[GROOVY-8000] Problem With Trait Generics

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.7
• Fix Version/s: 4.0.0-alpha-1, 3.0.6
• Assignee: Eric Milles
• Reporter: Jeff Scott Brown
• Created: 16/Nov/16 15:14
• Updated: 11/Nov/20 02:01
• Resolved: 12/Sep/20 22:45

Description

The project at https://github.com/jeffbrown/generictraits contains the following:

src/main/groovy/demo/TopTrait.groovy

package demo

trait TopTrait<T> {
    T getSomething() {}
}

src/main/groovy/demo/MiddleTrait.groovy

package demo

trait MiddleTrait<T> implements TopTrait<T> {}

src/main/groovy/demo/BottomTrait.groovy

package demo

trait BottomTrait<T> implements MiddleTrait<T> {}

src/main/groovy/demo/Demo.groovy

package demo

// if this class implements MiddleTrait instead
// of BottomTrait, it will compile...
class Demo implements BottomTrait<String> {}

 $ ./gradlew clean cG
:clean
:compileJava UP-TO-DATE
:compileGroovy
startup failed:
/Users/jeff/t/generictraits/src/main/groovy/demo/Demo.groovy: -1: The return type of java.lang.Object getSomething() in demo.Demo is incompatible with java.lang.String in demo.TopTrait
. At [-1:-1]  @ line -1, column -1.
1 error

:compileGroovy FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileGroovy'.
> Compilation failed; see the compiler error output for details.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 2.123 secs