Sourcemaps contain invalid references to node_modules/tslib when importHelpers: false in tsconfig.json

[justingrant]

Bili is emitting a reference to ../node_modules/tslib/tslib.es6.js in sourcemaps, even in projects where importHelpers is false in tsconfig.json. Because tslib helpers are emitted directly into transpiled source, that file ../node_modules/tslib/tslib.es6.js won't exist on disk when the library is installed from the npm/yarn registry. This missing file causes warnings in webpack, parcel, and other tools that validate sourcemaps.

I'm filing this issue here in bili (as opposed to rollup-plugin-typescript2, rollup, babel, etc.) because I was able to create a minimal rollup config (based on bili's rollup config) that doesn't exhibit this problem. So I'm assuming that something is happening in how bili is configuring rollup or its plugins that's triggering this problem.

Here's the problematic bili config:

import { Config } from 'bili';

const config: Config = {
  input: 'src/index.ts',
  output: {
    format: ['esm'],
    dir: './dist-bili',
    moduleName: 'repro-tslib-sourcemap',
    fileName: '[name].module.js',
    sourceMap: true
  },
  bundleNodeModules: true,
  extendRollupConfig(config) {
    // log the rollup config used by this bili config
    console.log(JSON.stringify(config));
    return config;
  }
};

export default config;

And here's the working rollup config:

import sourceMaps from 'rollup-plugin-sourcemaps';
import typescript from 'rollup-plugin-typescript2';

export default {
  input: './src/index.ts',
  plugins: [
    typescript(),
    sourceMaps()

    // The plugins below were included in bili's rollup config
    //    { name: 'progress' },
    //    { name: 'json' },
    //    { name: 'hashbang' },
    //    { name: 'bili-custom-resolve' },
    //    { name: 'postcss' },
    //    { name: 'rpt2' },
    //    { name: 'babel' },
    //    { name: 'buble' }
    //    { name: 'record-bundle' }
  ],
  output: {
    format: 'esm',
    dir: './dist-rollup',
    entryFileNames: '[name].module.js',
    name: 'repro-tslib-sourcemap',
    sourcemap: true,
    sourcemapExcludeSources: false
  }
};

Repro

1. git clone https://github.com/justingrant/repro-tslib-sourcemap.git
2. cd repro-tslib-sourcemap
3. yarn
4. yarn build - This will run both bili and rollup and produce two output folders: ./dist-bili and ./dist-rollup
5. Open dist-rollup/index.module.js.map. You'll see that tslib is not present in the sources array of the sourcemap:

{"version":3,"file":"index.module.js","sources":["../src/index.ts"],"sourcesContent":["export default function useTsLib(a: number, b: number[]) {\n  // Uses the __spreadArrays function from tslib\n  return [a, ...b];\n}\n"],"names":[],"mappings":";;;;;;;;;;;;;;;;;;;;;;;SAAwB,QAAQ,CAAC,CAAS,EAAE,CAAW;;IAErD,uBAAQ,CAAC,GAAK,CAAC,EAAE;CAClB;;;;"}

5. Now open dist-bili/index.module.js.map

Expected: sourcemap file doesn't contains tslib in its sources array.

Actual: sourcemap file refers to a file that won't actually exist on disk when this library is packaged, because of "importHelpers": false in tsconfig.json. Here's the bad sourcemap:

{"version":3,"file":"index.module.js","sources":["../node_modules/tslib/tslib.es6.js","../src/index.ts"],"sourcesContent":["/*! *****************************************************************************\r\nCopyright (c) Microsoft Corporation. All rights reserved.\r\nLicensed under the Apache License, Version 2.0 (the \"License\"); you may not use\r\nthis file except in compliance with the License. You may obtain a copy of the\r\nLicense at http://www.apache.org/licenses/LICENSE-2.0\r\n\r\nTHIS CODE IS PROVIDED ON AN *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY\r\nKIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED\r\nWARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,\r\nMERCHANTABLITY OR NON-INFRINGEMENT.\r\n\r\nSee the Apache Version 2.0 License for specific language governing permissions\r\nand limitations under the License.\r\n***************************************************************************** */\r\n/* global Reflect, Promise */\r\n\r\nvar extendStatics = function(d, b) {\r\n    extendStatics = Object.setPrototypeOf ||\r\n        ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||\r\n        function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };\r\n    return extendStatics(d, b);\r\n};\r\n\r\nexport function __extends(d, b) {\r\n    extendStatics(d, b);\r\n    function __() { this.constructor = d; }\r\n    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());\r\n}\r\n\r\nexport var __assign = function() {\r\n    __assign = Object.assign || function __assign(t) {\r\n        for (var s, i = 1, n = arguments.length; i < n; i++) {\r\n            s = arguments[i];\r\n            for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p)) t[p] = s[p];\r\n        }\r\n        return t;\r\n    }\r\n    return __assign.apply(this, arguments);\r\n}\r\n\r\nexport function __rest(s, e) {\r\n    var t = {};\r\n    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)\r\n        t[p] = s[p];\r\n    if (s != null && typeof Object.getOwnPropertySymbols === \"function\")\r\n        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) {\r\n            if (e.indexOf(p[i]) < 0 && Object.prototype.propertyIsEnumerable.call(s, p[i]))\r\n                t[p[i]] = s[p[i]];\r\n        }\r\n    return t;\r\n}\r\n\r\nexport function __decorate(decorators, target, key, desc) {\r\n    var c = arguments.length, r = c < 3 ? 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[ajlende]

I also just ran across this problem since I don't want tslib included at all in my build. I found that rollup-plugin-typescript2 forces importHelpers: true regardless of what is set in tsconfig.json. Do your build files still include tslib, just not the sourcemap?

[justingrant]

@ajlende - Yep, the docs that you linked to (https://github.com/ezolenko/rollup-plugin-typescript2#some-compiler-options-are-forced) look like at least part of the explanation of what's going on. Thanks for finding that info. I still don't understand why the sourcemap paths are broken though. Do you know?

Do your build files still include tslib, just not the sourcemap?

Both the bili and the rollup version of the dist folder include local (not imported) definitions of tslib functions. The generated code is identical in both cases except for minor whitespace differences. Here's the generated ESM code for an example:

/*! *****************************************************************************
Copyright (c) Microsoft Corporation. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use
this file except in compliance with the License. You may obtain a copy of the
License at http://www.apache.org/licenses/LICENSE-2.0

THIS CODE IS PROVIDED ON AN *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED
WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
MERCHANTABLITY OR NON-INFRINGEMENT.

See the Apache Version 2.0 License for specific language governing permissions
and limitations under the License.
***************************************************************************** */

function __spreadArrays() {
    for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
    for (var r = Array(s), k = 0, i = 0; i < il; i++)
        for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++)
            r[k] = a[j];
    return r;
}

function useTsLib(a, b) {
  // Uses the __spreadArrays function from tslib
  return __spreadArrays([a], b);
}

export default useTsLib;
//# sourceMappingURL=index.module.js.map

[ajlende]

@justingrant I did an experiment by editing rollup-plugin-typescript2 to force importHelpers: false to see what would happen, and the result was slightly different.

var __spreadArrays = (undefined && undefined.__spreadArrays) || function () {
    for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
    for (var r = Array(s), k = 0, i = 0; i < il; i++)
        for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++)
            r[k] = a[j];
    return r;
};
function useTsLib(a, b) {
    // Uses the __spreadArrays function from tslib
    return __spreadArrays([a], b);
}

export default useTsLib;
//# sourceMappingURL=index.module.js.map

1. The license comment isn't included.
2. It includes undefined && undefined.__spreadArrays which build warnings indicate was compiled from this && this.__spreadArrays.

Both of those differences lead me to believe that the build process with importHelpers: true actually does include the imported version—it just gets inlined during the build step.

To confirm my suspicion, I updated your example to include another file that made use of the spread operator, and found that when I forced importHelpers: false there were two instances of the __spreadArrays function while with importHelpers: true there was only one.

var __spreadArrays = undefined && undefined.__spreadArrays || function () {
  for (var s = 0, i = 0, il = arguments.length; i < il; i++) {
    s += arguments[i].length;
  }

  for (var r = Array(s), k = 0, i = 0; i < il; i++) {
    for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++) {
      r[k] = a[j];
    }
  }

  return r;
};

function merge(a, b) {
  // Uses the __spreadArrays function from tslib
  return __spreadArrays(a, b);
}

var __spreadArrays$1 = undefined && undefined.__spreadArrays || function () {
  for (var s = 0, i = 0, il = arguments.length; i < il; i++) {
    s += arguments[i].length;
  }

  for (var r = Array(s), k = 0, i = 0; i < il; i++) {
    for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++) {
      r[k] = a[j];
    }
  }

  return r;
};
function useTsLib(a, b) {
  // Uses the __spreadArrays function from tslib
  return merge(__spreadArrays$1([a], b), __spreadArrays$1(b, [a]));
}

export default useTsLib;
//# sourceMappingURL=index.module.js.map

As far as why sourcemapExcludeSources: false removes tslib.es6.js from the sources list, I can't say. But I do think, based on the output, that the imported version is getting bundled despite what the source map says.