Optimize version conflict strategy

[otakustay]

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

feature

What is the current behavior?

Suppose we have dependencies below:

• a depends on [email protected]
• b depends on [email protected]
• c depends on [email protected]
• main depends on a, b & c

after yarn install in main module, the node_modules tree could be:

node_modules
├── a
│   └── node_modules
│       └── underscore <-- 1.7.x
├── b
│   └── node_modules
│       └── underscore <-- 1.7.x
├── c
└── underscore <-- 1.5.x

What is the expected behavior?

It's not an optimized result since [email protected] is used more times than 1.5.x, it could be better to place 1.7.x under the top node_modules directory and only put a sub 1.5.x in c/node_modules

In frontend environment we really care about file sizes, but --flat flag may introduce compatibility issues, so to optimize the version conflict strategy can provide considerable benifits

Please mention your node.js, yarn and operating system version.

• Node: v6.8.0
• yarn: v0.15.1
• OS: macOS 10.12

[ghost]

@otakustay and @Daniel15, I believe this issue will be mitigated, if not entirely resolved by #2676

[gsklee]

@destroyerofbuilds indeed, thanks!