[GROOVY-8638] CompileStatic fails with Guava Multimap#asMap

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.5.0, 3.0.5
• Fix Version/s: 4.0.0-beta-1, 3.0.9, 2.5.16
• Component/s: Static Type Checker
• Assignee: Eric Milles
• Reporter: Dan Ziemba
• Created: 07/Jun/18 22:47
• Updated: 30/Apr/23 14:31
• Resolved: 01/Jun/21 16:12

Description

When using CompileStatic and groovy 2.5.0, type checking appears wrong with Guava's Multimap.asMap method.  Return type from that method is Map<K, Collection<V>>, but attempting to assign to a variable of that type results in the error message:

Incompatible generic argument types. Cannot assign java.util.Map <K, V> to: java.util.Map <K, Collection>

This previously worked fine with Groovy 2.4.15. Adding an explicit cast to the asMap() call appears to work around the error.

Here is a small script demonstrating the problem:

@Grab('com.google.guava:guava:25.1-jre')

import com.google.common.collect.ArrayListMultimap
import com.google.common.collect.ListMultimap
import groovy.transform.CompileStatic

@CompileStatic
class Test {

    void test() {
        ListMultimap<String, Integer> mmap = ArrayListMultimap.create()
        // This extra cast fixes all the errors...
        //ListMultimap<String, Integer> mmap = ArrayListMultimap.create() as ListMultimap<String, Integer>
        Map<String, Collection<Integer>> map = mmap.asMap()
        
        Set<Map.Entry<String, Collection<Integer>>> entrySet = map.entrySet()
        Iterator<Map.Entry<String, Collection<Integer>>> iter = entrySet.iterator()
        
        while (iter.hasNext()) {
            Map.Entry<String, Collection<Integer>> group = iter.next()
            Collection<Integer> values = group.value
        }
    }
    
    static void main(String... args) {
        Test test = new Test()
        test.test()
    }
    
}

And the full error output:

5 compilation errors:

[Static type checking] - Incompatible generic argument types. Cannot assign java.util.Map <java.lang.String, java.lang.Integer> to: java.util.Map <String, Collection>
 at line: 14, column: 48

[Static type checking] - Incompatible generic argument types. Cannot assign java.util.Set <java.util.Map$Entry> to: java.util.Set <Map.Entry>
 at line: 16, column: 64

[Static type checking] - Incompatible generic argument types. Cannot assign java.util.Iterator <java.util.Map$Entry> to: java.util.Iterator <Map.Entry>
 at line: 17, column: 65

[Static type checking] - Incompatible generic argument types. Cannot assign java.util.Map$Entry <java.lang.String, java.lang.Integer> to: java.util.Map$Entry <String, Collection>
 at line: 20, column: 60

[Static type checking] - Cannot assign value of type java.lang.Integer to variable of type java.util.Collection <Integer>
 at line: 21, column: 42

Issue Links

• is cloned by: GROOVY-10120 STC: Guava Multimap#asMap bridge method
• relates to: GROOVY-11012 Wrong type is inferred when calling method defined in the parent class
• relates to: GROOVY-11035 Inferred type is Object when having a complex inheritance chain of interfaces