Modules mapped through tsconfig.json risk being bundled differently than the same module mapped with default Webpack resolution

[christoffer]

Some context from: https://github.com/dividab/tsconfig-paths/pull/46:

The browser field supports objects as well as strings to allow more specific overrides than a single file: unofficial, but most prominent, spec.

It seems like Webpack supports this spec: https://github.com/christoffer/webpack-resolution-example, and while the PR above (if merged) will adopt a part of the behavior, it would probably be a good idea to support the same behavior so that users end up with the same bundle whether or not the path is mapped through tsconfig-paths or a webpack alias.

For example, a module containing a package.json file like:

{
  "name": "my-module",
  "main": "./main.js",
  "browser": {
    "./main.js": "browser.js"
  }
}

would bundle "main.js" if a pattern in tsconfig.json matches the module path, but "browser.js" if not (on account to falling back to the Webpack standard resolver).

[majo44]

I noticed this issue when I tried to use paths mapping like:

{
    "compilerOptions": {
        ...
        "paths": {
            "*": [
                "*",
                "./node_modules/@types/*",
                "./node_modules/*",
                "./packages/*"
            ]
        }
    }
}

The browser field from package.json is not interpreted in same way as is done by webpack: https://webpack.js.org/configuration/resolve/#resolvealiasfields , "Specify a field, such as browser, to be parsed according to this specification" : https://github.com/defunctzombie/package-browser-field-spec

[cyrilchapon]

I'm having a huge treeshaking issue, which I suspect is related to what's explained here.

Setup

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "ES2020",
    "lib": ["ES2020", "DOM"],
    "jsx": "react",

    "rootDir": "./src",
    "noEmit": true,

    "strict": true,

    "moduleResolution": "node",
    "baseUrl": "./",
    "paths": {
      "$components/*": ["src/components/*"],
      "*": ["node_modules/*"]
    },
    "esModuleInterop": true,

    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  }
}

webpack.config.ts

const path = require("path");
const BundleAnalyzerPlugin = require("webpack-bundle-analyzer")
  .BundleAnalyzerPlugin;
const { TsconfigPathsPlugin } = require("tsconfig-paths-webpack-plugin")

module.exports = {
  mode: "production",
  entry: {
    main: [
      "./src/index"
    ]
  },
  resolve: {
    extensions: [".js", ".jsx", ".ts", ".tsx"],
    plugins: [new TsconfigPathsPlugin()]
  },
  output: {
    filename: "[name].js",
    path: path.resolve(__dirname, "dist")
  },
  module: {
    rules: [
      {
        test: /\.(j|t)sx?$/,
        exclude: /node_modules/,
        use: {
          loader: "babel-loader"
        }
      }
    ]
  },
  plugins: [new BundleAnalyzerPlugin()]
};

Sources

src /
  index.tsx
  components /
    heading.tsx
    index.tsx
tsconfig.json
webpack.config.ts

---

Result

If I comment this plugins: [new TsconfigPathsPlugin()], I get that =>

But if I leave plugins: [new TsconfigPathsPlugin()], I get this =>

---

Assumptions

The trouble is when parsing this line

import { faCoffee } from "@fortawesome/free-solid-svg-icons";

As you can see

• Without the plugin, this line resolves to (tree-shakeable version) node_modules/@fortawesome/free-solid-svg-icons/index.es.js
• With the plugin, it resolves to (CJS, I guess) node_modules/@fortawesome/free-solid-svg-icons/index.js

[cyrilchapon]

EDIT:

This line

"*": ["node_modules/*"]

Seems to cause the issue.