Redundant.class is still in the build/classes directory, even though its source is gone.

Remove $projectDir/.gradle (simulating a version upgrade).

Create Main.java and Redundant.java with some trivial code in them.

Having an index like that would have an performance impact. given a file, has this file been produced by another Gradle task. Or we could create an index which could answer this kind of question - i.e. We can do this in an ad-hoc way - so whenever we have no history we search the task history for tasks producing files in the output directory and delete all the other files. In order to do that, we need to find out (via the task history), which files have been produced by other tasks in that directory. With overlapping output directories we need to delete everything in the output which has not been produced by another task ran by the same Gradle version. This would be fine as long as we do not have overlapping output directories (if we ignore things like have / as an output directory). Regarding 2) What should we do when we have no history for a task? What we want to do is to delete all the files in the output directories/files of the task. We have no history for a task exactly when we run the task for the first time with this version of Gradle (and nobody deleted.

Regarding 1) When we do the Gradle upgrade this means that we have no history for a task. Users are sometimes forced to run clean after upgrading Gradle or moving files around. Output files from incremental tasks are not invalidated upon certain changes to inputs. Gradle should detect that outputs from incremental tasks are invalid due to at least Gradle version and inputs changes.

When one changes Gradle versions or moves packages, output files from incremental tasks are not cleaned up, causing some tasks to be incorrectly considered UP-TO-DATE.

Android studio gradle output