Maven does't download parent from Google Artifact Registry

Question

I have a project that is moving from the self-hosted Nexus to Google Artifact Registry. Migration was smooth till I've got deal with parent-dependency.

Everything is running in GitActions on ubuntu-22.04.

I have a project that builds and deploys as POM file like this:

mvn deploy:deploy-file -Dpackaging=pom -Dfile=$svcname-$version.pom -DrepositoryId=${{ inputs.maven-registry-type }} -Durl=${{ inputs.maven-registry }} -DgroupId="$grpname" -DartifactId="$svcname" -Dversion="$revision"

I can see that package appears in GCR. Works great.

Next, another project(another repo) needs this package and has to use it as parent. In my pom.xml file I have:

<parent>
        <groupId>com.company.name</groupId>
        <artifactId>common-parent</artifactId>
        <version>VERSRION</version>
</parent>

    <repositories>
        <repository>
            <id>common-parent</id>
            <url>artifactregistry://region-maven.pkg.dev/project/common-parent</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
    </repositories>

    <build>
        <extensions>
            <extension>
                <groupId>com.google.cloud.artifactregistry</groupId>
                <artifactId>artifactregistry-maven-wagon</artifactId>
                <version>2.2.1</version>
            </extension>
        </extensions>
    </build>

Package from Nexus was working great! But from GCR doesn't want to be downloaded. I'm getting error:

Cannot access artifactregistry://region-maven.pkg.dev/project/common-parent with type default using the available connector factories: BasicRepositoryConnectorFactory and 'parent.relativePath' points at wrong local POM @ line 10, column 10'

Locally behavior the same till I install parent package manually. With Nexus I haven't install it separately.

I was playing around and noticed that if I put the package to dependencies - it will be downloaded, but as parent doesn't work.

What am I missing?

UPD: I saw possible fix with adding empty parent.relativePath to pom.xml

<parent>
  ...
  <relativePath />
</parent>

It didn't help.

Also, didn't help tricks with adding to maven -U like:

mvn install -U

But, I've found a solution, it is in the answer.

Answer 1

After hours of investigation I ran maven in debug more

mvn package -U -X

And got detailed errors in the output:

Caused by: org.eclipse.aether.transfer.NoTransporterException: Unsupported transport protocol artifactregistry
    at org.eclipse.aether.transport.wagon.WagonTransporter.<init> (WagonTransporter.java:131)
    at org.eclipse.aether.transport.wagon.WagonTransporterFactory.newInstance (WagonTransporterFactory.java:116)
    at org.eclipse.aether.internal.impl.DefaultTransporterProvider.newTransporter (DefaultTransporterProvider.java:104)
    at org.eclipse.aether.connector.basic.BasicRepositoryConnector.<init> (BasicRepositoryConnector.java:129)
    at org.eclipse.aether.connector.basic.BasicRepositoryConnectorFactory.newInstance (BasicRepositoryConnectorFactory.java:155)
    at org.eclipse.aether.internal.impl.DefaultRepositoryConnectorProvider.newRepositoryConnector (DefaultRepositoryConnectorProvider.java:107)

This error pointed me on a git issue opened back in 2021: wagon is not loaded for parent pom resolution. Which, eventually, points on the official doc page with notice:

Maven resolves some dependencies before applying a wagon defined in pom.xml, including:

• References in a child Maven project to a parent project using the element.
• Plugin dependencies stored in Artifact Registry.

Ok, so, parent is exactly my case, where solution is to add to the project folder .mvn with the file extensions.xml in it:

<extensions xmlns="http://maven.apache.org/EXTENSIONS/1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/EXTENSIONS/1.0.0 http://maven.apache.org/xsd/core-extensions-1.0.0.xsd">
  <extension>
    <groupId>com.google.cloud.artifactregistry</groupId>
    <artifactId>artifactregistry-maven-wagon</artifactId>
    <version>2.2.1</version>
  </extension>
</extensions>