slachiewicz opened a new issue, #608:
URL: https://github.com/apache/maven-apache-parent/issues/608
Since 32 (MPOM-264, #479) the `jdk9+` profile sets `maven.compiler.release`
to `${javaVersion}`, which defaults to 8. maven-compiler-plugin gives `release`
precedence over `source`/`target` (plexus-compiler emits `--release` whenever
the value is non-empty), so a child POM that declares `maven.compiler.source`
and `maven.compiler.target` but no `release`, which is every child written
against a parent before 32, is compiled for Java 8 on JDK 9+ regardless of its
own settings.
Observed on flink-connector-parent moving from `org.apache:apache:20` to 39
with source 11 / target 17:
```
[INFO] Compiling 130 source files with javac [debug release 8] to
target/classes
[ERROR] TransactionOwnership.java:[74,29] method orElseThrow in class
java.util.Optional<T> cannot be applied to given types
```
The compile error is the good outcome. A child whose sources happen to be
Java 8 compatible is silently downgraded to bytecode 52 instead.
Each available workaround has a cost:
- Setting `javaVersion` fixes `release`, but it is a single value. A child
with different source and target levels, or with per-profile targets, cannot
express that through `--release`.
- Blanking `maven.compiler.release` restores `-source`/`-target` for javac,
but maven-javadoc-plugin fails on the empty string (apache/maven-javadoc-plugin
issue linked below).
- Overriding the compiler plugin's `release` parameter in the child works,
but nothing points a user at it.
A POM profile cannot see whether the child set `maven.compiler.source`, so
the profile itself cannot be made conditional. What would help:
1. Call this out in the release notes and on the parent's site: a child that
sets `maven.compiler.source`/`target` must also set `javaVersion` or override
`maven.compiler.release`, or its levels are ignored.
2. Consider having the parent's enforcer execution fail when
`maven.compiler.source` or `maven.compiler.target` differs from `javaVersion`
on JDK 9+, so the mismatch fails loudly instead of downgrading silently.
Context: [FLINK-40630](https://issues.apache.org/jira/browse/FLINK-40630).
*This issue was created with AI assistance.*
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