how to add jar dependency to xtext maven build - maven

Question

What is the correct way to use a maven jar file in my xtext dsl project?
What I have tried is this:
use the maven-dependency-plugin in the pom.xml file of the *.dsl project to download the .jar file from a maven repository into the ./lib/ directory. This is done as early as possible in the build process: in the maven validate phase
in MANIFEST.MF: add the jar to the classpath: e.g. Bundle-ClassPath: ., lib/value-2.5.6-annotations.jar
in build.properties: add it to the bin.includes
The problem is, that the build only works when I call mvn install twice.
The first time, the .jar file is downloaded to the lib directory as expected (early in the build process), but then the build fails because it cannot resolve the types in my jar file.
When I then run mvn install again (the .jar file now already exists in the lib directory before the build), it works fine.
Any ideas how to resolve this?

Answer 1

Short answer
Currently it does not work as expected, because of bugs in Tycho
#353889: Defer target&dependency resolution to the normal build
#393978 maven-dependency-plugin:copy-dependencies goal does not work reliably with Tycho projects - "error copying ....jar.jar"
Long answer
Here is what I did to make it work (for now) in the xxx.dsl project:
pom.xml file
I use the maven-dependency-plugin to download the jar file in the maven validate phase (as early in the build as possible) to the lib directory.
Note, that I use stripVersion=true so that the file in the lib dir is called value-annotations.jar (and not value-2.5.6-annotations.jar). If I ever want to update the version in the future, I only need to update it in one place in the pom.xml file.
The jar file must also be specified as a dependency, because otherwise the users of the dsl plugin cannot build the project: i.e. the generateXtext task of the xtext-gradle-plugin will fail because it cannot find the classes in the jar file.
Relevant pom.xml code:
<project ...>
<properties>
<xtextVersion>2.13.0</xtextVersion>
<immutablesVersion>2.5.6</immutablesVersion>
...
</properties>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>3.0.2</version>
<executions>
<execution>
<id>copy-libraries</id>
<phase>validate</phase>
<goals>
<goal>copy</goal>
</goals>
<configuration>
<artifactItems>
<artifactItem>
<groupId>org.immutables</groupId>
<artifactId>value</artifactId>
<version>${immutablesVersion}</version>
<classifier>annotations</classifier>
<outputDirectory>lib</outputDirectory>
</artifactItem>
</artifactItems>
<stripVersion>true</stripVersion>
</configuration>
</execution>
</executions>
</plugin>
...
</build>
<dependencies>
<dependency>
<groupId>org.immutables</groupId>
<artifactId>value</artifactId>
<version>${immutablesVersion}</version>
<classifier>annotations</classifier>
</dependency>
</dependencies>
</project>
META-INF/MANIFEST.MF file
Add the jar file to the Bundle-ClassPath, so that we can use it: e.g. in the DslJvmModelInferrer.xtend
Add the package of the jar file to Export-Package, so that these files can be accessed by the xxx.dsl.tests project
Relevant parts of MANIFEST.MF:
Bundle-ClassPath: ., lib/value-annotations.jar
Export-Package: xxx.xtext,
...
xxx.xtext.validation,
org.immutables.value
build.properties file
Add the jar file to the bin.includes so that it will be copied to the generated jar file (in the target directory):
bin.includes=model/generated/,\
.,\
META-INF/,\
lib/value-annotations.jar,\
plugin.xml
Build
Now the build works in Eclipse.
On the command line (and in my continuous integration server script), I must execute maven twice (because of the mentioned bugs):
mvn verify (to download the jars)
mvn install