Compilation fails with Webpack 4.2.0 when using `au run` through the CLI.

I’m submitting a bug report

• Library Version: 0.33.1

Please tell us about your environment:

• Operating System: OSX 10.13

• Node Version: 8.10.0

• NPM Version: 5.6.0

• Browser: all

• Language: all

• Loader/bundler: Webpack

Current behavior: When running au run with Webpack 4.2.0 in a brand new project, an error occurs which prevents the application from compiling successfully:

✖ ｢wdm｣: ConcurrentCompilationError: You ran Webpack twice. Each instance only supports a single concurrent compilation at a time.
    at Compiler.run (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack/lib/Compiler.js:147:37)
    at rebuild (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack-dev-middleware/lib/context.js:81:24)
    at done (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack-dev-middleware/lib/context.js:59:7)
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/u0117404/Projects/test-webpack-broke/node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:18:1)
    at AsyncSeriesHook.lazyCompileHook [as _callAsync] (/Users/u0117404/Projects/test-webpack-broke/node_modules/tapable/lib/Hook.js:35:21)
    at emitRecords.err (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack/lib/Compiler.js:199:22)
    at Compiler.emitRecords (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack/lib/Compiler.js:311:39)
    at emitAssets.err (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack/lib/Compiler.js:193:10)
    at hooks.afterEmit.callAsync.err (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack/lib/Compiler.js:297:14)
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/u0117404/Projects/test-webpack-broke/node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:15:1)
    at AsyncSeriesHook.lazyCompileHook [as _callAsync] (/Users/u0117404/Projects/test-webpack-broke/node_modules/tapable/lib/Hook.js:35:21)
    at asyncLib.forEach.err (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack/lib/Compiler.js:294:27)
    at done (/Users/u0117404/Projects/test-webpack-broke/node_modules/neo-async/async.js:2809:11)
    at /Users/u0117404/Projects/test-webpack-broke/node_modules/neo-async/async.js:2760:7
    at MemoryFileSystem.writeFile (/Users/u0117404/Projects/test-webpack-broke/node_modules/memory-fs/lib/MemoryFileSystem.js:328:9)
    at writeOut (/Users/u0117404/Projects/test-webpack-broke/node_modules/webpack/lib/Compiler.js:280:29)

This behavior does not occur if you run the project using nps or if you roll the Webpack version back to 4.1.1.

This appears to be somewhat related to this Pull Request in Webpack 8 days ago: https://github.com/webpack/webpack/pull/6691

Reproduction is fairly easy:

1. Create a fresh project using au new.
2. Install all dependencies using either npm or yarn. (I tested both.)
3. Run au run and try to navigate to the page in any browser.

The error will occur.

• What is the expected behavior?

With a fresh CLI project we should see “Hello world!” when hitting the application for the first time.

[JeroenVinke]

After consideration we don’t see any use cases for au run without a watch mode. So I’ve made --watch the default for the run command (https://github.com/aurelia/cli/commit/26cce92ae8e3315c4c2b738c937e4c1752a5b801).

[CasiOo]

People are still running into this issue when creating new projects. Maybe we should stop them from installing webpack 4.2.x until they fix the issue (or we do) ?

https://github.com/aurelia/cli/blob/master/lib/dependencies.json#L105 Change it to something like ~4 for the time being ?