Configuration Cache Miss due to idea.io.use.nio2 system property change

[cdsap]

Current Behavior

Given a Gradle project where one of the components (incorrectly) calls System.getProperties(), if we populate the configuration cache with a simple help, the subsequent build cannot reuse the cache entry because:

Calculating task graph as configuration cache cannot be reused because system property 'idea.io.use.nio2' has changed.

The third build hits the configuration cache correctly.

Initially, we thought this issue might be related to working in local environments when switching between the IDE and command-line. However, we were able to reproduce this issue in CI ephemeral agents where the build is only executed through the command line.

Upon checking the Kotlin GitHub repository, we observed that the property is set here: Kotlin GitHub Link. This function has various references in the repository, as seen here: Search Results for setIdeaIoUseFallback in Kotlin.

Additionally, we noticed that this function is called within Gradle code: Search Results for setIdeaIoUseFallback in Gradle.

It’s unclear if this is happening during the compilation of the Kotlin scripts.

Expected Behavior

The second build hits the configuration cache

Context (optional)

No response

Steps to Reproduce

1. Download https://github.com/cdsap/IdeaIoUseNio2Issue
2. Stop gradle daemon/kill gradle processes
3. Execute ./gradlew :help --configuration-cache
4. Execute again ./gradlew :help --configuration-cache

Gradle version

8.9

Build scan URL (optional)

https://ge.solutions-team.gradle.com/s/at7gzw5arneok/console-log?page=1#L0

Your Environment (optional)

No response

[mlopatkin]

The issue is in the backlog of the relevant team and is prioritized by them.

---

This probably happens because Gradle modifies the property in a way that bypasses CC sysprop change detection.