${READTHEDOCS_VERSION_TYPE:-}" != "external" ]; then
          echo "Not a PR build (version type: '${READTHEDOCS_VERSION_TYPE:-unset}'); building docs."
          exit 0
        fi
        git fetch --depth=500 origin master 2>/dev/null || true
        if ! git merge-base origin/master HEAD >/dev/null 2>&1; then
          echo "Could not determine merge-base with origin/master; building docs to be safe."
          exit 0
        fi
        if git diff --quiet origin/master...HEAD -- doc/ ':!doc/.claude/' .readthedocs.yaml; then
          echo "No doc-affecting files changed in this PR; skipping Sphinx build."
          echo "Files changed in PR:"
          git diff --name-only origin/master...HEAD
          exit 183
        fi
        echo "Doc-affecting files changed; building docs. Changed doc-relevant paths:"
        git diff --name-only origin/master...HEAD -- doc/ ':!doc/.claude/' .readthedocs.yaml
    # Override the html build step so every build runs a full clean Sphinx
    # build via the doc/Makefile html target, for PR (external) previews and
    # branch/tag builds alike.
    #
    # The incremental-from-master-cache path added in #64277 is disabled for
    # now. On every PR preview Sphinx discards the restored cache because a
    # config value differs between the environment that produced the cache and
    # the RTD build environment, so it rebuilds all documents anyway while
    # still paying the cache download and extract cost, and it risks a second
    # clean rebuild when the incremental leg trips a warning. A clean build is
    # faster and lower-variance in practice today. Re-enable the incremental
    # path only once cache reuse is confirmed (Sphinx logs "N changed" rather
    # than "NNNN added") and stale-artifact pruning lands for PRs that rename
    # or delete sources. The rtd and rtd-fallback Makefile targets and
    # doc/load_doc_cache.py stay in the tree for that re-enable.
    # Raise pip's retry budget for the dependency install below.
    # files.pythonhosted.org has been returning intermittent 502s
    # (https://github.com/pypi/support/issues/11895), and one failed wheel fetch
    # fails the whole docs build. pip defaults to 5 retries with exponential
    # backoff, which gives up in about 8 seconds of sleeping.
    #
    # Written as a config file rather than PIP_RETRIES because the install step
    # is python.install below, run by Read the Docs rather than by us, and each
    # job command runs in its own shell so an export here would not reach it.
    # pip reads this path on every invocation in the build, including that one.
    #
    # Only the retry count is raised. The observed failures are immediate 502
    # responses rather than hangs, so a larger timeout would only lengthen the
    # worst case without making a fetch more likely to succeed.
    pre_install:
      - mkdir -p ~/.config/pip
      - |
        echo "[global]" > ~/.config/pip/pip.conf
        echo "retries = 10" >> ~/.config/pip/pip.conf
        cat ~/.config/pip/pip.conf
    # Build with fewer Sphinx workers than there are CPUs.
    #
    # doc/Makefile defaults SPHINX_JOBS to auto, one write worker per CPU.
    # This builder has 4 CPUs and a 7,130,316,800 byte cgroup memory ceiling
    # (about 6.64 GiB, the documented Business limit), and each worker holds
    # its own copy of the build environment. At -j auto the build peaked at
    # 6,503,370,752 bytes on a run that passed and 6,371,254,272 on one that
    # was OOM-killed, leaving roughly 600 MB of headroom either way. When the
    # kernel kills a write worker the parent Sphinx process reports only a
    # bare EOFError from multiprocessing/connection.py, naming no document,
    # and the document it dies on moves from build to build.
    #
    # At SPHINX_JOBS=2 the same build peaked at 5,566,427,136 bytes with
    # memory.events oom_kill 0, so headroom goes from about 600 MB to about
    # 1.5 GiB. The cost is wall clock: a paired run measured 349 seconds at
    # -j auto against 620 seconds at 2 on one builder, and the 2 arm had a
    # warm cache, so treat that as a lower bound on the slowdown.
    #
    # Only this job sets it. Local builds and the Buildkite doc build keep
    # -j auto, so nothing off this builder pays for the reduced parallelism.
    # Raising the RtD memory limit would let the parallelism come back; that
    # is a separate ask to Read the Docs, not a change in this repo.
    build:
      html:
        - |
          make -C doc html HTMLDIR="$READTHEDOCS_OUTPUT/html" SPHINX_JOBS=2

# Build documentation in the docs/ directory with Sphinx
sphinx:
  configuration: doc/source/conf.py
  fail_on_warning: true

# We recommend specifying your dependencies to enable reproducible builds:
# https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
python:
  install:
    - requirements: doc/requirements-doc.lock.txt