[jira] [Commented] (MNG-5771) improved user-configurable core extensions mechanism

["Yuri (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MNG-5771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14643251#comment-14643251 ] 

Yuri commented on MNG-5771:
---------------------------

{quote}
I don't think settings.xml in project basedir is a good idea. User settings are meant to provide environment specific configuration, like user credentials, which cannot be shared across different build system.
{quote}
I agree 100%.

{quote}
Using ~/.m2/settings.xml to configure extensions is not a good idea because it will break earlier versions of maven. I don't have strong opinion about ~/.m2/extension.xml (or something like that). It is probably okay to for environment specific extensions, like your custom repository extension, assuming I understood your usercase correctly. I have no immediate plans to implement this myself, however.
{quote}
I didn't realize it would break earlier versions of maven. In any case, something like *~/.m2/extension.xml* would work just the same. 

Just to be a bit more specific, we are using Spring's S3 Wagon and it provides us a scalable and fault tolerant storage for our artifacts without the need for something like Artifactory or Nexus. We used to set this S3 wagon extension in a parent POM that was released independently, but then we got into a chicken and egg problem, specially when we have new hires or when bootstrapping a new laptop or when recreating *~/.m2/repo*: how to download the parent POM when it is the one that would tell maven how.

So we moved the <repository/> urls to settings.xml as properties in an active-by-default profile and we started distributing a custom Maven distribution with the S3 wagon jars embedded in the *lib/ext* folder. It works but it is a bit of a pain specially when there are new versions etc. If we were able to provide every developer a *~/.m2/settings.xml* and a *~/.m2/extension.xml* then both the S3 urls and the S3 wagon that can read/write these urls, then we would be done with it.

> improved user-configurable core extensions mechanism
> ----------------------------------------------------
>
>                 Key: MNG-5771
>                 URL: https://issues.apache.org/jira/browse/MNG-5771
>             Project: Maven
>          Issue Type: Improvement
>          Components: Class Loading
>            Reporter: Igor Fedorenko
>            Assignee: igorfie
>             Fix For: 3.3.1
>
>
> As of version 3.2.5 maven provides two mechanisms to contribute additional components to maven core runtime. It is possible to add component jars to {{$M2_HOME/lib/ext directory}}. It is also possible to specify component jars using {{-Dmaven.ext.class.path}} command line parameter. Neither of the mechanisms is user friendly. In both cases, the user is expected to manually locate and download all required jar file. In both cases, this has to be done on all systems where the extensions are needed. In both cases, all extra jars are loaded into single classloader so all extensions must agree of the same set of dependencies.
> This jira is to track changes needed to make it possible to configure core extensions in terms of groupId/artifactId/version and share set of required extensions across multiple systems.
> More specifically, 
> * introduce new {{$\{maven.projectBasedir\}/.mvn/extensions.xml}} descriptor to specify list of extensions. Initially, the descriptor will only allow specification of extension groupId/artifactId/version, but can be extended to support dependency includes/excludes mechanism and configuration parameters later
> {code:xml}
> <?xml version="1.0" encoding="UTF-8"?>
> <extensions>
>   <extension>
>     <groupId>...</groupId>
>     <artifactId>...</artifactId>
>     <version>...</version>
>   </extension>
>   <extension>...</extension>
>   ...
> </extensions>
> {code}
> * change maven to read and load core extensions in separate class realms as part of plexus container setup.
> * provide mechanism for extensions to declare exported artifacts and packages using {{META-INF/maven/extension.xml}} descriptor.



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