[jira] [Created] (GROOVY-10067) STC: Wrong return value type inferred for generic method with upper bound without parameters

["Lyuben Atanasov (Jira)" <ji...@apache.org>]

Lyuben Atanasov created GROOVY-10067:
----------------------------------------

             Summary: STC: Wrong return value type inferred for generic method with upper bound without parameters
                 Key: GROOVY-10067
                 URL: https://issues.apache.org/jira/browse/GROOVY-10067
             Project: Groovy
          Issue Type: Bug
          Components: Static Type Checker
    Affects Versions: 4.0.0-alpha-3, 3.0.8
         Environment: OpenJDK8
            Reporter: Lyuben Atanasov


When static compilation is enabled, and we have a method call for a generic method that returns a generic value with an upper bound, and the method does not have any parameters, the inferred return type is the upper bound instead of the type of the variable to which that value is assigned. To better illustrate the issue, here's an example of what doesn't work and some work-arounds:
{code}
class Test {

	<T extends Number> T getValue() {
		return null;
	}
	
	void methodWithIntParam(Integer param) {
		// do nothing
	}
	
	void test() {
		// not working
		Integer int1 = getValue();
		methodWithIntParam(getValue());
		
		// working
		Integer int2 = this.<Integer>getValue();
		Integer int3 = (Integer) getValue();
		methodWithIntParam(this.<Integer>getValue());
		methodWithIntParam((Integer) getValue());
	}
}
{code}
Compiling this code with static type checking enabled causes the following errors:
{noformat}
Script_e94ec281a61eb83bce1a38580b498a48.groovy: 13: [Static type checking] - Cannot assign value of type java.lang.Number to variable of type java.lang.Integer
 @ line 13, column 18.
   		Integer int1 = getValue();

Script_e94ec281a61eb83bce1a38580b498a48.groovy: 14: [Static type checking] - Cannot find matching method Test#methodWithIntParam(java.lang.Number). Please check if the declared type is correct and if the method exists.
 @ line 14, column 3.
   		methodWithIntParam(getValue());
{noformat}

Note that if we just a define a generic method without any upper bounds to the generic value, type checking works as expected:
{code}
<T> T getNumber() {
    return null;
}

Integer myInt = getNumber(); // this works!
{code}



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