Correctly resolve scoped packages in yarn create.

[chriskrycho]

Summary

Fixes #5981 by using the scope as part of the path lookup, if it exists.

Note: this does not yet work on Windows, and it seems like we'll need to do some explicit platform checking to make it work on Windows.

Test plan

Output on macOS:

yarn create @olo/ember-app
yarn create v1.7.0
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
[4/4] 📃  Building fresh packages...

success Installed "@olo/create-ember-app@0.1.0" with binaries:
      - @olo/create-ember-app
[#######################################################################################] 1007/1008
App name:

Current (broken) output on Windows:

yarn create @olo/ember-app
yarn create v1.6.0
[1/4] Resolving packages...
warning @olo/create-ember-app > ember-cli > exists-sync@0.0.4: Please replace with usage of fs.existsSync
warning @olo/create-ember-app > ember-cli > broccoli-stew > broccoli-funnel > exists-sync@0.0.4: Please replace with usage of fs.existsSync
warning @olo/create-ember-app > ember-cli > ember-cli-preprocess-registry > exists-sync@0.0.3: Please replace with usage of fs.existsSync
[2/4] Fetching packages...
info fsevents@1.2.4: The platform "win32" is incompatible with this module.
info "fsevents@1.2.4" is an optional dependency and failed compatibility check. Excluding it from installation.
[3/4] Linking dependencies...
[4/4] Building fresh packages...
warning Your current version of Yarn is out of date. The latest version is "1.7.0", while you're on "1.6.0".
success Installed "@olo/create-ember-app@0.1.0" with binaries:
      - @olo/create-ember-app
The directory name is invalid.
error Command failed.
Exit code: 1
Command: C:\Users\chris\AppData\Local\Yarn\bin\@olo\create-ember-app
Arguments:
Directory: C:\Code\platform
Output:

info Visit https://yarnpkg.com/en/docs/cli/create for documentation about this command.

[chriskrycho]

I have taken a number of stabs at this on Windows, but am running into a bigger problem there: the binaries aren’t getting installed to the correct location at all in my local testing. It’s working fine with unscoped packages (create-react-app, for example) but while it reports that it installs the binaries, they don’t show up in the same location, possibly because Windows is unhappy about the @ in the package name? Would appreciate some guidance!

[hulkish]

@chriskrycho would be good to add a test for this. Heck, I guess that means you'd have to make a __tests__/commands/create.js, since there isn't one yet, lol.

[chriskrycho]

I was thinking the same but am actually quite unsure what such a test would look like!

[arcanis]

Sounds good, thanks! :)

[fenduru]

I believe this is the change that caused the regression in #6266. path/prefix/bin/@scope/create-foo simply is not created when running yarn global add @scope/create-foo, create-foo is added to path/prefix/bin/create-foo (which is necessary for it to be included in the PATH that Yarn installer adds).