Should runtime scoped dependencies be included in main classloader?

[zregvart]

Seems like dependencies scoped as runtime are not included in the main classloader. For example if I addch.qos.logback:logback-classic dependency in runtime scope, org.slf4j:slf4j-api in compile scope will not detect it and will issue a warning about missing org.slf4j.impl.StaticLoggerBinder class.

The only workaround I've found is to run in isolation of MERGED or NONE. I've created an example to help illustrate this. When running with 1.1.2 I get:

$ mvn test
...
[INFO] --- junit-platform-maven-plugin:1.1.2:launch (injected-launch) @ junit-maven-runtime ---
[INFO] Launching JUnit Platform 1.7.2...
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
...

And if I change the isolation to MERGED or NONE I get:

$ mvn test
...
[INFO] --- junit-platform-maven-plugin:1.1.2:launch (injected-launch) @ junit-maven-runtime ---
[INFO] Launching JUnit Platform 1.7.2...
12:42:31.608 [pool-3-thread-1] INFO  io.github.zregvart.Log - Hello from main
12:42:31.616 [pool-3-thread-1] INFO  i.g.zregvart.RuntimeClasspathTest - Hello from test
...

The real issue I'm having with this is that I would like to declare some dependencies in runtime scope so the main code doesn't depend on them at compile time, and have the implementation discovered via service loader mechanism at runtime.

This might be a conscious decision and I'm wondering about the reason behind this?

[sormuras]

Hi Zoran,

The underlying reasoning to have separate class loaders is layed out here: sormuras/junit-platform-isolator#1

As I didn't touch boths projects (isolator and this plugin) for months, I'm not sure this behaviour is a bug or a feature. Will try to examine your example later ... have you tried running with the JAVA executor? Does that trigger the same results?

[zregvart]

Thanks for the reply, running with <executor>JAVA</executor> and <isolation>ABSOLUTE</isolation> seems to add dependencies in runtime scope to the main classloader.

[zregvart]

I had a look at the MavenDriver and I think to get the main classloader to load both compile and runtime dependencies this line:

junit-platform-maven-plugin/src/main/java/de/sormuras/junit/platform/maven/plugin/MavenDriver.java

Line 111 in 9fb4d36

addAll(project.getCompileClasspathElements(), mainPaths);

Should be:

addAll(project.getRuntimeClasspathElements(), mainPaths); 

This will add dependencies in compile and in runtime scope:

https://github.com/apache/maven/blob/ef62d7a4bd57cdd315dfa187780790e3449321aa/maven-core/src/main/java/org/apache/maven/project/MavenProject.java#L418

One strong argument for including the runtime in addition to compile scope is within the Maven documentation:

runtime
This scope indicates that the dependency is not required for compilation, but is for execution. Maven includes a dependency with this scope in the runtime and test classpaths, but not the compile classpath.

From my understanding this is what Surefire does, but I struggle to find documentation on this.

[sormuras]

Sounds reasonable. Will turn this discussion into an issue...