[DatePicker] Installing @material-ui/lab with npm 7 installs moment, date-fns, luxon, dayjs

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

All the date engines are installed and in the package-lock.json

Expected Behavior 🤔

Only the date engine I need is installed and in the package-lock.json

Steps to Reproduce 🕹

Steps:

1. check npm 7 is installed
2. npm install @material-ui/lab@5.0.0-alpha16

Context 🔦

In https://github.com/dmtrKovalenko/date-io/issues/500, I was reporting a similar issue with yarn v1, the following warnings are raised

warning "@material-ui/lab > @date-io/dayjs@2.10.6" has unmet peer dependency "dayjs@^1.8.17".
warning "@material-ui/lab > @date-io/luxon@2.10.6" has unmet peer dependency "luxon@^1.21.3".
warning "@material-ui/lab > @date-io/moment@2.10.6" has unmet peer dependency "moment@^2.24.0".

Your Environment 🌎

Tech	Version
Material-UI	v5.0.0-alpha.16
npm	7.0.11

[eps1lon]

If you don’t want to listen then I don’t have anything to say. Npm installs peer dependencies automatically now. If you want to solve this on your own without involving package manager folks then good luck.

Note that your analysis is wrong. You wanted to integrate pickers so you can’t declare their peers as “unrelated” all of the sudden. Either include pickers or not. Good luck.

[oliviertassinari]

Does npm 7 installs optional peer dependencies automatically?

I went on testing it, it looks like npm 7 doesn’t install optional peer dependencies. So as far as I understand, each of the four options presented are possible. I don’t think that Material-UI will have a weight in influencing the outcome of npm 7 installing or not peer dependencies. I also think that the warnings in yarn v1 need to be solved. I don’t know what the story looks like with yarn v2, I have never used it.