    // generate an inventory from the virtual tree in the lockfile
    const virtualArb = new Arborist(opts)
    try {
      await virtualArb.loadVirtual()
    } catch (err) {
      log.verbose('loadVirtual', err.stack)
      const msg =
        'The `npm ci` command can only install with an existing\n' +
        'package-lock.json with lockfileVersion >= 1. Run an install with npm@5\n' +
        'or later to generate a package-lock.json file, then try again.'
      throw this.usageError(msg)
    }
    const virtualInventory = new Map(virtualArb.virtualTree.inventory)

    // Now we make our real Arborist.
    // We need a new one because the virtual tree from the lockfile can have extraneous dependencies in it that won't install on this platform
    const arb = new Arborist(opts)
    await arb.buildIdealTree()
    await strictAllowScriptsPreflight({ arb, npm: this.npm, idealTreeOpts: opts })

    // Verifies that the packages from the ideal tree will match the same versions that are present in the virtual tree (lock file).
    const errors = validateLockfile(virtualInventory, arb.idealTree.inventory)
    // Verifies that the root packageExtensions state matches the lockfile and is still consistent with the locked tree.
    errors.push(...validatePackageExtensions(virtualArb.virtualTree, arb.idealTree))
    // Verifies that the root .npm-extension file matches the lockfile hash.
    // The hash comes from discovering the file (no import or execution), so this holds even under ignore-extension/ignore-scripts.
    const { NpmExtension } = require('@npmcli/arborist')
    let fileHash = null
    try {
      fileHash = new NpmExtension({ root: where, extensionFile: opts.extensionFile }).hash
    } catch (err) {
      errors.push(`Invalid: ${err.message}`)
    }
    errors.push(...validateNpmExtension(virtualArb.virtualTree, fileHash))
    if (errors.length) {
      throw this.usageError(
        '`npm ci` can only install packages when your package.json and package-lock.json are in sync. ' +
        'Please update your lock file with `npm install` before continuing.\n\n' +
        errors.join('\n')
      )
    }
Échauffement
