How to upload maven plugin to Github packages?

Question

Consider I have a maven plugin project and I want to publish it to Github's public maven repository called "Github Packages". I've done everything by instruction and for normal projects everything works fine out of the box. But for maven plugin projects with packaging=maven-plugin the instruction doesn't work.

In build log I see something like this:

[WARNING] Could not transfer metadata repo-name/maven-metadata.xml from/to github (https://maven.pkg.github.com/user-name/repo-name): Failed to transfer file: https://maven.pkg.github.com/user-name/repo-name/group-id/maven-metadata.xml. Return code is: 422 , ReasonPhrase:Unprocessable Entity.

It seems the maven deploy plugin needs maven-metadata.xml in the group-id's root, but can't find it and no one puts it there. How to solve this problem?

I use Apache Maven 3.3.9, and use the command:

mvn clean deploy

--Addition: example of pom file I'm using:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<modelVersion>4.0.0</modelVersion>

<repositories>
    <repository>
        <id>central</id>
        <url>https://repo1.maven.org/maven2</url>
        <releases>
            <enabled>true</enabled>
        </releases>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </repository>
    <repository>
        <id>github</id>
        <name>GitHub my_repo Apache Maven Packages</name>
        <url>https://maven.pkg.github.com/my_nick/my_repo</url>
    </repository>
</repositories>

<version>1.0.0</version>
<groupId>x</groupId>
<artifactId>some-plugin</artifactId>
<packaging>maven-plugin</packaging>

<dependencies>
    <dependency>
        <groupId>x</groupId>
        <artifactId>my-dependency</artifactId>
        <version>1.0.0</version>
    </dependency>

    <dependency>
        <groupId>com.github.javaparser</groupId>
        <artifactId>javaparser-core</artifactId>
        <version>3.15.12</version>
    </dependency>
    <dependency>
        <groupId>org.apache.maven.plugin-tools</groupId>
        <artifactId>maven-plugin-annotations</artifactId>
        <version>3.6.0</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-plugin-api</artifactId>
        <version>3.6.3</version>
    </dependency>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-core</artifactId>
        <version>3.6.3</version>
    </dependency>
</dependencies>
<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-plugin-plugin</artifactId>
            <version>3.6.0</version>
        </plugin>
    </plugins>
</build>
</project>

Answer 1

Unfortunately I haven't found the right answer to my question, it seems that for now it's impossible to add Maven plugins to Github Packages.

However I found a workaround which uses S3 as a repository backend, so you don't need heavyweight solutions like Nexus or JFrog. You can read this and this on how to do it.