From cd933db27a27d7aae8c133a0cd43478544675acb Mon Sep 17 00:00:00 2001
From: Neil Bartlett <njbartlett@gmail.com>
Date: Sun, 12 Apr 2020 13:40:11 +0100
Subject: [PATCH] Use Maven Toolchain in native-image-maven-plugin

This adds support for Maven Toolchains in the native-image-plugin.
Toolchains are the best practice for multi-module Maven projects where
each module may need to build with a different Java version.

For example, in a shared library project one might want to build most
modules using a conservatively low Java version such as 1.8, to allow
those libraries to be used by a larger population of developers. But
within the same multi-module project you might have a "leaf" module that
builds a standalone application and exports that application as an
executable using GraalVM native-image.

Toolchains allow each module to define the JDK flavour and version it
requires. Toolchains are supported by all the basic Maven plugins such
as maven-compiler-plugin, maven-surefire-plugin etc. Since the
native-image plugin does not currently support toolchains, we have to
run the entire Maven build using GraalVM as the JAVA_HOME, which may not
work for some projects.

To use this support, we can define a <toolchain> section in our
$HOME/.m2/toolchains.xml such as:

    <toolchain>
        <type>jdk</type>
        <provides>
            <id>JavaSE-11</id>
            <version>11</version>
            <vendor>GraalVM</vendor>
        </provides>
        <configuration>
            <jdkHome>/Library/Java/JavaVirtualMachines/graalvm-ce-java11-20.0.0/Contents/Home</jdkHome>
        </configuration>
    </toolchain>

Then in a module that uses GraalVM native-image we declare:

      <plugin>
        <artifactId>maven-toolchains-plugin</artifactId>
        <configuration>
          <toolchains>
            <jdk>
              <version>11</version>
              <vendor>GraalVM</vendor>
            </jdk>
          </toolchains>
        </configuration>
      </plugin>

Note that if a module does not declare toolchain support, then the
native-image-maven-plugin falls back to its existing mechanism, i.e.
picking up the JAVA_HOME used to run Maven itself. Therefore, there will
be no effect on existing projects that do not opt-in to using
toolchains.
---
 .../oracle/substratevm/NativeImageMojo.java   | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/substratevm/src/native-image-maven-plugin/src/main/java/com/oracle/substratevm/NativeImageMojo.java b/substratevm/src/native-image-maven-plugin/src/main/java/com/oracle/substratevm/NativeImageMojo.java
index 20eb311a2fac..f167720df6e8 100644
--- a/substratevm/src/native-image-maven-plugin/src/main/java/com/oracle/substratevm/NativeImageMojo.java
+++ b/substratevm/src/native-image-maven-plugin/src/main/java/com/oracle/substratevm/NativeImageMojo.java
@@ -36,12 +36,14 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Optional;
 import java.util.Scanner;
 import java.util.ServiceLoader;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import org.apache.maven.artifact.Artifact;
+import org.apache.maven.execution.MavenSession;
 import org.apache.maven.model.ConfigurationContainer;
 import org.apache.maven.model.Plugin;
 import org.apache.maven.model.PluginExecution;
@@ -49,9 +51,12 @@
 import org.apache.maven.plugin.MojoExecutionException;
 import org.apache.maven.plugin.descriptor.PluginDescriptor;
 import org.apache.maven.plugins.annotations.LifecyclePhase;
+import org.apache.maven.plugins.annotations.Component;
 import org.apache.maven.plugins.annotations.Mojo;
 import org.apache.maven.plugins.annotations.Parameter;
 import org.apache.maven.project.MavenProject;
+import org.apache.maven.toolchain.ToolchainManager;
+import org.apache.maven.toolchain.java.DefaultJavaToolChain;
 import org.codehaus.plexus.archiver.tar.TarGZipUnArchiver;
 import org.codehaus.plexus.logging.AbstractLogger;
 import org.codehaus.plexus.logging.Logger;
@@ -88,6 +93,12 @@ public class NativeImageMojo extends AbstractMojo {
     @Parameter(property = "skip", defaultValue = "false")//
     private boolean skip;
 
+    @Parameter(defaultValue = "${session}", readonly = true)//
+    private MavenSession session;
+
+    @Component
+    private ToolchainManager toolchainManager;
+
     private Logger tarGzLogger = new AbstractLogger(Logger.LEVEL_WARN, "NativeImageMojo.tarGzLogger") {
         @Override
         public void debug(String message, Throwable throwable) {
@@ -302,8 +313,12 @@ private void addClasspath(Artifact artifact) throws MojoExecutionException {
         classpath.add(jarFilePath);
     }
 
-    private static Path getMojoJavaHome() {
-        return Paths.get(System.getProperty("java.home"));
+    private Path getMojoJavaHome() {
+        return Paths.get(Optional.ofNullable(toolchainManager)
+            .map(tm -> tm.getToolchainFromBuildContext("jdk", session))
+            .filter(DefaultJavaToolChain.class::isInstance).map(DefaultJavaToolChain.class::cast)
+            .map(DefaultJavaToolChain::getJavaHome)
+            .orElse(System.getProperty("java.home")));
     }
 
     private Path getWorkingDirectory() {