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

I guess a bug.

What is the current behavior?
If the current behavior is a bug, please provide the steps to reproduce.

Say you have the following project structure:

component-foo/
└── package.json
└── index.js

yarn-test/
└── package.json

With the following files:

component-foo/package.json:

{
  "name": "component-foo",
  "version": "1.0.0",
  "private": true,
  "main": "index.js"
}

component-foo/index.js:

console.log('foo');

yarn-test/package.json:

{
  "name": "yarn-test",
  "version": "1.0.0",
  "private": true,
  "dependencies": {
    "component-foo": "file:../component-foo"
  }
}

Now you run $ yarn install inside yarn-test/ and yarn-test/node_modules/component-foo/index.js is:

console.log('foo');

Now remove yarn-test/node_modules/ and yarn-test/yarn.lock and change component-foo/index.js to this:

console.log('bar');

Now you run $ yarn install inside yarn-test/ again and yarn-test/node_modules/component-foo/index.js will be:

console.log('foo');

It uses the cached version of component-foo, but component-foo/index.js has changed.

What is the expected behavior?

I'd expect that yarn-test/node_modules/component-foo/index.js should be this at the end:

console.log('bar');

Maybe packages installed with local paths like file:../ shouldn't be cached at all, if we can't figure out, if they have changed.

(FYI: It looks like npm doesn't cache them.)

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

$ node -v
v6.9.1

$ yarn -V
0.18.0

macOS 10.12.1