Function resolveDeepImport

packages/vite/src/node/plugins/resolve.ts:1046–1113

(
  id: string,
  { setResolvedCache, getResolvedCache, dir, data }: PackageData,
  options: InternalResolveOptions,
  externalize?: boolean,
)

}

function resolveDeepImport(
  id: string,
  { setResolvedCache, getResolvedCache, dir, data }: PackageData,
  options: InternalResolveOptions,
  externalize?: boolean,
): string | undefined {
  const cache = getResolvedCache(id, options)
  if (cache) {
    return cache
  }

  let relativeId: string | undefined | void = id
  const { exports: exportsField, browser: browserField } = data

  // map relative based on exports data
  if (exportsField) {
    if (isObject(exportsField) && !Array.isArray(exportsField)) {
      // resolve without postfix (see #7098)
      const { file, postfix } = splitFileAndPostfix(relativeId)
      const exportsId = resolveExportsOrImports(
        data,
        file,
        options,
        'exports',
        externalize,
      )
      if (exportsId !== undefined) {
        relativeId = exportsId + postfix
      } else {
        relativeId = undefined
      }
    } else {
      // not exposed
      relativeId = undefined
    }
    if (!relativeId) {
      throw new Error(
        `Package subpath '${relativeId}' is not defined by "exports" in ` +
          `${path.join(dir, 'package.json')}.`,
      )
    }
  } else if (options.mainFields.includes('browser') && isObject(browserField)) {
    // resolve without postfix (see #7098)
    const { file, postfix } = splitFileAndPostfix(relativeId)
    const mapped = mapWithBrowserField(file, browserField)
    if (mapped) {
      relativeId = mapped + postfix
    } else if (mapped === false) {
      setResolvedCache(id, browserExternalId, options)
      return browserExternalId
    }
  }

  if (relativeId) {
    const resolved = tryFsResolve(
      path.join(dir, relativeId),
      options,
      !exportsField, // try index only if no exports field