Benjamin Marwell created MCOMPILER-550:
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Summary: Make 'outputDirectory' writeable
Key: MCOMPILER-550
URL: https://issues.apache.org/jira/browse/MCOMPILER-550
Project: Maven Compiler Plugin
Issue Type: Improvement
Reporter: Benjamin Marwell
Assignee: Benjamin Marwell
h2. Description of Improvement
Currently, the property 'outputDirectory' is not writeable, i.e. not meant to
be modified.
However, making it writeable has at least two major advantages.
h2. Use case one -- variable is already used
Some Tutorials (e.g. https://www.baeldung.com/maven-multi-release-jars) already
make use of rewriting the variable.
h2. Use case two: MR-Jars with different bytecode level.
Another use case is Multi-Release-Jars. Currently, they can officially only be
controlled by setting the {{release}} property. That will not only require a
suitable JDK or Toolchain-JDK, it will also require the bytecode for that
version to be the bytecode of that version.
E.g. using {{release}} and {{multiReleaseOutput}}, the bytecode in
{{META-INF/version/java9}} MUST be exactly Java 9 bytecode.
However, the JDK does not know of such restrictions.
Using {{outputDirectory}}, you can now create Java 8 bytecode to run in e.g.
Java 24. Here is an example use case:
https://github.com/groovy/GMavenPlus/pull/287
Granted, this could also be done differently, but this way it seems a little
more elegant.
The actual advantage is, that some developers can now plan ahead. For example,
the SecurityManager is not just deprecated, it is deprecated for removal. The
moment we know which Java version it is, we can create a MR-Jar for e.g. Java
30, even though Java 30 SDKs are not available then (currently we have Java 21
GA).
h2. Proposed solution
Make variable writeable as suggested in Slack.
PR available locally.
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