overlookmotel / livepack / 6890751424

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

 * livepack module

 * Replacements for `eval` which instrument code before executing.

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

'use strict';

// Modules

const generate = require('@babel/generator').default,

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

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

// Imports

const createTracker = require('./tracker.js'),

        getScopeId = require('./getScopeId.js'),

        {parseImpl} = require('../instrument/instrument.js'),

        modifyAst = require('../instrument/modify.js'),

        {

                createBlockWithId, createThisBinding, createNewTargetBinding, createBindingWithoutNameCheck

        } = require('../instrument/blocks.js'),

        {

                INTERNAL_VAR_NAMES_PREFIX, TRACKER_VAR_NAME_BODY, GET_SCOPE_ID_VAR_NAME_BODY

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

        specialFunctions = require('../shared/internal.js').functions,

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

// Constants

const DEBUG = !!process.env.LIVEPACK_DEBUG_INSTRUMENT;

// Exports

/**

 * Add eval methods to tracker.

 * @param {Function} tracker - Tracker function for file

 * @param {string} filename - File path

 * @param {Object} blockIdCounter - Block ID counter for file

 * @param {number} prefixNum - Internal vars prefix num

 * @returns {undefined}

 */

module.exports = function addEvalFunctionsToTracker(tracker, filename, blockIdCounter, prefixNum) {

        const evalIndirectLocal = {

                eval(code) {

                        return evalIndirect(code, tracker, filename, blockIdCounter, prefixNum, evalIndirectLocal);

                }

        }.eval;

        const evalDirectLocal = (...args) => evalDirect(

                args, filename, blockIdCounter, prefixNum, evalDirectLocal

        );

        tracker.evalIndirect = evalIndirectLocal;

        tracker.evalDirect = evalDirectLocal;

        // Record eval shim so it can be switched back to `eval` if it's serialized

        specialFunctions.set(evalIndirectLocal, {type: 'eval', parent: null, key: filename});

};

/**

 * Shimmed version of `eval` exposed as `livepack_tracker.evalIndirect`.

 * Instrumentation replaces an uses of `eval` which are not `eval()` calls with this.

 * Instruments code before executing it.

 * @param {*} code - Argument to `eval`

 * @param {Function} tracker - Tracker function for file

 * @param {string} filename - File path

 * @param {Object} blockIdCounter - Block ID counter for file

 * @param {number} externalPrefixNum - Internal vars prefix num outside `eval`

 * @param {Function} evalIndirectLocal - Function which was called (used for stack traces if error)

 * @returns {*} - Result of `eval()` call

 */

function evalIndirect(code, tracker, filename, blockIdCounter, externalPrefixNum, evalIndirectLocal) {

        // If `code` arg is not a string, eval it unchanged - it won't be evaluated as code

        // eslint-disable-next-line no-eval

        // Compile code with no external scope.

        // Code returned is for a function which takes arguments `(livepack_tracker, livepack_getScopeId)`.

        const {code: fnCode, shouldThrow, internalPrefixNum} = compile(

                code, filename, blockIdCounter, externalPrefixNum, true, false, undefined, false

        );

        // If prefix num inside `eval` is different from outside, create new tracker

        // `eval()` code without external scope and inject in Livepack's vars

        // eslint-disable-next-line no-eval

        const fn = execEvalCode(eval, fnCode, shouldThrow, code, evalIndirectLocal);

        return fn(tracker, getScopeId);

}

/**

 * Shimmed version of `eval` exposed as `livepack_tracker.evalDirect`.

 * Instrumentation replaces any uses of `eval` which are direct `eval()` calls with this.

 * Instrumentation also passes details of all vars accessible from outside `eval()`.

 * Reconstruct blocks, then instrument code before executing it.

 * @param {Array<*>} args - Arguments `eval()` called with

 * @param {string} filename - File path

 * @param {Object} blockIdCounter - Block ID counter for file

 * @param {number} externalPrefixNum - Internal vars prefix num outside `eval`

 * @param {Function} evalDirectLocal - Function which was called (used for stack traces if error)

 * @returns {*} - Result of `eval()` call

 */

function evalDirect(args, filename, blockIdCounter, externalPrefixNum, evalDirectLocal) {

        const callArgs = args.slice(0, -5),

                code = callArgs[0],

                [possibleEval, execEvalSingleArg, execEvalSpread, scopeDefs, isStrict] = args.slice(-5);

        // If var `eval` where `eval()` is called is not global `eval`,

        // call `eval()` with original args unaltered

        // eslint-disable-next-line no-eval

        // If `code` arg is not a string, eval it unchanged - it won't be evaluated as code

        // Create blocks

        const state = {

                currentBlock: undefined,

                currentThisBlock: undefined,

                currentSuperBlock: undefined

        };

        let allowNewTarget = false;

        for (const [blockId, blockName, scopeId, ...varDefs] of scopeDefs) {

                const block = createBlockWithId(blockId, blockName, true, state);

                block.scopeIdVarNode = t.numericLiteral(scopeId);

                state.currentBlock = block;

                for (const [varName, isConst, isSilentConst, argNames] of varDefs) {

                        if (varName === 'this') {

                                createThisBinding(block);

                                state.currentThisBlock = block;

                        } else if (varName === 'new.target') {

                                createNewTargetBinding(block);

                                allowNewTarget = true;

                        } else {

                                // TODO: Also need to set `superIsProto` and create a new temp var for `super` target

                                // (the external var could be shadowed inside `eval()` if prefix num is changing)

                                if (varName === 'super') state.currentSuperBlock = block;

                                // Whether var is function is not relevant because it will always be in external scope

                                // of the functions it's being recorded on, and value of `isFunction` only has any effect

                                // for internal vars

                                createBindingWithoutNameCheck(

                                        block, varName, {isConst: !!isConst, isSilentConst: !!isSilentConst, argNames}

                                );

                        }

                }

        }

        // Compile to executable code with tracking code inserted.

        // If var names prefix inside code has to be different from outside,

        // code is wrapped in a function which injects tracker and getScopeId functions:

        // `() => foo` -> `(livepack1_tracker, livepack1_getScopeId) => () => foo`

        const {

                code: codeInstrumented, shouldThrow, internalPrefixNum

        } = compile(code, filename, blockIdCounter, externalPrefixNum, false, allowNewTarget, state, isStrict);

        // Call `eval()` with amended code

        let res = execEvalCode(execEvalSingleArg, codeInstrumented, shouldThrow, code, evalDirectLocal);

        // If was wrapped in a function, create new tracker and inject tracker and `getScopeId` into function

        if (internalPrefixNum !== externalPrefixNum) {

                const tracker = createTracker(filename, blockIdCounter, internalPrefixNum);

                res = res(tracker, getScopeId);

        }

        return res;

}

/**

 * Execute eval call.

 * If `shouldThrowSyntaxError` is set and `eval()` doesn't throw, throw an error.

 * This is to check that if parsing the code threw an error, it is indeed a genuine syntax error.

 * @param {Function} exec - Function to call

 * @param {*} arg - Argument to call `exec` with

 * @param {boolean} shouldThrowSyntaxError - `true` if `exec(arg)` should throw

 * @param {string} code - Code being executed (for error message)

 * @param {Function} fn - Wrapper function

 * @returns {*} - Return value of `exec(arg)`

 * @throws {*} - Error thrown by `exec(arg)` or internal error if should have thrown but didn't

 */

function execEvalCode(exec, arg, shouldThrowSyntaxError, code, fn) {

        let hasThrown = false;

        try {

                return exec(arg);

        } catch (err) {

                hasThrown = true;

                Error.captureStackTrace(err, fn);

                throw err;

                assertBug(

                        !shouldThrowSyntaxError || hasThrown,

                        'Failed to parse `eval` expression',

                        () => `Eval expression: ${JSON.stringify(code)}`

                );

        }

}

/**

 * Instrument code.

 * If is indirect `eval`, wraps the code in a function which takes `livepack_tracker`

 * and `livepack_getScopeId` arguments. This is to inject Livepack's internal functions into scope.

 * If is direct `eval()` and internal vars prefix number outside `eval()` and inside `eval()` differ,

 * wrap in an IIFE to inject the internal vars with new names:

 * `((livepack20_tracker, livepack20_getScopeId) => { ... })(livepack_tracker, livepack_getScopeId)`

 *

 * @param {string} code - Code string passed to `eval()`

 * @param {string} filename - File path

 * @param {Object} blockIdCounter - Block ID counter for file

 * @param {number} externalPrefixNum - Internal vars prefix num outside `eval()`

 * @param {boolean} isIndirectEval - `true` if is indirect eval

 * @param {boolean} allowNewTarget - `true` if `new.target` is legal at top level

 * @param {Object} [state] - State to initialize instrumentation state (only if direct `eval()` call)

 * @param {boolean} isStrict - `true` if environment outside `eval()` is strict mode

 * @returns {Object} - Object with properties:

 *   {string} .code - Instrumented code (or input code if parsing failed)

 *   {boolean} .shouldThrow - `true` if could not parse code, so calling `eval()` with this code

 *     should throw syntax error

 *   {number} .internalPrefixNum - Internal vars prefix num inside `eval()`

 */

function compile(

        code, filename, blockIdCounter, externalPrefixNum, isIndirectEval, allowNewTarget, state, isStrict

) {

        // Parse code.

        // If parsing fails, swallow error. Expression will be passed to `eval()`

        // which should throw - this maintains native errors.

        let ast;

        try {

                ast = parseImpl(

                        code, filename, false, false, allowNewTarget, false, isStrict, false, undefined

                ).ast;

        } catch (err) {

                return {code, shouldThrow: true, internalPrefixNum: externalPrefixNum};

        }

        // Instrument code.

        // Filename in eval code will be same as host file.

        // Block IDs in created code will be higher than block IDs used in this file (to avoid clashes).

        // Var name prefix will be kept same as in host file if possible,

        // to avoid wrapping in a function unless impossible to avoid.

        // Details of vars which can be obtained from external scopes is passed in.

        state = {

                nextBlockId: blockIdCounter.nextBlockId,

                isStrict,

                internalVarsPrefixNum: externalPrefixNum,

                ...state

        };

        modifyAst(ast, filename, false, isStrict, undefined, state);

        // Update next block ID for file

        blockIdCounter.nextBlockId = state.nextBlockId;

        // If indirect `eval`, or direct `eval()` with different prefix nums inside and outside `eval()`,

        // wrap in function to inject Livepack's internal vars.

        // `123` => `(livepack_tracker, livepack_getScopeId) => eval('123')`.

        // Wrapping in a 2nd `eval()` is required to ensure it returns its value.

        const internalPrefixNum = state.internalVarsPrefixNum;

        if (isIndirectEval || internalPrefixNum !== externalPrefixNum) {

                ast = wrapInFunction(ast, internalPrefixNum);

        }

        // Return instrumented code

        code = generate(ast, {retainLines: true, compact: true}).code;

        return {code, shouldThrow: false, internalPrefixNum};

}

function wrapInFunction(ast, internalPrefixNum) {

        return t.program([

                t.expressionStatement(

                        t.arrowFunctionExpression(

                                [

                                        internalVarNode(TRACKER_VAR_NAME_BODY, internalPrefixNum),

                                        internalVarNode(GET_SCOPE_ID_VAR_NAME_BODY, internalPrefixNum)

                                ],

                                t.callExpression(

                                        t.identifier('eval'), [

                                                t.stringLiteral(generate(ast, {retainLines: true, compact: true}).code)

                                        ]

                                )

                        )

                )

        ]);

}

function internalVarNode(name, prefixNum) {

        return t.identifier(`${INTERNAL_VAR_NAMES_PREFIX}${prefixNum || ''}_${name}`);

}