[GROOVY-10047] STC infers Closure instead of SAM for method references

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.8
• Fix Version/s: 4.0.0-beta-1, 3.0.9
• Component/s: Static Type Checker
• Assignee: Eric Milles
• Reporter: Christopher Smith
• Created: 20/Apr/21 21:31
• Updated: 29/Apr/22 20:45
• Resolved: 22/Apr/21 15:41

Description

I thought I had reported this earlier, but I couldn't find the duplicate.

When using a very basic method reference, the STC is inferring Closure as the type instead of the proper functional interface. Explicitly specify as works, which I think might not have with the :: syntax previously.

In my particular case, I'm wrapping a List<DeleteItemRequest> (from the Amazon SDK 2 DynamoDB client) into a Map<String, List<DeleteItemRequest>> to feed to its batch API. The line is:

def requestItems = batch.stream().collect(toMap(DeleteItemRequest::tableName, List::of))

In contrast to GROOVY-9881, it seems the STC is correctly identifying the signature, at least, but it's inferring Closure where Function is expected:

/home/christopher/path/CleanupHandler.groovy: 50: [Static type checking] - Cannot call <T,K,U> java.util.stream.Collectors#toMap(java.util.function.Function <? super T, ? extends K>, java.util.function.Function <? super T, ? extends U>) with arguments [groovy.lang.Closure <java.lang.String>, groovy.lang.Closure <java.util.List>]

Adding an explicit as Function to each reference fixes the problem (though it is still using getMethodPointer instead of real method references).

Issue Links

• is duplicated by: GROOVY-10613 Fail to infer correct types for fluent method calls