expression.js

// A recursive descent parser operates by defining functions for all
// syntactic elements, and recursively calling those, each function
// advancing the input stream and returning an AST node. Precedence
// of constructs (for example, the fact that `!x[1]` means `!(x[1])`
// instead of `(!x)[1]` is handled by the fact that the parser
// function that parses unary prefix operators is called first, and
// in turn calls the function that parses `[]` subscripts — that
// way, it'll receive the node for `x[1]` already parsed, and wraps
// *that* in the unary operator node.
//
// Acorn uses an [operator precedence parser][opp] to handle binary
// operator precedence, because it is much more compact than using
// the technique outlined above, which uses different, nesting
// functions to specify precedence, for all of the ten binary
// precedence levels that JavaScript defines.
//
// [opp]: http://en.wikipedia.org/wiki/Operator-precedence_parser

import {types as tt} from "./tokentype.js"
import {types as tokenCtxTypes} from "./tokencontext.js"
import {Parser} from "./state.js"
import {DestructuringErrors} from "./parseutil.js"
import {lineBreak} from "./whitespace.js"
import {functionFlags, SCOPE_ARROW, SCOPE_SUPER, SCOPE_DIRECT_SUPER, BIND_OUTSIDE, BIND_VAR} from "./scopeflags.js"

const pp = Parser.prototype

// Check if property name clashes with already added.
// Object/class getters and setters are not allowed to clash —
// either with each other or with an init property — and in
// strict mode, init properties are also not allowed to be repeated.

pp.checkPropClash = function(prop, propHash, refDestructuringErrors) {
  if (this.options.ecmaVersion >= 9 && prop.type === "SpreadElement")
    return
  if (this.options.ecmaVersion >= 6 && (prop.computed || prop.method || prop.shorthand))
    return
  let {key} = prop, name
  switch (key.type) {
  case "Identifier": name = key.name; break
  case "Literal": name = String(key.value); break
  default: return
  }
  let {kind} = prop
  if (this.options.ecmaVersion >= 6) {
    if (name === "__proto__" && kind === "init") {
      if (propHash.proto) {
        if (refDestructuringErrors) {
          if (refDestructuringErrors.doubleProto < 0) {
            refDestructuringErrors.doubleProto = key.start
          }
        } else {
          this.raiseRecoverable(key.start, "Redefinition of __proto__ property")
        }
      }
      propHash.proto = true
    }
    return
  }
  name = "$" + name
  let other = propHash[name]
  if (other) {
    let redefinition
    if (kind === "init") {
      redefinition = this.strict && other.init || other.get || other.set
    } else {
      redefinition = other.init || other[kind]
    }
    if (redefinition)
      this.raiseRecoverable(key.start, "Redefinition of property")
  } else {
    other = propHash[name] = {
      init: false,
      get: false,
      set: false
    }
  }
  other[kind] = true
}

// ### Expression parsing

// These nest, from the most general expression type at the top to
// 'atomic', nondivisible expression types at the bottom. Most of
// the functions will simply let the function(s) below them parse,
// and, *if* the syntactic construct they handle is present, wrap
// the AST node that the inner parser gave them in another node.

// Parse a full expression. The optional arguments are used to
// forbid the `in` operator (in for loops initalization expressions)
// and provide reference for storing '=' operator inside shorthand
// property assignment in contexts where both object expression
// and object pattern might appear (so it's possible to raise
// delayed syntax error at correct position).

pp.parseExpression = function(forInit, refDestructuringErrors) {
  let startPos = this.start, startLoc = this.startLoc
  let expr = this.parseMaybeAssign(forInit, refDestructuringErrors)
  if (this.type === tt.comma) {
    let node = this.startNodeAt(startPos, startLoc)
    node.expressions = [expr]
    while (this.eat(tt.comma)) node.expressions.push(this.parseMaybeAssign(forInit, refDestructuringErrors))
    return this.finishNode(node, "SequenceExpression")
  }
  return expr
}

// Parse an assignment expression. This includes applications of
// operators like `+=`.

pp.parseMaybeAssign = function(forInit, refDestructuringErrors, afterLeftParse) {
  if (this.isContextual("yield")) {
    if (this.inGenerator) return this.parseYield(forInit)
    // The tokenizer will assume an expression is allowed after
    // `yield`, but this isn't that kind of yield
    else this.exprAllowed = false
  }

  let ownDestructuringErrors = false, oldParenAssign = -1, oldTrailingComma = -1, oldDoubleProto = -1
  if (refDestructuringErrors) {
    oldParenAssign = refDestructuringErrors.parenthesizedAssign
    oldTrailingComma = refDestructuringErrors.trailingComma
    oldDoubleProto = refDestructuringErrors.doubleProto
    refDestructuringErrors.parenthesizedAssign = refDestructuringErrors.trailingComma = -1
  } else {
    refDestructuringErrors = new DestructuringErrors
    ownDestructuringErrors = true
  }

  let startPos = this.start, startLoc = this.startLoc
  if (this.type === tt.parenL || this.type === tt.name) {
    this.potentialArrowAt = this.start
    this.potentialArrowInForAwait = forInit === "await"
  }
  let left = this.parseMaybeConditional(forInit, refDestructuringErrors)
  if (afterLeftParse) left = afterLeftParse.call(this, left, startPos, startLoc)
  if (this.type.isAssign) {
    let node = this.startNodeAt(startPos, startLoc)
    node.operator = this.value
    if (this.type === tt.eq)
      left = this.toAssignable(left, false, refDestructuringErrors)
    if (!ownDestructuringErrors) {
      refDestructuringErrors.parenthesizedAssign = refDestructuringErrors.trailingComma = refDestructuringErrors.doubleProto = -1
    }
    if (refDestructuringErrors.shorthandAssign >= left.start)
      refDestructuringErrors.shorthandAssign = -1 // reset because shorthand default was used correctly
    if (this.type === tt.eq)
      this.checkLValPattern(left)
    else
      this.checkLValSimple(left)
    node.left = left
    this.next()
    node.right = this.parseMaybeAssign(forInit)
    if (oldDoubleProto > -1) refDestructuringErrors.doubleProto = oldDoubleProto
    return this.finishNode(node, "AssignmentExpression")
  } else {
    if (ownDestructuringErrors) this.checkExpressionErrors(refDestructuringErrors, true)
  }
  if (oldParenAssign > -1) refDestructuringErrors.parenthesizedAssign = oldParenAssign
  if (oldTrailingComma > -1) refDestructuringErrors.trailingComma = oldTrailingComma
  return left
}

// Parse a ternary conditional (`?:`) operator.

pp.parseMaybeConditional = function(forInit, refDestructuringErrors) {
  let startPos = this.start, startLoc = this.startLoc
  let expr = this.parseExprOps(forInit, refDestructuringErrors)
  if (this.checkExpressionErrors(refDestructuringErrors)) return expr
  if (this.eat(tt.question)) {
    let node = this.startNodeAt(startPos, startLoc)
    node.test = expr
    node.consequent = this.parseMaybeAssign()
    this.expect(tt.colon)
    node.alternate = this.parseMaybeAssign(forInit)
    return this.finishNode(node, "ConditionalExpression")
  }
  return expr
}

// Start the precedence parser.

pp.parseExprOps = function(forInit, refDestructuringErrors) {
  let startPos = this.start, startLoc = this.startLoc
  let expr = this.parseMaybeUnary(refDestructuringErrors, false, false, forInit)
  if (this.checkExpressionErrors(refDestructuringErrors)) return expr
  return expr.start === startPos && expr.type === "ArrowFunctionExpression" ? expr : this.parseExprOp(expr, startPos, startLoc, -1, forInit)
}

// Parse binary operators with the operator precedence parsing
// algorithm. `left` is the left-hand side of the operator.
// `minPrec` provides context that allows the function to stop and
// defer further parser to one of its callers when it encounters an
// operator that has a lower precedence than the set it is parsing.

pp.parseExprOp = function(left, leftStartPos, leftStartLoc, minPrec, forInit) {
  let prec = this.type.binop
  if (prec != null && (!forInit || this.type !== tt._in)) {
    if (prec > minPrec) {
      let logical = this.type === tt.logicalOR || this.type === tt.logicalAND
      let coalesce = this.type === tt.coalesce
      if (coalesce) {
        // Handle the precedence of `tt.coalesce` as equal to the range of logical expressions.
        // In other words, `node.right` shouldn't contain logical expressions in order to check the mixed error.
        prec = tt.logicalAND.binop
      }
      let op = this.value
      this.next()
      let startPos = this.start, startLoc = this.startLoc
      let right = this.parseExprOp(this.parseMaybeUnary(null, false, false, forInit), startPos, startLoc, prec, forInit)
      let node = this.buildBinary(leftStartPos, leftStartLoc, left, right, op, logical || coalesce)
      if ((logical && this.type === tt.coalesce) || (coalesce && (this.type === tt.logicalOR || this.type === tt.logicalAND))) {
        this.raiseRecoverable(this.start, "Logical expressions and coalesce expressions cannot be mixed. Wrap either by parentheses")
      }
      return this.parseExprOp(node, leftStartPos, leftStartLoc, minPrec, forInit)
    }
  }
  return left
}

pp.buildBinary = function(startPos, startLoc, left, right, op, logical) {
  if (right.type === "PrivateIdentifier") this.raise(right.start, "Private identifier can only be left side of binary expression")
  let node = this.startNodeAt(startPos, startLoc)
  node.left = left
  node.operator = op
  node.right = right
  return this.finishNode(node, logical ? "LogicalExpression" : "BinaryExpression")
}

// Parse unary operators, both prefix and postfix.

pp.parseMaybeUnary = function(refDestructuringErrors, sawUnary, incDec, forInit) {
  let startPos = this.start, startLoc = this.startLoc, expr
  if (this.isContextual("await") && this.canAwait) {
    expr = this.parseAwait(forInit)
    sawUnary = true
  } else if (this.type.prefix) {
    let node = this.startNode(), update = this.type === tt.incDec
    node.operator = this.value
    node.prefix = true
    this.next()
    node.argument = this.parseMaybeUnary(null, true, update, forInit)
    this.checkExpressionErrors(refDestructuringErrors, true)
    if (update) this.checkLValSimple(node.argument)
    else if (this.strict && node.operator === "delete" &&
             node.argument.type === "Identifier")
      this.raiseRecoverable(node.start, "Deleting local variable in strict mode")
    else if (node.operator === "delete" && isPrivateFieldAccess(node.argument))
      this.raiseRecoverable(node.start, "Private fields can not be deleted")
    else sawUnary = true
    expr = this.finishNode(node, update ? "UpdateExpression" : "UnaryExpression")
  } else if (!sawUnary && this.type === tt.privateId) {
    if (forInit || this.privateNameStack.length === 0) this.unexpected()
    expr = this.parsePrivateIdent()
    // only could be private fields in 'in', such as #x in obj
    if (this.type !== tt._in) this.unexpected()
  } else {
    expr = this.parseExprSubscripts(refDestructuringErrors, forInit)
    if (this.checkExpressionErrors(refDestructuringErrors)) return expr
    while (this.type.postfix && !this.canInsertSemicolon()) {
      let node = this.startNodeAt(startPos, startLoc)
      node.operator = this.value
      node.prefix = false
      node.argument = expr
      this.checkLValSimple(expr)
      this.next()
      expr = this.finishNode(node, "UpdateExpression")
    }
  }

  if (!incDec && this.eat(tt.starstar)) {
    if (sawUnary)
      this.unexpected(this.lastTokStart)
    else
      return this.buildBinary(startPos, startLoc, expr, this.parseMaybeUnary(null, false, false, forInit), "**", false)
  } else {
    return expr
  }
}

function isPrivateFieldAccess(node) {
  return (
    node.type === "MemberExpression" && node.property.type === "PrivateIdentifier" ||
    node.type === "ChainExpression" && isPrivateFieldAccess(node.expression)
  )
}

// Parse call, dot, and `[]`-subscript expressions.

pp.parseExprSubscripts = function(refDestructuringErrors, forInit) {
  let startPos = this.start, startLoc = this.startLoc
  let expr = this.parseExprAtom(refDestructuringErrors, forInit)
  if (expr.type === "ArrowFunctionExpression" && this.input.slice(this.lastTokStart, this.lastTokEnd) !== ")")
    return expr
  let result = this.parseSubscripts(expr, startPos, startLoc, false, forInit)
  if (refDestructuringErrors && result.type === "MemberExpression") {
    if (refDestructuringErrors.parenthesizedAssign >= result.start) refDestructuringErrors.parenthesizedAssign = -1
    if (refDestructuringErrors.parenthesizedBind >= result.start) refDestructuringErrors.parenthesizedBind = -1
    if (refDestructuringErrors.trailingComma >= result.start) refDestructuringErrors.trailingComma = -1
  }
  return result
}

pp.parseSubscripts = function(base, startPos, startLoc, noCalls, forInit) {
  let maybeAsyncArrow = this.options.ecmaVersion >= 8 && base.type === "Identifier" && base.name === "async" &&
      this.lastTokEnd === base.end && !this.canInsertSemicolon() && base.end - base.start === 5 &&
      this.potentialArrowAt === base.start
  let optionalChained = false

  while (true) {
    let element = this.parseSubscript(base, startPos, startLoc, noCalls, maybeAsyncArrow, optionalChained, forInit)

    if (element.optional) optionalChained = true
    if (element === base || element.type === "ArrowFunctionExpression") {
      if (optionalChained) {
        const chainNode = this.startNodeAt(startPos, startLoc)
        chainNode.expression = element
        element = this.finishNode(chainNode, "ChainExpression")
      }
      return element
    }

    base = element
  }
}

pp.parseSubscript = function(base, startPos, startLoc, noCalls, maybeAsyncArrow, optionalChained, forInit) {
  let optionalSupported = this.options.ecmaVersion >= 11
  let optional = optionalSupported && this.eat(tt.questionDot)
  if (noCalls && optional) this.raise(this.lastTokStart, "Optional chaining cannot appear in the callee of new expressions")

  let computed = this.eat(tt.bracketL)
  if (computed || (optional && this.type !== tt.parenL && this.type !== tt.backQuote) || this.eat(tt.dot)) {
    let node = this.startNodeAt(startPos, startLoc)
    node.object = base
    if (computed) {
      node.property = this.parseExpression()
      this.expect(tt.bracketR)
    } else if (this.type === tt.privateId && base.type !== "Super") {
      node.property = this.parsePrivateIdent()
    } else {
      node.property = this.parseIdent(this.options.allowReserved !== "never")
    }
    node.computed = !!computed
    if (optionalSupported) {
      node.optional = optional
    }
    base = this.finishNode(node, "MemberExpression")
  } else if (!noCalls && this.eat(tt.parenL)) {
    let refDestructuringErrors = new DestructuringErrors, oldYieldPos = this.yieldPos, oldAwaitPos = this.awaitPos, oldAwaitIdentPos = this.awaitIdentPos
    this.yieldPos = 0
    this.awaitPos = 0
    this.awaitIdentPos = 0
    let exprList = this.parseExprList(tt.parenR, this.options.ecmaVersion >= 8, false, refDestructuringErrors)
    if (maybeAsyncArrow && !optional && !this.canInsertSemicolon() && this.eat(tt.arrow)) {
      this.checkPatternErrors(refDestructuringErrors, false)
      this.checkYieldAwaitInDefaultParams()
      if (this.awaitIdentPos > 0)
        this.raise(this.awaitIdentPos, "Cannot use 'await' as identifier inside an async function")
      this.yieldPos = oldYieldPos
      this.awaitPos = oldAwaitPos
      this.awaitIdentPos = oldAwaitIdentPos
      return this.parseArrowExpression(this.startNodeAt(startPos, startLoc), exprList, true, forInit)
    }
    this.checkExpressionErrors(refDestructuringErrors, true)
    this.yieldPos = oldYieldPos || this.yieldPos
    this.awaitPos = oldAwaitPos || this.awaitPos
    this.awaitIdentPos = oldAwaitIdentPos || this.awaitIdentPos
    let node = this.startNodeAt(startPos, startLoc)
    node.callee = base
    node.arguments = exprList
    if (optionalSupported) {
      node.optional = optional
    }
    base = this.finishNode(node, "CallExpression")
  } else if (this.type === tt.backQuote) {
    if (optional || optionalChained) {
      this.raise(this.start, "Optional chaining cannot appear in the tag of tagged template expressions")
    }
    let node = this.startNodeAt(startPos, startLoc)
    node.tag = base
    node.quasi = this.parseTemplate({isTagged: true})
    base = this.finishNode(node, "TaggedTemplateExpression")
  }
  return base
}

// Parse an atomic expression — either a single token that is an
// expression, an expression started by a keyword like `function` or
// `new`, or an expression wrapped in punctuation like `()`, `[]`,
// or `{}`.

pp.parseExprAtom = function(refDestructuringErrors, forInit) {
  // If a division operator appears in an expression position, the
  // tokenizer got confused, and we force it to read a regexp instead.
  if (this.type === tt.slash) this.readRegexp()

  let node, canBeArrow = this.potentialArrowAt === this.start
  switch (this.type) {
  case tt._super:
    if (!this.allowSuper)
      this.raise(this.start, "'super' keyword outside a method")
    node = this.startNode()
    this.next()
    if (this.type === tt.parenL && !this.allowDirectSuper)
      this.raise(node.start, "super() call outside constructor of a subclass")
    // The `super` keyword can appear at below:
    // SuperProperty:
    //     super [ Expression ]
    //     super . IdentifierName
    // SuperCall:
    //     super ( Arguments )
    if (this.type !== tt.dot && this.type !== tt.bracketL && this.type !== tt.parenL)
      this.unexpected()
    return this.finishNode(node, "Super")

  case tt._this:
    node = this.startNode()
    this.next()
    return this.finishNode(node, "ThisExpression")

  case tt.name:
    let startPos = this.start, startLoc = this.startLoc, containsEsc = this.containsEsc
    let id = this.parseIdent(false)
    if (this.options.ecmaVersion >= 8 && !containsEsc && id.name === "async" && !this.canInsertSemicolon() && this.eat(tt._function)) {
      this.overrideContext(tokenCtxTypes.f_expr)
      return this.parseFunction(this.startNodeAt(startPos, startLoc), 0, false, true, forInit)
    }
    if (canBeArrow && !this.canInsertSemicolon()) {
      if (this.eat(tt.arrow))
        return this.parseArrowExpression(this.startNodeAt(startPos, startLoc), [id], false, forInit)
      if (this.options.ecmaVersion >= 8 && id.name === "async" && this.type === tt.name && !containsEsc &&
          (!this.potentialArrowInForAwait || this.value !== "of" || this.containsEsc)) {
        id = this.parseIdent(false)
        if (this.canInsertSemicolon() || !this.eat(tt.arrow))
          this.unexpected()
        return this.parseArrowExpression(this.startNodeAt(startPos, startLoc), [id], true, forInit)
      }
    }
    return id

  case tt.regexp:
    let value = this.value
    node = this.parseLiteral(value.value)
    node.regex = {pattern: value.pattern, flags: value.flags}
    return node

  case tt.num: case tt.string:
    return this.parseLiteral(this.value)

  case tt._null: case tt._true: case tt._false:
    node = this.startNode()
    node.value = this.type === tt._null ? null : this.type === tt._true
    node.raw = this.type.keyword
    this.next()
    return this.finishNode(node, "Literal")

  case tt.parenL:
    let start = this.start, expr = this.parseParenAndDistinguishExpression(canBeArrow, forInit)
    if (refDestructuringErrors) {
      if (refDestructuringErrors.parenthesizedAssign < 0 && !this.isSimpleAssignTarget(expr))
        refDestructuringErrors.parenthesizedAssign = start
      if (refDestructuringErrors.parenthesizedBind < 0)
        refDestructuringErrors.parenthesizedBind = start
    }
    return expr

  case tt.bracketL:
    node = this.startNode()
    this.next()
    node.elements = this.parseExprList(tt.bracketR, true, true, refDestructuringErrors)
    return this.finishNode(node, "ArrayExpression")

  case tt.braceL:
    this.overrideContext(tokenCtxTypes.b_expr)
    return this.parseObj(false, refDestructuringErrors)

  case tt._function:
    node = this.startNode()
    this.next()
    return this.parseFunction(node, 0)

  case tt._class:
    return this.parseClass(this.startNode(), false)

  case tt._new:
    return this.parseNew()

  case tt.backQuote:
    return this.parseTemplate()

  case tt._import:
    if (this.options.ecmaVersion >= 11) {
      return this.parseExprImport()
    } else {
      return this.unexpected()
    }

  default:
    this.unexpected()
  }
}

pp.parseExprImport = function() {
  const node = this.startNode()

  // Consume `import` as an identifier for `import.meta`.
  // Because `this.parseIdent(true)` doesn't check escape sequences, it needs the check of `this.containsEsc`.
  if (this.containsEsc) this.raiseRecoverable(this.start, "Escape sequence in keyword import")
  const meta = this.parseIdent(true)

  switch (this.type) {
  case tt.parenL:
    return this.parseDynamicImport(node)
  case tt.dot:
    node.meta = meta
    return this.parseImportMeta(node)
  default:
    this.unexpected()
  }
}

pp.parseDynamicImport = function(node) {
  this.next() // skip `(`

  // Parse node.source.
  node.source = this.parseMaybeAssign()

  // Verify ending.
  if (!this.eat(tt.parenR)) {
    const errorPos = this.start
    if (this.eat(tt.comma) && this.eat(tt.parenR)) {
      this.raiseRecoverable(errorPos, "Trailing comma is not allowed in import()")
    } else {
      this.unexpected(errorPos)
    }
  }

  return this.finishNode(node, "ImportExpression")
}

pp.parseImportMeta = function(node) {
  this.next() // skip `.`

  const containsEsc = this.containsEsc
  node.property = this.parseIdent(true)

  if (node.property.name !== "meta")
    this.raiseRecoverable(node.property.start, "The only valid meta property for import is 'import.meta'")
  if (containsEsc)
    this.raiseRecoverable(node.start, "'import.meta' must not contain escaped characters")
  if (this.options.sourceType !== "module" && !this.options.allowImportExportEverywhere)
    this.raiseRecoverable(node.start, "Cannot use 'import.meta' outside a module")

  return this.finishNode(node, "MetaProperty")
}

pp.parseLiteral = function(value) {
  let node = this.startNode()
  node.value = value
  node.raw = this.input.slice(this.start, this.end)
  if (node.raw.charCodeAt(node.raw.length - 1) === 110) node.bigint = node.raw.slice(0, -1).replace(/_/g, "")
  this.next()
  return this.finishNode(node, "Literal")
}

pp.parseParenExpression = function() {
  this.expect(tt.parenL)
  let val = this.parseExpression()
  this.expect(tt.parenR)
  return val
}

pp.parseParenAndDistinguishExpression = function(canBeArrow, forInit) {
  let startPos = this.start, startLoc = this.startLoc, val, allowTrailingComma = this.options.ecmaVersion >= 8
  if (this.options.ecmaVersion >= 6) {
    this.next()

    let innerStartPos = this.start, innerStartLoc = this.startLoc
    let exprList = [], first = true, lastIsComma = false
    let refDestructuringErrors = new DestructuringErrors, oldYieldPos = this.yieldPos, oldAwaitPos = this.awaitPos, spreadStart
    this.yieldPos = 0
    this.awaitPos = 0
    // Do not save awaitIdentPos to allow checking awaits nested in parameters
    while (this.type !== tt.parenR) {
      first ? first = false : this.expect(tt.comma)
      if (allowTrailingComma && this.afterTrailingComma(tt.parenR, true)) {
        lastIsComma = true
        break
      } else if (this.type === tt.ellipsis) {
        spreadStart = this.start
        exprList.push(this.parseParenItem(this.parseRestBinding()))
        if (this.type === tt.comma) this.raise(this.start, "Comma is not permitted after the rest element")
        break
      } else {
        exprList.push(this.parseMaybeAssign(false, refDestructuringErrors, this.parseParenItem))
      }
    }
    let innerEndPos = this.lastTokEnd, innerEndLoc = this.lastTokEndLoc
    this.expect(tt.parenR)

    if (canBeArrow && !this.canInsertSemicolon() && this.eat(tt.arrow)) {
      this.checkPatternErrors(refDestructuringErrors, false)
      this.checkYieldAwaitInDefaultParams()
      this.yieldPos = oldYieldPos
      this.awaitPos = oldAwaitPos
      return this.parseParenArrowList(startPos, startLoc, exprList, forInit)
    }

    if (!exprList.length || lastIsComma) this.unexpected(this.lastTokStart)
    if (spreadStart) this.unexpected(spreadStart)
    this.checkExpressionErrors(refDestructuringErrors, true)
    this.yieldPos = oldYieldPos || this.yieldPos
    this.awaitPos = oldAwaitPos || this.awaitPos

    if (exprList.length > 1) {
      val = this.startNodeAt(innerStartPos, innerStartLoc)
      val.expressions = exprList
      this.finishNodeAt(val, "SequenceExpression", innerEndPos, innerEndLoc)
    } else {
      val = exprList[0]
    }
  } else {
    val = this.parseParenExpression()
  }

  if (this.options.preserveParens) {
    let par = this.startNodeAt(startPos, startLoc)
    par.expression = val
    return this.finishNode(par, "ParenthesizedExpression")
  } else {
    return val
  }
}

pp.parseParenItem = function(item) {
  return item
}

pp.parseParenArrowList = function(startPos, startLoc, exprList, forInit) {
  return this.parseArrowExpression(this.startNodeAt(startPos, startLoc), exprList, false, forInit)
}

// New's precedence is slightly tricky. It must allow its argument to
// be a `[]` or dot subscript expression, but not a call — at least,
// not without wrapping it in parentheses. Thus, it uses the noCalls
// argument to parseSubscripts to prevent it from consuming the
// argument list.

const empty = []

pp.parseNew = function() {
  if (this.containsEsc) this.raiseRecoverable(this.start, "Escape sequence in keyword new")
  let node = this.startNode()
  let meta = this.parseIdent(true)
  if (this.options.ecmaVersion >= 6 && this.eat(tt.dot)) {
    node.meta = meta
    let containsEsc = this.containsEsc
    node.property = this.parseIdent(true)
    if (node.property.name !== "target")
      this.raiseRecoverable(node.property.start, "The only valid meta property for new is 'new.target'")
    if (containsEsc)
      this.raiseRecoverable(node.start, "'new.target' must not contain escaped characters")
    if (!this.allowNewDotTarget)
      this.raiseRecoverable(node.start, "'new.target' can only be used in functions and class static block")
    return this.finishNode(node, "MetaProperty")
  }
  let startPos = this.start, startLoc = this.startLoc, isImport = this.type === tt._import
  node.callee = this.parseSubscripts(this.parseExprAtom(), startPos, startLoc, true, false)
  if (isImport && node.callee.type === "ImportExpression") {
    this.raise(startPos, "Cannot use new with import()")
  }
  if (this.eat(tt.parenL)) node.arguments = this.parseExprList(tt.parenR, this.options.ecmaVersion >= 8, false)
  else node.arguments = empty
  return this.finishNode(node, "NewExpression")
}

// Parse template expression.

pp.parseTemplateElement = function({isTagged}) {
  let elem = this.startNode()
  if (this.type === tt.invalidTemplate) {
    if (!isTagged) {
      this.raiseRecoverable(this.start, "Bad escape sequence in untagged template literal")
    }
    elem.value = {
      raw: this.value,
      cooked: null
    }
  } else {
    elem.value = {
      raw: this.input.slice(this.start, this.end).replace(/\r\n?/g, "\n"),
      cooked: this.value
    }
  }
  this.next()
  elem.tail = this.type === tt.backQuote
  return this.finishNode(elem, "TemplateElement")
}

pp.parseTemplate = function({isTagged = false} = {}) {
  let node = this.startNode()
  this.next()
  node.expressions = []
  let curElt = this.parseTemplateElement({isTagged})
  node.quasis = [curElt]
  while (!curElt.tail) {
    if (this.type === tt.eof) this.raise(this.pos, "Unterminated template literal")
    this.expect(tt.dollarBraceL)
    node.expressions.push(this.parseExpression())
    this.expect(tt.braceR)
    node.quasis.push(curElt = this.parseTemplateElement({isTagged}))
  }
  this.next()
  return this.finishNode(node, "TemplateLiteral")
}

pp.isAsyncProp = function(prop) {
  return !prop.computed && prop.key.type === "Identifier" && prop.key.name === "async" &&
    (this.type === tt.name || this.type === tt.num || this.type === tt.string || this.type === tt.bracketL || this.type.keyword || (this.options.ecmaVersion >= 9 && this.type === tt.star)) &&
    !lineBreak.test(this.input.slice(this.lastTokEnd, this.start))
}

// Parse an object literal or binding pattern.

pp.parseObj = function(isPattern, refDestructuringErrors) {
  let node = this.startNode(), first = true, propHash = {}
  node.properties = []
  this.next()
  while (!this.eat(tt.braceR)) {
    if (!first) {
      this.expect(tt.comma)
      if (this.options.ecmaVersion >= 5 && this.afterTrailingComma(tt.braceR)) break
    } else first = false

    const prop = this.parseProperty(isPattern, refDestructuringErrors)
    if (!isPattern) this.checkPropClash(prop, propHash, refDestructuringErrors)
    node.properties.push(prop)
  }
  return this.finishNode(node, isPattern ? "ObjectPattern" : "ObjectExpression")
}

pp.parseProperty = function(isPattern, refDestructuringErrors) {
  let prop = this.startNode(), isGenerator, isAsync, startPos, startLoc
  if (this.options.ecmaVersion >= 9 && this.eat(tt.ellipsis)) {
    if (isPattern) {
      prop.argument = this.parseIdent(false)
      if (this.type === tt.comma) {
        this.raise(this.start, "Comma is not permitted after the rest element")
      }
      return this.finishNode(prop, "RestElement")
    }
    // To disallow parenthesized identifier via `this.toAssignable()`.
    if (this.type === tt.parenL && refDestructuringErrors) {
      if (refDestructuringErrors.parenthesizedAssign < 0) {
        refDestructuringErrors.parenthesizedAssign = this.start
      }
      if (refDestructuringErrors.parenthesizedBind < 0) {
        refDestructuringErrors.parenthesizedBind = this.start
      }
    }
    // Parse argument.
    prop.argument = this.parseMaybeAssign(false, refDestructuringErrors)
    // To disallow trailing comma via `this.toAssignable()`.
    if (this.type === tt.comma && refDestructuringErrors && refDestructuringErrors.trailingComma < 0) {
      refDestructuringErrors.trailingComma = this.start
    }
    // Finish
    return this.finishNode(prop, "SpreadElement")
  }
  if (this.options.ecmaVersion >= 6) {
    prop.method = false
    prop.shorthand = false
    if (isPattern || refDestructuringErrors) {
      startPos = this.start
      startLoc = this.startLoc
    }
    if (!isPattern)
      isGenerator = this.eat(tt.star)
  }
  let containsEsc = this.containsEsc
  this.parsePropertyName(prop)
  if (!isPattern && !containsEsc && this.options.ecmaVersion >= 8 && !isGenerator && this.isAsyncProp(prop)) {
    isAsync = true
    isGenerator = this.options.ecmaVersion >= 9 && this.eat(tt.star)
    this.parsePropertyName(prop, refDestructuringErrors)
  } else {
    isAsync = false
  }
  this.parsePropertyValue(prop, isPattern, isGenerator, isAsync, startPos, startLoc, refDestructuringErrors, containsEsc)
  return this.finishNode(prop, "Property")
}

pp.parsePropertyValue = function(prop, isPattern, isGenerator, isAsync, startPos, startLoc, refDestructuringErrors, containsEsc) {
  if ((isGenerator || isAsync) && this.type === tt.colon)
    this.unexpected()

  if (this.eat(tt.colon)) {
    prop.value = isPattern ? this.parseMaybeDefault(this.start, this.startLoc) : this.parseMaybeAssign(false, refDestructuringErrors)
    prop.kind = "init"
  } else if (this.options.ecmaVersion >= 6 && this.type === tt.parenL) {
    if (isPattern) this.unexpected()
    prop.kind = "init"
    prop.method = true
    prop.value = this.parseMethod(isGenerator, isAsync)
  } else if (!isPattern && !containsEsc &&
             this.options.ecmaVersion >= 5 && !prop.computed && prop.key.type === "Identifier" &&
             (prop.key.name === "get" || prop.key.name === "set") &&
             (this.type !== tt.comma && this.type !== tt.braceR && this.type !== tt.eq)) {
    if (isGenerator || isAsync) this.unexpected()
    prop.kind = prop.key.name
    this.parsePropertyName(prop)
    prop.value = this.parseMethod(false)
    let paramCount = prop.kind === "get" ? 0 : 1
    if (prop.value.params.length !== paramCount) {
      let start = prop.value.start
      if (prop.kind === "get")
        this.raiseRecoverable(start, "getter should have no params")
      else
        this.raiseRecoverable(start, "setter should have exactly one param")
    } else {
      if (prop.kind === "set" && prop.value.params[0].type === "RestElement")
        this.raiseRecoverable(prop.value.params[0].start, "Setter cannot use rest params")
    }
  } else if (this.options.ecmaVersion >= 6 && !prop.computed && prop.key.type === "Identifier") {
    if (isGenerator || isAsync) this.unexpected()
    this.checkUnreserved(prop.key)
    if (prop.key.name === "await" && !this.awaitIdentPos)
      this.awaitIdentPos = startPos
    prop.kind = "init"
    if (isPattern) {
      prop.value = this.parseMaybeDefault(startPos, startLoc, this.copyNode(prop.key))
    } else if (this.type === tt.eq && refDestructuringErrors) {
      if (refDestructuringErrors.shorthandAssign < 0)
        refDestructuringErrors.shorthandAssign = this.start
      prop.value = this.parseMaybeDefault(startPos, startLoc, this.copyNode(prop.key))
    } else {
      prop.value = this.copyNode(prop.key)
    }
    prop.shorthand = true
  } else this.unexpected()
}

pp.parsePropertyName = function(prop) {
  if (this.options.ecmaVersion >= 6) {
    if (this.eat(tt.bracketL)) {
      prop.computed = true
      prop.key = this.parseMaybeAssign()
      this.expect(tt.bracketR)
      return prop.key
    } else {
      prop.computed = false
    }
  }
  return prop.key = this.type === tt.num || this.type === tt.string ? this.parseExprAtom() : this.parseIdent(this.options.allowReserved !== "never")
}

// Initialize empty function node.

pp.initFunction = function(node) {
  node.id = null
  if (this.options.ecmaVersion >= 6) node.generator = node.expression = false
  if (this.options.ecmaVersion >= 8) node.async = false
}

// Parse object or class method.

pp.parseMethod = function(isGenerator, isAsync, allowDirectSuper) {
  let node = this.startNode(), oldYieldPos = this.yieldPos, oldAwaitPos = this.awaitPos, oldAwaitIdentPos = this.awaitIdentPos

  this.initFunction(node)
  if (this.options.ecmaVersion >= 6)
    node.generator = isGenerator
  if (this.options.ecmaVersion >= 8)
    node.async = !!isAsync

  this.yieldPos = 0
  this.awaitPos = 0
  this.awaitIdentPos = 0
  this.enterScope(functionFlags(isAsync, node.generator) | SCOPE_SUPER | (allowDirectSuper ? SCOPE_DIRECT_SUPER : 0))

  this.expect(tt.parenL)
  node.params = this.parseBindingList(tt.parenR, false, this.options.ecmaVersion >= 8)
  this.checkYieldAwaitInDefaultParams()
  this.parseFunctionBody(node, false, true, false)

  this.yieldPos = oldYieldPos
  this.awaitPos = oldAwaitPos
  this.awaitIdentPos = oldAwaitIdentPos
  return this.finishNode(node, "FunctionExpression")
}

// Parse arrow function expression with given parameters.

pp.parseArrowExpression = function(node, params, isAsync, forInit) {
  let oldYieldPos = this.yieldPos, oldAwaitPos = this.awaitPos, oldAwaitIdentPos = this.awaitIdentPos

  this.enterScope(functionFlags(isAsync, false) | SCOPE_ARROW)
  this.initFunction(node)
  if (this.options.ecmaVersion >= 8) node.async = !!isAsync

  this.yieldPos = 0
  this.awaitPos = 0
  this.awaitIdentPos = 0

  node.params = this.toAssignableList(params, true)
  this.parseFunctionBody(node, true, false, forInit)

  this.yieldPos = oldYieldPos
  this.awaitPos = oldAwaitPos
  this.awaitIdentPos = oldAwaitIdentPos
  return this.finishNode(node, "ArrowFunctionExpression")
}

// Parse function body and check parameters.

pp.parseFunctionBody = function(node, isArrowFunction, isMethod, forInit) {
  let isExpression = isArrowFunction && this.type !== tt.braceL
  let oldStrict = this.strict, useStrict = false

  if (isExpression) {
    node.body = this.parseMaybeAssign(forInit)
    node.expression = true
    this.checkParams(node, false)
  } else {
    let nonSimple = this.options.ecmaVersion >= 7 && !this.isSimpleParamList(node.params)
    if (!oldStrict || nonSimple) {
      useStrict = this.strictDirective(this.end)
      // If this is a strict mode function, verify that argument names
      // are not repeated, and it does not try to bind the words `eval`
      // or `arguments`.
      if (useStrict && nonSimple)
        this.raiseRecoverable(node.start, "Illegal 'use strict' directive in function with non-simple parameter list")
    }
    // Start a new scope with regard to labels and the `inFunction`
    // flag (restore them to their old value afterwards).
    let oldLabels = this.labels
    this.labels = []
    if (useStrict) this.strict = true

    // Add the params to varDeclaredNames to ensure that an error is thrown
    // if a let/const declaration in the function clashes with one of the params.
    this.checkParams(node, !oldStrict && !useStrict && !isArrowFunction && !isMethod && this.isSimpleParamList(node.params))
    // Ensure the function name isn't a forbidden identifier in strict mode, e.g. 'eval'
    if (this.strict && node.id) this.checkLValSimple(node.id, BIND_OUTSIDE)
    node.body = this.parseBlock(false, undefined, useStrict && !oldStrict)
    node.expression = false
    this.adaptDirectivePrologue(node.body.body)
    this.labels = oldLabels
  }
  this.exitScope()
}

pp.isSimpleParamList = function(params) {
  for (let param of params)
    if (param.type !== "Identifier") return false
  return true
}

// Checks function params for various disallowed patterns such as using "eval"
// or "arguments" and duplicate parameters.

pp.checkParams = function(node, allowDuplicates) {
  let nameHash = Object.create(null)
  for (let param of node.params)
    this.checkLValInnerPattern(param, BIND_VAR, allowDuplicates ? null : nameHash)
}

// Parses a comma-separated list of expressions, and returns them as
// an array. `close` is the token type that ends the list, and
// `allowEmpty` can be turned on to allow subsequent commas with
// nothing in between them to be parsed as `null` (which is needed
// for array literals).

pp.parseExprList = function(close, allowTrailingComma, allowEmpty, refDestructuringErrors) {
  let elts = [], first = true
  while (!this.eat(close)) {
    if (!first) {
      this.expect(tt.comma)
      if (allowTrailingComma && this.afterTrailingComma(close)) break
    } else first = false

    let elt
    if (allowEmpty && this.type === tt.comma)
      elt = null
    else if (this.type === tt.ellipsis) {
      elt = this.parseSpread(refDestructuringErrors)
      if (refDestructuringErrors && this.type === tt.comma && refDestructuringErrors.trailingComma < 0)
        refDestructuringErrors.trailingComma = this.start
    } else {
      elt = this.parseMaybeAssign(false, refDestructuringErrors)
    }
    elts.push(elt)
  }
  return elts
}

pp.checkUnreserved = function({start, end, name}) {
  if (this.inGenerator && name === "yield")
    this.raiseRecoverable(start, "Cannot use 'yield' as identifier inside a generator")
  if (this.inAsync && name === "await")
    this.raiseRecoverable(start, "Cannot use 'await' as identifier inside an async function")
  if (this.currentThisScope().inClassFieldInit && name === "arguments")
    this.raiseRecoverable(start, "Cannot use 'arguments' in class field initializer")
  if (this.inClassStaticBlock && (name === "arguments" || name === "await"))
    this.raise(start, `Cannot use ${name} in class static initialization block`)
  if (this.keywords.test(name))
    this.raise(start, `Unexpected keyword '${name}'`)
  if (this.options.ecmaVersion < 6 &&
    this.input.slice(start, end).indexOf("\\") !== -1) return
  const re = this.strict ? this.reservedWordsStrict : this.reservedWords
  if (re.test(name)) {
    if (!this.inAsync && name === "await")
      this.raiseRecoverable(start, "Cannot use keyword 'await' outside an async function")
    this.raiseRecoverable(start, `The keyword '${name}' is reserved`)
  }
}

// Parse the next token as an identifier. If `liberal` is true (used
// when parsing properties), it will also convert keywords into
// identifiers.

pp.parseIdent = function(liberal, isBinding) {
  let node = this.startNode()
  if (this.type === tt.name) {
    node.name = this.value
  } else if (this.type.keyword) {
    node.name = this.type.keyword

    // To fix https://github.com/acornjs/acorn/issues/575
    // `class` and `function` keywords push new context into this.context.
    // But there is no chance to pop the context if the keyword is consumed as an identifier such as a property name.
    // If the previous token is a dot, this does not apply because the context-managing code already ignored the keyword
    if ((node.name === "class" || node.name === "function") &&
        (this.lastTokEnd !== this.lastTokStart + 1 || this.input.charCodeAt(this.lastTokStart) !== 46)) {
      this.context.pop()
    }
  } else {
    this.unexpected()
  }
  this.next(!!liberal)
  this.finishNode(node, "Identifier")
  if (!liberal) {
    this.checkUnreserved(node)
    if (node.name === "await" && !this.awaitIdentPos)
      this.awaitIdentPos = node.start
  }
  return node
}

pp.parsePrivateIdent = function() {
  const node = this.startNode()
  if (this.type === tt.privateId) {
    node.name = this.value
  } else {
    this.unexpected()
  }
  this.next()
  this.finishNode(node, "PrivateIdentifier")

  // For validating existence
  if (this.privateNameStack.length === 0) {
    this.raise(node.start, `Private field '#${node.name}' must be declared in an enclosing class`)
  } else {
    this.privateNameStack[this.privateNameStack.length - 1].used.push(node)
  }

  return node
}

// Parses yield expression inside generator.

pp.parseYield = function(forInit) {
  if (!this.yieldPos) this.yieldPos = this.start

  let node = this.startNode()
  this.next()
  if (this.type === tt.semi || this.canInsertSemicolon() || (this.type !== tt.star && !this.type.startsExpr)) {
    node.delegate = false
    node.argument = null
  } else {
    node.delegate = this.eat(tt.star)
    node.argument = this.parseMaybeAssign(forInit)
  }
  return this.finishNode(node, "YieldExpression")
}

pp.parseAwait = function(forInit) {
  if (!this.awaitPos) this.awaitPos = this.start

  let node = this.startNode()
  this.next()
  node.argument = this.parseMaybeUnary(null, true, false, forInit)
  return this.finishNode(node, "AwaitExpression")
}