[Docs] Only build docs if `documentation` or `ready` labels are present (#36135)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

.readthedocs.yaml

@@ -9,6 +9,7 @@ build:
     python: "3.12"
   jobs:
     post_checkout:
+      - bash docs/maybe_skip_pr_build.sh
       - git fetch origin main --unshallow --no-tags --filter=blob:none || true
     pre_create_environment:
       - pip install uv

docs/maybe_skip_pr_build.sh

+#!/bin/bash
+# SPDX-License-Identifier: Apache-2.0
+# Skip PR builds unless the PR has the "documentation" or "ready" label.
+# Used by Read the Docs (see .readthedocs.yaml).
+
+if [[ "$READTHEDOCS_VERSION_TYPE" != "external" ]]; then
+  exit 0
+fi
+
+PR_URL="https://api.github.com/repos/vllm-project/vllm/pulls/${READTHEDOCS_VERSION}"
+CURL_ARGS=(-s -o /tmp/pr_response.json -w "%{http_code}")
+if [[ -n "$GITHUB_TOKEN" ]]; then
+  CURL_ARGS+=(-H "Authorization: token ${GITHUB_TOKEN}")
+fi
+HTTP_CODE=$(curl "${CURL_ARGS[@]}" "$PR_URL")
+
+if [[ "$HTTP_CODE" -ne 200 ]]; then
+  echo "GitHub API returned HTTP ${HTTP_CODE}, proceeding with build."
+elif grep -qE '"name": *"(documentation|ready)"' /tmp/pr_response.json; then
+  echo "Found required label, proceeding with build."
+else
+  echo "PR #${READTHEDOCS_VERSION} lacks 'documentation' or 'ready' label, skipping build."
+  exit 183
+fi