Jake Wharton recounts a debugging story where Jetpack Compose tests failed on macOS and Windows CI workers due to case-insensitive filesystems. Two nested local functions inside the same test method — `Item` and `item` — generated class files that differed only in casing, causing one to silently overwrite the other on case-insensitive filesystems. The root cause is that the Kotlin compiler generates class names based on local function names without guarding against case-insensitive collisions. The immediate fix was renaming one function (which JetBrains coincidentally applied 12 hours earlier). Wharton argues this is a Kotlin compiler bug and has filed KT-47123, proposing the compiler should automatically mangle names to avoid such collisions. Java is noted to have the same issue.
