Java Lambda Expression Method Resolution

We have two build environments for release to production  - one we build and regularly test; other is maintained by the global build team that generates certified binaries for release.

We got a compilation issue in the environment maintained by the global team. The compilation is fine in our environments and release environment it fails. We looked at all tagging etc...no problem. Finally it came down to compiler version. We used javac -> 1.8.0_66-b17 and release environment uses  javac -> 1.8.0_05. The upgrade fixed the issue.

But, what did we code that has caught a bug in this range? Here it is.

Following are two overloaded methods that execute the given function in the context of a tenant.

public static R executeForTenant(String tenantId, Function function)

public static void executeForTenant(String tenantId, Consumer consumer)

public void loadPreferenceInto(String tenant, Configuration configuration)

The usage is as follows..

executeForTenant(tenant, (t) -> loadPreferenceInto(t, configuration));

This is ambiguous, compiler cannot determine which one to pick. The void-ness is also compatible with Function generic type R since the statement body is an expression.

So we changed the invocation to

executeForTenant(tenant, (t) -> { loadPreferenceInto(t, configuration); });

This {} ensures the statement body is not an expression. So it should pick Consumer parameter based  executeForTenant method.

The change worked in our environment but failed in release; obviously the bug was fixed in between the builds - 1.8.0_20 to be precise.

Here are the bugs:
http://bugs.java.com/bugdatabase/view_bug.do?bug_id=8043734
http://bugs.java.com/bugdatabase/view_bug.do?bug_id=8029718

Compiler commit that fixes the bug

http://hg.openjdk.java.net/jdk8u/jdk8u-dev/langtools/rev/acd64168cf8b

Lambda expression resolution (from above link)

A lambda expression (15.27) is potentially compatible with a functional interface type (9.8) if all of the following are true:
- The arity of the targeted type's function type is the same as the arity of the lambda expression.
- If the targeted type's function type has a void return, then the lambda body is either a statement expression (14.8) or a void-compatible block (15.27.2).
- If the targeted type's function type has a (non-void) return type, then the lambda body is either an expression or a value-compatible block (15.27.2).

Interesting ride, it has been for last 2 days....