What does it mean for a gradle property to be "experimental and unsupported"?

Question

Several times, to solve an issue or update dependencies, I had to enable a given gradle option setting.

• For example, Robolectric 4.0 Migration guide states:

  Put this in your gradle.properties:

  android.enableUnitTestBinaryResources=true

• Likewise, to debug a databinding compile error I followed the advice printed in Gradle's build log:

  Gradle may disable incremental compilation [...].
  Consider setting the experimental feature flag android.enableSeparateAnnotationProcessing=true in the gradle.properties file to run annotation processing in a separate task and make compilation incremental.

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From both examples, I get that the authors (Robolectric/gradle maintainers) are confident that enabling this option will have a positive impact on each situation.
However, in both cases I get this warning in my build output:

WARNING: The option setting 'android.enableUnitTestBinaryResources=true' is experimental and unsupported. The current default is 'false'.

WARNING: The option setting 'android.enableSeparateAnnotationProcessing=true' is experimental and unsupported. The current default is 'false'.

I had in my gradle.properties since a few months the flag android.databinding.enableV2=true. To see how it's handled, I tried to put it to false, which brought the same The option setting 'android.databinding.enableV2=false' is experimental and unsupported. warning (which seems to suggest an unsupported setting is ignored).

• I understand these are experimental feature flags. But what about unsupported? Does this mean I should not expect support if anything goes wrong, or does it mean they will be ignored?

• If it means they are ignored, how are those properties meant to be used?

Answer 1

This is the default warning for new, experimental AGP features. This generally means, in case you'd file a bug against them, it may or may not be considered. It also means, that they may eventually be retracted at any given time (or future version); it is nothing to rely on. For example, it may as well warn that such a feature switch is not supported anymore and that it has no effect.