util.ts

import { types as t } from "@babel/core";
import type { File } from "@babel/core";
import type { Scope, NodePath } from "@babel/traverse";
import type { TraversalAncestors } from "@babel/types";

/**
 * Test if an ArrayPattern's elements contain any RestElements.
 */

function hasArrayRest(pattern: t.ArrayPattern) {
  return pattern.elements.some(elem => t.isRestElement(elem));
}

/**
 * Test if an ObjectPattern's properties contain any RestElements.
 */

function hasObjectRest(pattern: t.ObjectPattern) {
  return pattern.properties.some(prop => t.isRestElement(prop));
}

interface Unpackable {
  elements: Array<null | t.Expression>;
}

const STOP_TRAVERSAL = {};

interface ArrayUnpackVisitorState {
  deopt: boolean;
  bindings: Record<string, t.Identifier>;
}

// NOTE: This visitor is meant to be used via t.traverse
const arrayUnpackVisitor = (
  node: t.Node,
  ancestors: TraversalAncestors,
  state: ArrayUnpackVisitorState,
) => {
  if (!ancestors.length) {
    // Top-level node: this is the array literal.
    return;
  }

  if (
    t.isIdentifier(node) &&
    t.isReferenced(node, ancestors[ancestors.length - 1].node) &&
    state.bindings[node.name]
  ) {
    state.deopt = true;
    throw STOP_TRAVERSAL;
  }
};

type DestructuringTransformerNode =
  | t.VariableDeclaration
  | t.ExpressionStatement
  | t.ReturnStatement;

interface DestructuringTransformerOption {
  blockHoist?: number;
  operator?: t.AssignmentExpression["operator"];
  nodes?: DestructuringTransformerNode[];
  kind?: t.VariableDeclaration["kind"];
  scope: Scope;
  arrayLikeIsIterable: boolean;
  iterableIsArray: boolean;
  objectRestNoSymbols: boolean;
  useBuiltIns: boolean;
  addHelper: File["addHelper"];
}
export class DestructuringTransformer {
  private blockHoist: number;
  private operator: t.AssignmentExpression["operator"];
  arrayRefSet: Set<string>;
  private nodes: DestructuringTransformerNode[];
  private scope: Scope;
  private kind: t.VariableDeclaration["kind"];
  private iterableIsArray: boolean;
  private arrayLikeIsIterable: boolean;
  private objectRestNoSymbols: boolean;
  private useBuiltIns: boolean;
  private addHelper: File["addHelper"];
  constructor(opts: DestructuringTransformerOption) {
    this.blockHoist = opts.blockHoist;
    this.operator = opts.operator;
    this.arrayRefSet = new Set();
    this.nodes = opts.nodes || [];
    this.scope = opts.scope;
    this.kind = opts.kind;
    this.iterableIsArray = opts.iterableIsArray;
    this.arrayLikeIsIterable = opts.arrayLikeIsIterable;
    this.objectRestNoSymbols = opts.objectRestNoSymbols;
    this.useBuiltIns = opts.useBuiltIns;
    this.addHelper = opts.addHelper;
  }

  getExtendsHelper() {
    return this.useBuiltIns
      ? t.memberExpression(t.identifier("Object"), t.identifier("assign"))
      : this.addHelper("extends");
  }

  buildVariableAssignment(
    id:
      | t.Identifier
      | t.MemberExpression
      | t.RestElement
      | t.TSParameterProperty,
    init: t.Expression,
  ) {
    let op = this.operator;
    if (t.isMemberExpression(id)) op = "=";

    let node: t.ExpressionStatement | t.VariableDeclaration;

    if (op) {
      node = t.expressionStatement(
        t.assignmentExpression(
          op,
          id,
          t.cloneNode(init) || this.scope.buildUndefinedNode(),
        ),
      );
    } else {
      let nodeInit: t.Expression;

      if (this.kind === "const" && init === null) {
        nodeInit = this.scope.buildUndefinedNode();
      } else {
        nodeInit = t.cloneNode(init);
      }

      node = t.variableDeclaration(this.kind, [
        t.variableDeclarator(id, nodeInit),
      ]);
    }

    //@ts-expect-error(todo): document block hoist property
    node._blockHoist = this.blockHoist;

    return node;
  }

  buildVariableDeclaration(id: t.Identifier, init: t.Expression) {
    const declar = t.variableDeclaration("var", [
      t.variableDeclarator(t.cloneNode(id), t.cloneNode(init)),
    ]);
    // @ts-expect-error todo(flow->ts): avoid mutations
    declar._blockHoist = this.blockHoist;
    return declar;
  }

  push(id: t.LVal, _init: t.Expression) {
    const init = t.cloneNode(_init);
    if (t.isObjectPattern(id)) {
      this.pushObjectPattern(id, init);
    } else if (t.isArrayPattern(id)) {
      this.pushArrayPattern(id, init);
    } else if (t.isAssignmentPattern(id)) {
      this.pushAssignmentPattern(id, init);
    } else {
      this.nodes.push(this.buildVariableAssignment(id, init));
    }
  }

  toArray(node: t.Expression, count?: boolean | number) {
    if (
      this.iterableIsArray ||
      (t.isIdentifier(node) && this.arrayRefSet.has(node.name))
    ) {
      return node;
    } else {
      return this.scope.toArray(node, count, this.arrayLikeIsIterable);
    }
  }

  pushAssignmentPattern(
    { left, right }: t.AssignmentPattern,
    valueRef: t.Expression,
  ) {
    // handle array init hole
    // const [x = 42] = [,];
    // -> const x = 42;
    if (valueRef === null) {
      this.nodes.push(this.buildVariableAssignment(left, right));
      return;
    }

    // we need to assign the current value of the assignment to avoid evaluating
    // it more than once
    const tempId = this.scope.generateUidIdentifierBasedOnNode(valueRef);

    this.nodes.push(this.buildVariableDeclaration(tempId, valueRef));

    const tempConditional = t.conditionalExpression(
      t.binaryExpression(
        "===",
        t.cloneNode(tempId),
        this.scope.buildUndefinedNode(),
      ),
      right,
      t.cloneNode(tempId),
    );

    if (t.isPattern(left)) {
      let patternId;
      let node;

      if (this.kind === "const" || this.kind === "let") {
        patternId = this.scope.generateUidIdentifier(tempId.name);
        node = this.buildVariableDeclaration(patternId, tempConditional);
      } else {
        patternId = tempId;

        node = t.expressionStatement(
          t.assignmentExpression("=", t.cloneNode(tempId), tempConditional),
        );
      }

      this.nodes.push(node);
      this.push(left, patternId);
    } else {
      this.nodes.push(this.buildVariableAssignment(left, tempConditional));
    }
  }

  pushObjectRest(
    pattern: t.ObjectPattern,
    objRef: t.Expression,
    spreadProp: t.RestElement,
    spreadPropIndex: number,
  ) {
    // get all the keys that appear in this object before the current spread

    const keys = [];
    let allLiteral = true;
    let hasTemplateLiteral = false;
    for (let i = 0; i < pattern.properties.length; i++) {
      const prop = pattern.properties[i];

      // we've exceeded the index of the spread property to all properties to the
      // right need to be ignored
      if (i >= spreadPropIndex) break;

      // ignore other spread properties
      if (t.isRestElement(prop)) continue;

      const key = prop.key;
      if (t.isIdentifier(key) && !prop.computed) {
        keys.push(t.stringLiteral(key.name));
      } else if (t.isTemplateLiteral(key)) {
        keys.push(t.cloneNode(key));
        hasTemplateLiteral = true;
      } else if (t.isLiteral(key)) {
        // @ts-expect-error todo(flow->ts) NullLiteral
        keys.push(t.stringLiteral(String(key.value)));
      } else {
        keys.push(t.cloneNode(key));
        allLiteral = false;
      }
    }

    let value;
    if (keys.length === 0) {
      value = t.callExpression(this.getExtendsHelper(), [
        t.objectExpression([]),
        t.cloneNode(objRef),
      ]);
    } else {
      let keyExpression: t.Expression = t.arrayExpression(keys);

      if (!allLiteral) {
        keyExpression = t.callExpression(
          t.memberExpression(keyExpression, t.identifier("map")),
          [this.addHelper("toPropertyKey")],
        );
      } else if (!hasTemplateLiteral && !t.isProgram(this.scope.block)) {
        // Hoist definition of excluded keys, so that it's not created each time.
        const program = this.scope.path.findParent(path => path.isProgram());
        const id = this.scope.generateUidIdentifier("excluded");

        program.scope.push({
          id,
          init: keyExpression,
          kind: "const",
        });

        keyExpression = t.cloneNode(id);
      }

      value = t.callExpression(
        this.addHelper(
          `objectWithoutProperties${this.objectRestNoSymbols ? "Loose" : ""}`,
        ),
        [t.cloneNode(objRef), keyExpression],
      );
    }

    // @ts-expect-error: The argument of a RestElement in ObjectPattern must not be an ArrayPattern
    this.nodes.push(this.buildVariableAssignment(spreadProp.argument, value));
  }

  pushObjectProperty(prop: t.ObjectProperty, propRef: t.Expression) {
    if (t.isLiteral(prop.key)) prop.computed = true;

    const pattern = prop.value as t.LVal;
    const objRef = t.memberExpression(
      t.cloneNode(propRef),
      prop.key,
      prop.computed,
    );

    if (t.isPattern(pattern)) {
      this.push(pattern, objRef);
    } else {
      this.nodes.push(this.buildVariableAssignment(pattern, objRef));
    }
  }

  pushObjectPattern(pattern: t.ObjectPattern, objRef: t.Expression) {
    // https://github.com/babel/babel/issues/681

    if (!pattern.properties.length) {
      this.nodes.push(
        t.expressionStatement(
          t.callExpression(this.addHelper("objectDestructuringEmpty"), [
            objRef,
          ]),
        ),
      );
    }

    // if we have more than one properties in this pattern and the objectRef is a
    // member expression then we need to assign it to a temporary variable so it's
    // only evaluated once

    if (pattern.properties.length > 1 && !this.scope.isStatic(objRef)) {
      const temp = this.scope.generateUidIdentifierBasedOnNode(objRef);
      this.nodes.push(this.buildVariableDeclaration(temp, objRef));
      objRef = temp;
    }

    // Replace impure computed key expressions if we have a rest parameter
    if (hasObjectRest(pattern)) {
      let copiedPattern;
      for (let i = 0; i < pattern.properties.length; i++) {
        const prop = pattern.properties[i];
        if (t.isRestElement(prop)) {
          break;
        }
        const key = prop.key;
        if (prop.computed && !this.scope.isPure(key)) {
          const name = this.scope.generateUidIdentifierBasedOnNode(key);
          this.nodes.push(this.buildVariableDeclaration(name, key));
          if (!copiedPattern) {
            copiedPattern = pattern = {
              ...pattern,
              properties: pattern.properties.slice(),
            };
          }
          copiedPattern.properties[i] = {
            ...copiedPattern.properties[i],
            key: name,
          };
        }
      }
    }
    //

    for (let i = 0; i < pattern.properties.length; i++) {
      const prop = pattern.properties[i];
      if (t.isRestElement(prop)) {
        this.pushObjectRest(pattern, objRef, prop, i);
      } else {
        this.pushObjectProperty(prop, objRef);
      }
    }
  }

  canUnpackArrayPattern(
    pattern: t.ArrayPattern,
    arr: t.Expression,
  ): arr is t.ArrayExpression & Unpackable {
    // not an array so there's no way we can deal with this
    if (!t.isArrayExpression(arr)) return false;

    // pattern has less elements than the array and doesn't have a rest so some
    // elements wont be evaluated
    if (pattern.elements.length > arr.elements.length) return;
    if (
      pattern.elements.length < arr.elements.length &&
      !hasArrayRest(pattern)
    ) {
      return false;
    }

    for (const elem of pattern.elements) {
      // deopt on holes
      if (!elem) return false;

      // deopt on member expressions as they may be included in the RHS
      if (t.isMemberExpression(elem)) return false;
    }

    for (const elem of arr.elements) {
      // deopt on spread elements
      if (t.isSpreadElement(elem)) return false;

      // deopt call expressions as they might change values of LHS variables
      if (t.isCallExpression(elem)) return false;

      // deopt on member expressions as they may be getter/setters and have side-effects
      if (t.isMemberExpression(elem)) return false;
    }

    // deopt on reference to left side identifiers
    const bindings = t.getBindingIdentifiers(pattern);
    const state: ArrayUnpackVisitorState = { deopt: false, bindings };

    try {
      t.traverse(arr, arrayUnpackVisitor, state);
    } catch (e) {
      if (e !== STOP_TRAVERSAL) throw e;
    }

    return !state.deopt;
  }

  pushUnpackedArrayPattern(
    pattern: t.ArrayPattern,
    arr: t.ArrayExpression & Unpackable,
  ) {
    for (let i = 0; i < pattern.elements.length; i++) {
      const elem = pattern.elements[i];
      if (t.isRestElement(elem)) {
        this.push(elem.argument, t.arrayExpression(arr.elements.slice(i)));
      } else {
        this.push(elem, arr.elements[i]);
      }
    }
  }

  pushArrayPattern(pattern: t.ArrayPattern, arrayRef: t.Expression) {
    if (!pattern.elements) return;

    // optimise basic array destructuring of an array expression
    //
    // we can't do this to a pattern of unequal size to it's right hand
    // array expression as then there will be values that wont be evaluated
    //
    // eg: let [a, b] = [1, 2];

    if (this.canUnpackArrayPattern(pattern, arrayRef)) {
      return this.pushUnpackedArrayPattern(pattern, arrayRef);
    }

    // if we have a rest then we need all the elements so don't tell
    // `scope.toArray` to only get a certain amount

    const count = !hasArrayRest(pattern) && pattern.elements.length;

    // so we need to ensure that the `arrayRef` is an array, `scope.toArray` will
    // return a locally bound identifier if it's been inferred to be an array,
    // otherwise it'll be a call to a helper that will ensure it's one

    const toArray = this.toArray(arrayRef, count);

    if (t.isIdentifier(toArray)) {
      // we've been given an identifier so it must have been inferred to be an
      // array
      arrayRef = toArray;
    } else {
      arrayRef = this.scope.generateUidIdentifierBasedOnNode(arrayRef);
      this.arrayRefSet.add(arrayRef.name);
      this.nodes.push(this.buildVariableDeclaration(arrayRef, toArray));
    }

    //

    for (let i = 0; i < pattern.elements.length; i++) {
      const elem = pattern.elements[i];

      // hole
      if (!elem) continue;

      let elemRef;

      if (t.isRestElement(elem)) {
        elemRef = this.toArray(arrayRef);
        elemRef = t.callExpression(
          t.memberExpression(elemRef, t.identifier("slice")),
          [t.numericLiteral(i)],
        );

        // set the element to the rest element argument since we've dealt with it
        // being a rest already
        this.push(elem.argument, elemRef);
      } else {
        elemRef = t.memberExpression(arrayRef, t.numericLiteral(i), true);
        this.push(elem, elemRef);
      }
    }
  }

  init(pattern: t.LVal, ref: t.Expression) {
    // trying to destructure a value that we can't evaluate more than once so we
    // need to save it to a variable

    if (!t.isArrayExpression(ref) && !t.isMemberExpression(ref)) {
      const memo = this.scope.maybeGenerateMemoised(ref, true);
      if (memo) {
        this.nodes.push(this.buildVariableDeclaration(memo, t.cloneNode(ref)));
        ref = memo;
      }
    }

    //

    this.push(pattern, ref);

    return this.nodes;
  }
}

export function convertVariableDeclaration(
  path: NodePath<t.VariableDeclaration>,
  addHelper: File["addHelper"],
  arrayLikeIsIterable: boolean,
  iterableIsArray: boolean,
  objectRestNoSymbols: boolean,
  useBuiltIns: boolean,
) {
  const { node, scope } = path;

  const nodeKind = node.kind;
  const nodeLoc = node.loc;
  const nodes = [];

  for (let i = 0; i < node.declarations.length; i++) {
    const declar = node.declarations[i];

    const patternId = declar.init;
    const pattern = declar.id;

    const destructuring = new DestructuringTransformer({
      // @ts-expect-error(todo): avoid internal properties access
      blockHoist: node._blockHoist,
      nodes: nodes,
      scope: scope,
      kind: node.kind,
      iterableIsArray,
      arrayLikeIsIterable,
      useBuiltIns,
      objectRestNoSymbols,
      addHelper,
    });

    if (t.isPattern(pattern)) {
      destructuring.init(pattern, patternId);

      if (+i !== node.declarations.length - 1) {
        // we aren't the last declarator so let's just make the
        // last transformed node inherit from us
        t.inherits(nodes[nodes.length - 1], declar);
      }
    } else {
      nodes.push(
        t.inherits(
          destructuring.buildVariableAssignment(pattern, patternId),
          declar,
        ),
      );
    }
  }

  let tail: t.VariableDeclaration | null = null;
  const nodesOut = [];
  for (const node of nodes) {
    if (tail !== null && t.isVariableDeclaration(node)) {
      // Create a single compound declarations
      tail.declarations.push(...node.declarations);
    } else {
      // Make sure the original node kind is used for each compound declaration
      node.kind = nodeKind;
      // Propagate the original declaration node's location
      if (!node.loc) {
        node.loc = nodeLoc;
      }
      nodesOut.push(node);
      tail = t.isVariableDeclaration(node) ? node : null;
    }
  }

  // Need to unmark the current binding to this var as a param, or other hoists
  // could be placed above this ref.
  // https://github.com/babel/babel/issues/4516
  for (const nodeOut of nodesOut) {
    if (!nodeOut.declarations) continue;
    for (const declaration of nodeOut.declarations) {
      const { name } = declaration.id;
      if (scope.bindings[name]) {
        scope.bindings[name].kind = nodeOut.kind;
      }
    }
  }

  if (nodesOut.length === 1) {
    path.replaceWith(nodesOut[0]);
  } else {
    path.replaceWithMultiple(nodesOut);
  }
}

export function convertAssignmentExpression(
  path: NodePath<t.AssignmentExpression>,
  addHelper: File["addHelper"],
  arrayLikeIsIterable: boolean,
  iterableIsArray: boolean,
  objectRestNoSymbols: boolean,
  useBuiltIns: boolean,
) {
  const { node, scope } = path;

  const nodes = [];

  const destructuring = new DestructuringTransformer({
    operator: node.operator,
    scope: scope,
    nodes: nodes,
    arrayLikeIsIterable,
    iterableIsArray,
    objectRestNoSymbols,
    useBuiltIns,
    addHelper,
  });

  let ref: t.Identifier | void;
  if (path.isCompletionRecord() || !path.parentPath.isExpressionStatement()) {
    ref = scope.generateUidIdentifierBasedOnNode(node.right, "ref");

    nodes.push(
      t.variableDeclaration("var", [t.variableDeclarator(ref, node.right)]),
    );

    if (t.isArrayExpression(node.right)) {
      destructuring.arrayRefSet.add(ref.name);
    }
  }

  destructuring.init(node.left, ref || node.right);

  if (ref) {
    if (path.parentPath.isArrowFunctionExpression()) {
      path.replaceWith(t.blockStatement([]));
      nodes.push(t.returnStatement(t.cloneNode(ref)));
    } else {
      nodes.push(t.expressionStatement(t.cloneNode(ref)));
    }
  }

  path.replaceWithMultiple(nodes);
  path.scope.crawl();
}