Make ArchUnit JUnit 5 support Java Modules compatible #827
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Since we use the `MANIFEST` entry `Automatic-Module-Name` the JUnit 5 modules are principally ready to be used on the modulepath. However, we automatically expose **all** packages declared, which means that the modules `junit5-api`, `junit5-engine` and `junit5-engine-api` all export the same package `com.tngtech.archunit.junit`, which is illegal for Java Modules. As a first step we move all classes contained in `junit5-engine-api` to a separate package to resolve part of the conflict. Unfortunately, this demands that we make some methods public that did not have to be before. Signed-off-by: Peter Gafert <peter.gafert@tngtech.com>
Since we use the `MANIFEST` entry `Automatic-Module-Name` the JUnit 5 modules are principally ready to be used on the modulepath. However, we automatically expose **all** packages declared, which means that the modules `junit5-api` and `junit5-engine` all export the same package `com.tngtech.archunit.junit`, which is illegal for Java Modules. We move all implementation details to a subpackage `internal` and only keep API toplevel. This way the module `junit5-engine` does not expose the root package `com.tngtech.archunit.junit` anymore, because all the contained classes are `internal`. While this separation works nicely and cleanly for `junit5`, the separation for `junit4` is a lot less pretty. Because the architecture of JUnit 4 makes it impossible to hide implementation details in a clean way, e.g. by demanding to annotate a `Runner` implementation, which should be pure hidden implementation detail. I added some separation by introducing `ArchUnitRunnerInternal` so we do not need to make all classes public, but have one (obviously not mean for outside usage) public gateway into the `internal` part. Signed-off-by: Peter Gafert <peter.gafert@tngtech.com>
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Unfortunately it is not trivial to test that the final artifacts work in a Java modules project. To keep the effort low we just add a test that catches the most probable error: The dependencies change and suddenly two artifacts comprising the JUnit 5 support export the same package. To simplify this even further we can just assume that each JUnit 5 artifact exports exactly one package and by asserting that this is exactly the expected package we effectively prevent collisions. If we use automatic module names we have to assume that artifacts will export all of their packages on the module path. Signed-off-by: Peter Gafert <peter.gafert@tngtech.com>
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So far, even though we added
Automatic-Module-Nameto theMANIFESTto make it compatible with Java Modules, ArchUnit's JUnit 5 support could not be used on the modulepath. The reason is that all three modulesarchunit-junit5-api,archunit-junit5-engineandarchunit-junit5-engine-apiexport the same packagecom.tngtech.archunit.junit.We now fix this by splitting the three modules into separate packages. This is a little tricky since there is also code that is shared with ArchUnit JUnit 4 support and we want to keep as many internals package private as possible. I tried to find a good compromise between backwards compatibility and public surface, the result is
c.t.archunit.junitc.t.archunit.junit.internal(this causes no problem, because engine dependencies were always only transparent runtime dependencies viaServiceLoader, never compile time dependencies)c.t.archunit.junit.engine_api. This is a breaking change, however theengine-apiis a very specific artifact that is only needed for frameworks to integrate with JUnit Platform. So it should only affect a very limited number of users.Unfortunately the JUnit 4 design makes it very hard to cleanly split API and implementation. I.e. by making the
Runnertype public API (having to explicitly declare it as@RunWith(..)) tends to cause a chain reaction pulling more and more into the public scope. In particular if now the classes that are used internally (likeClassCache) don't reside in the same package anymore. I tried to find some compromise by creating an internal delegate that is loaded via Reflection. This way we can keep the things inside ofinternalconceiled with package-private scope. Hopefully this will not cause any problem in the long term.Note that it will still not possible to put both JUnit 4 and JUnit 5 support on the modulepath together, but I also don't see any reason why anybody should want to do this, since they serve exactly the same purpose and JUnit 5 support is just more future proof.
Resolves: #206