@netlify/config/src/api/build_settings.js

Netlify config module

import { removeFalsy } from '../utils/remove_falsy.js'

// Netlify UI build settings are used as default configuration values in
// production. In local builds, we retrieve them with `getSite` (`siteInfo`)
// instead.
// This also includes UI-installed plugins.
export const addBuildSettings = function ({
  defaultConfig,
  baseRelDir,
  siteInfo: { build_settings: buildSettings, plugins },
}) {
  if (buildSettings === undefined) {
    return { defaultConfig, baseRelDir }
  }

  const defaultConfigA = getDefaultConfig(buildSettings, defaultConfig, plugins)
  const baseRelDirA = getBaseRelDir(buildSettings, baseRelDir)
  return { defaultConfig: defaultConfigA, baseRelDir: baseRelDirA }
}

// From the `getSite` API response to the corresponding configuration properties
const getDefaultConfig = function (
  { cmd: command, dir: publish, functions_dir: functionsDirectory, base },
  { build, plugins = [], ...defaultConfig },
  uiPlugins = [],
) {
  const siteBuild = removeFalsy({ command, publish, base })
  const functions = functionsDirectory ? { functionsDirectory, functionsDirectoryOrigin: 'ui' } : {}
  const uiPluginsA = uiPlugins.map(normalizeUiPlugin)
  const pluginsA = [...uiPluginsA, ...plugins]
  return { ...defaultConfig, build: { ...siteBuild, ...build }, plugins: pluginsA, ...functions }
}

// Make sure we know which fields we are picking from the API
const normalizeUiPlugin = function ({ package: packageName, inputs, pinned_version: pinnedVersion }) {
  return { package: packageName, inputs, pinned_version: pinnedVersion }
}

const getBaseRelDir = function ({ base_rel_dir: siteBaseRelDir }, baseRelDir = siteBaseRelDir) {
  return Boolean(baseRelDir)
}