function createRamBundleGroups()

in packages/metro/src/Bundler/util.js [165:220]

• 45 lines of code
• 7 McCabe index (conditional complexity)

function createRamBundleGroups<T: ModuleTransportLike>(
  ramGroups: $ReadOnlyArray<string>,
  groupableModules: $ReadOnlyArray<T>,
  subtree: SubTree<T>,
): Map<number, Set<number>> {
  // build two maps that allow to lookup module data
  // by path or (numeric) module id;
  const byPath: Map<string, T> = new Map();
  const byId: Map<number, string> = new Map();
  groupableModules.forEach((m: T) => {
    byPath.set(m.sourcePath, m);
    byId.set(m.id, m.sourcePath);
  });

  // build a map of group root IDs to an array of module IDs in the group
  const result: Map<number, Set<number>> = new Map(
    ramGroups.map((modulePath: string) => {
      const root = byPath.get(modulePath);
      if (root == null) {
        throw Error(`Group root ${modulePath} is not part of the bundle`);
      }
      return [
        root.id,
        // `subtree` yields the IDs of all transitive dependencies of a module
        new Set(subtree(root, byPath)),
      ];
    }),
  );

  if (ramGroups.length > 1) {
    // build a map of all grouped module IDs to an array of group root IDs
    const all = new ArrayMap();
    for (const [parent, children] of result) {
      for (const module of children) {
        all.get(module).push(parent);
      }
    }

    // find all module IDs that are part of more than one group
    const doubles = filter(all, ([, parents]) => parents.length > 1);
    for (const [moduleId, parents] of doubles) {
      // $FlowFixMe[method-unbinding] added when improving typing for this parameters
      const parentNames = parents.map(byId.get, byId);
      const lastName = parentNames.pop();
      throw new Error(
        `Module ${
          byId.get(moduleId) || moduleId
        } belongs to groups ${parentNames.join(', ')}, and ${String(
          lastName,
        )}. Ensure that each module is only part of one group.`,
      );
    }
  }

  return result;
}