babel/packages/babel-traverse/src/visitors.js

/* @flow */

import * as virtualTypes from "./path/lib/virtual-types";
import * as messages from "babel-messages";
import * as t from "babel-types";
import clone from "lodash/lang/clone";

export function explode(visitor) {
  if (visitor._exploded) return visitor;
  visitor._exploded = true;

  // normalise pipes
  for (let nodeType in visitor) {
    if (shouldIgnoreKey(nodeType)) continue;

    let parts = nodeType.split("|");
    if (parts.length === 1) continue;

    let fns = visitor[nodeType];
    delete visitor[nodeType];

    for (let part of (parts: Array)) {
      visitor[part] = fns;
    }
  }

  // verify data structure
  verify(visitor);

  // make sure there's no __esModule type since this is because we're using loose mode
  // and it sets __esModule to be enumerable on all modules :(
  delete visitor.__esModule;

  // ensure visitors are objects
  ensureEntranceObjects(visitor);

  // ensure enter/exit callbacks are arrays
  ensureCallbackArrays(visitor);

  // add type wrappers
  for (let nodeType of (Object.keys(visitor): Array)) {
    if (shouldIgnoreKey(nodeType)) continue;

    let wrapper = virtualTypes[nodeType];
    if (!wrapper) continue;

    // wrap all the functions
    let fns = visitor[nodeType];
    for (let type in fns) {
      fns[type] = wrapCheck(wrapper, fns[type]);
    }

    // clear it from the visitor
    delete visitor[nodeType];

    if (wrapper.types) {
      for (let type of (wrapper.types: Array)) {
        // merge the visitor if necessary or just put it back in
        if (visitor[type]) {
          mergePair(visitor[type], fns);
        } else {
          visitor[type] = fns;
        }
      }
    } else {
      mergePair(visitor, fns);
    }
  }

  // add aliases
  for (let nodeType in visitor) {
    if (shouldIgnoreKey(nodeType)) continue;

    let fns = visitor[nodeType];

    let aliases = t.FLIPPED_ALIAS_KEYS[nodeType];
    if (!aliases) continue;

    // clear it from the visitor
    delete visitor[nodeType];

    for (let alias of (aliases: Array)) {
      let existing = visitor[alias];
      if (existing) {
        mergePair(existing, fns);
      } else {
        visitor[alias] = clone(fns);
      }
    }
  }

  for (let nodeType in visitor) {
    if (shouldIgnoreKey(nodeType)) continue;

    ensureCallbackArrays(visitor[nodeType]);
  }

  return visitor;
}

export function verify(visitor) {
  if (visitor._verified) return;

  if (typeof visitor === "function") {
    throw new Error(messages.get("traverseVerifyRootFunction"));
  }

  for (let nodeType in visitor) {
    if (shouldIgnoreKey(nodeType)) continue;

    if (t.TYPES.indexOf(nodeType) < 0) {
      throw new Error(messages.get("traverseVerifyNodeType", nodeType));
    }

    let visitors = visitor[nodeType];
    if (typeof visitors === "object") {
      for (let visitorKey in visitors) {
        if (visitorKey === "enter" || visitorKey === "exit") continue;
        throw new Error(messages.get("traverseVerifyVisitorProperty", nodeType, visitorKey));
      }
    }
  }

  visitor._verified = true;
}

export function merge(visitors: Array, states: Array = []) {
  let rootVisitor = {};

  for (let i = 0; i < visitors.length; i++) {
    let visitor = visitors[i];
    let state = states[i];

    explode(visitor);

    for (let type in visitor) {
      let visitorType = visitor[type];

      // if we have state then overload the callbacks to take it
      if (state) {
        let oldVisitorType = visitorType;
        visitorType = {};

        for (let key in oldVisitorType) {
          let fns = oldVisitorType[key];

          // not an enter/exit array of callbacks
          if (!Array.isArray(fns)) continue;

          fns = fns.map(function (fn) {
            if (typeof fn === "function") {
              let newFn = function (path) {
                return fn.call(state, path, state);
              };
              newFn.toString = () => fn.toString();
              return newFn;
            } else {
              return fn;
            }
          });

          visitorType[key] = fns;
        }
      }

      let nodeVisitor = rootVisitor[type] = rootVisitor[type] || {};
      mergePair(nodeVisitor, visitorType);
    }
  }

  return rootVisitor;
}

function ensureEntranceObjects(obj) {
  for (let key in obj) {
    if (shouldIgnoreKey(key)) continue;

    let fns = obj[key];
    if (typeof fns === "function") {
      obj[key] = { enter: fns };
    }
  }
}

function ensureCallbackArrays(obj){
  if (obj.enter && !Array.isArray(obj.enter)) obj.enter = [obj.enter];
  if (obj.exit && !Array.isArray(obj.exit)) obj.exit = [obj.exit];
}

function wrapCheck(wrapper, fn) {
  let newFn = function (path) {
    if (wrapper.checkPath(path)) {
      return fn.apply(this, arguments);
    }
  };
  newFn.toString = () => fn.toString();
  return newFn;
}

function shouldIgnoreKey(key) {
  // internal/hidden key
  if (key[0] === "_") return true;

  // ignore function keys
  if (key === "enter" || key === "exit" || key === "shouldSkip") return true;

  // ignore other options
  if (key === "blacklist" || key === "noScope" || key === "skipKeys") return true;

  return false;
}

function mergePair(dest, src) {
  for (let key in src) {
    dest[key] = [].concat(dest[key] || [], src[key]);
  }
}