/**
* Determines what constraint (supertype, subtype or equal) should be generated for type parameter
* {@code T} in a constraint like (in this example subtype one): <br>
* {@code MyClass<in/out/- A> <: MyClass<in/out/- B>}, where {@code MyClass<in/out/- T>} is
* declared. <br>
* The parameters description is given according to the example above.
*
* @param typeParameterVariance declared variance of T
* @param subjectTypeProjection {@code in/out/- A}
* @param constrainingTypeProjection {@code in/out/- B}
* @param upperConstraintKind kind of the constraint {@code MyClass<...A> <: MyClass<...B>}
* (subtype in this example).
* @return kind of constraint to be generated: {@code A <: B} (subtype), {@code A >: B}
* (supertype) or {@code A = B} (equal).
*/
@NotNull
private static ConstraintKind getTypeParameterConstraintKind(
@NotNull Variance typeParameterVariance,
@NotNull TypeProjection subjectTypeProjection,
@NotNull TypeProjection constrainingTypeProjection,
@NotNull ConstraintKind upperConstraintKind) {
// If variance of type parameter is non-trivial, it should be taken into consideration to infer
// result constraint type.
// Otherwise when type parameter declared as INVARIANT, there might be non-trivial use-site
// variance of a supertype.
//
// Example: Let class MyClass<T> is declared.
//
// If super type has 'out' projection:
// MyClass<A> <: MyClass<out B>,
// then constraint A <: B can be generated.
//
// If super type has 'in' projection:
// MyClass<A> <: MyClass<in B>,
// then constraint A >: B can be generated.
//
// Otherwise constraint A = B should be generated.
Variance varianceForTypeParameter;
if (typeParameterVariance != INVARIANT) {
varianceForTypeParameter = typeParameterVariance;
} else if (upperConstraintKind == SUPER_TYPE) {
varianceForTypeParameter = constrainingTypeProjection.getProjectionKind();
} else if (upperConstraintKind == SUB_TYPE) {
varianceForTypeParameter = subjectTypeProjection.getProjectionKind();
} else {
varianceForTypeParameter = INVARIANT;
}
return getTypeParameterConstraintKind(varianceForTypeParameter, upperConstraintKind);
}
