[jira] [Created] (GROOVY-10765) STC: Closure implementation of Java @FunctionalInterface loses type information

[Kyle Moore (Jira)]

Kyle Moore created GROOVY-10765:
-----------------------------------

             Summary: STC: Closure implementation of Java @FunctionalInterface 
loses type information 
                 Key: GROOVY-10765
                 URL: https://issues.apache.org/jira/browse/GROOVY-10765
             Project: Groovy
          Issue Type: Bug
          Components: Static compilation, Static Type Checker
    Affects Versions: 4.0.5
            Reporter: Kyle Moore


The following fails to compile with Groovy 4.0.5:
{code:groovy}
import java.util.function.BiFunction

@groovy.transform.CompileStatic
class MapTransformEntries {
    private static <K, V1, V2> Map<K, V2> transformEntries(Map<K, V1> map, 
BiFunction<? super K, ? super V1, V2> transformer) {
        throw new UnsupportedOperationException("implementation not relevant");
    }

    {
        Map<String, ? extends File> outputFiles
        Map<String, Integer> outputFileSpecs = transformEntries(outputFiles, { 
key, value -> value.hashCode() }) 
    }
}
{code}

Producing result:
{noformat}
1 compilation error:

[Static type checking] - Incompatible generic argument types. Cannot assign 
java.util.Map<? extends java.lang.Object, java.lang.Integer> to: 
java.util.Map<java.lang.String, java.lang.Integer>
 at line: 11, column: 48
{noformat}

At first glance, this seems similar to GROOVY-10613 and some of its related 
issues.

We can workaround by casting the above to {{Map<String, Integer>}}, but this 
was not necessary in Groovy 3.x.

Thanks to [~otogami] for creating the reproducer



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