arturobernalg opened a new pull request, #13760:
URL: https://github.com/apache/maven/pull/13760
Maven installs a `LoggingPrintStream` as `System.out`/`System.err`
(`LookupInvoker`) and registers a shutdown closeable that calls
`LoggingOutputStream.forceFlush(ps)` on it. That static helper guards with
`instanceof LoggingPrintStream`, but the instance method it then calls,
`LoggingPrintStream.forceFlush()`, casts its inherited `out` field
unconditionally:
```java
public void forceFlush() {
((LoggingOutputStream) out).forceFlush();
}
```
`PrintStream#close()` sets `out` to null. If anything closes
`System.out`/`System.err` itself before the shutdown hook runs -- for example a
build tool like Spotless's `spotlessIdeHook` -- `forceFlush()` then throws
`NullPointerException: Cannot invoke
"org.apache.maven.logging.LoggingOutputStream.forceFlush()" because "this.out"
is null`. This is what's reported in
https://github.com/apache/maven-mvnd/issues/1271; the bug is in maven-core,
mvnd just surfaces it (one commenter confirms it reproduces on plain Maven
4.0.0-rc-3-SNAPSHOT too).
Fix mirrors the same `instanceof` guard the static helper already uses, so a
closed/non-`LoggingOutputStream` target is a no-op instead of an NPE.
Added `LoggingOutputStreamTest` with a test that reproduces the NPE pre-fix
(closes the stream, then calls `forceFlush()`) and a second test confirming the
normal flush-before-close path still works. Full `maven-core` suite, checkstyle
and spotless pass locally.
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