[GROOVY-10054] STC: Cannot infer lambda parameter types for a stream collector

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 4.0.0
• Component/s: Static Type Checker
• Assignee: Eric Milles
• Reporter: Lyuben Atanasov
• Created: 23/Apr/21 14:55
• Updated: 25/Apr/23 12:26

Description

This is a follow-up to GROOVY-10049. After the issue there had been fixed I was able to progress further with a chain of Stream method calls. However, the fix doesn't seem to cover the following case:

import java.util.stream.Collectors;

class Test {

	static interface Named {
		String getName();
	}

	<T extends Named> Map<String, List<T>> group(Set<T> namedObjects) {
		return namedObjects.stream()
			.collect(Collectors.groupingBy(named -> named.getName()));
	}
	
}

With static type checking enabled, an error is produced:

Script_ce61a645759c941d687680111f9bedbd.groovy: 11: [Static type checking] - Cannot find matching method java.lang.Object#getName(). Please check if the declared type is correct and if the method exists.
 @ line 11, column 44.
   ollectors.groupingBy(named -> named.getN

The difference between this issue and GROOVY-10049 is that the lambda passed here is not directly assigned to a Stream method. Of course, the issue is probably not limited to Collectors, but this is how I am able to reproduce it.
I've tested this against https://github.com/apache/groovy/commit/e07f0112c5eff8d9c6828bd0ddb69e4b7f7cc1d6

Issue Links

• is duplicated by: GROOVY-10613 Fail to infer correct types for fluent method calls
• relates to: GROOVY-10544 Static compiler chooses superinterface return type
• relates to: GROOVY-11024 STC NPE when using Collectors.toMap() with a generic result
• relates to: GROOVY-10734 STC doesn't resolve zero-argument method references in nested generics
• relates to: GROOVY-10741 STC method pointer or reference to generated property method
• relates to: GROOVY-10749 STC: closure/lambda/reference parameter as type witness for SAM type generics