[jira] [Commented] (GROOVY-10049) STC fails when calling a generic method from another generic method

["Lyuben Atanasov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GROOVY-10049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17326780#comment-17326780 ] 

Lyuben Atanasov commented on GROOVY-10049:
------------------------------------------

Upon debugging the static type checker, I've found out that the return value of the {{stream()}} method is actually correct. What doesn't work is type inference for the lambda/closure arguments. For some reason the generic type for the SAM parameter is resolved to {{T -> java.lang.Object}} instead of {{T -> java.lang.Number}}.

> STC fails when calling a generic method from another generic method
> -------------------------------------------------------------------
>
>                 Key: GROOVY-10049
>                 URL: https://issues.apache.org/jira/browse/GROOVY-10049
>             Project: Groovy
>          Issue Type: Bug
>          Components: Static Type Checker
>    Affects Versions: 3.0.8, 4.0.0-alpha-3
>         Environment: OpenJDK 8
>            Reporter: Lyuben Atanasov
>            Assignee: Eric Milles
>            Priority: Major
>
> The static type checker fails to properly determine the return type of a generic method when that method is called from another generic method. Here's an example:
> {code}
> class Test {
> 	<T extends Number> Set<T> generateNumbers(Class<T> numberType) {
> 		// mock return value, needed to demonstrate the issue
> 		return Collections.emptySet();
> 	}
> 	<T extends Number> void printNumbers(Class<T> numberType) {
> 		generateNumbers(numberType).stream()
> 			.filter(num -> num.doubleValue() > 0)
> 			.forEach(num -> println "$num");
> 	}
> 	
> }
> {code}
> With static type checking enabled, compilation of this class fails:
> {noformat}
> Script_bbf0c00c9b2872d2a3528c2d80bbaa49.groovy: 10: [Static type checking] - Cannot find matching method java.lang.Object#doubleValue(). Please check if the declared type is correct and if the method exists.
>  @ line 10, column 19.
>    			.filter(num -> num.doubleValue() > 0)
> {noformat}
> If we call the {{generateNumbers()}} method with a specific class, everything works:
> {code}
> class Test {
> 	<T extends Number> Set<T> generateNumbers(Class<T> numberType) {
> 		return Collections.emptySet();
> 	}
> 	void printNumbers() {
> 		generateNumbers(Integer).stream()
> 			.filter(num -> num.doubleValue() > 0)
> 			.forEach(num -> println "$num");
> 	}
> 	
> }
> {code}
> It looks like the static type checker does not properly take into account the generic types of the surrounding method and thus fails to determine the type of the returned value.



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