desruisseaux opened a new pull request, #998:
URL: https://github.com/apache/maven-compiler-plugin/pull/998
When building a project which is both multi-module and multi-release as
described in #959, the output directory which is currently named
`META-INF/versions` should use another name, for example
`META-INF/versions-modular`. Therefore, the full pattern of the path to the
class files become `META-INF/versions-modular/${release}/${module}`.
**This change has no impact on classical Maven projects.** Projects that do
not use multi-module will continue to have their multi-release class files
written in the `META-INF/versions/` directory.
# Rational
The `${module}` subdirectory in above-cited path is inserted by `javac` when
module hierarchy is used. We have no control on that. However, there is no
multi-module JAR file format as of November 2025. Therefore, dispatching the
files for different modules in each JAR file would be the work of the Maven JAR
plugin. A prototype is almost ready
(https://github.com/apache/maven-jar-plugin/issues/495), but experience with
that prototype shows that it is difficult to guess whether the
`META-INF/versions/${release}` directory is expected to be followed by a
`${module}` subdirectory. Renaming `versions` to anything else would avoid that
ambiguity. We propose `versions-modular` as a short way to mean "versions for a
modular project". The directory name is not very important because this
directory will not appear in any JAR or any other file to be distributed. Only
its *content* is dispatched in JAR files.
**Note:** the need to modify the Maven JAR plugin for dispatching the
content of `META-INF/versions-modular` is not really a complication, because we
should do that anyway even with classical Maven projects. As said in
https://github.com/apache/maven-jar-plugin/issues/484, We should use the
`--release` option instead of just including blindly whatever is below the
`META-INF/versions` directory.
# Compatibility
Strictly speaking, this is a breaking change. However, since output of
multi-module & multi-release projects can be processed only by the Maven JAR
plugin prototype, we assume that there is no dependency to the current
directory name yet.
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