FileCollection iteration order is not stable accross different operating systems

[martinbonnin]

Current Behavior

Iterating a FileCollection yields different results depending the operating system the build is run on.

Expected Behavior

Iterating a FileCollection should be stable, no matter what the operating system is.

This is especially important for @Classpath inputs where the order matters.

Context (optional)

Gradle community slack thread: https://www.linen.dev/s/gradle-community/t/18849228/is-the-iteration-order-of-a-filecollection-predictable#9f987382-a54f-493a-89c5-3474e22a97dd

Steps to Reproduce

I put a reproducer here. The gist of it is:

val sourceDirectorySet = objects.sourceDirectorySet("graphql", "graphql").apply {
    srcDirs("graphql")
    include("**/*.graphql")
}

val files = mutableListOf<String>()
sourceDirectorySet.asFileTree.visit {
    files.add(this.path)
}

check(
    listOf(/* ... */) == files
) {
    "The order is not the expected one"
}

The GitHub action fail on linux while it succeeds on MacOS (action run)

Gradle version

8.7

Build scan URL (optional)

No response

Your Environment (optional)

No response

[martinbonnin]

Looks like this is working as designed, cf https://docs.gradle.org/current/userguide/declaring_dependencies.html#ex-declaring-multiple-file-dependencies:

The order of the files in a FileTree is not stable, even on a single computer. It means that dependency configuration seeded with such a construct may produce a resolution result which has a different ordering, possibly impacting the cacheability of tasks using the result as an input.

It'd be nice to have different input types/annotations to convey order vs unordered but in all cases, my question is answered, I'll close this issue.