overlookmotel / livepack / 6956685087

/* --------------------

 * livepack module

 * Parse function code

 * ------------------*/

'use strict';

// Modules

const pathJoin = require('path').join,

        {isString} = require('is-it-type'),

        mapValues = require('lodash/mapValues'),

        t = require('@babel/types');

// Imports

const {isJsIdentifier, isNumberKey, setAddFrom} = require('./utils.js'),

        {

                isReservedVarName, createArrayOrPush, combineArraysWithDedup,

                getProp, getProps, setProp, traverseAll

        } = require('../shared/functions.js'),

        {

                SUPER_CALL, SUPER_EXPRESSION, CONST_VIOLATION_SILENT, CONST_VIOLATION_NEEDS_VAR

        } = require('../shared/constants.js'),

        assertBug = require('../shared/assertBug.js');

// Constants

const RUNTIME_DIR_PATH = pathJoin(__dirname, '../runtime/');

// Exports

/**

 * Assemble AST for function code, identify Identifier nodes referring to internal/external variables,

 * replace const violations, transpile `super`, get other info about function.

 * Most of this information is pre-prepared by instrumentation, just needs some late processing here.

 *

 * @this {Object} Serializer

 * @param {Function} fn - Function

 * @param {number} fnId - Function ID

 * @param {Function} getFunctionInfo - Function info getter function

 * @param {boolean} isClass - `true` if is a class

 * @param {boolean} isAsync - `true` if is an async function

 * @param {boolean} isGenerator - `true` if is a generator function

 * @param {string} filename - File path

 * @returns {Object} - Function definition object with props:

 *   {Object} .node - AST node for function

 *   {Map} .scopeDefs - Scope definitions map, keyed by block ID

 *   {Object} .externalVars - Object keyed by var name, values are arrays of identifier nodes

 *   {Object} .internalVars - Object keyed by var name, values are arrays of identifier nodes

 *   {Set<string>} .globalVarNames - Set of names of global vars used

 *   {Set<string>} .reservedVarNames - Set of reserved var names (function names which are frozen)

 *   {string} .name - `.name` of created function

 *   {number} .numParams - `.length` of created function

 *   {boolean} .isClass - `true` if is class

 *   {boolean} .isAsync - `true` if is async function

 *   {boolean} .isGenerator - `true` if is generator

 *   {boolean} .isArrow - `true` if is arrow function

 *   {boolean} .isMethod - `true` if is a method

 *   {boolean|null} .isStrict - `true` if is strict mode, `false` if sloppy, `null` if indeterminate

 *     (classes and runtime functions are indeterminate)

 *   {boolean} .containsEval - `true` if contains direct `eval()`

 *   {Array<string>|undefined} .argNames - Array of `arguments` var names

 * @throws {Error} - If function contains `import`

 */

module.exports = function parseFunction(

        fn, fnId, getFunctionInfo, isClass, isAsync, isGenerator, filename

) {

        // Get function info and AST from info getter function

        const [fnInfoJson, getChildFnInfos, getSources] = getFunctionInfo();

        const fnInfo = JSON.parse(fnInfoJson);

        // Throw error if function contains `import()`

        // Assemble scope definitions

        const scopeDefs = new Map(),

                externalVars = Object.create(null);

        for (const {blockId, blockName, vars} of fnInfo.scopes) {

                scopeDefs.set(blockId, {

                        blockName,

                        vars: mapValues(vars, (varProps, varName) => {

                                externalVars[varName] = [];

                                return {

                                        isReadFrom: !!varProps.isReadFrom,

                                        isAssignedTo: !!varProps.isAssignedTo,

                                        isFrozenName: !!varProps.isFrozenName

                                };

                        })

                });

        }

        // Add child functions into AST, get external/internal var nodes, and get amendments to be made

        // (const violations / incidences of `super` to be transpiled)

        const internalVars = Object.create(null),

                globalVarNames = new Set(),

                reservedVarNames = new Set(),

                amendments = [];

        resolveFunctionInfo(

                fnInfo, getChildFnInfos, false, fnId, scopeDefs,

                externalVars, internalVars, globalVarNames, reservedVarNames, amendments

        );

        let node = fnInfo.ast;

        // If source maps enabled, add source files to `sourceFiles` map and set `loc.filename` for all nodes.

        // Create `copyLoc()` function to copy location info for AST nodes befing replaced.

        let copyLoc;

        if (this.options.sourceMaps) {

                const {filesHaveSourcesFor} = this;

                if (!filesHaveSourcesFor.has(filename)) {

                        Object.assign(this.sourceFiles, JSON.parse(getSources()));

                        filesHaveSourcesFor.add(filename);

                }

                traverseAll(node, ({loc}) => {

                        if (loc && !loc.filename) loc.filename = filename;

                });

                copyLoc = (destNode, srcNode) => {

                        destNode.start = srcNode.start;

                        destNode.end = srcNode.end;

                        destNode.loc = srcNode.loc;

                        return destNode;

                };

        } else {

                copyLoc = destNode => destNode;

        }

        // Get whether strict mode and remove use strict directive

        let isStrict;

        if (!isClass) {

                isStrict = !!fnInfo.isStrict;

                if (isStrict) {

                        removeUseStrictDirective(node);

                } else if (filename.startsWith(RUNTIME_DIR_PATH)) {

                        // Runtime functions are treated as indeterminate strict/sloppy mode unless explicitly strict

                        isStrict = null;

                }

        }

        // Create `super` var node if required

        let superVarNode;

        if (externalVars.super) {

                superVarNode = t.identifier('super');

                externalVars.super.push(superVarNode); // NB: `externalVars.super` is always an empty array

                globalVarNames.add('Reflect');

                globalVarNames.add('Object');

        }

        // Conform function/class, get function name

        let isMethod, name, thisVarNode, constructorStatementNodes, firstSuperStatementIndex,

                paramNodes = node.params;

        const {type} = node,

                isArrow = type === 'ArrowFunctionExpression',

                containsEval = !!fnInfo.containsEval;

        if (isArrow) {

                // Arrow function

                name = '';

                isMethod = false;

                // If contains `super`, needs `this` too

                if (externalVars.super) {

                        thisVarNode = t.identifier('this');

                        externalVars.this.push(thisVarNode);

                }

        } else {

                // Class, method or function declaration/expression.

                // Get function name.

                name = (Object.getOwnPropertyDescriptor(fn, 'name') || {}).value;

                if (!isString(name)) name = '';

                // Identify if method and convert class method to object method

                if (type === 'ClassMethod') {

                        node.type = 'ObjectMethod';

                        node.static = undefined;

                        isMethod = true;

                } else if (type === 'ObjectMethod') {

                        isMethod = true;

                }

                if (isMethod) {

                        // Class/object method.

                        // Convert getter/setter to plain method, and disable computed keys.

                        node.kind = 'method';

                        node.computed = false;

                        // Wrap in object.

                        // NB: Must be defined as method, to avoid it having prototype.

                        let keyNode, accessComputed;

                        } else if (isJsIdentifier(name)) {

                                keyNode = t.identifier(name);

                                accessComputed = false;

                        } else {

                                keyNode = isNumberKey(name) ? t.numericLiteral(name * 1) : t.stringLiteral(name);

                                accessComputed = true;

                        }

                        node = t.memberExpression(t.objectExpression([node]), keyNode, accessComputed);

                        // `this` within method is actual `this`

                        thisVarNode = t.thisExpression();

                } else {

                        // Set function name

                        const idNode = node.id;

                        if (containsEval) {

                                // Function contains `eval()`.

                                // Cannot change name from original as would create a new var in scope of `eval()`.

                                // If is a named function expression, name must be retained, to maintain const violation

                                // error behavior (error in strict mode, silent failure in sloppy mode).

                                // If is a named function declaration, name must be removed to allow read/write access

                                // to external var holding function in upper scope.

                                if (idNode) {

                                        name = idNode.name;

                                        if (externalVars[name]) name = '';

                                } else {

                                        name = '';

                                }

                        } else if (

                                name && (!isJsIdentifier(name) || isReservedVarName(name) || globalVarNames.has(name))

                        ) {

                                // Name cannot be used as is illegal, or would block access to a global var

                                name = '';

                        }

                        if (!name) {

                                node.id = null;

                        } else {

                                if (!idNode || idNode.name !== name) {

                                        node.id = t.identifier(name);

                                        if (idNode) copyLoc(node.id, idNode);

                                }

                                reservedVarNames.add(name);

                        }

                        if (isClass) {

                                // Class

                                if (type === 'ClassDeclaration') node.type = 'ClassExpression';

                                // Classes have indeterminate strict/sloppy status - never require conforming to strict/sloppy

                                // as they're automatically strict.

                                isStrict = null;

                                // Remove all members except constructor and prototype properties

                                let constructorNode;

                                const classBodyNode = node.body;

                                const memberNodes = classBodyNode.body = classBodyNode.body.filter((memberNode) => {

                                        if (!memberNode) return false;

                                        const memberType = memberNode.type;

                                        if (memberType === 'ClassMethod') {

                                                constructorNode = memberNode;

                                                return true;

                                        }

                                });

                                paramNodes = constructorNode ? constructorNode.params : [];

                                if (fnInfo.hasSuperClass) {

                                        // Remove `extends`

                                        node.superClass = null;

                                        // Add constructor if none present

                                        if (!constructorNode) {

                                                // `constructor(...args) {

                                                //   return Reflect.construct(Object.getPrototypeOf(super$0), args, super$0);

                                                // }`

                                                const argsVarNode = t.identifier('args');

                                                internalVars.args = [argsVarNode];

                                                // TODO: Can using `.unshift()` interfere with replacing const violations further on?

                                                // Indexes of any class properties will be altered.

                                                memberNodes.unshift(t.classMethod(

                                                        'constructor',

                                                        t.identifier('constructor'),

                                                        [t.restElement(argsVarNode)],

                                                        t.blockStatement([

                                                                t.returnStatement(

                                                                        t.callExpression(

                                                                                t.memberExpression(t.identifier('Reflect'), t.identifier('construct')),

                                                                                [

                                                                                        t.callExpression(

                                                                                                t.memberExpression(t.identifier('Object'), t.identifier('getPrototypeOf')),

                                                                                                [superVarNode]

                                                                                        ),

                                                                                        argsVarNode,

                                                                                        superVarNode

                                                                                ]

                                                                        )

                                                                )

                                                        ])

                                                ));

                                        } else {

                                                // Class has constructor - prepare for transpiling `super()`

                                                const thisInternalVars = internalVars.this;

                                                if (thisInternalVars) {

                                                        // Constructor contains `this` or `super` expression (e.g. `super.foo()`).

                                                        // Var for `this$0` is going to be needed.

                                                        thisVarNode = t.identifier('this');

                                                        thisInternalVars.push(thisVarNode);

                                                }

                                                firstSuperStatementIndex = fnInfo.firstSuperStatementIndex;

                                                constructorStatementNodes = constructorNode.body.body;

                                        }

                                } else {

                                        // Class which doesn't extend a super class. `this` within constructor is actual `this`.

                                        thisVarNode = t.thisExpression();

                                }

                        } else {

                                // Function declaration/expression. `this` is actual `this`.

                                if (type === 'FunctionDeclaration') node.type = 'FunctionExpression';

                                thisVarNode = t.thisExpression();

                        }

                }

        }

        // Replace const violations + `super`.

        // Amendments are in reverse order:

        // - Nested functions before their parent.

        // - Within a function, deeper nested expressions/statements before their parent.

        // - Within a function, later statements before earlier statements.

        // Reverse order ensures correct handling of nested amendments

        // e.g. 2 const violations `c = c2 = 1` or const violation + super `super.foo(c = 1)`.

        const superIsProto = isClass || fnInfo.superIsProto || false;

        for (const amendment of amendments) {

                const {type: amendmentType, trail, trailNodes} = amendment;

                if (amendmentType === SUPER_CALL) {

                        replaceSuperCall(

                                trail, trailNodes, superVarNode, thisVarNode, firstSuperStatementIndex, copyLoc

                        );

                } else if (amendmentType === SUPER_EXPRESSION) {

                        replaceSuperExpression(

                                trail, trailNodes, superVarNode, thisVarNode, superIsProto, internalVars, copyLoc

                        );

                } else if (amendmentType === CONST_VIOLATION_SILENT) {

                        replaceConstViolation(trail, trailNodes, true, internalVars, copyLoc);

                } else {

                        // A non-silent const violation

                        replaceConstViolation(trail, trailNodes, false, internalVars, copyLoc);

                }

        }

        // If is class extending a super class, insert `let this$0;` and `return this$0;` statements

        // if required

        if (constructorStatementNodes && thisVarNode) {

                // Add `let this$0` at start of constructor

                if (firstSuperStatementIndex === undefined) {

                        constructorStatementNodes.unshift(

                                t.variableDeclaration('let', [t.variableDeclarator(thisVarNode, null)])

                        );

                }

                // Add `return this$0` to end of constructor

                if (!fnInfo.returnsSuper) constructorStatementNodes.push(t.returnStatement(thisVarNode));

        }

        // Determine what value of `fn.length` will be

        let numParams = 0;

        for (const {type: paramNodeType} of paramNodes) {

                if (paramNodeType === 'RestElement' || paramNodeType === 'AssignmentPattern') break;

                numParams++;

        }

        // Return function definition object

        return {

                node,

                scopeDefs,

                externalVars,

                internalVars,

                globalVarNames,

                reservedVarNames,

                name,

                numParams,

                isClass,

                isAsync,

                isGenerator,

                isArrow,

                isMethod,

                isStrict,

                containsEval,

                argNames: fnInfo.argNames

        };

};

/**

 * Remove 'use strict' directive from function.

 * @param {Object} fnNode - Function AST node

 * @returns {undefined}

 */

function removeUseStrictDirective(fnNode) {

        const bodyNode = fnNode.body;

        if (bodyNode.type !== 'BlockStatement') return;

        const directiveNodes = bodyNode.directives;

        if (directiveNodes.length === 0) return;

        const index = directiveNodes.findIndex(directiveNode => directiveNode.value.value === 'use strict');

        if (index === -1) return;

        // Relocate any comments attached to directive

        const directiveNode = directiveNodes[index];

        const commentNodes = [

                ...(directiveNode.leadingComments || []),

                ...(directiveNode.trailingComments || [])

        ];

        if (commentNodes.length !== 0) {

                const statementNodes = bodyNode.body;

                } else if (statementNodes.length !== 0) {

                        statementNodes[0].leadingComments = combineArraysWithDedup(

                                commentNodes, statementNodes[0].leadingComments

                        );

        }

        // Remove directive

        directiveNodes.splice(index, 1);

}

/**

 * Replace const violation expression with expression which throws.

 * e.g. `c = f()` -> `f(), (() => {const c = 0; c = 0;})()`

 * If is silent violation (function expression name assigned to in sloppy mode),

 * just remove the assignment.

 * e.g. `c += f()` -> `c + f()`

 *

 * @param {Array<string|number>} trail - Keys trail

 * @param {Array<Object>} trailNodes - Trail nodes

 * @param {boolean} isSilent - `true` if is a silent violation (i.e. doesn't throw)

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @param {Function} copyLoc - Function to copy location from old to new AST node

 * @returns {undefined}

 */

function replaceConstViolation(trail, trailNodes, isSilent, internalVars, copyLoc) {

        const trailLen = trail.length,

                node = trailNodes[trailLen],

                parentNode = trailNodes[trailLen - 1];

        function replaceParent(replacementNode) {

                trailNodes[trailLen - 2][trail[trailLen - 2]] = copyLoc(replacementNode, parentNode);

        }

        const {type} = parentNode;

        if (type === 'AssignmentExpression') {

                const {operator} = parentNode;

                if (operator === '=') {

                        // `c = x` -> `x, throw()`

                        replaceParent(

                                createConstViolationThrowNode(parentNode.right, node.name, isSilent, internalVars)

                        );

                } else if (['&&=', '||=', '??='].includes(operator)) {

                        // `c &&= x` -> `c && (x, throw())`

                        replaceParent(

                                t.logicalExpression(

                                        operator.slice(0, -1),

                                        node,

                                        createConstViolationThrowNode(parentNode.right, node.name, isSilent, internalVars)

                                )

                        );

                } else {

                        // Other assignment operator e.g. `+=`, `-=`, `>>>=`

                        // `c += x` -> `c + x, throw()`

                        replaceParent(

                                createConstViolationThrowNode(

                                        t.binaryExpression(operator.slice(0, -1), node, parentNode.right),

                                        node.name, isSilent, internalVars

                                )

                        );

                }

        } else if (type === 'UpdateExpression') {

                // `c++` -> `(n => n++)(c), throw()`

                // `--c` -> `(n => --n)(c), throw()`

                // See https://github.com/overlookmotel/livepack/issues/528#issuecomment-1773242897

                const varNode = createTempVarNode(node.name, internalVars),

                        replacementNode = t.callExpression(

                                t.arrowFunctionExpression(

                                        [varNode], t.updateExpression(parentNode.operator, varNode, parentNode.prefix)

                                ),

                                [node]

                        );

                replaceParent(createConstViolationThrowNode(replacementNode, node.name, isSilent, internalVars));

        } else if (type === 'AssignmentPattern') {

                // `[c = x] = []`

                // -> `[(e => ({set a(v) {v === void 0 && e(); const c = 0; c = 0;}}))(() => x).a] = []`

                // `{c = x} = {}`

                // -> `{c: (e => ({set a(v) {v === void 0 && e(); const c = 0; c = 0;}}))(() => x).a} = {}`

                replaceParent(

                        createConstViolationThrowPatternNode(node.name, parentNode.right, isSilent, internalVars)

                );

        } else if (

                type === 'ForOfStatement' || type === 'ForInStatement'

                || type === 'ObjectProperty' || type === 'RestElement'

                || trailNodes[trailLen - 2].type === 'ArrayPattern'

        ) {

                // `for (c of [1]) { foo(); }`

                // -> `for ({ set a(v) { const c = 0; c = 0; } }.a of [1]) { foo(); }`

                // `{x: c} = {}` -> `{x: {set a(v) { const c = 0; c = 0; }}.a} = {}`

                // `[...c] = []` -> `[...{set a(v) { const c = 0; c = 0; }}.a] = []`

                // `{...c} = {}` -> `{...{set a(v) { const c = 0; c = 0; }}.a} = {}`

                // `[c] = [1]` -> `[{set a(v) { const c = 0; c = 0; }}.a] = [1]`

                parentNode[trail[trailLen - 1]] = copyLoc(

                        createConstViolationThrowAssignNode(node.name, isSilent, internalVars), node

                );

}

/**

 * Create expression node which throws 'Assignment to constant variable' TypeError.

 * @param {Object} node - AST node to wrap

 * @param {string} name - Var name

 * @param {boolean} isSilent - `true` if violation does not throw

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @returns {Object} - AST Node object

 */

function createConstViolationThrowNode(node, name, isSilent, internalVars) {

        // If silent failure, return node unchanged

        if (isSilent) return node;

        // `(x, (() => { const c = 0; c = 0; })())`

        return t.sequenceExpression([

                node,

                t.callExpression(

                        t.arrowFunctionExpression([], createConstViolationThrowBlockNode(name, internalVars)), []

                )

        ]);

}

/**

 * Create expression node which throws when assigned to.

 * @param {string} name - Var name

 * @param {boolean} isSilent - `true` if violation does not throw

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @returns {Object} - AST Node object

 */

function createConstViolationThrowAssignNode(name, isSilent, internalVars) {

        // If silent failure, return expression which assignment to is a no-op

        // `{ set a(v) { const c = 0; c = 0; } }.a`

        return t.memberExpression(

                t.objectExpression([

                        t.objectMethod(

                                'set',

                                t.identifier('a'),

                                createConstViolationThrowBlockNode(name, internalVars)

                        )

                ]),

                t.identifier('a')

        );

}

/**

 * Create expression node to replace an assignment pattern which:

 * 1. Evaluates right hand side of pattern expression only if incoming assignment value is `undefined`

 * 2. Throws when assigned to

 *

 * @param {string} name - Var name

 * @param {Object} rightNode - AST Node for right-hand side of assignment pattern

 * @param {boolean} isSilent - `true` if violation does not throw

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @returns {Object} - AST Node object

 */

function createConstViolationThrowPatternNode(name, rightNode, isSilent, internalVars) {

        // `v === void 0 && e()`

        const statementNodes = [t.expressionStatement(t.logicalExpression(

                '&&',

                t.binaryExpression('===', valueVarNode, t.unaryExpression('void', t.numericLiteral(0))),

                t.callExpression(rightGetterVarNode, [])

        ))];

        if (!isSilent) statementNodes.push(...createConstViolationThrowStatementNodes(name, internalVars));

        // `(e => ({ set a(v) { v === void 0 && e(); const c = 0; c = 0; }}))(() => x).a`

        return t.memberExpression(

                t.callExpression(

                        t.arrowFunctionExpression(

                                [rightGetterVarNode],

                                t.objectExpression([

                                        t.objectMethod('set', t.identifier('a'), [valueVarNode], t.blockStatement(statementNodes))

                                ])

                        ),

                        [t.arrowFunctionExpression([], rightNode)]

                ),

                t.identifier('a')

        );

}

/**

 * Create block statement which throws 'Assignment to constant variable' TypeError.

 * @param {string} name - Var name

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @returns {Object} - AST Node object

 */

function createConstViolationThrowBlockNode(name, internalVars) {

        // `{ const c = 0; c = 0; }`

        return t.blockStatement(createConstViolationThrowStatementNodes(name, internalVars));

}

/**

 * Create statements which throw 'Assignment to constant variable' TypeError.

 * @param {string} name - Var name

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @returns {Array<Object>} - Array of AST Node objects

 */

function createConstViolationThrowStatementNodes(name, internalVars) {

        // `const c = 0; c = 0;`

        const varNode = createTempVarNode(name, internalVars);

        return [

                t.variableDeclaration('const', [t.variableDeclarator(varNode, t.numericLiteral(0))]),

                t.expressionStatement(t.assignmentExpression('=', varNode, t.numericLiteral(0)))

        ];

}

/**

 * Replace `super()` call with transpiled version.

 * @param {Array<string|number>} trail - Keys trail

 * @param {Array<Object>} trailNodes - Trail nodes

 * @param {Object} superVarNode - Var node for home object for `super`

 * @param {Object} [thisVarNode] - Var node for `this` (Identifier)

 * @param {number} [firstSuperStatementIndex] - Index of first top-level `super()` statement

 * @param {Function} copyLoc - Function to copy location from old to new AST node

 * @returns {undefined}

 */

function replaceSuperCall(

        trail, trailNodes, superVarNode, thisVarNode, firstSuperStatementIndex, copyLoc

) {

        const trailLen = trail.length,

                callNode = trailNodes[trailLen - 1];

        // Convert to `super(x, y)` -> `Reflect.construct(Object.getPrototypeOf(super$0), [x, y], super$0)`.

        // NB: Cannot optimize `super(...x)` to `Reflect.construct(Object.getPrototypeOf(super$0), x, super$0)`

        // in case `x` is an iterator not an array.

        const argumentsNodes = callNode.arguments;

        callNode.callee = copyLoc(

                t.memberExpression(t.identifier('Reflect'), t.identifier('construct')),

                callNode.callee

        );

        callNode.arguments = [

                t.callExpression(

                        t.memberExpression(t.identifier('Object'), t.identifier('getPrototypeOf')),

                        [superVarNode]

                ),

                t.arrayExpression(argumentsNodes),

                superVarNode

        ];

        // If is `return super()`, just substitute transpiled super

        // `return super(x)` -> `return Reflect.construct(Object.getPrototypeOf(super$0), [x], super$0)`

        const grandParentNode = trailNodes[trailLen - 2],

                grandParentType = grandParentNode.type;

        if (grandParentType === 'ReturnStatement') {

                return;

        }

        // If is a top-level statement in constructor

        // (i.e. is statement which is purely `super()`, directly in constructor body block):

        // - Last statement: `return Reflect.construct(...)`

        //   or if `this` used in constructor: `return this$0 = Reflect.construct(...)`

        // - First statement: `const this$0 = Reflect.construct(...)`

        // - Any other statement: `this$0 = Reflect.construct(...)`

        if (grandParentType === 'ExpressionStatement') {

                const fnType = trailNodes[0].type;

                if ((fnType === 'ClassDeclaration' || fnType === 'ClassExpression') && trail.length === 8) {

                        // Top-level statement in constructor

                        const statementNodes = trailNodes[5],

                                statementIndex = trail[5];

                        if (statementIndex === statementNodes.length - 1) {

                                // Last statement in constructor

                                // `return Reflect.construct(...);` or `return this$0 = Reflect.construct(...);`

                                statementNodes[statementIndex] = copyLoc(

                                        t.returnStatement(thisVarNode ? t.assignmentExpression('=', thisVarNode, callNode) : callNode),

                                        callNode

                                );

                                return;

                        }

                        if (statementIndex === firstSuperStatementIndex) {

                                // First `super()` statement - replace with `const this$0 = Reflect.construct(...);`

                                statementNodes[statementIndex] = copyLoc(

                                        t.variableDeclaration('const', [t.variableDeclarator(thisVarNode, callNode)]),

                                        grandParentNode

                                );

                                return;

                        }

                }

        }

        // Replace with `this$0 = Reflect.construct(...)`

        grandParentNode[trail[trailLen - 2]] = copyLoc(

                t.assignmentExpression('=', thisVarNode, callNode), callNode

        );

}

/**

 * Replace `super` expression with transpiled version.

 * `super.prop` / `super[prop]` / `super.prop(...)` / `super[prop](...)` /

 * `super.prop = ...` / `super[prop] = ...`

 *

 * @param {Array<string|number>} trail - Keys trail

 * @param {Array<Object>} trailNodes - Trail nodes

 * @param {Object} superVarNode - Var node for home object for `super`

 * @param {Object} [thisVarNode] - Var node for `this` (may be Identifier or ThisExpression)

 * @param {boolean} superIsProto - `true` if `super` is within context of class prototype method

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @param {Function} copyLoc - Function to copy location from old to new AST node

 * @returns {undefined}

 */

function replaceSuperExpression(

        trail, trailNodes, superVarNode, thisVarNode, superIsProto, internalVars, copyLoc

) {

        const trailLen = trail.length,

                expressionNode = trailNodes[trailLen - 1];

        // `super.prop` -> `Reflect.get(Object.getPrototypeOf(super$0.prototype), 'prop', this$0)`

        // or in static class method `Reflect.get(Object.getPrototypeOf(super$0), 'prop', this$0)`

        let propNode = expressionNode.property;

        if (!expressionNode.computed) propNode = copyLoc(t.stringLiteral(propNode.name), propNode);

        let replacementNode = t.callExpression(

                t.memberExpression(t.identifier('Reflect'), t.identifier('get')),

                [

                        t.callExpression(

                                t.memberExpression(t.identifier('Object'), t.identifier('getPrototypeOf')),

                                [

                                        superIsProto

                                                ? t.memberExpression(superVarNode, t.identifier('prototype'))

                                                : superVarNode

                                ]

                        ),

                        propNode,

                        thisVarNode

                ]

        );

        // `super.prop = ...` -> `Reflect.set(Object.getPrototypeOf(super$0.prototype), 'prop', value, this$0)`

        const parentNode = trailNodes[trailLen - 2],

                parentKey = trail[trailLen - 2],

                parentType = parentNode.type;

        if (parentType === 'AssignmentExpression' && parentKey === 'left') {

                // Convert `Reflect.get(...)` to `Reflect.set(...)`

                replacementNode.callee.property.name = 'set';

                const valueNode = parentNode.right,

                        grandParentNode = trailNodes[trailLen - 3];

                if (grandParentNode.type === 'ExpressionStatement') {

                        // Standalone expression - add value to `Reflect.set()` arguments

                        replacementNode.arguments.splice(2, 0, valueNode);

                } else {

                        // Not standalone expression - wrap in function which return values.

                        // This avoids evaluating the value expression twice.

                        // `x = super.foo = y();` =>

                        // `x = ((key, value) => (Reflect.set(..., key, value, this$0), value))('foo', y());`

                        // NB: Key is passed to function as argument too as it could be a complex expression

                        // referencing many vars. Evaluating it outside the temp closure ensures no var name clashes.

                        const keyVarNode = createTempVarNode('key', internalVars),

                                valueVarNode = createTempVarNode('value', internalVars);

                        replacementNode.arguments[1] = keyVarNode;

                        replacementNode.arguments.splice(2, 0, valueVarNode);

                        replacementNode = t.callExpression(

                                t.arrowFunctionExpression(

                                        [keyVarNode, valueVarNode],

                                        t.sequenceExpression([replacementNode, valueVarNode])

                                ),

                                [propNode, valueNode]

                        );

                }

                grandParentNode[trail[trailLen - 3]] = copyLoc(replacementNode, parentNode);

                return;

        }

        // `super.prop(x, y)` -> `Reflect.get(...).call(this$0, x, y)`

        if (parentType === 'CallExpression') {

                replacementNode = t.memberExpression(replacementNode, t.identifier('call'));

                parentNode.arguments.unshift(thisVarNode);

        }

        copyLoc(replacementNode, expressionNode);

        parentNode[parentKey] = replacementNode;

}

/**

 * Create temp var node and add to internal vars.

 * @param {string} name - Var name

 * @param {Object} internalVars - Map of internal vars, keyed by var name

 * @returns {Object} - Identifier AST node

 */

function createTempVarNode(name, internalVars) {

        const node = t.identifier(name);

        createArrayOrPush(internalVars, name, node);

        return node;

}

/**

 * Add ASTs of nested functions to AST.

 * A function which has other functions nested within it will have left those nodes defined as `null`

 * in JSON-serialized AST. Get those child functions' ASTs from their own `getFnInfo()` functions

 * and insert them into the parent AST.

 * @param {Object} fnInfo - Function info object which was encoded as JSON to fn info getter function

 * @param {Array<Function>} getInfos - Function info getter functions for child functions

 * @param {boolean} isNestedFunction - `true` if is nested function

 * @param {number} fnId - Block ID of function being serialized

 * @param {Map} scopeDefs - Scope definitions map, keyed by block ID

 * @param {Object} externalVars - Map of var name to array of var nodes

 * @param {Object} internalVars - Map of var name to array of var nodes

 * @param {Set<string>} globalVarNames - Set of global var names

 * @param {Set<string>} reservedVarNames - Set of var names which are reserved

 *   (function names which are frozen)

 * @param {Array<Object>} amendments - Array of amendments (const violations or `super`)

 * @returns {undefined}

 */

function resolveFunctionInfo(

        fnInfo, getInfos, isNestedFunction, fnId, scopeDefs,

        externalVars, internalVars, globalVarNames, reservedVarNames, amendments

) {

        // Init internal vars.

        // Converting trails to nodes needs to be done after child functions added into AST

        // because some vars recorded as internal to this function may be within the ASTs of child functions.

        // These are class `extends` clauses and computed method keys.

        // Initializing properties of `internalVars` needs to happen before processing child functions,

        // as external vars in child functions can become internal vars in this function.

        const internalVarTrails = [];

        for (const [varName, trails] of Object.entries(fnInfo.internalVars)) {

                if (!internalVars[varName]) internalVars[varName] = [];

                internalVarTrails.push({varName, trails});

        }

        // Process child functions

        const fnNode = fnInfo.ast;

        fnInfo.childFns.forEach((trail, index) => {

                const [childJson, childGetInfos] = getInfos[index](),

                        childInfo = JSON.parse(childJson);

                resolveFunctionInfo(

                        childInfo, childGetInfos, true, fnId, scopeDefs,

                        externalVars, internalVars, globalVarNames, reservedVarNames, amendments

                );

                // Insert child function's AST into this function's AST

                setProp(fnNode, trail, childInfo.ast);

        });