Fix NPE when Model.getLocation() returns null

[EricBlanquer]

Summary

Maven core extensions such as maven-git-versioning-extension modify the Maven model at runtime without preserving InputLocation metadata. This causes Model.getLocation("") to return null, leading to NullPointerException during project import and update.

Stack trace:

java.lang.NullPointerException: Cannot invoke "org.apache.maven.model.InputLocation.getSource()"
  because the return value of "org.apache.maven.model.Model.getLocation(Object)" is null
    at o.e.m2e.core.internal.lifecyclemapping.AnnotationMappingMetadataSource.parsePIs(AnnotationMappingMetadataSource.java:174)

java.lang.NullPointerException: Cannot invoke "org.apache.maven.model.InputLocation.getSource()"
  because "inputLocation" is null
    at o.e.m2e.core.internal.markers.SourceLocationHelper.getSourceLocation(SourceLocationHelper.java:243)

Changes

• AnnotationMappingMetadataSource: add null checks in constructor and parsePIs() for Model.getLocation() and InputLocation.getSource()
• SourceLocationHelper: add null checks in getSourceLocation(), findLocation() and getMavenDependency() for all getLocation(SELF) dereferences

Reproducer

Use any Maven core extension declared in .mvn/extensions.xml (e.g. maven-git-versioning-extension) and try to import or update a Maven project in Eclipse.

Fixes #1310

[laeubi]

Use any Maven core extension declared in .mvn/extensions.xml (e.g. maven-git-versioning-extension) and try to import or update a Maven project in Eclipse.

We already have some tests that use extensions (mostly Tycho), so would you mind to try adding such test for the maven-git-versioning-extension (I don't think it is reproducible with any extension obviously)?

Beside that you must sign the Eclipse ECA so we can accept your contribution.

[EricBlanquer]

@laeubi I've added a test (testGitVersioningExtension in ExtensionsTest) that imports a project using maven-git-versioning-extension as a core extension. The test initializes a git repo in the workspace (required for the extension to activate and modify the model), then imports the project and asserts no errors.

Proof that the fix prevents the NPE

Without the fix, when maven-git-versioning-extension modifies the model, Model.getLocation("") returns null:

AnnotationMappingMetadataSource constructor (line 82):

projectId = project.getModel().getLocation(SELF).getSource().getModelId();
//                              ↑ returns null → NPE on .getSource()

AnnotationMappingMetadataSource.parsePIs() (line 174):

InputSource source = project.getModel().getLocation(SELF).getSource();
//                                      ↑ returns null → NPE

SourceLocationHelper (line 120):

if(pomFile.getAbsolutePath().equals(inputLocation.getSource().getLocation()))
//                                                ↑ getSource() is null → NPE

With the fix, null checks and graceful fallbacks prevent the crash:

InputLocation selfLocation = project.getModel().getLocation(SELF);
if(selfLocation != null && selfLocation.getSource() != null) {
    projectId = selfLocation.getSource().getModelId();
} else {
    projectId = project.getGroupId() + ":" + project.getArtifactId() + ":" + project.getVersion();
}

All SourceLocationHelper code paths now check for null on getSource(), getParent(), and getLocation() before dereferencing.

Also, my ECA is now valid and up to date.