This is a Bug Report

It is possible to define a project that never resolves variable population.

Description

• What went wrong?
  I attempted to package a project. SLS loaded and then hung indefinitely.

• What did you expect should have happened?
  I expected a package to be produced

• What was the config you used?
  Simple config:
  serverless.yml:

service: test
provider:
  name: aws
custom:
  project: ${file(./project.yml)}

project.yml:

foo: baz
bar:
  name: ${self:custom.project.foo}

• What stacktrace or error message from your provider did you see?
  none is given

Additional Data

I've instrumented the code and produced the following list of unresolved variable resolutions:

unsettled promises:
file(./project.yml) waited on by:
${file(./project.yml)}
${file(./project.yml)}

self:custom.project.foo waited on by:
${self:custom.project.foo}

The problem is that resolving ${file(./project.yml)} involves, prior to replacing the custom.project attribute on the service object, attempting to resolve ${self:custom.project.foo} which then circularly attempts to resolve ${file(./project.yml)} again, resulting in a deadlock since ${file(./project.yml)} now cannot resolve until ${file(./project.yml)} is resolved.

It could have been any asynchronously resolving variable that referred to itself prior to being replaced in the origin object.

• Serverless Framework Version you're using: 1.25.0 / master
• Operating System: osx
• Stack Trace: n/a
• Provider Error messages: n/a