babel/src/parser/lval.js

import { types as tt } from "../tokenizer/types";
import Parser from "./index";

const pp = Parser.prototype;

// Convert existing expression atom to assignable pattern
// if possible.

pp.toAssignable = function (node, isBinding, contextDescription) {
  if (node) {
    switch (node.type) {
      case "Identifier":
      case "ObjectPattern":
      case "ArrayPattern":
      case "AssignmentPattern":
        break;

      case "ObjectExpression":
        node.type = "ObjectPattern";
        for (const prop of (node.properties: Array<Object>)) {
          if (prop.type === "ObjectMethod") {
            if (prop.kind === "get" || prop.kind === "set") {
              this.raise(prop.key.start, "Object pattern can't contain getter or setter");
            } else {
              this.raise(prop.key.start, "Object pattern can't contain methods");
            }
          } else {
            this.toAssignable(prop, isBinding, "object destructuring pattern");
          }
        }
        break;

      case "ObjectProperty":
        this.toAssignable(node.value, isBinding, contextDescription);
        break;

      case "SpreadProperty":
        node.type = "RestProperty";
        break;

      case "ArrayExpression":
        node.type = "ArrayPattern";
        this.toAssignableList(node.elements, isBinding, contextDescription);
        break;

      case "AssignmentExpression":
        if (node.operator === "=") {
          node.type = "AssignmentPattern";
          delete node.operator;
        } else {
          this.raise(node.left.end, "Only '=' operator can be used for specifying default value.");
        }
        break;

      case "MemberExpression":
        if (!isBinding) break;

      default: {
        const message = "Invalid left-hand side" +
          (contextDescription ? " in " + contextDescription : /* istanbul ignore next */ "expression");
        this.raise(node.start, message);
      }
    }
  }
  return node;
};

// Convert list of expression atoms to binding list.

pp.toAssignableList = function (exprList, isBinding, contextDescription) {
  let end = exprList.length;
  if (end) {
    const last = exprList[end - 1];
    if (last && last.type === "RestElement") {
      --end;
    } else if (last && last.type === "SpreadElement") {
      last.type = "RestElement";
      const arg = last.argument;
      this.toAssignable(arg, isBinding, contextDescription);
      if (arg.type !== "Identifier" && arg.type !== "MemberExpression" && arg.type !== "ArrayPattern") {
        this.unexpected(arg.start);
      }
      --end;
    }
  }
  for (let i = 0; i < end; i++) {
    const elt = exprList[i];
    if (elt) this.toAssignable(elt, isBinding, contextDescription);
  }
  return exprList;
};

// Convert list of expression atoms to a list of

pp.toReferencedList = function (exprList) {
  return exprList;
};

// Parses spread element.

pp.parseSpread = function (refShorthandDefaultPos) {
  const node = this.startNode();
  this.next();
  node.argument = this.parseMaybeAssign(false, refShorthandDefaultPos);
  return this.finishNode(node, "SpreadElement");
};

pp.parseRest = function () {
  const node = this.startNode();
  this.next();
  node.argument = this.parseBindingIdentifier();
  return this.finishNode(node, "RestElement");
};

pp.shouldAllowYieldIdentifier = function () {
  return this.match(tt._yield) && !this.state.strict && !this.state.inGenerator;
};

pp.parseBindingIdentifier = function () {
  return this.parseIdentifier(this.shouldAllowYieldIdentifier());
};

// Parses lvalue (assignable) atom.

pp.parseBindingAtom = function () {
  switch (this.state.type) {
    case tt._yield:
      if (this.state.strict || this.state.inGenerator) this.unexpected();
      // fall-through
    case tt.name:
      return this.parseIdentifier(true);

    case tt.bracketL:
      const node = this.startNode();
      this.next();
      node.elements = this.parseBindingList(tt.bracketR, true);
      return this.finishNode(node, "ArrayPattern");

    case tt.braceL:
      return this.parseObj(true);

    default:
      this.unexpected();
  }
};

pp.parseBindingList = function (close, allowEmpty) {
  const elts = [];
  let first = true;
  while (!this.eat(close)) {
    if (first) {
      first = false;
    } else {
      this.expect(tt.comma);
    }
    if (allowEmpty && this.match(tt.comma)) {
      elts.push(null);
    } else if (this.eat(close)) {
      break;
    } else if (this.match(tt.ellipsis)) {
      elts.push(this.parseAssignableListItemTypes(this.parseRest()));
      this.expect(close);
      break;
    } else {
      const decorators = [];
      while (this.match(tt.at)) {
        decorators.push(this.parseDecorator());
      }
      const left = this.parseMaybeDefault();
      if (decorators.length) {
        left.decorators = decorators;
      }
      this.parseAssignableListItemTypes(left);
      elts.push(this.parseMaybeDefault(left.start, left.loc.start, left));
    }
  }
  return elts;
};

pp.parseAssignableListItemTypes = function (param) {
  return param;
};

// Parses assignment pattern around given atom if possible.

pp.parseMaybeDefault = function (startPos, startLoc, left) {
  startLoc = startLoc || this.state.startLoc;
  startPos = startPos || this.state.start;
  left = left || this.parseBindingAtom();
  if (!this.eat(tt.eq)) return left;

  const node = this.startNodeAt(startPos, startLoc);
  node.left = left;
  node.right = this.parseMaybeAssign();
  return this.finishNode(node, "AssignmentPattern");
};

// Verify that a node is an lval — something that can be assigned
// to.

pp.checkLVal = function (expr, isBinding, checkClashes, contextDescription) {
  switch (expr.type) {
    case "Identifier":
      this.checkReservedWord(expr.name, expr.start, false, true);

      if (checkClashes) {
        // we need to prefix this with an underscore for the cases where we have a key of
        // `__proto__`. there's a bug in old V8 where the following wouldn't work:
        //
        //   > var obj = Object.create(null);
        //   undefined
        //   > obj.__proto__
        //   null
        //   > obj.__proto__ = true;
        //   true
        //   > obj.__proto__
        //   null
        const key = `_${expr.name}`;

        if (checkClashes[key]) {
          this.raise(expr.start, "Argument name clash in strict mode");
        } else {
          checkClashes[key] = true;
        }
      }
      break;

    case "MemberExpression":
      if (isBinding) this.raise(expr.start, (isBinding ? "Binding" : "Assigning to") + " member expression");
      break;

    case "ObjectPattern":
      for (let prop of (expr.properties: Array<Object>)) {
        if (prop.type === "ObjectProperty") prop = prop.value;
        this.checkLVal(prop, isBinding, checkClashes, "object destructuring pattern");
      }
      break;

    case "ArrayPattern":
      for (const elem of (expr.elements: Array<Object>)) {
        if (elem) this.checkLVal(elem, isBinding, checkClashes, "array destructuring pattern");
      }
      break;

    case "AssignmentPattern":
      this.checkLVal(expr.left, isBinding, checkClashes, "assignment pattern");
      break;

    case "RestProperty":
      this.checkLVal(expr.argument, isBinding, checkClashes, "rest property");
      break;

    case "RestElement":
      this.checkLVal(expr.argument, isBinding, checkClashes, "rest element");
      break;

    default: {
      const message = (isBinding ? /* istanbul ignore next */ "Binding invalid" : "Invalid") +
        " left-hand side" +
        (contextDescription ? " in " + contextDescription : /* istanbul ignore next */ "expression");
      this.raise(expr.start, message);
    }
  }
};