[GROOVY-10807] STC seems to lose type information through method references

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.12, 3.0.13, 4.0.6
• Fix Version/s: 3.0.14, 4.0.7
• Component/s: Static compilation
• Assignee: Eric Milles
• Reporter: Sterling Greene
• Created: 01/Nov/22 22:49
• Updated: 10/Feb/23 21:40
• Resolved: 04/Nov/22 18:33

Description

This compiles in Groovy 3.0.11, but it does not compile in Groovy 3.0.12 or 3.0.13.

import groovy.transform.CompileStatic

@CompileStatic
abstract class NoticeRenderer {
    private static final Comparator<String> COMPARATOR = Comparator<String>.comparing(NoticeRenderer::getComponentDisplayName)
   
    public static String getComponentDisplayName(String component) {
        return component;
    }
} 

The error is

Failed to find the expected method[getComponentDisplayName(java.lang.Object)] in the type[NoticeRenderer] at line: 5, column: 79

I think something is going sideways when inferring the types to comparing.

Removing the type bound on the Comparator doesn't change the error.

private static final Comparator<String> COMPARATOR = Comparator.comparing(NoticeRenderer::getComponentDisplayName)

The type bound could be on the method itself. This produces the same error.

private static final Comparator<String> COMPARATOR = Comparator.<String>comparing(NoticeRenderer::getComponentDisplayName)

But comparing actually has two type parameters, so it's a little weird that the above doesn't complain. Specifying both type parameters still produces the same error.

private static final Comparator<String> COMPARATOR = Comparator.<String, String>comparing(NoticeRenderer::getComponentDisplayName)

If I mistakenly put the type bounds on Comparator, I don't expect this to work, but it produces BUG! output:
private static final Comparator<String> COMPARATOR = Comparator<String, String>.comparing(NoticeRenderer::getComponentDisplayName)

BUG! exception in phase 'instruction selection' in source unit 'ConsoleScript34' Expected earlier checking to detect generics parameter arity mismatch

Expected: java.util.Comparator<T>

Supplied: java.util.Comparator<java.lang.String,java.lang.String>

In Java, you don't need the type information at all:

private static final Comparator<String> COMPARATOR = Comparator.comparing(NoticeRenderer::getComponentDisplayName);

If you wanted to be verbose in Java, you could specify the bounds:

private static final Comparator<String> COMPARATOR = Comparator.<String, String>comparing(NoticeRenderer::getComponentDisplayName);

As a workaround...
If I avoid the use of the method reference, I can make something pass the static compiler:

private static final Comparator<String> COMPARATOR = Comparator.<String>comparing( { String it -> getComponentDisplayName(it) })

I need both the type bound on comparing and the type of the parameter.