IDE hook crashes Maven 4

Start in plugin-maven/src/main/java/com/diffplug/spotless/maven/IdeHook.java at the referenced lines, then reproduce with Maven 4 using the mvn spotless:apply command and the supplied minimal mojo that closes stdout and stderr. Determine whether the IDE hook still needs those streams closed; done means the Maven 4 invocation completes without the cleanup crash while the IDE hook continues to work.

I am looking at developing a VSCode plugin for Spotless that works with Maven. For performance reasons I want to use mvnd which is a daemon-based version of Maven, and which is based on Maven 4.x.

I have found that on Maven 4, if I invoke:

$ mvn spotless:apply -DspotlessIdeHook=/home/jay/Projects/vscode-spotless-maven/test-project/src/main/java/com/mycompany/app/App.java

then it executes successfully but crashes Maven while cleaning up:

[INFO] Scanning for projects...
[INFO] 
[INFO] -----------------------------------------------< com.mycompany.app:my-app >-----------------------------------------------
[INFO] Building my-app 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] ---------------------------------------------------------[ jar ]----------------------------------------------------------
[INFO] 
[INFO] --- spotless:2.46.1:apply (default-cli) @ my-app ---
[WARNING] [stderr] IS CLEAN
[INFO] --------------------------------------------------------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] --------------------------------------------------------------------------------------------------------------------------
[INFO] Total time:  0.802 s
[INFO] Finished at: 2025-08-02T16:33:13+01:00
[INFO] --------------------------------------------------------------------------------------------------------------------------
[ERROR] Unable to close context
org.apache.maven.api.cli.InvokerException: Unable to close context
        at org.apache.maven.cling.invoker.LookupContext.close(LookupContext.java:128)
        at org.apache.maven.cling.invoker.LookupInvoker.invoke(LookupInvoker.java:143)
        at org.apache.maven.cling.ClingSupport.run(ClingSupport.java:76)
        at org.apache.maven.cling.MavenCling.main(MavenCling.java:51)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
        at java.base/java.lang.reflect.Method.invoke(Method.java:565)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:255)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:201)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:361)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:314)
        Suppressed: java.lang.NullPointerException: Cannot invoke "org.apache.maven.logging.LoggingOutputStream.forceFlush()" because "this.out" is null
                at org.apache.maven.logging.LoggingOutputStream$LoggingPrintStream.forceFlush(LoggingOutputStream.java:88)
                at org.apache.maven.logging.LoggingOutputStream.forceFlush(LoggingOutputStream.java:94)
                at org.apache.maven.cling.invoker.LookupInvoker.lambda$doConfigureWithTerminalWithRawStreamsDisabled$3(LookupInvoker.java:378)
                at org.apache.maven.cling.invoker.LookupContext.close(LookupContext.java:118)
                ... 9 more
        Suppressed: java.lang.NullPointerException: Cannot invoke "org.apache.maven.logging.LoggingOutputStream.forceFlush()" because "this.out" is null
                at org.apache.maven.logging.LoggingOutputStream$LoggingPrintStream.forceFlush(LoggingOutputStream.java:88)
                at org.apache.maven.logging.LoggingOutputStream.forceFlush(LoggingOutputStream.java:94)
                at org.apache.maven.cling.invoker.LookupInvoker.lambda$doConfigureWithTerminalWithRawStreamsDisabled$1(LookupInvoker.java:376)
                at org.apache.maven.cling.invoker.LookupContext.close(LookupContext.java:118)
                ... 9 more

Note that Spotless doesn't crash Maven if you don't use the IDE hook.

I have been able to narrow this down to the following code in the Maven IDE hook:

https://github.com/diffplug/spotless/blob/7d5c826973a900713fe7b23ed20113b0c2c2315e/plugin-maven/src/main/java/com/diffplug/spotless/maven/IdeHook.java#L69-L72

I believe this code is the cause because if I make my own minimal mojo on Maven 4.x which looks like this:

package sample.plugin;
import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugins.annotations.Mojo;

@Mojo(name = "sayhi")
public class GreetingMojo extends AbstractMojo
{
    @Override
    public void execute() throws MojoExecutionException
    {
        getLog().info("Hello, world.");

        System.err.close();
        System.out.close();
    }
}

then I am able to reproduce the same crash with mvn sample.plugin:hello-maven-plugin:1.0-SNAPSHOT:sayhi. If I then comment those two lines of code out, the crash disappears.

I wanted to ask why we need to close stdout/stderr after the IDE hook has finished? It might well be that this is a Maven issue rather than a Spotless issue (it doesn't feel like a plugin should be able to crash the host build system) but if we can do a quick fix here rather than waiting for a change in Maven that would be great.

Issue template

spotless version: 2.46.1
maven version: Apache Maven 4.0.0-rc-4 (bed0f8174bf728978f86fac533aa38a9511f3872)
repro: https://github.com/SapiensAnatis/vscode-spotless-maven/tree/master/test-project (but any Spotless project will work fine if my understanding of the cause is correct)