[MNG-8037] Restrict project to the entity being built and make it immutable

[gnodet]

Follow-up to #1387
JIRA issue: https://issues.apache.org/jira/browse/MNG-8037

[cstamas]

Merge this one, close out the other one

[cstamas]

Just FTR as we discussed:

• IMHO baseDir != "pom file parent"
• especially as a project may (could) have baseDir but no POM file (but have model provided)
• possible use case: generate some POM (ie is in tmp directory), create a Project that is "placed" on top of some existing module, and have it built?

[gnodet]

Just FTR as we discussed:

• IMHO baseDir != "pom file parent"
• especially as a project may (could) have baseDir but no POM file (but have model provided)
• possible use case: generate some POM (ie is in tmp directory), create a Project that is "placed" on top of some existing module, and have it built?

So we're looking at Maven being used as a library, right ? That's clearly not supported from the CLI.
Right, now, in the Maven 4 API (let's limit to that use case) the only way to obtain a Project is by using the ProjectBuilder and the only way to use it is to give either a Path, Source, Artifact or ArtifactCoordinate.
My understanding (it closely maps the v3 api) is that it you pass an ArtifactCoordinate (or Artifact), that artifact is resolved (it must point to a POM), then loaded. I need to double check, but this results in a Project which has no POM file and no BaseDir.
I think that's the current situation, i.e.: either you have both or none, but it's linked. The POM file cannot point to the local repository, it's always a build POM in your project file system, and it always define the base directory.

I'll also double check the DefaultMavenProjectBuilder. But I'm sure the use case you describe is currently supported.

In any case, the API is lacking some doc, especially this notion of "transient" projects which is not defined and very confusing/blurry.

[gnodet]

@cstamas I've removed the mutable bits from the Project, removed the optionals on pomPath and basedir. I think we'll miss a ModelBuilder service to get effective models for artifacts, but I'll add those in a separate PR.