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https://issues.apache.org/jira/browse/GROOVY-12757?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18142393#comment-18142393
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ASF GitHub Bot commented on GROOVY-12757:
-----------------------------------------
testlens-app[bot] commented on PR #3290:
URL: https://github.com/apache/groovy/pull/3290#issuecomment-6776467527
## ✅ All tests passed ✅
🏷️ Commit: 491ceebe7ff93358c7151667dd1643c2210ffbc1
▶️ Tests: 131375 executed
⚪️ Checks: 26/26 completed
---
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> STC: a lambda result naming a type parameter of the calling method takes the
> receiver's type argument for that name
> -------------------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12757
> URL: https://issues.apache.org/jira/browse/GROOVY-12757
> Project: Groovy
> Issue Type: Bug
> Components: Static Type Checker
> Affects Versions: 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> When a generic method of a generic receiver is called with a lambda whose
> result names a type parameter of the calling method, and the receiver's class
> has a type parameter of the same name, static type checking replaces the
> caller's type parameter with the receiver's type argument:
> {code:groovy}
> import java.util.concurrent.CompletableFuture
> import java.util.function.Function
> @groovy.transform.CompileStatic
> class C {
> static <T> Optional<List<T>> wrap(Optional<String> value, T item) {
> Optional<List<T>> result = value.map((String s) -> [item] as List<T>)
> result
> }
> static <T> CompletableFuture<List<T>>
> each(CompletableFuture<List<Object>> future, Function<Object, T> fn) {
> CompletableFuture<List<T>> result = future.thenApply((List<Object>
> values) -> values.collect { fn.apply(it) } as List<T>)
> result
> }
> }
> {code}
> {noformat}
> [Static type checking] - Incompatible generic argument types. Cannot assign
> java.util.Optional<java.util.List<java.lang.String>> to:
> java.util.Optional<java.util.List<T>>
> [Static type checking] - Incompatible generic argument types. Cannot assign
> java.util.concurrent.CompletableFuture<java.util.List<java.util.List<java.lang.Object>>>
> to: java.util.concurrent.CompletableFuture<java.util.List<T>>
> {noformat}
> {{map}}'s {{U}} is inferred from the lambda as {{List<T>}}, with the calling
> method's {{T}}, and then {{Optional}}'s own {{T}}, here {{String}}, is
> applied to the result. Groovy before GROOVY-12714 inferred the same wrong
> type, but its assignment check accepted it. Renaming the calling method's
> type parameter avoids the problem, and javac accepts the equivalent Java.
> {{StaticTypeCheckingVisitor#inferReturnTypeGenerics}} resolves the method's
> type parameters from the arguments first, and then applies the receiver's
> type arguments to the result. Applying the receiver's type arguments to the
> declared return type first keeps them away from the types the arguments
> supply. {{extractPlaceHoldersVisibleToDeclaration}} already leaves out the
> method's own type parameters (GROOVY-10322), so a method type parameter that
> shadows the class's is unaffected.
> Grails' {{AwaitablePromiseFactory}}, which calls
> {{groovy.concurrent.Awaitable#then}} that way, no longer compiles against
> GROOVY_6_0_X because of this.
> Pull request: https://github.com/apache/groovy/pull/3290
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