overlookmotel / livepack / 6972989751

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

 * livepack module

 * Process blocks (holding scopes)

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

'use strict';

// Modules

const assert = require('simple-invariant'),

        upperFirst = require('lodash/upperFirst'),

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

// Imports

const {

                createRecord, createDependency, createAssignment, createBlock, createScope

        } = require('./records.js'),

        {addStrictDirectiveToFunction} = require('./strict.js'),

        {

                replaceRecordNode, getNodeWithinWrapperParent, setAddFrom, firstMapValue, deleteFirst

        } = require('./utils.js');

// Exports

module.exports = {

        initBlocks() {

                const rootBlock = createBlock(0, 'root', null);

                this.rootBlock = rootBlock;

                this.rootScope = createScope(null, rootBlock, null);

                this.rootStrictFnRecords = [];

                this.rootSloppyFnRecords = [];

        },

        processBlocks() {

                // Create scopes and functions

                const {rootBlock, rootScope} = this;

                createMissingScopes(rootBlock, null);

                const createScopeRecord = createRecord('createScopeRoot');

                const {node: blockNode, globalVarNames: functionsGlobalVarNames} = this.processBlock(

                        rootBlock, () => createScopeRecord, Object.create(null), new Set(), true

                );

                const {elements} = blockNode.body;

                this.globalVarNames.push(...functionsGlobalVarNames);

                // Flatten out contents of root scope

                const rootScopeRecord = rootScope.record;

                for (const {record: dependentRecord} of rootScopeRecord.dependents) {

                        // Substitute root scope calls for functions

                        replaceRecordNode(dependentRecord, elements.shift());

                        dependentRecord.dependencies = dependentRecord.dependencies.filter(

                                dependency => dependency.record !== rootScopeRecord

                        );

                }

        },

        processBlock(block, getParentCreateScopeRecord, inheritedVars, frozenNames, isRoot) {

                const returnNodes = [];

                // Init param objects and add frozen param names to `frozenNames`

                const {containsEval} = block,

                        paramsByName = Object.create(null);

                let frozenNamesIsCloned = false;

                const params = [...block.params.keys()].map((name) => {

                        const param = {

                                name,

                                // Identifier nodes referring to this param

                                localVarNodes: [],

                                // If param always contains another function defined in this block,

                                // function definition and array of function records

                                fnDef: null,

                                fnRecords: null,

                                // Set to `true` if param does not always contain another function defined in this block

                                isNotLocalFunction: false,

                                // Count of scopes which define a value for this param

                                definedCount: 0,

                                // Index of function to inject value for param in returned functions

                                injectionIndex: null,

                                // Node for parameter to injection function

                                injectionVarNode: null

                        };

                        paramsByName[name] = param;

                        // `super` and `new.target` are not actually frozen

                        if (containsEval && !['super', 'new.target'].includes(name)) {

                                if (!frozenNamesIsCloned) {

                                        frozenNames = new Set(frozenNames);

                                        frozenNamesIsCloned = true;

                                }

                                frozenNames.add(name);

                        }

                        return param;

                });

                // Identify scope vars which refer to functions within this scope.

                // If value of a scope var is consistently a function created within this block

                // (consistent across all scopes for this block), scope var can be set inline within scope function.

                // i.e. `(x, getX) => [getX = () => x, () => getX()]` (note `getX = `).

                // If function is not used elsewhere in code except by other functions in this block, it doesn't

                // need to be returned from the scope function at all.

                // i.e. `(x, getX) => (getX = () => x, () => getX())` (only 2nd function is returned).

                // Any other reference to a function defined in this block or blocks above is flagged as circular.

                // Also count which params are most used in calls to create scope function, so params

                // which are most often undefined (or circular, and so undefined in initial call to scope function)

                // go last.

                const {functions: blockFunctions, scopes: blockScopes, children: childBlocks} = block,

                        localFunctions = new Map();

                for (const fnDef of blockFunctions) {

                        for (const [scope, fnRecord] of fnDef.scopes) {

                                localFunctions.set(fnRecord, {scope, fnDef});

                        }

                }

                const undefinedRecord = this.serializeValue(undefined);

                let numLocalFunctions = 0;

                for (const scope of blockScopes.values()) {

                        const {values} = scope;

                        for (const param of params) {

                                const valProps = values[param.name];

                                if (!valProps) continue;

                                // Flag references to functions within this block as circular and increment count where not

                                const valRecord = valProps.record;

                                let localFunction;

                                if (valRecord === undefinedRecord) {

                                        // Value is undefined - treat same as unused

                                        values[param.name] = undefined;

                                } else {

                                        localFunction = localFunctions.get(valRecord);

                                        if (localFunction) {

                                                valProps.isCircular = true;

                                        } else if (!valProps.isCircular) {

                                                // Check if value or its dependencies are functions in this block or above

                                                const isCircular = (function referencesSameScopeOrDeeper(depRecord) {

                                                        // If value is a function, and it's in this scope or one nested within it,

                                                        // needs to be injected later. Flag as circular if so.

                                                        // NB: `.scope` property is only set for functions.

                                                        let fnScope = depRecord.scope;

                                                        if (fnScope) {

                                                                do {

                                                                        if (fnScope.block === block) return true;

                                                                        fnScope = fnScope.parent;

                                                                } while (fnScope);

                                                        }

                                                        // Iterate through value's dependencies too

                                                        const {dependencies} = depRecord;

                                                        if (dependencies) {

                                                                for (const dependency of dependencies) {

                                                                        if (referencesSameScopeOrDeeper(dependency.record)) return true;

                                                                }

                                                        }

                                                        return false;

                                                }(valRecord));

                                                if (isCircular) {

                                                        valProps.isCircular = true;

                                                } else {

                                                        param.definedCount++;

                                                }

                                        }

                                }

                                // Determine if param value refers to a function in this scope

                                if (param.isNotLocalFunction) continue; // Already discounted

                                const isLocalFunction = !!localFunction && localFunction.scope === scope;

                                if (!param.fnDef) {

                                        if (isLocalFunction) {

                                                param.fnDef = localFunction.fnDef;

                                                param.fnRecords = [valRecord];

                                                numLocalFunctions++;

                                        } else {

                                                param.isNotLocalFunction = true;

                                        }

                                } else if (isLocalFunction && param.fnDef === localFunction.fnDef) {

                                        param.fnRecords.push(valRecord);

                                } else {

                                        param.isNotLocalFunction = true;

                                        param.fnDef = null;

                                        param.fnRecords = null;

                                        numLocalFunctions--;

                                }

                        }

                }

                let numInternalOnlyFunctions = 0;

                if (numLocalFunctions > 0) {

                        const internalFunctions = new Set();

                        for (const {name: paramName, fnDef, fnRecords} of params) {

                                if (!fnDef) continue;

                                // Record param name containing this function in function def object

                                (fnDef.internalScopeParamNames || (fnDef.internalScopeParamNames = [])).push(paramName);

                                // Delete values for this param from all scopes.

                                // Delete the dependencies created between scope record and value record for all scopes.

                                for (const fnRecord of fnRecords) {

                                        const {scope} = fnRecord;

                                        scope.values[paramName] = undefined;

                                        const scopeRecord = scope.record;

                                        deleteFirst(scopeRecord.dependencies, dependency => dependency.record === fnRecord);

                                        deleteFirst(

                                                fnRecord.dependents,

                                                dependent => dependent.record === scopeRecord && dependent.node === undefined

                                        );

                                }

                                internalFunctions.add(fnDef);

                        }

                        // Determine if functions are only referenced by other functions within the scope

                        // they are defined in. If so, they don't need to be returned from the scope function.

                        for (const fnDef of internalFunctions) {

                                if (![...fnDef.scopes.values()].some(fnRecord => (

                                        fnRecord.assignments || fnRecord.dependents.length > 0 || t.isCallExpression(fnRecord.node)

                                ))) {

                                        fnDef.isScopeInternalOnly = true;

                                        numInternalOnlyFunctions++;

                                }

                        }

                }

                // Re-order params with least often defined last

                params.sort(({definedCount: count1}, {definedCount: count2}) => (

                        count1 > count2 ? -1 : count2 > count1 ? 1 : 0

                ));

                // Function to create functions to inject values into scope

                function createInjection(param) {

                        const inputParamNode = t.identifier(`_${param.name}`),

                                outputParamNode = t.identifier(param.name);

                        param.injectionVarNode = inputParamNode;

                        param.localVarNodes.push(outputParamNode);

                        const injectNode = t.arrowFunctionExpression(

                                [inputParamNode],

                                t.assignmentExpression('=', outputParamNode, inputParamNode)

                        );

                        const index = returnNodes.length;

                        param.injectionIndex = index;

                        returnNodes.push(injectNode);

                        return index;

                }

                // Create scopes

                for (const scope of blockScopes.values()) {

                        // Create node for calling createScope function to create scope object

                        const createScopeRecord = getParentCreateScopeRecord(scope.parent);

                        const argumentNodes = [],

                                callNode = t.callExpression(createScopeRecord.varNode, argumentNodes),

                                scopeRecord = scope.record;

                        scopeRecord.node = callNode;

                        // Get parameters

                        const {values} = scope,

                                undefinedIndexes = [];

                        let numTrailingUndefined = 0,

                                paramIndex = 0;

                        for (const param of params) {

                                const valProps = values[param.name];

                                let node;

                                if (!valProps) {

                                        // Value not required - insert `undefined` as empty value

                                        node = undefinedRecord.varNode;

                                        undefinedIndexes.push(paramIndex);

                                        numTrailingUndefined++;

                                } else {

                                        const valRecord = valProps.record,

                                                valDependents = valRecord.dependents,

                                                valDependent = valDependents

                                                        ? valDependents.find(dependent => dependent.record === scopeRecord && !dependent.node)

                                                        : undefined;

                                        node = valRecord.varNode;

                                        if (valProps.isCircular) {

                                                // Circular reference - inject into scope later

                                                const injectionIndex = param.injectionIndex ?? createInjection(param);

                                                // Create var for inject function for this scope.

                                                // Each var will only be injected once into each scope, so no need to guard against

                                                // duplicate inject function vars being created.

                                                const injectRecord = createRecord(

                                                        `inject${upperFirst(param.name)}Into${upperFirst(scopeRecord.varNode.name)}`

                                                );

                                                const injectFnNode = t.memberExpression(

                                                        scopeRecord.varNode,

                                                        t.numericLiteral(injectionIndex),

                                                        true

                                                );

                                                injectRecord.node = injectFnNode;

                                                createDependency(injectRecord, scopeRecord, injectFnNode, 'object');

                                                // Create assignment

                                                const argumentsNode = [node],

                                                        assignmentNode = t.callExpression(injectRecord.varNode, argumentsNode),

                                                        assignment = createAssignment(scopeRecord, assignmentNode);

                                                createDependency(assignment, injectRecord, assignmentNode, 'callee');

                                                // Move dependency on value from scope record to assignment

                                                valDependent.record = assignment;

                                                valDependent.node = argumentsNode;

                                                valDependent.key = 0;

                                                assignment.dependencies.push(

                                                        deleteFirst(scopeRecord.dependencies, dep => dep.record === valRecord)

                                                );

                                                // Insert `undefined` as empty value

                                                node = undefinedRecord.varNode;

                                                undefinedIndexes.push(paramIndex);

                                                numTrailingUndefined++;

                                        } else {

                                                // Complete dependent object with `.node` and `.key` properties

                                                if (valDependent) {

                                                        valDependent.node = argumentNodes;

                                                        valDependent.key = paramIndex;

                                                }

                                                numTrailingUndefined = 0;

                                        }

                                }

                                argumentNodes[paramIndex] = node;

                                paramIndex++;

                        }

                        // Trim off any trailing undefined params

                        if (numTrailingUndefined > 0) {

                                argumentNodes.length -= numTrailingUndefined;

                                undefinedIndexes.length -= numTrailingUndefined;

                        }

                        // Create dependencies for `undefined`

                        // Link scope object to createScope function (as 1st dependency)

                        createDependency(scopeRecord, createScopeRecord, callNode, 'callee');

                        const scopeDependencies = scopeRecord.dependencies;

                        scopeDependencies.unshift(scopeDependencies.pop());

                }

                // Determine if can output a singular value rather than an array.

                // NB: Root function always returns an array - it will be destructured in `processBlocks()`.

                let returnNodeIndex = returnNodes.length;

                const isSingular = !isRoot

                        && returnNodeIndex + blockFunctions.length - numInternalOnlyFunctions + childBlocks.length === 1;

                // Init vars to track strict/sloppy children

                const strictFns = [];

                let someSloppy = false;

                function recordStrict(node, isStrict) {

                        if (isStrict) {

                                strictFns.push({node, index: returnNodeIndex});

                        } else if (isStrict === false) {

                                someSloppy = true;

                        }

                }

                const {rootStrictFnRecords, rootSloppyFnRecords} = this;

                function recordRootStrict(fnRecord, isStrict) {

                        if (isStrict) {

                                rootStrictFnRecords.push(fnRecord);

                        } else if (isStrict === false) {

                                rootSloppyFnRecords.push(fnRecord);

                        }

                }

                // Create functions

                const globalVarNames = new Set(),

                        reservedVarNames = new Set(),

                        internalFunctionNodes = [];

                for (const blockFunction of blockFunctions) {

                        const {

                                scopes: fnScopes, externalVars, internalVars, globalVarNames: fnGlobalVarNames,

                                containsEval: fnContainsEval, isStrict, internalScopeParamNames, isScopeInternalOnly

                        } = blockFunction;

                        if (!isScopeInternalOnly) {

                                for (const [scope, fnRecord] of fnScopes) {

                                        let scopeRecord = scope.record;

                                        let fnNode;

                                        if (isSingular) {

                                                // Will output singular function rather than array.

                                                // The scope object is defunct - can go direct to createScope function.

                                                // Copy over `createScope(...)` node created above

                                                fnNode = scopeRecord.node;

                                                scopeRecord.node = null;

                                                // Transfer dependencies from scope object to function instance

                                                const {dependencies} = fnRecord,

                                                        scopeDependencies = scopeRecord.dependencies;

                                                for (const dependency of scopeDependencies) {

                                                        dependencies.push(dependency);

                                                        for (const dependent of dependency.record.dependents) {

                                                                if (dependent.record === scopeRecord) dependent.record = fnRecord;

                                                        }

                                                }

                                                scopeRecord = scopeDependencies[0].record;

                                                scopeDependencies.length = 0;

                                        } else {

                                                // Will output array - link function instance to scope object

                                                fnNode = t.memberExpression(

                                                        scopeRecord.varNode,

                                                        t.numericLiteral(returnNodeIndex),

                                                        true

                                                );

                                                createDependency(fnRecord, scopeRecord, fnNode, 'object');

                                                // Record strict/sloppy for top level functions

                                                if (isRoot && !fnContainsEval) recordRootStrict(fnRecord, isStrict);

                                        }

                                        // Replace placeholder var with reference to scope var

                                        const fnNodeWithWrapper = fnRecord.node,

                                                wrapperParentNode = getNodeWithinWrapperParent(fnNodeWithWrapper);

                                        if (!internalScopeParamNames) {

                                                // Replace placeholder var with reference to scope var

                                                if (wrapperParentNode) {

                                                        wrapperParentNode[0] = fnNode;

                                                } else {

                                                        fnRecord.node = fnNode;

                                                }

                                        } else {

                                                if (wrapperParentNode) {

                                                        wrapperParentNode[0] = fnRecord.varNode;

                                                        const assignment = createAssignment(scopeRecord, fnNodeWithWrapper);

                                                        createDependency(assignment, fnRecord, wrapperParentNode, 0);

                                                        // Re-assign function record's dependencies to scope record

                                                        const assignmentDependencies = assignment.dependencies;

                                                        fnRecord.dependencies = fnRecord.dependencies.filter((dependency) => {

                                                                const dependencyRecord = dependency.record;

                                                                if (dependencyRecord === scopeRecord) return true;

                                                                assignmentDependencies.push(dependency);

                                                                for (const dependent of dependencyRecord.dependents) {

                                                                        if (dependent.record === fnRecord) dependent.record = scopeRecord;

                                                                }

                                                                return false;

                                                        });

                                                }

                                                fnRecord.node = fnNode;

                                                // Re-assign function record's assignments to scope record

                                                const fnAssignments = fnRecord.assignments;

                                                if (fnAssignments) {

                                                        let {assignments} = scopeRecord;

                                                        if (!assignments) assignments = scopeRecord.assignments = [];

                                                        for (const assignment of fnAssignments) {

                                                                assignments.push(assignment);

                                                                if (!assignment.node) {

                                                                        // Re-assign prototype to depend on scope record.

                                                                        // Required to maintain circular dependency between function and prototype

                                                                        // when code-splitting.

                                                                        const protoRecord = assignment.dependencies[0].record;

                                                                        protoRecord.prototypeOf = scopeRecord;

                                                                }

                                                        }

                                                        fnRecord.assignments = undefined;

                                                }

                                        }

                                }

                        }

                        // Add var nodes to globals/locals

                        const fnReservedVarNames = new Set();

                        for (const varName in externalVars) {

                                const param = paramsByName[varName];

                                if (param) {

                                        // Local var

                                        param.localVarNodes.push(...externalVars[varName]);

                                } else {

                                        // Var referencing upper scope

                                        inheritedVars[varName].push(...externalVars[varName]);

                                }

                                // If var name is frozen, prevent an internal var taking same name

                                if (frozenNames.has(varName)) fnReservedVarNames.add(varName);

                        }

                        // Add global vars to globals

                        for (const varName of fnGlobalVarNames) {

                                if (!isRoot || !fnContainsEval) globalVarNames.add(varName);

                                fnReservedVarNames.add(varName);

                        }

                        // Add var names which are frozen internal to function to reserved names

                        // to prevent other vars clashing with them

                        for (const varName of blockFunction.reservedVarNames) {

                                reservedVarNames.add(varName);

                                fnReservedVarNames.add(varName);

                        }

                        // Rename internal vars.

                        // Names avoid clashing with internal and globals vars used within this function.

                        // Function names and vars which are frozen by `eval()` aren't included in `internalVars`.

                        const transformVarName = this.createVarNameTransform(fnReservedVarNames);

                        for (const varName in internalVars) {

                                // `this` is only included in `internalVars` if it's the faux `this` created for transpiled

                                // `super()`. If function contains `eval()`, make sure it's prefixed with "_".

                                const newName = transformVarName(varName, fnContainsEval && varName === 'this');

                                if (newName !== varName) {

                                        for (const varNode of internalVars[varName]) {

                                                varNode.name = newName;

                                        }

                                }

                                reservedVarNames.add(newName);

                        }

                        // Record if strict or sloppy

                        let {node} = blockFunction;

                        if (!isRoot) {

                                recordStrict(node, isStrict);

                        } else if (fnContainsEval) {

                                // Function in root scope containing eval - wrap in `(0, eval)(...)`

                                // to prevent access to outer vars

                                node = this.wrapInIndirectEval(node, isStrict);

                        }

                        // If param is a locally-defined function, add `x = ...` to node

                        if (internalScopeParamNames) {

                                // If unnamed function, wrap in `(0, ...)` to prevent implicit naming

                                if (!node.id) node = t.sequenceExpression([t.numericLiteral(0), node]);

                                for (const paramName of internalScopeParamNames) {

                                        const varNode = t.identifier(paramName);

                                        paramsByName[paramName].localVarNodes.push(varNode);

                                        node = t.assignmentExpression('=', varNode, node);

                                }

                        }

                        // Return function definition (as function/class expression)

                        if (isScopeInternalOnly) {

                                internalFunctionNodes.push(node);

                        } else {

                                returnNodes[returnNodeIndex++] = node;

                        }

                }

                const nextInheritedVars = Object.assign(Object.create(null), inheritedVars);

                for (const param of params) {

                        nextInheritedVars[param.name] = param.localVarNodes;

                }

                // Process child blocks

                for (const childBlock of childBlocks) {

                        const createScopes = new Map(),

                                createScopeName = `createScope${upperFirst(childBlock.name)}`;

                        let createScopeRecord;

                        // eslint-disable-next-line no-inner-declarations, no-loop-func

                        function getCreateScopeRecord(scope) {

                                // If already created, return it

                                createScopeRecord = createScopes.get(scope);

                                if (createScopeRecord) return createScopeRecord;

                                const scopeRecord = scope.record;

                                if (isSingular) {

                                        // Will output singular createScope function.

                                        // Repurpose the scope object created above as the createScope function.

                                        // NB: No need to do dependency linking - already done above.

                                        scopeRecord.varNode.name = createScopeName;

                                        createScopeRecord = scopeRecord;

                                } else {

                                        // Will output array of functions - createScope function will be an element of scope array

                                        createScopeRecord = createRecord(createScopeName);

                                        const createScopeNode = t.memberExpression(

                                                scopeRecord.varNode,

                                                t.numericLiteral(returnNodeIndex),

                                                true

                                        );

                                        createScopeRecord.node = createScopeNode;

                                        createDependency(createScopeRecord, scopeRecord, createScopeNode, 'object');

                                }

                                createScopes.set(scope, createScopeRecord);

                                return createScopeRecord;

                        }

                        let {

                                node: childNode, // eslint-disable-next-line prefer-const

                                globalVarNames: childGlobalVarNames, reservedVarNames: childReservedVarNames, isStrict

                        } = this.processBlock(childBlock, getCreateScopeRecord, nextInheritedVars, frozenNames, false);

                        if (isRoot && childBlock.containsEval) {

                                // Top-level block containing eval - wrap in `(0, eval)(...)`

                                // to prevent access to outer vars

                                childNode = this.wrapInIndirectEval(childNode, isStrict);

                        } else {

                                setAddFrom(globalVarNames, childGlobalVarNames);

                                setAddFrom(reservedVarNames, childReservedVarNames);

                                if (isRoot) {

                                        recordRootStrict(createScopeRecord, isStrict);

                                } else {

                                        recordStrict(childNode, isStrict);

                                }

                        }

                        returnNodes[returnNodeIndex++] = childNode;

                }

                // Rename params

                const transformVarName = this.createVarNameTransform(

                        new Set([...globalVarNames, ...reservedVarNames, ...frozenNames])

                );

                const paramNodes = [],

                        {mangle} = this.options;

                let hasArgumentsOrEvalParam = false,

                        frozenThisVarName, frozenArgumentsVarName;

                for (const param of params) {

                        const paramName = param.name;

                        let newName;

                        const renameInjectionVarNode = () => {

                                if (!param.injectionVarNode) return;

                                param.injectionVarNode.name = mangle

                                        ? (newName === 'a' ? 'b' : 'a')

                                        : `_${newName}`;

                        };

                        if (paramName === 'new.target') {

                                // `new.target` is always renamed as it can't be provided for `eval()` anyway

                                newName = transformVarName('newTarget', containsEval);

                                // Convert `MetaProperty` nodes into `Identifier`s with new name

                                for (const varNode of param.localVarNodes) {

                                        varNode.type = 'Identifier';

                                        varNode.name = newName;

                                        varNode.meta = undefined;

                                        varNode.property = undefined;

                                }

                                // Rename injection node

                                renameInjectionVarNode();

                        } else if (!containsEval || paramName === 'super') {

                                // Param can be renamed.

                                // NB: `super` param is always renamed.

                                newName = transformVarName(paramName, containsEval);

                                if (newName !== paramName) {

                                        // Rename all nodes

                                        for (const varNode of param.localVarNodes) {

                                                varNode.name = newName;

                                        }

                                        // Rename injection node

                                        renameInjectionVarNode();

                                }

                        } else {

                                // Frozen var name (potentially used in `eval()`)

                                // eslint-disable-next-line no-lonely-if

                                if (paramName === 'this' || (paramName === 'arguments' && paramsByName.this)) {

                                        // `this` or `arguments` captured from function.

                                        // `arguments` is only injected with a function wrapper if `this` is frozen too.

                                        // Otherwise, can just make `arguments` a normal param.

                                        // This can be the case if `arguments` is a user-defined variable,

                                        // not `arguments` created by a function.

                                        newName = transformVarName(paramName, true);

                                        if (paramName === 'this') {

                                                frozenThisVarName = newName;

                                        } else {

                                                frozenArgumentsVarName = newName;

                                        }

                                        assert(

                                                !param.injectionVarNode,

                                                'Cannot handle circular `this` or `arguments` where `this` cannot be renamed due to use of `eval()`'

                                        );

                                } else {

                                        newName = paramName;

                                        if (paramName === 'arguments' || paramName === 'eval') hasArgumentsOrEvalParam = true;

                                        // Rename injection node

                                        if (mangle) renameInjectionVarNode();

                                }

                        }

                        reservedVarNames.add(newName);

                        paramNodes.push(t.identifier(newName));

                }

                // Handle strict/sloppy mode

                let isStrict;

                if (!isRoot) {

                        if (hasArgumentsOrEvalParam) {

                                // If param named `arguments` or `eval`, scope function must be sloppy mode

                                // or it's a syntax error.

                                // NB: Only way param will be called `arguments` or `eval` is if it's frozen by an `eval()`.

                                isStrict = false;

                        } else if (strictFns.length === 0) {

                                // No strict child functions or child blocks. Block is sloppy if any sloppy children,

                                // or indeterminate (`null`) if all children are indeterminate.

                                isStrict = someSloppy ? false : null;

                        } else if (someSloppy) {

                                // Some sloppy and some strict children (and maybe some indeterminate). Block is sloppy.

                                isStrict = false;

                        } else {

                                // At least one strict child and no sloppy children. Block is strict.

                                isStrict = true;

                        }

                        // If block is sloppy, add 'use strict' directives to strict functions

                        if (isStrict === false) {

                                for (const strictFnProps of strictFns) {

                                        returnNodes[strictFnProps.index] = addStrictDirectiveToFunction(strictFnProps.node);

                                }

                        }

                }

                // Create block function - will return either array of functions or single function

                let returnNode = isSingular ? returnNodes[0] : t.arrayExpression(returnNodes);

                if (numInternalOnlyFunctions > 0) {

                        internalFunctionNodes.push(returnNode);

                        returnNode = t.sequenceExpression(internalFunctionNodes);

                }

                // If uses frozen `this`, wrap return value in an IIFE to inject actual `this`

                // (and `arguments`, if it's used too).

                // `() => eval(x)` -> `(function() { return () => eval(x); }).apply(this$0, arguments$0)`

                // TODO: In sloppy mode, it's possible for `arguments` to be re-defined as a non-iterable object

                // which would cause an error when this function is called.

                // A better solution when outputting sloppy mode code would be to just use a var called `arguments`,

                // rather than injecting. Of course this isn't possible in ESM.

                // TODO: Ensure scope function using `this` is strict mode if value of `this` is not an object.

                // In sloppy mode, literals passed as `this` get boxed.

                // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode#securing_javascript

                // TODO: Also doesn't work where `this` or `arguments` is circular and is injected late.

                if (frozenThisVarName) {

                        returnNode = t.callExpression(

                                t.memberExpression(

                                        t.functionExpression(null, [], t.blockStatement([t.returnStatement(returnNode)])),

                                ),

                                [

                                        t.identifier(frozenThisVarName),

                                ]

                        );

                }

                const node = t.arrowFunctionExpression(paramNodes, returnNode);

                // Return block function node, global var names, reserved var names + strict/sloppy mode flag

                return {node, globalVarNames, reservedVarNames, isStrict};

        }

};

function createMissingScopes(block, parentBlock) {

        for (const scope of block.scopes.values()) {

                // If scope's parent is not in block's parent, select a scope for it

                // (any which is nested in scope's current parent will work)

                let parentScope = scope.parent;

                const currentParentBlock = parentScope && parentScope.block;

                if (currentParentBlock === parentBlock) continue;

                // Get missing blocks

                const missingBlocks = [parentBlock];

                let thisBlock = parentBlock;

                while (true) { // eslint-disable-line no-constant-condition

                        thisBlock = thisBlock.parent;

                        if (thisBlock === currentParentBlock) break;

                        missingBlocks.unshift(thisBlock);

                }

                let possibleParentScopes = new Set([parentScope]),

                        index;

                for (index = 0; index < missingBlocks.length; index++) {

                        const interveningBlock = missingBlocks[index],

                                possibleScopes = new Set();

                        for (const possibleScope of interveningBlock.scopes.values()) {

                                if (possibleParentScopes.has(possibleScope.parent)) possibleScopes.add(possibleScope);

                        }

                        if (possibleScopes.size === 0) break;

                        possibleParentScopes = possibleScopes;

                }

                parentScope = firstMapValue(possibleParentScopes);

                // If some missing scopes don't exist, create them

                for (; index < missingBlocks.length; index++) {

                        parentScope = createScope(null, missingBlocks[index], parentScope);

                }

                // Set new parent

                scope.parent = parentScope;

        }

        // Traverse through child blocks

        for (const childBlock of block.children) {

                createMissingScopes(childBlock, block);

                // If a child block contains eval, this block does too

                if (childBlock.containsEval) block.containsEval = true;

        }

}