Resolve issues with using as a pom extension

[rnc]

Fixes #832

See https://issues.apache.org/jira/browse/MNG-7160

Thanks to @gnodet

[codecov]

Codecov Report

Merging #896 (bb2f169) into main (adc8ec2) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main     #896      +/-   ##
============================================
- Coverage     83.57%   83.56%   -0.02%     
+ Complexity     1882     1881       -1     
============================================
  Files           116      116              
  Lines          7014     7015       +1     
  Branches       1210     1210              
============================================
  Hits           5862     5862              
  Misses          672      672              
- Partials        480      481       +1     

Impacted Files	Coverage Δ
...mmonjava/maven/ext/integrationtest/ITestUtils.java	81.88% <100.00%> (+0.13%)	⬆️
...a/maven/ext/io/resolver/MavenLocationExpander.java	75.45% <0.00%> (-0.91%)	⬇️

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[dwalluck]

It looks good to me. It looks like we "just" had to exclude all instances of plexus-utils from our classpath.

I just wanted to be clear on two things said on https://issues.apache.org/jira/browse/MNG-7160:

1. That "this will only work when the extension does not actually need plexus-utils classes other than the XPP3 ones exported from the maven api realm". I guess we just get lucky there, otherwise it would not be possible?
2. That "this state means that it's always possible to use the same extension as a core extension or as a build extension, which I don't think is a good state". So is this a bug or a feature? In other words, even though we have a workaround, I suppose we could have left it as only "officially" supported as a build extension.

[gnodet]

It looks good to me. It looks like we "just" had to exclude all instances of plexus-utils from our classpath.

I just wanted to be clear on two things said on https://issues.apache.org/jira/browse/MNG-7160:

1. That "this will only work when the extension does not actually need plexus-utils classes other than the XPP3 ones exported from the maven api realm". I guess we just get lucky there, otherwise it would not be possible?

Yes, that's right. This is fixed by the PR apache/maven#616.

2. That "this state means that it's always possible to use the same extension as a core extension or as a build extension, which I don't think is a good state". So is this a bug or a feature? In other words, even though we have a workaround, I suppose we could have left it as only "officially" supported as a build extension.

Sorry, I meant "it's not always possible", I fixed the comment... The goal is to reconcile core and build extensions when possible. The apache/maven#616 PR offers some ways to configure the classloading strategy for core extensions in way which is similar to build extensions, so this bridges the classloading gap.

[dwalluck]

Sorry, I meant "it's not always possible", I fixed the comment... The goal is to reconcile core and build extensions when possible. The apache/maven#616 PR offers some ways to configure the classloading strategy for core extensions in way which is similar to build extensions, so this bridges the classloading gap.

OK, thanks. We had only been using the extension via the POM method before this PR, so I just wanted to make sure we weren't doing anything out of the ordinary.