webpacker uses tsloader 4 which requires webpack 4

[sunnyrjuneja]

Hello there!

As of 4 days ago, ts-loader 4 is released. According to the ts loader read me, they no longer support webpack 2 / 3 in version 4. https://github.com/TypeStrong/ts-loader#compatibility

If you do:

rails new webpacker-ts-issue --webpack=typescript

It produces a package.json of:

{                                                                                                                                        
  "name": "webpacker-ts-issue",                                                                                                          
  "private": true,                                                                                                                       
  "dependencies": {                                                                                                                      
    "@rails/webpacker": "^3.2.2",                                                                                                        
    "ts-loader": "^4.0.0",                                                                                                               
    "typescript": "^2.7.2"                                                                                                               
  },                                                                                                                                     
  "devDependencies": {                                                                                                                   
    "webpack-dev-server": "^3.1.0"                                                                                                       
  }                                                                                                                                      
}                                                                                                                                        

If you go to any page that uses the pack, you'll see this error in your console:

bootstrap 1c9266352ca2b91cf17c:62 Uncaught Error: Module build failed: TypeError: Cannot read property 'afterCompile' of undefined
    at successfulTypeScriptInstance (/home/wasd/Programs/webpacker-ts-issue/node_modules/ts-loader/dist/instances.js:147:28)
    at Object.getTypeScriptInstance (/home/wasd/Programs/webpacker-ts-issue/node_modules/ts-loader/dist/instances.js:48:12)
    at Object.loader (/home/wasd/Programs/webpacker-ts-issue/node_modules/ts-loader/dist/index.js:16:41)
    at successfulTypeScriptInstance (/home/wasd/Programs/webpacker-ts-issue/node_modules/ts-loader/dist/instances.js:147:28)
    at Object.getTypeScriptInstance (/home/wasd/Programs/webpacker-ts-issue/node_modules/ts-loader/dist/instances.js:48:12)
    at Object.loader (/home/wasd/Programs/webpacker-ts-issue/node_modules/ts-loader/dist/index.js:16:41)
    at Object.<anonymous> (http://www.lvh.me:3000/packs/hello_typescript-7e7af262ac0ad77286c1.js:76:7)
    at __webpack_require__ (http://www.lvh.me:3000/packs/hello_typescript-7e7af262ac0ad77286c1.js:20:30)
    at http://www.lvh.me:3000/packs/hello_typescript-7e7af262ac0ad77286c1.js:63:18
    at http://www.lvh.me:3000/packs/hello_typescript-7e7af262ac0ad77286c1.js:66:10

If you change your package.json to read:

    "ts-loader": "^3.5.0",

Everything will operate normally.

Sorry for all the issues I've created over the last two weeks but I'm really excited to use webpacker and typescript :).