[jira] [Created] (GROOVY-8638) CompileStatic fails with Guava Multimap#asMap

["Dan Ziemba (JIRA)" <ji...@apache.org>]

Dan Ziemba created GROOVY-8638:
----------------------------------

             Summary: CompileStatic fails with Guava Multimap#asMap
                 Key: GROOVY-8638
                 URL: https://issues.apache.org/jira/browse/GROOVY-8638
             Project: Groovy
          Issue Type: Bug
    Affects Versions: 2.5.0
            Reporter: Dan Ziemba


When using CompileStatic and groovy 2.5.0, type checking appears wrong with [Guava's Multimap.asMap |https://google.github.io/guava/releases/25.1-jre/api/docs/com/google/common/collect/ListMultimap.html#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:
{noformat}
Incompatible generic argument types. Cannot assign java.util.Map <K, V> to: java.util.Map <K, Collection>
{noformat}
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:
{code:java}
@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()
    }
    
}
{code}
And the full error output:
{noformat}
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
{noformat}



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