Function includeSymbolMergeHandler

src/resolveIncludes.js:11–48

(objVal, srcVal)

 */
// eslint-disable-next-line consistent-return
function includeSymbolMergeHandler(objVal, srcVal) {
  const newObjVal = objVal;
  let include;

  if (srcVal && srcVal[INCLUDE]) {
    include =
      newObjVal && newObjVal[INCLUDE]
        ? [...newObjVal[INCLUDE], ...srcVal[INCLUDE]]
        : srcVal[INCLUDE];
  }

  // if objVal doesn't exists create new from source
  if (_.isUndefined(newObjVal) && _.isPlainObject(srcVal)) {
    // Copy symbol fix.
    // { ...srcVal } copies symbol wrong, it adds symbol value to the property defined just after it
    // Problem example: { SYMBOL: ['Test'], someProp: 10 } => { someProp: ['Test'] }
    // mergeWith prevents wrong copy because it doesn't iterate trough Symbols so it skips INCLUDE
    // We do not INCLUDE symbol to be copied actually in this function
    // because it is copied manually. This whole function is fixing Symbol problems.
    const newObj = _.mergeWith({}, srcVal, (o, s) => s);
    // Assigning INCLUDE after object definition to avoid Object.assign when code transpiled.
    // Object.assign in RN uses polyfill which doesn't copy Symbols that's why INCLUDE symbol
    // must be set manually after spread.
    // TODO(Braco) - once Object.assign polyfill is no longer used use commented code bellow
    // Check if `customizer` is needed still at all after polyfill is removed!
    // return { ...srcVal, [INCLUDE]: include }; // add new lines for each property
    if (include) {
      newObj[INCLUDE] = include;
    }
    return newObj;
  }

  // otherwise let lodash default merge (return undefined)
  // and add INCLUDE to objVal if any in srcVal
  if (_.isPlainObject(newObjVal) && include) {
    newObjVal[INCLUDE] = include;
  }
}

/**
 * Recursively include required target styles from target and base root.