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https://issues.apache.org/jira/browse/MNG-6016?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Robert Scholte closed MNG-6016.
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Resolution: Not A Problem
Assignee: Robert Scholte
The issue here is that the configuration-content is just a bunch of xml tags.
When Maven tries to merge because of inheritence it is a per-element
comparison; it is not aware of lists or maps.
So what's happening here is that the second transformer of the parent is merged
with the second of the child.
With Lists you can simply add the magic attribute {{combine.children="append"}}
to the transformers-element, which means that the transformer-elements won't be
merged but appended.
Since Maven 3.3.9 it is also possible to specify {{combine.id}}, which is
useful in case of Maps. Transformers having the same combine.id in parent and
child will be merged, the rest will be appended.
Also read
http://blog.sonatype.com/2011/01/maven-how-to-merging-plugin-configuration-in-complex-projects/
for more details.
> Maven incorrectly builds POM when you override Shade transformers in a child
> ----------------------------------------------------------------------------
>
> Key: MNG-6016
> URL: https://issues.apache.org/jira/browse/MNG-6016
> Project: Maven
> Issue Type: Bug
> Components: Inheritance and Interpolation, POM
> Affects Versions: 3.3.9
> Reporter: Steven Schlansker
> Assignee: Robert Scholte
>
> Consider the project:
> https://github.com/stevenschlansker/maven-configure-transformer-bug/
> Simple 2 module project. Parent defines some Shade plugin configuration,
> notably a {{ResourceTransformer}} with a {{mainClass}} declaration.
> Child then tries to add a {{PropertiesMergingResourceTransformer}}, but
> somehow the {{mainClass}} declaration from the parent gets merged into this
> other transformer, causing a build failure:
> {quote}
> [ERROR] Failed to execute goal
> org.apache.maven.plugins:maven-shade-plugin:2.4.3:shade (assemble-app) on
> project maven-configure-transformer-bug-child: Unable to parse configuration
> of mojo org.apache.maven.plugins:maven-shade-plugin:2.4.3:shade for parameter
> mainClass: Cannot find 'mainClass' in class
> org.springframework.boot.maven.PropertiesMergingResourceTransformer -> [Help
> 1]
> {quote}
> The effective POM shows that something extremely unintuitive is going on with
> model merging:
> {code}
> <plugin>
> <artifactId>maven-shade-plugin</artifactId>
> <version>2.4.3</version>
> <executions>
> <execution>
> <id>assemble-app</id>
> <phase>package</phase>
> <goals>
> <goal>shade</goal>
> </goals>
> <configuration>
> <transformers>
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
> <resource>META-INF/spring.handlers</resource>
> </transformer>
> <transformer
> implementation="org.springframework.boot.maven.PropertiesMergingResourceTransformer">
> <resource>META-INF/spring.factories</resource>
> <mainClass>foo</mainClass>
> <collectSections>true</collectSections>
> </transformer>
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
> <resource>META-INF/spring.schemas</resource>
> </transformer>
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"
> />
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer"
> />
> </transformers>
> </configuration>
> </execution>
> </executions>
> <dependencies>
> <dependency>
> <groupId>org.springframework.boot</groupId>
> <artifactId>spring-boot-maven-plugin</artifactId>
> <version>1.3.3.RELEASE</version>
> <scope>compile</scope>
> </dependency>
> </dependencies>
> <configuration>
> <transformers>
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
> <resource>META-INF/spring.handlers</resource>
> </transformer>
> <transformer
> implementation="org.springframework.boot.maven.PropertiesMergingResourceTransformer">
> <resource>META-INF/spring.factories</resource>
> <mainClass>foo</mainClass>
> <collectSections>true</collectSections>
> </transformer>
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
> <resource>META-INF/spring.schemas</resource>
> </transformer>
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"
> />
> <transformer
> implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer"
> />
> </transformers>
> </configuration>
> </plugin>
> {code}
> It is possible to escape this by adding {{combine.self="override"}} to the
> {{<transformers>}} node. But I think the configuration ending up on the
> wrong transformer is a bug, and the fact that it causes duplicate
> configuration sections is also extremely confusing. And somewhere in the
> shuffle the original {{CollectingManifestResourceTransformer}} is lost
> entirely. (Note that it's not even on the plugin path, so referencing it
> should be an error!)
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