vanilla.js

/* eslint max-len: 0 */

import type { NodePath } from "babel-traverse";
import { visitors } from "babel-traverse";
import ReplaceSupers from "babel-helper-replace-supers";
import optimiseCall from "babel-helper-optimise-call-expression";
import * as defineMap from "babel-helper-define-map";
import template from "babel-template";
import * as t from "babel-types";

let buildDerivedConstructor = template(`
  (function () {
    super(...arguments);
  })
`);

let noMethodVisitor = {
  "FunctionExpression|FunctionDeclaration"(path) {
    if (!path.is("shadow")) {
      path.skip();
    }
  },

  Method(path) {
    path.skip();
  }
};

let verifyConstructorVisitor = visitors.merge([noMethodVisitor, {
  Super(path) {
    if (this.isDerived && !this.hasBareSuper && !path.parentPath.isCallExpression({ callee: path.node })) {
      throw path.buildCodeFrameError("'super.*' is not allowed before super()");
    }
  },

  CallExpression: {
    exit(path) {
      if (path.get("callee").isSuper()) {
        this.hasBareSuper = true;

        if (!this.isDerived) {
          throw path.buildCodeFrameError("super() is only allowed in a derived constructor");
        }
      }
    }
  },

  ThisExpression(path) {
    if (this.isDerived && !this.hasBareSuper) {
      if (!path.inShadow("this")) {
        throw path.buildCodeFrameError("'this' is not allowed before super()");
      }
    }
  }
}]);

let findThisesVisitor = visitors.merge([noMethodVisitor, {
  ThisExpression(path) {
    this.superThises.push(path);
  }
}]);

export default class ClassTransformer {
  constructor(path: NodePath, file) {
    this.parent = path.parent;
    this.scope  = path.scope;
    this.node   = path.node;
    this.path   = path;
    this.file   = file;

    this.clearDescriptors();

    this.instancePropBody = [];
    this.instancePropRefs = {};
    this.staticPropBody   = [];
    this.body             = [];

    this.bareSuperAfter   = [];
    this.bareSupers       = [];

    this.pushedConstructor = false;
    this.pushedInherits    = false;
    this.isLoose           = false;

    this.superThises = [];

    // class id
    this.classId = this.node.id;

    // this is the name of the binding that will **always** reference the class we've constructed
    this.classRef = this.node.id ? t.identifier(this.node.id.name) : this.scope.generateUidIdentifier("class");

    this.superName = this.node.superClass || t.identifier("Function");
    this.isDerived = !!this.node.superClass;
  }

  run() {
    let superName = this.superName;
    let file      = this.file;
    let body      = this.body;

    //

    let constructorBody = this.constructorBody = t.blockStatement([]);
    this.constructor    = this.buildConstructor();

    //

    let closureParams = [];
    let closureArgs = [];

    //
    if (this.isDerived) {
      closureArgs.push(superName);

      superName = this.scope.generateUidIdentifierBasedOnNode(superName);
      closureParams.push(superName);

      this.superName = superName;
    }

    //
    this.buildBody();

    // make sure this class isn't directly called
    constructorBody.body.unshift(t.expressionStatement(t.callExpression(file.addHelper("classCallCheck"), [
      t.thisExpression(),
      this.classRef
    ])));

    body = body.concat(this.staticPropBody.map((fn) => fn(this.classRef)));

    if (this.classId) {
      // named class with only a constructor
      if (body.length === 1) return t.toExpression(body[0]);
    }

    //
    body.push(t.returnStatement(this.classRef));

    let container = t.functionExpression(null, closureParams, t.blockStatement(body));
    container.shadow = true;
    return t.callExpression(container, closureArgs);
  }

  buildConstructor() {
    let func = t.functionDeclaration(this.classRef, [], this.constructorBody);
    t.inherits(func, this.node);
    return func;
  }

  pushToMap(node, enumerable, kind = "value", scope?) {
    let mutatorMap;
    if (node.static) {
      this.hasStaticDescriptors = true;
      mutatorMap = this.staticMutatorMap;
    } else {
      this.hasInstanceDescriptors = true;
      mutatorMap = this.instanceMutatorMap;
    }

    let map = defineMap.push(mutatorMap, node, kind, this.file, scope);

    if (enumerable) {
      map.enumerable = t.booleanLiteral(true);
    }

    return map;
  }

  /**
   * [Please add a description.]
   * https://www.youtube.com/watch?v=fWNaR-rxAic
   */

  constructorMeMaybe() {
    let hasConstructor = false;
    let paths = this.path.get("body.body");
    for (let path of (paths: Array)) {
      hasConstructor = path.equals("kind", "constructor");
      if (hasConstructor) break;
    }
    if (hasConstructor) return;

    let params, body;

    if (this.isDerived) {
      let constructor = buildDerivedConstructor().expression;
      params = constructor.params;
      body = constructor.body;
    } else {
      params = [];
      body = t.blockStatement([]);
    }

    this.path.get("body").unshiftContainer("body", t.classMethod(
      "constructor",
      t.identifier("constructor"),
      params,
      body
    ));
  }

  buildBody() {
    this.constructorMeMaybe();
    this.pushBody();
    this.verifyConstructor();

    if (this.userConstructor) {
      let constructorBody = this.constructorBody;
      constructorBody.body = constructorBody.body.concat(this.userConstructor.body.body);
      t.inherits(this.constructor, this.userConstructor);
      t.inherits(constructorBody, this.userConstructor.body);
    }

    this.pushDescriptors();
  }

  pushBody() {
    let classBodyPaths: Array<Object> = this.path.get("body.body");

    for (let path of classBodyPaths) {
      let node = path.node;

      if (path.isClassProperty()) {
        throw path.buildCodeFrameError("Missing class properties transform.");
      }

      if (node.decorators) {
        throw path.buildCodeFrameError("Method has decorators, put the decorator plugin before the classes one.");
      }

      if (t.isClassMethod(node)) {
        let isConstructor = node.kind === "constructor";

        if (isConstructor) {
          path.traverse(verifyConstructorVisitor, this);

          if (!this.hasBareSuper && this.isDerived) {
            throw path.buildCodeFrameError("missing super() call in constructor");
          }
        }

        let replaceSupers = new ReplaceSupers({
          forceSuperMemoisation: isConstructor,
          methodPath:            path,
          methodNode:            node,
          objectRef:             this.classRef,
          superRef:              this.superName,
          isStatic:              node.static,
          isLoose:               this.isLoose,
          scope:                 this.scope,
          file:                  this.file
        }, true);

        replaceSupers.replace();

        if (isConstructor) {
          this.pushConstructor(replaceSupers, node, path);
        } else {
          this.pushMethod(node, path);
        }
      }
    }
  }

  clearDescriptors() {
    this.hasInstanceDescriptors = false;
    this.hasStaticDescriptors   = false;

    this.instanceMutatorMap = {};
    this.staticMutatorMap   = {};
  }

  pushDescriptors() {
    this.pushInherits();

    let body = this.body;

    let instanceProps;
    let staticProps;

    if (this.hasInstanceDescriptors) {
      instanceProps = defineMap.toClassObject(this.instanceMutatorMap);
    }

    if (this.hasStaticDescriptors) {
      staticProps = defineMap.toClassObject(this.staticMutatorMap);
    }

    if (instanceProps || staticProps) {
      if (instanceProps) instanceProps = defineMap.toComputedObjectFromClass(instanceProps);
      if (staticProps) staticProps = defineMap.toComputedObjectFromClass(staticProps);

      let nullNode = t.nullLiteral();

      // (Constructor, instanceDescriptors, staticDescriptors, instanceInitializers, staticInitializers)
      let args = [this.classRef, nullNode, nullNode, nullNode, nullNode];

      if (instanceProps) args[1] = instanceProps;
      if (staticProps) args[2] = staticProps;

      if (this.instanceInitializersId) {
        args[3] = this.instanceInitializersId;
        body.unshift(this.buildObjectAssignment(this.instanceInitializersId));
      }

      if (this.staticInitializersId) {
        args[4] = this.staticInitializersId;
        body.unshift(this.buildObjectAssignment(this.staticInitializersId));
      }

      let lastNonNullIndex = 0;
      for (let i = 0; i < args.length; i++) {
        if (args[i] !== nullNode) lastNonNullIndex = i;
      }
      args = args.slice(0, lastNonNullIndex + 1);


      body.push(t.expressionStatement(
        t.callExpression(this.file.addHelper("createClass"), args)
      ));
    }

    this.clearDescriptors();
  }

  buildObjectAssignment(id) {
    return t.variableDeclaration("var", [
      t.variableDeclarator(id, t.objectExpression([]))
    ]);
  }

  wrapSuperCall(bareSuper, superRef, thisRef, body) {
    let bareSuperNode = bareSuper.node;

    if (this.isLoose) {
      bareSuperNode.arguments.unshift(t.thisExpression());
      if (bareSuperNode.arguments.length === 2 && t.isSpreadElement(bareSuperNode.arguments[1]) && t.isIdentifier(bareSuperNode.arguments[1].argument, { name: "arguments" })) {
        // special case single arguments spread
        bareSuperNode.arguments[1] = bareSuperNode.arguments[1].argument;
        bareSuperNode.callee = t.memberExpression(superRef, t.identifier("apply"));
      } else {
        bareSuperNode.callee = t.memberExpression(superRef, t.identifier("call"));
      }
    } else {
      bareSuperNode = optimiseCall(
        t.logicalExpression(
          "||",
          t.memberExpression(this.classRef, t.identifier("__proto__")),
          t.callExpression(
            t.memberExpression(t.identifier("Object"), t.identifier("getPrototypeOf")),
            [this.classRef]
          )
        ),
        t.thisExpression(),
        bareSuperNode.arguments
      );
    }

    let call = t.callExpression(
      this.file.addHelper("possibleConstructorReturn"),
      [t.thisExpression(), bareSuperNode]
    );

    let bareSuperAfter = this.bareSuperAfter.map((fn) => fn(thisRef));

    if (bareSuper.parentPath.isExpressionStatement() && bareSuper.parentPath.container === body.node.body && body.node.body.length - 1 === bareSuper.parentPath.key) {
      // this super call is the last statement in the body so we can just straight up
      // turn it into a return

      if (this.superThises.length || bareSuperAfter.length) {
        bareSuper.scope.push({ id: thisRef });
        call = t.assignmentExpression("=", thisRef, call);
      }

      if (bareSuperAfter.length) {
        call = t.toSequenceExpression([call, ...bareSuperAfter, thisRef]);
      }

      bareSuper.parentPath.replaceWith(t.returnStatement(call));
    } else {
      bareSuper.replaceWithMultiple([
        t.variableDeclaration("var", [
          t.variableDeclarator(thisRef, call)
        ]),
        ...bareSuperAfter,
        t.expressionStatement(thisRef)
      ]);
    }

  }

  verifyConstructor() {
    if (!this.isDerived) return;

    let path = this.userConstructorPath;
    let body = path.get("body");

    path.traverse(findThisesVisitor, this);

    let guaranteedSuperBeforeFinish = !!this.bareSupers.length;

    let superRef = this.superName || t.identifier("Function");
    let thisRef = path.scope.generateUidIdentifier("this");

    for (let bareSuper of this.bareSupers) {
      this.wrapSuperCall(bareSuper, superRef, thisRef, body);

      if (guaranteedSuperBeforeFinish) {
        bareSuper.find(function (parentPath) {
          // hit top so short circuit
          if (parentPath === path) {
            return true;
          }

          if (parentPath.isLoop() || parentPath.isConditional()) {
            guaranteedSuperBeforeFinish = false;
            return true;
          }
        });
      }
    }

    for (let thisPath of this.superThises) {
      thisPath.replaceWith(thisRef);
    }

    let wrapReturn = (returnArg) => t.callExpression(
      this.file.addHelper("possibleConstructorReturn"),
      [thisRef].concat(returnArg || [])
    );

    // if we have a return as the last node in the body then we've already caught that
    // return
    let bodyPaths = body.get("body");
    if (bodyPaths.length && !bodyPaths.pop().isReturnStatement()) {
      body.pushContainer("body", t.returnStatement(guaranteedSuperBeforeFinish ? thisRef : wrapReturn()));
    }

    for (let returnPath of this.superReturns) {
      if (returnPath.node.argument) {
        let ref = returnPath.scope.generateDeclaredUidIdentifier("ret");
        returnPath.get("argument").replaceWithMultiple([
          t.assignmentExpression("=", ref, returnPath.node.argument),
          wrapReturn(ref)
        ]);
      } else {
        returnPath.get("argument").replaceWith(wrapReturn());
      }
    }
  }

  /**
   * Push a method to its respective mutatorMap.
   */

  pushMethod(node: { type: "ClassMethod" }, path?: NodePath) {
    let scope = path ? path.scope : this.scope;

    if (node.kind === "method") {
      if (this._processMethod(node, scope)) return;
    }

    this.pushToMap(node, false, null, scope);
  }

  _processMethod() {
    return false;
  }

  /**
   * Replace the constructor body of our class.
   */

  pushConstructor(replaceSupers, method: { type: "ClassMethod" }, path: NodePath) {
    this.bareSupers = replaceSupers.bareSupers;
    this.superReturns = replaceSupers.returns;

    // https://github.com/babel/babel/issues/1077
    if (path.scope.hasOwnBinding(this.classRef.name)) {
      path.scope.rename(this.classRef.name);
    }

    let construct = this.constructor;

    this.userConstructorPath = path;
    this.userConstructor     = method;
    this.hasConstructor      = true;

    t.inheritsComments(construct, method);

    construct._ignoreUserWhitespace = true;
    construct.params                = method.params;

    t.inherits(construct.body, method.body);
    construct.body.directives = method.body.directives;

    // push constructor to body
    this._pushConstructor();
  }

  _pushConstructor() {
    if (this.pushedConstructor) return;
    this.pushedConstructor = true;

    // we haven't pushed any descriptors yet
    if (this.hasInstanceDescriptors || this.hasStaticDescriptors) {
      this.pushDescriptors();
    }

    this.body.push(this.constructor);

    this.pushInherits();
  }

  /**
   * Push inherits helper to body.
   */

  pushInherits() {
    if (!this.isDerived || this.pushedInherits) return;

    // Unshift to ensure that the constructor inheritance is set up before
    // any properties can be assigned to the prototype.
    this.pushedInherits = true;
    this.body.unshift(t.expressionStatement(t.callExpression(
      this.file.addHelper("inherits"),
      [this.classRef, this.superName]
    )));
  }
}