Non reproducible index serialization

[gnodet]

I was experimenting with switching Apache Camel to use spotless instead of impsort/formatter plugins.
While doing so, and experimenting with the performance cost of running the spotless plugin, I realised the plugin was running again on subsequent builds.
Here's the maven output I end up with in roughly 20 out of 500 modules:

[INFO] --- spotless:2.35.0:apply (default) @ camel-seda ---
[INFO] Index file corresponds to a different configuration of the plugin. Either the plugin version or its configuration has changed. Fallback to an empty index
[INFO] Sorting file /var/folders/27/cvb78knj3xbdvty_5406llg40000gn/T/pom4948897720195268327.xml
[INFO] Pom file is already sorted, exiting
[INFO] Spotless.Pom is keeping 1 files clean - 0 were changed to be clean, 1 were already clean, 0 were skipped because caching determined they were already clean
[INFO] Spotless.Java is keeping 12 files clean - 0 were changed to be clean, 12 were already clean, 0 were skipped because caching determined they were already clean

The configuration obviously does not change, as I run the same maven command multiple times in a raw.

I thus suspect a non-reproductible serialisation issue in the Formatter.

Environment:

Apache Maven 3.9.0 (9b58d2bad23a66be161c4664ef21ce219c2c8584)
Maven home: /Users/gnodet/.sdkman/candidates/maven/3.9.0
Java version: 17.0.6, vendor: GraalVM Community, runtime: /Users/gnodet/.sdkman/candidates/java/22.3.1.r17-grl
Default locale: en_FR, platform encoding: UTF-8
OS name: "mac os x", version: "13.2.1", arch: "aarch64", family: "mac"

Not sure why, but the problem is much more easily reproducible using maven daemon, but it also happens with stock maven 3.9.0 as seen above.

Steps to reproduce:

git clone https://github.com/gnodet/camel.git
cd camel
git checkout build-improvements
mvn install -DskipTests
cd components/camel-seda
for i in $(seq 1 100)
do
    echo -n .
    mvn install -DskipTests | grep "Index file corresponds to a different configuration of the plugin"
done

the last command must be run continuously until the line Index file corresponds to a different configuration of the plugin appears.

[gnodet]

I can't reproduce the problem with maven 3.9.1

➜  camel-seda git:(build-improvements) for i in $(seq 1 100)
do
    echo -n .
    ~/.sdkman/candidates/maven/3.9.1/bin/mvn install -DskipTests | grep "Index file corresponds to a different configuration of the plugin"
done

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[gnodet]

The problem seems to come from the order in which formatters are stored in the list to compute the checksum. I have two formatters and sometime the order is Java, Pom, while in some other cases, I have Pom, Java...

[nedtwigg]

Fixed in plugin-maven 2.36.0, thanks to @gnodet!