Marc Philipp created MNG-6906:
---------------------------------
Summary: Whether a core extension can access classes exported by
another core extension should not depend on how it is registered
Key: MNG-6906
URL: https://issues.apache.org/jira/browse/MNG-6906
Project: Maven
Issue Type: Bug
Components: Class Loading
Reporter: Marc Philipp
We have a Maven core extension
(https://search.maven.org/artifact/com.gradle/gradle-enterprise-maven-extension/1.5/jar)
that declares two packages as exported in its {{META-INF/maven/extension.xml}}:
{code}
<?xml version="1.0" encoding="UTF-8"?>
<extension>
<exportedPackages>
<exportedPackage>com.gradle.maven.extension.api.scan</exportedPackage>
<exportedPackage>com.gradle.maven.mojo</exportedPackage>
</exportedPackages>
<exportedArtifacts>
<exportedArtifact>com.gradle:gradle-enterprise-maven-extension</exportedArtifact>
</exportedArtifacts>
</extension>
{code}
The first package ({{com.gradle.maven.extension.api.scan}}) contains a
{{BuildScanApi}} interface for which the extension registers a component in an
{{EventSpy}} at runtime.
We would now like to consume that component in another core extension (let's
call it consuming-extension) that has a {{provided}} dependency to
{{com.gradle:gradle-enterprise-maven-extension}} like this:
{code}
BuildScanApi buildScan = (BuildScanApi)
session.lookup("com.gradle.maven.extension.api.scan.BuildScanApi");
{code}
However, whether that works depends on how the core extensions are registered.
Relevant for us are the following registration locations:
{{<maven-home>/lib/ext}}, {{-Dmaven.ext.class.path}}, and
{{.mvn/extensions.xml}}.
||consuming-extension||gradle-enterprise-maven-extension||Result||
|{{<maven-home>/lib/ext}}|{{<maven-home>/lib/ext}}|(/)|
|{{.mvn/extensions.xml}}|{{<maven-home>/lib/ext}}|(/)|
|{{-Dmaven.ext.class.path}}|{{<maven-home>/lib/ext}}|(/)|
|{{<maven-home>/lib/ext}}|{{.mvn/extensions.xml}}|(x) {{NoClassDefFoundError}}|
|{{.mvn/extensions.xml}}|{{.mvn/extensions.xml}}|(x) {{NoClassDefFoundError}}|
|{{-Dmaven.ext.class.path}}|{{.mvn/extensions.xml}}|(/)|
|{{<maven-home>/lib/ext}}|{{-Dmaven.ext.class.path}}|(x)
{{NoClassDefFoundError}}|
|{{.mvn/extensions.xml}}|{{-Dmaven.ext.class.path}}|(x)
{{NoClassDefFoundError}}|
|{{-Dmaven.ext.class.path}}|{{-Dmaven.ext.class.path}}|(/)|
With this workaround, I was able to get it working in all cases:
{code}
ClassRealm extensionRealm = (ClassRealm) this.getClass().getClassLoader();
if (!"maven.ext".equals(extensionRealm.getId())) {
extensionRealm.getWorld().getRealms().stream()
.filter(realm ->
realm.getId().startsWith("coreExtension>com.gradle:gradle-enterprise-maven-extension:")
|| realm.getId().equals("maven.ext"))
.max(comparing((ClassRealm realm) -> realm.getId().length()))
.ifPresent(realm -> {
try {
extensionRealm.importFrom(realm.getId(),
"com.gradle.maven.extension.api.scan");
} catch (Exception e) {
throw new RuntimeException("Could not import package from realm", e);
}
});
}
{code}
Please let me know if I have misunderstood the intention of declaring exported
packages in {{extension.xml}}. I was unable to find documentation on it,
unfortunately.
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