yarn does not report peerdependency version conflicts

[dre-hh]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
yarn install does not always report peer dependency version conflicts

If the current behavior is a bug, please provide the steps to reproduce.
https://github.com/dre-hh/yarndep

What is the expected behavior?
yarn must always report peer dependency version conflicts

Please mention your node.js, yarn and operating system version.
OS X Siera 10.12.6 , node v8.9.0, yarn 1.3.2 and yarn 1.3.2-20171114.1200

Here is a similar request for yarn check
#4594
and a bit related bug regarding warnings about actually installed peerDependencies
#4850

[rally25rs]

I believe the issue here is that if node_modules appears up-to-date according to the lockfile, Yarn just exits without bothering to check peerDeps because that check is done in the "linking" phase, which never happens.

[rally25rs]

Some initial research notes so I don't forget;

I tried making a branch where I copy/pasted the peerDep checking code from package-linker out to its own class, and then called that during Phase1/"Resolving Packages".

It seemed like the Manifest peerDependencies were not populated at that time. It seemed like they were not populated until Phase2/"Fetching packages", which again is not run if everything appears to be up to date.

Summary; it wasn't as quick and easy as I hoped it would be. If no one else makes a PR, I'll try to come back around to this at a later time, but I have some higher-priority issues to fix first...

[dre-hh]

@rally25rs, @torifat could you untriage this, if you are not working on it?

This is a very dangerous bug.
We see people running in this all the time with our package.
There is no command at all, to report peer dependency conflicts.

This is not some toy project. It is advertised by facebook and was supposed to solve such problems.

I am sorry, but it is beyond my understanding, why a software which calls itself a package manager leaves a critical bug which is dealing .. you know.. with managing dependencies open for almost a year.