AssignmentContext.java

import org.checkerframework.checker.nullness.qual.*;

interface FunctionAC {
    String apply(String s);
}

interface FunctionAC2 {
    String apply(@Nullable String s);
}

class AssignmentContext {
    // Test assign
    FunctionAC f1 = String::toString;
    //:: error: (methodref.receiver.invalid)
    FunctionAC2 f2 = String::toString;

    // Test casts
    Object o1 = (Object) (FunctionAC) String::toString;
    //:: error: (methodref.receiver.invalid)
    Object o2 = (Object) (FunctionAC2) String::toString;

    void take(FunctionAC f) {
        // Test argument assingment
        take(String::toString);
    }

    void take2(FunctionAC2 f) {
        // Test argument assingment
        //:: error: (methodref.receiver.invalid)
        take2(String::toString);
    }

    FunctionAC supply() {
        // Test return assingment
        return String::toString;
    }

    FunctionAC2 supply2() {
        // Test return assingment
        //:: error: (methodref.receiver.invalid)
        return String::toString;
    }
}