The problematic behaviour affects only the mapping to IDEA or Eclipse. When Gradle builds stuff, it works fine.

Given:

dependencies

Then:

When x <= y, the mapping to the IDE is fine (version y is selected and included once)

When x > y, the mapping to the IDE includes both versions in the project's classpath. The classpath for consuming projects is fine.

Keep in mind that these conflicts might be dragged in transitively.

As a point of reference, let's take a look at how the mapping behaves with conflicts in other places:

Given:

dependencies

Then:

When x >= y, the mapping is fine.

When x < y, the mapping to the IDE includes both versions in the project's classpath. The classpath for consuming projects is fine.

You can replace (compile, runtime) with a bunch of other combinations, such as (compile, testCompile) or (compile, testRuntime) or (testCompile, testRuntime).

This behaviour has been there since time began (more or less).

The symptoms that we're seeing here are from the same cause, namely that we merge dependency graphs into IDE classpath buckets using the identity of the resolved files, rather than the identity of the library.