Support for semver hash in hosted git dependency

[lenkan]

Summary

npm supports referencing hosted github dependencies in the format github:user/repo#semver:^1.6.0. This is currently not supported by yarn as it resolves the hash into #semver/^1.6.0. Note the added / instead of the :.

Thus, yarn outputs the error: "Couldn't find match for "semver/^1.6.0" in ...."

Motivation
Given an empty yarn package:

// package.json 
{
  "name": "tjosan",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "yarn": "github:yarnpkg/yarn#semver:^1.6.0"
  }
}

When running yarn:

yarn

It errors with:

error Couldn't find match for "semver/^1.6.0" in ....

Whereas npm resolved the dependency without errors.

Test plan

Given an empty yarn package:

// package.json 
{
  "name": "tjosan",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "yarn": "github:yarnpkg/yarn#semver:^1.6.0"
  }
}

When running yarn:

yarn

It should resolve the dependencies:

yarn install v1.6.0
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
[4/4] Building fresh packages...
success Saved lockfile.
Done in x.xxs.

[buildsize]

File name	Previous Size	New Size	Change
yarn-[version].noarch.rpm	917.28 KB	915.63 KB	-1.65 KB (0%)
yarn-[version].js	3.97 MB	3.96 MB	-7.71 KB (0%)
yarn-legacy-[version].js	4.13 MB	4.12 MB	-9.14 KB (0%)
yarn-v[version].tar.gz	922.34 KB	920.96 KB	-1.39 KB (0%)
yarn_[version]all.deb	681.06 KB	680.34 KB	-744 bytes (0%)

[lenkan]

It seems like older node doesn't support the negative lookahead regex, I will look into it if this is something you want.

[BYK]

Thanks a lot for the patch! I'll let @rally25rs and @imsnif look into this since they have worked on similar pieces recently.

It seems like older node doesn't support the negative lookahead regex, I will look into it if this is something you want.

Tests seem to be failing even on Node 10 so we need to get those fixed before we can merge or even review this.

[BYK]

Rejecting for CI failures.

[kruncher]

I too ran into this issue today when attempting to use yarn in a project.

[lenkan]

I tried to figure out an easy way to do it without the negative lookbehind regex. But I couldn't understand the existing method too well. From the tests, all I could gather was that we should find the user, repo and hash from a git reference string. So I thought, isn't that just to:

1. Strip hash
2. Strip anything leading up to the user name.
3. Split the remaining parts on / where the last bit is the repo, and the second last is the user?

All the initial tests passed, I added a bunch of new test cases. Did I miss any test cases? I can't see what some of the string splits were achieving.

[imsnif]

Hey @lenkan - this LGTM.

I feel it's cleaner, easier to understand while keeping all previous functionality and adding this new use case.
I also think the new tests are a step up!

My only issue is with the tests being generated, as my personal opinion is that they're a little harder to work with when debugging (as opposed to "normal" imperative tests) - but since the code base is filled with such examples, I feel it's fine to leave them in. :)

Thanks for this!

Concerns addressed

[kruncher]

Many thanks! Quick question, how long until this reaches the npm release channel?