Eclipse 2026-03: problem in resolving overridden method from interfaces

[notoriux]

Version: 2026-03 M1 (4.39.0 M1)
Build id: 20260108-0821

The attached POC cannot be compiled because of a Type Mismatch on line 27 of MainClass;

Type mismatch: cannot convert from Streamable to Box

But it's correct, in fact it compiles and runs under Eclipse 2025-09 (20250905-1456) and standalone Maven (3.9.11).

(part of the sources are copied from Spring Data 3.4.11 in order to minimize dependencies)

eclipsebugpoc.zip

[iloveeclipse]

May I ask you to resolve all dependencies, create Eclipse project & attach the self contained project here? It would simplify reproduction on our side.

[srikanth-sankaran]

I think this is very likely connected to the recently reopened issue #1600 - watch this space.

[notoriux]

May I ask you to resolve all dependencies, create Eclipse project & attach the self contained project here? It would simplify reproduction on our side.

The project itself doesn't have any other dependencies other than JDK itself. I've attached a basic Eclipse Java project showing the same behaviour.

Thank you for your time.

eclipsebugstandalone.zip

[srikanth-sankaran]

@stephan-herrmann - I am assigning this to you under the gut feel assumption that this is the same as what we encountered in #1600 - If my guess is wildly off, please feel free to reassign to me. Thanks.

[stephan-herrmann]

Version: 2026-03 M1 (4.39.0 M1)
Build id: 20260108-0821

I was about to close, because I don't see the error with 4.49.0 M1 (20260103-1800) nor with 20260108-0821.

Only then I noticed that this indeed a regression caused by #4727 which appeared only in I20260110-1800

[stephan-herrmann]

Problem can be fixed by either of

• Revert "Problem with calling super in overridden default method (#4727)" #4775
• Problem with calling super in overridden default method #4776

[srikanth-sankaran]

• Revert "Problem with calling super in overridden default method (Problem with calling super in overridden default method #4727)" Revert "Problem with calling super in overridden default method (#4727)" #4775

I suggest we do this for 4.38 M2 and take a fresh look at this for M3. I am happy to collaborate on this task

[srikanth-sankaran]

The project itself doesn't have any other dependencies other than JDK itself. I've attached a basic Eclipse Java project showing the same behaviour.

Thank you for your time.

eclipsebugstandalone.zip

Thanks! I have captured this as a regression test in #4775 and the code compiles again