Inconsistent work with local (file:)/ remote (git) dependencies

[wclr]

I decided to create this issue following #1214 to make a consistent description of yarn's (probably inconsistent) behaviour when dealing with local (file:) dependencies.

If we have dependency in package.json:

"my-local": "file:../relative/path/to/my-local"

I On first install, or when the dependency is added (using yarn add), happens following:

1. in yarn creates node_modules/my-local and copies the full content of the source folder, then install dependencies that are in my-local/package.json
2. places in cache *full content (including my-local/node_modules) in the cache under the name like npm-my-local-1.0.0 (considering version in my-local/package.json)

II Then suppose we made some changes to my-local (original source folder):

1. added some new code
2. added new dependency
3. did not change package.json version (1.0.0)

III Then we want to update the content of my-local dependency in the project.
we may do it by yarn upgrade (but will try to upgrade other package) so we do yarn upgrade file:../relative/path/to/my-local or yarn add file:../relative/path/to/my-local, while this yarn does folling:

1. takes (changed) package.json from original sources my-local folder, parses changed dependencies, links them
2. then it does strange thing (in my view): it just takes version from cache npm-my-local-1.0.0 and copies its content to our project node_modules/my-local

So you may see inconsistency here - it takes new package.json from source and handles dependencies, but takes old content from cache.

IV If we would change the version in my-local/package.json (-> 1.0.1) and would try to upgrade it we would got what wee need:

1. new version say npm-my-local-1.0.1 would be placed in cache
2. new content is in project's node_modules/my-local
3. new dependencies installed

Absolutely the same behaviour is happening when dealing with remote git dependencies: it too checks source package.json (and apppies it) and gets content from cache.

Symlinks problems

As described in #1214 and other issues
Of course we are in a trouble when we use symlinks, when we add local dependency and make simklink
/relative/path/to/my-local <==> node_modules/my-local and after upgrade procedure (step III) yarn will replace content for node_modules/my-local (and that means in linked source folder) with a version from cache.

Probably yarn shouldn't be using cache for local ('file:')/ git remote dependencies at all. I consider this as a kind of critical bug in yarn that should be fixed ASAP.

[guncha]

I'm seeing the same issue with Yarn caching the local folder and ignoring all changes to it until I run yarn cache clean. What's interesting is that the actual dependencies in node_modules reflect the changes to the package.json file in the local folder, but yarn.lock still has the old dependencies listed.

[wclr]

What's interesting is that the actual dependencies in node_modules reflect the changes to the package.json file in the local folder, but yarn.lock still has the old dependencies listed.

Yes, behaviour is inconsistent.

[eTorAken]

Related to #2165.