Save some recompile time with nest start --watch by enabling cache on webpack

[ajubin]

I'm submitting a...

[ ] Regression 
[ ] Bug report
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

When starting nest in watch mode nest start --watch, every change on a single source file recompile the entire project.

With some measurement, it takes about 7.5 sec for my project

Expected behavior

Webpack should recompile only the changed files thanks to cache: true or mode: 'development' in default webpack config.

Documentation:

• https://webpack.js.org/configuration/cache/#cache
• https://webpack.js.org/configuration/mode/

By setting one of these options, on my project, recompile time drops from 7.5s to less than 1s

I'm open to do a Pull Request, but i'm not sure about the strategy.

I think we should change

nest-cli/lib/compiler/defaults/webpack-defaults.ts

Line 57 in 770a9e4

mode: 'none',

to development by adding another variable in the webpackDefaultFactory

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

It will save up some time for everyone using nest in watch mode

Environment

[System Information]
OS Version     : macOS
NodeJS Version : v14.17.1
YARN Version    : 1.22.10 

[Nest CLI]
Nest CLI Version : 7.5.4 

[Nest Platform Information]
platform-express version : 7.6.12
terminus version         : 7.1.2
swagger version          : 4.7.12
typeorm version          : 7.1.5
common version           : 7.6.12
config version           : 1.0.1
bull version             : 0.3.1
core version             : 7.6.15
cqrs version             : 7.0.1

[kamilmysliwiec]

I think adding mode: 'development' here https://github.com/nestjs/nest-cli/blob/master/lib/compiler/webpack-compiler.ts#L71-L74 only if watchMode || webpackConfiguration.watch should be sufficient :) Would you like to create PR for this issue?

[ajubin]

Yes I can do that :) I will be happy to contribute

[kamilmysliwiec]

Let's track this here #1319