Maven: Using inherited property in dependency classifier causes build failure - maven-2

Question

Given three POM files:
C depends on B.
B inherits from A.
I can build A and B
C fails to build because of its dependency on B.
The full source-code and build output is included below for your review.
Here is A's POM:
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.foo</groupId>
<artifactId>A</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<name>A</name>
<repositories>
<repository>
<id>foo releases</id>
<name>libs-releases-local</name>
<layout>default</layout>
<url>http://foo.net/artifactory/libs-releases-local</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>org.eclipse.swt</groupId>
<artifactId>swt</artifactId>
<classifier>${swt.classifier}</classifier>
<version>3.6.1</version>
</dependency>
</dependencies>
<profiles>
<profile>
<id>windows-x86</id>
<properties>
<swt.classifier>win32-x86</swt.classifier>
</properties>
</profile>
</profiles>
</project>
Here is B's POM:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.foo</groupId>
<artifactId>A</artifactId>
<version>1.0-SNAPSHOT</version>
<relativePath>../A</relativePath>
</parent>
<artifactId>B</artifactId>
<packaging>jar</packaging>
<name>B</name>
<profiles>
<profile>
<id>windows-x86</id>
<properties>
<swt.classifier>win32-x86</swt.classifier>
</properties>
</profile>
</profiles>
</project>
Here is C's POM:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.foo</groupId>
<artifactId>C</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>C</name>
<dependencies>
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>B</artifactId>
<version>${project.version}</version>
</dependency>
</dependencies>
</project>
Here is the build output from C:
------------------------------------------------------------------------
Building C
task-segment: [install]
------------------------------------------------------------------------
[compiler:compile]
Nothing to compile - all classes are up to date
Downloading: http://foo.net/artifactory/libs-releases-local/org/eclipse/swt/swt/3.6.1/swt-3.6.1-${swt.classifier}.jar
[WARNING] Unable to get resource 'org.eclipse.swt:swt:jar:${swt.classifier}:3.6.1' from repository foo releases (http://foo.net/artifactory/libs-releases-local): Error transferring file: foo.net
Downloading: http://repo1.maven.org/maven2/org/eclipse/swt/swt/3.6.1/swt-3.6.1-${swt.classifier}.jar
Unable to find resource 'org.eclipse.swt:swt:jar:${swt.classifier}:3.6.1' in repository central (http://repo1.maven.org/maven2)
------------------------------------------------------------------------
[ERROR]BUILD ERROR
------------------------------------------------------------------------
Failed to resolve artifact.
Missing:
----------
1) org.eclipse.swt:swt:jar:${swt.classifier}:3.6.1
I know this issue is related to https://issues.apache.org/jira/browse/MNG-3228 but I'm not sure how to fix it. Please help!
UPDATE:
Adding a classifier to B helped. Now C builds so long as the repository only contains B's jar file. If I upload B's POM file alongside the JAR in the repository, C fails with the aforementioned error (${swt.classifier} not defined). Any ideas?

Answer 1

In a comment you write, "I am expecting SWT's classifier to get resolved at B's build-time, not C's build-time", but that is wrong - you need the classifier at C's build time because C has a dependency on swt (transitive via A). That dependency is only fully-determined by a property, so you have to have a way of evaluating the property in C's pom.
A depends on swt-${classifier}
C depends on A
therefore C depends on swt-${classifier}
therefore C's pom must define the property. It can be defined by a profile (as in A), or manually at runtime (bad for reproducibility), but you can't build C without it.
It's as simple (and puzzling) as that.
If you're expecting the property to somehow get fully "resolved" along the way, and be already well-defined by the time you build C, you are not understanding how Maven treats those properties. It leaves them alone. There was an attempt to do some different stuff in Maven 2.1 (the classifier property expression would be transformed to its value when you installed A), but it was not successful, caused many surprising behaviours, it was reverted for 2.2, and in fact caused 2.1 to be quickly deprecated. For more details, and some hints as to how complicated the problem really is, see the link below.
https://cwiki.apache.org/confluence/display/MAVENOLD/Artifact-Coordinate+Expression+Transformation
Until the Maven developers decide otherwise, I think we will continue to have the behaviour that has been around since 2.0: "Expressions in artifact coordinates are ignored. Users have plenty of rope with which to hang themselves"
Once you get used to it, though, it's not confusing anymore. It's only when you're trying to second-guess Maven that you get surprised.

Answer 2

Maven is trying to find the artifact org.eclipse.swt:swt:3.6.1 but the coordinates aren't being resolved correctly. The error is saying that ${swt.classifier} isn't being recognized from a <properties/> block in your POM.xml. Since that value shows up in a <profile/> block, can you verify what Maven command you are running?
Try this: mvn dependency:resolve -P windows-x86
Also, verify that both the version of SWT and the Classifier are actually correct. The latest version I see on Maven Central is not 3.6.0, but 3.3.0-v3346

Answer 3

This isn't possible as of Maven 3.1.0. Here is the relevant feature request: https://issues.apache.org/jira/browse/MNG-1388

Answer 4

I know this issue is related to https://issues.apache.org/jira/browse/MNG-3228 but I'm not sure how to fix it.
I'm not sure there is a link with this issue, I don't see anything related to profile activation in the pom.xml shown above.
Actually, I'm not even sure to understand the expected result. From where is the classifier supposed to come? Maybe I'm missing some parts but I think you should install/deploy a qualified version of B (with a fully resolved POM) and have C depend on this qualified version.
How would I need to modify B's POM to deploy a qualified version? I am expecting SWT's classifier to get resolved at B's build-time, not C's build-time.
Yes but at C's build-time, C needs B and B's dependencies so the installed/deployed .pom of B has to be fully resolved. At least, that's how I think things can work.
But I must admit I'm not sure how to handle this case exactly and after reading issues like MNG-4140 or the Artifact-Coordinate Expression Transformation page, I'm totally confused.
I suggest to post this on the maven users list for the right way (and I'll follow the thread closely because I think I have some broken POMs using profiles, properties and dependencies to fix now, thanks :)