Define a baseline loading Moose only if not present

Moose is a big project and loading it each time can take a long time.

Multiple people came to me asking if there was a way in the baseline of a project to say “Load Moose only if needed”.

Since it is a common question, here is a guide on how to do that!

One way to do it is to use custom project attributes from Metacello. The principle is simple; depending on the state of your image, you can define project attributes and use them in your baseline.

To define the attributes you need to implement a method #customProjectAttributes that will return an array with the custom attributes.

For example, if I just want to ensure any version of Famix is present I can implement it like this:

customProjectAttributes
    self class environment at: #MooseEntity ifAbsent: [ ^ #(#WithoutFamix) ].

    ^ #()

If I want to ensure Moose is in the image I can define it like this:

customProjectAttributes
    RPackageOrganizer default packages detect: [ :package | package name = 'BaselineOfMoose' ] ifNone: [ ^#(#WithoutMoose) ].

    ^ #()

Or I can also define both:

customProjectAttributes
    | attributes |
    attributes := OrderedCollection new.
    self class environment at: #MooseEntity ifAbsent: [ attributes add: #WithoutFamix ].

    RPackageOrganizer default packages detect: [ :package | package name = 'BaselineOfMoose' ] ifNone: [ attributes add: #WithoutMoose ].

    ^ attributes asArray

And now I can use those attributes in a baseline via the #for:do: message.

Full example

customProjectAttributes
    self class environment at: #MooseEntity ifAbsent: [ ^ #(#WithoutFamix) ].

    ^ #()

baseline: spec
    <baseline>
    spec
        for: #common
        do: [
            spec package: 'MyProject'.

            spec
                for: #(#'WithoutFamix') do: [
                    spec baseline: 'Moose' with: [ spec repository: 'github://moosetechnology/Moose:development/src' ]
                    spec package: 'MyProject' with: [ spec requires: #('Moose') ] ]