adangel opened a new pull request, #726:
URL: https://github.com/apache/maven-pmd-plugin/pull/726
This change improves the correctness of PMD violations: For type resolution,
PMD loads the classes to see the available type hierarchy, methods, return
types etc. The project's dependencies are already provided to PMD by the plugin
with the aux classpath. But the Java platform classes where still resolved from
the current Java runtime. This can lead for specific cases in either false
positives or false negatives. Examples are: `ExecutorService` is
`AutoCloseable` since Java 19. If maven/PMD is executed with Java 25 but the
target is Java 17, then PMD's CloseResource would wrongly suggest to use
try-with-resources for ExecutorServices. Another example is `ByteBuffer#flip`:
In Java 8, it returns `Buffer` (inherited), in Java 9+ it returns `ByteBuffer`.
In Java 8, one must cast, in Java 9, the cast might be unnecessary, triggering
PMD's UnnecessaryCast rule.
Historically, PMD 6.x loaded the types via reflection from a custom
classloader - so it was not able to load classes from newer runtimes then it
was running at. Hence the solution with the toolchains (MPMD-304 #277). With
PMD 7, the classes are loaded via ASM, which allows to decouple the Java
version used for executing PMD (runtime) from the Java version of the project
under analysis (targetJdk). Since PMD 7, PMD running under Java 8 can analyze
e.g. Java 25 projects. But one crucial step was missing: The Java platform
classes.
To resolve Java platform classes, PMD by default used the current runtime.
With the next PMD version 7.27.0, we'll log a warning, if this happens.
This change prepares for that and tries to add the correct Java platform
classes to the aux classpath for PMD.
Note: This change is independent of the PMD version. Providing the
jrt-fs.jar or rt.jar on the aux classpath was supported since PMD 7.0.0, but
just not used. The only change in PMD 7.27.0 in that regard is, that a warning
is logged, if neither jrt-fs.jar or rt.jar is found on the aux classpath.
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