Correctly resolve peerDependencies for concurrent installs

[kamilogorek]

Summary

When installing multiple packages at the same time eg. yarn add react react-dom, peerDependencies were incorrectly resolved and triggered warnings.

Related: #2132

Test plan

Before:

λ: yarn add request request-promise-native
yarn add v0.21.3
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
warning "[email protected]" has unmet peer dependency "request@^2.34".
warning "[email protected]" has unmet peer dependency "request@^2.34".
[4/4] 📃  Building fresh packages...
success Saved 2 new dependencies.
├─ [email protected]
└─ [email protected]
✨  Done in 6.05s.

λ: yarn add react react-dom
yarn add v0.21.3
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
warning "[email protected]" has unmet peer dependency "react@^15.4.2".
[4/4] 📃  Building fresh packages...
success Saved 2 new dependencies.
├─ [email protected]
└─ [email protected]
✨  Done in 5.65s.

After:

λ: yarn add request request-promise-native
yarn add v0.21.3
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
[4/4] 📃  Building fresh packages...
success Saved 2 new dependencies.
├─ [email protected]
└─ [email protected]
✨  Done in 5.67s.

λ: yarn add react react-dom
yarn add v0.21.3
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
[4/4] 📃  Building fresh packages...
success Saved 2 new dependencies.
├─ [email protected]
└─ [email protected]
✨  Done in 5.65s.

[bestander]

Cool, thanks a lot!
Can you add a case when warning is expected to the Test Plan?
Could you add unit tests for the test plan?

[evenstensberg]

Sweet, I'll close my PR :)

[kamilogorek]

@bestander updated PR with tests for all 3 cases

[bestander]

🥇