[GROOVY-9891] Wrongly detected incompatible generic arguments for Java collections

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.7, 4.0.0-alpha-2
• Fix Version/s: 3.0.8, 4.0.0-alpha-3, 2.5.18
• Component/s: Static compilation, Static Type Checker
• Assignee: Eric Milles
• Reporter: Arthur Sengileyev
• Created: 10/Jan/21 20:18
• Updated: 18/Jul/22 18:25
• Resolved: 02/Mar/21 15:02

Description

When static type checks are enabled, then groovyc sometimes fails to assign compatible (with the same generic type selected) java Collection to java Iterable.

This code fails to compile with groovyc (tested with 3.0.7 and 4.0.0-alpha-2)

@Grab(group='org.apache.kafka', module='kafka-clients', version='2.7.0')
@Grab(group='org.apache.kafka', module='kafka-streams', version='2.7.0')

import org.apache.kafka.streams.KafkaStreams
import org.apache.kafka.common.MetricName
import org.apache.kafka.common.Metric

import java.lang.Iterable
import java.util.Collections
import java.util.Map

import groovy.transform.CompileStatic

@CompileStatic
class TestStaticChecks {
  KafkaStreams streams

  void method1() {
    Map<MetricName, ? extends Metric> metricsMap = Collections.emptyMap()
    Iterable<? extends Metric> metrics = metricsMap.values()
  }

  void method2() {
    Map<MetricName, ? extends Metric> metricsMap = streams.metrics()
    Iterable<? extends Metric> metrics = metricsMap.values()
  }

  void method3() {
    Iterable<? extends Metric> metrics = streams.metrics().values()
  }
}

method2 and method3 will fail to compile with error

[Static type checking] - Incompatible generic argument types. Cannot assign java.util.Collection <? extends org.apache.kafka.common.Metric> to: java.lang.Iterable <? extends org.apache.kafka.common.Metric>

 

Same code reworked to Java compiles just fine with javac (when dependencies are in classapath)

import org.apache.kafka.streams.KafkaStreams;
import org.apache.kafka.common.MetricName;
import org.apache.kafka.common.Metric;

import java.lang.Iterable;
import java.util.Collections;
import java.util.Map;

class TestStaticChecks {
  KafkaStreams streams;

  void method1() {
    Map<MetricName, ? extends Metric> metricsMap = Collections.emptyMap();
    Iterable<? extends Metric> metrics = metricsMap.values();
  }

  void method2() {
    Map<MetricName, ? extends Metric> metricsMap = streams.metrics();
    Iterable<? extends Metric> metrics = metricsMap.values();
  }

  void method3() {
    Iterable<? extends Metric> metrics = streams.metrics().values();
  }
}