Use pacakge.json from 'main'

Update the docs build to use the `package.json` file from the
`main` branch.

See gh-40072

run.js

@@ -0,0 +1,50 @@
+;(function () {
+  'use strict'
+
+  const childProcess = require('child_process')
+  const fs = require('fs');
+
+  async function main() {
+    try {
+      checkout(process.argv.includes('--no-checkout'))
+      install(process.argv.includes('--no-install'))
+      run(process.argv.includes('--no-run'))
+    } catch (error) {
+      console.log("Unexpected error")
+      process.exitCode = (error.exitCode) ? error.exitCode : 1
+    }
+  }
+
+  function checkout(skip) {
+    if (skip) return
+    console.log('Checking out Antora package.json files from `main`')
+    const packageJson = childProcess.execSync('git show main:antora/package.json', {env: process.env})
+    const packageLockJson = childProcess.execSync('git show main:antora/package-lock.json', {env: process.env})
+    fs.writeFileSync('package.json', packageJson)
+    fs.writeFileSync('package-lock.json', packageLockJson)
+  }
+
+  function install(skip) {
+    if (skip) return
+    console.log('Installing modules')
+    childProcess.execSync('npm ci --silent --no-progress', {stdio: 'inherit', env: process.env})
+  }
+
+  function run(skip) {
+    const packageJson = JSON.parse(fs.readFileSync('package.json', 'utf8'))
+    const uiBundleUrl = packageJson.config['ui-bundle-url'];
+    const command = `npx antora antora-playbook.yml --stacktrace --ui-bundle-url ${uiBundleUrl}`
+    if (uiBundleUrl.includes('/latest/')) {
+      console.log('Refusing to run Antora with development build of UI')
+      console.log(`$ ${command}`)
+      process.exitCode = 1
+      return
+    }
+    console.log((!skip) ? 'Running Antora' : 'Use the following command to run Antora')
+    console.log(`$ ${command}`)
+    if (!skip) childProcess.execSync(command, {stdio: 'inherit', env: process.env})
+  }
+
+  main()
+
+})()