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https://issues.apache.org/jira/browse/GROOVY-12606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18140526#comment-18140526
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ASF GitHub Bot commented on GROOVY-12606:
-----------------------------------------
codeconsole commented on PR #3133:
URL: https://github.com/apache/groovy/pull/3133#issuecomment-6717051561
@daniellansun Merged current master (492ae79db4) for a fresh run of the
Windows cell. Once #3126 lands, this PR drops its private
`isClosureCoercibleToSAM` for
`StaticTypeCheckingSupport.isClosureCoercibleToSAM`. The land order and a local
check of that end state are on #3113.
> STC rejects a closure or lambda returning a Closure<R> value where a
> functional interface return type is expected
> -----------------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12606
> URL: https://issues.apache.org/jira/browse/GROOVY-12606
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 4.0.33, 5.0.8, 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> {code:groovy}
> import java.util.function.Supplier
> @groovy.transform.CompileStatic // or @TypeChecked
> class C {
> static String take(Supplier<Supplier<String>> s) { s.get().get() }
> static void main(args) {
> Closure<String> c = { 'x' }
> assert take { c } == 'x'
> assert take(() -> c) == 'x'
> }
> }
> {code}
> Actual:
> {noformat}
> [Static type checking] - Cannot return value of type
> groovy.lang.Closure<java.lang.String> for closure expecting
> java.util.function.Supplier<java.lang.String>
> [Static type checking] - Cannot return value of type
> groovy.lang.Closure<java.lang.String> for lambda expecting
> java.util.function.Supplier<java.lang.String>
> {noformat}
> Expected: both calls compile and the returned closure is converted to the
> functional interface, as it is when a Closure value is passed as a Supplier
> argument. A Closure<Integer> should still be rejected.
> The return check for closures and lambdas only accepts subtypes of the
> expected return type and does not consider closure-to-SAM coercion. A
> returned closure literal and a raw Closure are rejected the same way. Under
> static compilation, a lambda also needs its generated method to declare the
> SAM type, so that the returned closure is converted instead of being returned
> as a Closure.
> Seen in 4.0.33, 5.0.8 and 6.0.0.
> PR: https://github.com/apache/groovy/pull/3133
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