Scheme not generated for Aggregate Target

[CraigSiemens]

Our project/workspace has IDEWorkspaceSharedSettings_AutocreateContextsIfNeeded set to false to prevent Xcode from autogenerating schemes, to avoid opening the project being really slow and enforce that all the schemes come from the project spec.

If we add an aggregate target, a scheme will not be generated for it.

name: Example
configs:
  Debug: debug
  Release: release
targets:
  Foo:
    type: bundle
    platform: macOS
    scheme:
      environmentVariables:
        MY_ENV_VAR: VALUE
aggregateTargets:
  Run-Script:
    buildScripts:
      - name: Run script
        script: |
          echo("Hello")
    scheme:
      environmentVariables:
        MY_ENV_VAR: VALUE

Steps to reproduce

1. Run xcodegen on the above project.yml.
2. Open the project
3. Go to Project > Schemes > Manage Schemes...
4. Uncheck "Autocreate schemes"
   
5. Run xcodegen again

Expected Result

There should be a scheme generated for the aggregate target Run-Script.

Actual Result

There was no scheme generated.

Workaround

A scheme has to be added to schemes for it to be generated. It still doesnt use any of the settings from scheme under Aggregate Target

schemes:
  Run-Script:
    build:
      targets:
        Run-Script: all