I encountered this confusing issue when working on a larger project, so I’ve created a simple reproduction project to better reproduce and explain my issue. I’m not sure if it is possible for me to upload a zip with the whole structure, but it is only 5 files: https://paste.gg/p/anonymous/f502a8e613a64aeeae671b4c41587c43.

I have a parent module MavenTest with 3 submodules: A, B, and C.

A only contains the class org.example.maventest.A.

B shades A like so:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>3.6.0</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <relocations>
                            <relocation>
                                <pattern>org.example.maventest</pattern>
                                <shadedPattern>org.example.maventest.a</shadedPattern>
                            </relocation>
                        </relocations>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

This relocates the org.example.maventest.A class to org.example.maventest.a.A.

C shades B like so:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>3.6.0</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

This should simply shade in the relocated org.example.maventest.a.A class from module B into C’s jar.

Expected behavior: running mvn clean install to build all the modules should create a jar C that only includes the relocated org.example.maventest.a.A file.

Actual behavior: When the shade plugin runs for module C, it reports this:

[INFO] --- shade:3.6.0:shade (default) @ C ---
[INFO] Including org.example:B:jar:1.0-SNAPSHOT in the shaded jar.
[INFO] Including org.example:A:jar:1.0-SNAPSHOT in the shaded jar.
[INFO] Dependency-reduced POM written at: /MavenTest/C/dependency-reduced-pom.xml

Module A seems to incorrectly be included in C’s jar, which causes the original A class to be shaded in as well (using IntelliJ to look inside the jar):

The strange part (and the specific title of this question), is that if I only build module C using mvn clean install -pl :C, maven correctly only includes the relocated class A:

[INFO] --- shade:3.6.0:shade (default) @ C ---
[INFO] Including org.example:B:jar:1.0-SNAPSHOT in the shaded jar.
[INFO] Dependency-reduced POM written at: /MavenTest/C/dependency-reduced-pom.xml

This suggests to me that is possible to only include the relocated class A from module B in C, but I can’t imagine why the shade plugin would be including different classes when I run a full build vs a single module build.

I think I need to change the configuration of my project in some way so that when I run a full build with mvn clean install, the C jar only includes org.example.maventest.a.A. When C shades B, it should not try to include module A, since B contains those module A classes already.

This also seems to affect compilation. For example, if I add this class to module C:

public class C {
    org.example.maventest.A first = null;
    org.example.maventest.a.A second = null;
}

When I run the full build (or look at it statically with IntelliJ), this code compiles.

However, when I build module C independently, this code fails because the org.example.maventest.A class cannot be found. I want the behavior of the independent build, where module A is seemingly excluded from the compile classpath.