feat: maven rockcraft plugin

Add overrides for craft-part maven plugin to allow
building Maven projects in rockcraft.

Namely:
 - Do not link /bin/java as it conflicts with the base-files_base slice
 - Restrict PATH to /usr/bin in order to avoid picking up unwanted JVM.
   Use can override PATH in the plugin environment settings if /usr/bin
   is not sufficient.

rockcraft/plugins/maven_plugin.py

@@ -0,0 +1,76 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright 2023 Canonical Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""The Rockcraft Maven plugin."""
+import logging
+from textwrap import dedent
+
+from craft_parts.plugins import maven_plugin
+from overrides import override  # type: ignore[reportUnknownVariableType]
+
+logger = logging.getLogger(__name__)
+
+# Template for the sitecustomize module that we'll add to the payload so that
+# the pip-installed packages are found regardless of how the interpreter is
+# called.
+SITECUSTOMIZE_TEMPLATE = dedent(
+    """
+    # sitecustomize added by Rockcraft.
+    import site
+    import sys
+
+    major, minor = sys.version_info.major, sys.version_info.minor
+    site_dir = f"/lib/python{major}.{minor}/site-packages"
+    dist_dir = "/usr/lib/python3/dist-packages"
+
+    # Add the directory that contains the venv-installed packages.
+    site.addsitedir(site_dir)
+
+    if dist_dir in sys.path:
+        # Make sure that this site-packages dir comes *before* the base-provided
+        # dist-packages dir in sys.path.
+        path = sys.path
+        site_index = path.index(site_dir)
+        dist_index = path.index(dist_dir)
+
+        if dist_index < site_index:
+            path[dist_index], path[site_index] = path[site_index], path[dist_index]
+
+    EOF
+    """
+).strip()
+
+
+class MavenPlugin(maven_plugin.MavenPlugin):
+    """A MavenPlugin plugin for Rockcraft.
+
+    This plugin extends Craft-parts' vanilla Maven plugin to properly
+    use and install the Java VM. Specifically:
+
+    - Do not link java executable to /bin/java
+    - Do not include staging area in the PATH
+    """
+
+    @override
+    def _get_java_link_commands(self) -> list[str]:
+        """Get the bash commands to provide /bin/java symlink."""
+        return []
+
+    @override
+    def get_build_environment(self) -> dict[str, str]:
+        env = super().get_build_environment()
+        env["PATH"] = "/usr/bin"
+        return env

rockcraft/plugins/register.py

@@ -19,6 +19,7 @@
 import craft_parts
 from craft_parts.plugins.plugins import PluginType
 
+from .maven_plugin import MavenPlugin
 from .poetry_plugin import PoetryPlugin
 from .python_plugin import PythonPlugin
 
@@ -30,4 +31,4 @@ def register() -> None:
 
 def get_plugins() -> dict[str, PluginType]:
     """Get a dict of Rockcraft-specific plugins."""
-    return {"poetry": PoetryPlugin, "python": PythonPlugin}
+    return {"poetry": PoetryPlugin, "python": PythonPlugin, "maven": MavenPlugin}

tests/spread/rockcraft/plugin-maven/rockcraft.yaml

@@ -0,0 +1,35 @@
+name: bare-build-2404
+base: bare
+build-base: ubuntu@24.04
+
+version: '0.1'
+summary: A rock that bundles a Maven project.
+description: A rock that bundles a Python project.
+license: GPL-3.0
+platforms:
+  amd64:
+
+services:
+  test:
+    command: /usr/lib/jvm/java-21-openjdk-${CRAFT_ARCH_BUILD_FOR}/bin/java -jar /jar/sample-0.0.1-SNAPSHOT.jar
+    override: replace
+    startup: enabled
+
+parts:
+  maven-sample:
+    plugin: maven
+    source: sample
+    stage-packages:
+     - openjdk-21-jre-headless_core
+     - base-files_base
+    build-packages:
+      - maven
+      - openjdk-21-jdk-headless
+    # replace chiselled image with jlink
+    override-stage: |
+      craftctl default
+      rm -rf ${CRAFT_STAGE}/usr/lib/jvm/java-21-openjdk-${CRAFT_ARCH_BUILD_FOR}
+      jlink --no-header-files --no-man-pages --strip-debug \
+        --add-modules java.base,java.xml,java.logging,jdk.net \
+        --output ${CRAFT_STAGE}/usr/lib/jvm/java-21-openjdk-${CRAFT_ARCH_BUILD_FOR}
+      touch ${CRAFT_STAGE}/usr/lib/jvm/java-21-openjdk-${CRAFT_ARCH_BUILD_FOR}/lib/jvm.cfg-default

tests/spread/rockcraft/plugin-maven/sample/pom.xml

@@ -0,0 +1,30 @@
+<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>test</groupId>
+    <artifactId>sample</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>sample</name>
+    <properties>
+        <maven.compiler.target>8</maven.compiler.target>
+        <maven.compiler.source>8</maven.compiler.source>
+    </properties>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>3.4.2</version>
+                <configuration>
+                    <archive>
+                        <manifest>
+                            <mainClass>test.Test</mainClass>
+                        </manifest>
+                    </archive>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

tests/spread/rockcraft/plugin-maven/sample/src/main/java/test/Test.java

@@ -0,0 +1,7 @@
+package test;
+
+public class Test {
+    public static void main(String[] args) {
+        System.out.println("hello world");
+    }
+}

tests/spread/rockcraft/plugin-maven/task.yaml

@@ -0,0 +1,21 @@
+summary: Maven plugin tests
+execute: |
+  SCENARIO="plugin-maven"
+  ROCK_FILE="${SCENARIO}_0.1_amd64.rock"
+  IMAGE="${SCENARIO}:0.1"
+
+  # Build the rock & load it into docker
+  run_rockcraft pack
+  test -f ${ROCK_FILE}
+  rockcraft.skopeo copy oci-archive:${ROCK_FILE} docker-daemon:${IMAGE}
+  docker images
+  rm ${ROCK_FILE}
+
+  # Run the packaged project, both via the console script and via "python -m"
+  docker run --rm $IMAGE exec hello | MATCH "hello world"
+
+  docker system prune -a -f
+
+  # Rebuild the java project
+  touch sample/src/main/java/test/Test.java
+  rockcraft pack