[MNG-7706] Deprecate ${localRepository} mojo parameter expression

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.9.1, 4.0.0-alpha-5, 4.0.0
• Component/s: Core
• Assignee: Tamas Cservenak
• Reporter: Tamas Cservenak
• Created: 21/Feb/23 15:06
• Updated: 21/Jul/23 08:04
• Resolved: 23/Feb/23 17:15

Description

The mojo parameter expression 'localRepository' injects type ArtifactRepository that is part of the suite coming from Maven2 (predates Mercury, that was superseded by Aether, today Maven Resolver).

The problem with this interface is that it is not compatible (nor is possible to adapt it) to Maven Resolver LocalRepositoryManager (LRM) due lack of context. Also, the use of this interface in Mojos causes issues like MNG-7663, as they fully (and blindly) re-implement Maven local repository with wired in layout.

Moreover, Mojos using this expression are usually dragging other (legacy) deprecated things as well, most typically maven-artifact-transfer, or maven-dependency-tree and so on, all things that predates Maven 3.1 (are done to "protect" from Aether package change happened between Maven 3.0 and Maven 3.1). Today baseline for plugins is 3.2.5, so none of these "indirection" are needed anymore. In fact, the use of this expression is very good sign of legacy and technical debt present in given plugin. And also, these plugins cripple Maven to adopt new features. This warning is a clear indicator for legacy or neglected plugins.

The type ArtifactRepository is used in Maven internally (most in maven-compat, a bit less in maven-core), this is telling as well, but IMHO there is no need to deprecate this interface, as:

• plugins who migrate from this ancient interface to Resolver will have much simpler job with maven 4 API (as it is much closer to Resolver than old Maven APIs)
• this tackles only Plugins, while Maven itself is fine, as post Maven 4 the internals will be shut off, so warning Mojo authors is enough
• still, we should look into core where and why is this type used for
• deprecate localRepository used of ArtifactRepository type on following: MavenExecutionRequest, MavenSession and ProjectBuildingRequest as instance created for these are effectively not used (and are created "too early" and they carry repository system session anyway

If a Mojo gets this WARNING, how should it be fixed?

• presence of parameter ${localRepository} (with presence of type ArtifactReposiory) usually means following things: Mojo uses maven-compat Maven2 compatibility layer, OR uses some deprecated libraries (most prominent example is maven-artifact-transfer). Both are technical debts, and remedy is to switch code to use current APIs.
• second most often reason for parameter is access to the base directory of local repository. In this case RepositorySystemSession should be injected instead, use expression ${repositorySystemSession} and get the LocalRepositoryManager (LRM) from it. Word of warning: in most cases you DO NOT want the base directory of local repository, as since Maven 3.9.0 the layout of it is not fixed. If you want to access contents of local repository, you must use LRM APIs instead (this is actually true since Maven 3.0.x)!

If user is stuck with plugin that issues this warning, user still can use it, but should avoid use of any advanced (split, etc) local repository features, available since 3.9.0. Inevitably, the deprecated APIs (maven-compat, etc) will get removed in the future, so if no way to update the Mojo, user should plan to migrate to some alternative solution (to buy out the affected Mojo).

Issue Links

• is related to: KARAF-7685 karaf-maven-plugin uses deprecated "localRepository" expression
• is related to: MNG-7663 The local ArtifactRepository is broken when using enhanced local repo
• is related to: MNG-7811 Plugins verification - reports are inconsistent
• is related to: MPLUGIN-457 Use Resolver API, get rid of localRepository
• relates to: SM-5531 depends-maven-plugin triggers a maven warning
• relates to: MNG-7717 Maven warns wrongly about ${localRepository} expression
• relates to: MRESOLVER-322 Local repository split (releases/snapshots) fails with flatten-maven-plugin and imported dependencies
• relates to: MNG-6561 New RepositorySystem implementation as replacement of deprecated from maven-compat
• relates to: MPH-195 Get rid of ${localRepository} from mojo parameter
• relates to: SUREFIRE-2154 Get rid of ${localRepository} from surefire mojo parameter, use Resolver API
• links to: GitHub Pull Request #245
• links to: GitHub Pull Request #1009
• links to: GitHub Pull Request #1012