/**
* Remember that we are trying to cast something of type {@code supertype} to {@code subtype}.
*
* <p>Since at runtime we can only check the class (type constructor), the rest of the subtype
* should be known statically, from supertype. This method reconstructs all static information
* that can be obtained from supertype.
*
* <p>Example 1: supertype = Collection<String> subtype = List<...> result = List<String>, all
* arguments are inferred
*
* <p>Example 2: supertype = Any subtype = List<...> result = List<*>, some arguments were not
* inferred, replaced with '*'
*/
public static TypeReconstructionResult findStaticallyKnownSubtype(
@NotNull JetType supertype, @NotNull TypeConstructor subtypeConstructor) {
assert !supertype.isNullable() : "This method only makes sense for non-nullable types";
// Assume we are casting an expression of type Collection<Foo> to List<Bar>
// First, let's make List<T>, where T is a type variable
ClassifierDescriptor descriptor = subtypeConstructor.getDeclarationDescriptor();
assert descriptor != null : "Can't create default type for " + subtypeConstructor;
JetType subtypeWithVariables = descriptor.getDefaultType();
// Now, let's find a supertype of List<T> that is a Collection of something,
// in this case it will be Collection<T>
JetType supertypeWithVariables =
TypeCheckingProcedure.findCorrespondingSupertype(subtypeWithVariables, supertype);
final List<TypeParameterDescriptor> variables =
subtypeWithVariables.getConstructor().getParameters();
Map<TypeConstructor, TypeProjection> substitution;
if (supertypeWithVariables != null) {
// Now, let's try to unify Collection<T> and Collection<Foo> solution is a map from T to Foo
TypeUnifier.UnificationResult solution =
TypeUnifier.unify(
new TypeProjectionImpl(supertype),
new TypeProjectionImpl(supertypeWithVariables),
new Predicate<TypeConstructor>() {
@Override
public boolean apply(TypeConstructor typeConstructor) {
ClassifierDescriptor descriptor = typeConstructor.getDeclarationDescriptor();
return descriptor instanceof TypeParameterDescriptor
&& variables.contains(descriptor);
}
});
substitution = Maps.newHashMap(solution.getSubstitution());
} else {
// If there's no corresponding supertype, no variables are determined
// This may be OK, e.g. in case 'Any as List<*>'
substitution = Maps.newHashMapWithExpectedSize(variables.size());
}
// If some of the parameters are not determined by unification, it means that these parameters
// are lost,
// let's put stars instead, so that we can only cast to something like List<*>, e.g. (a: Any) as
// List<*>
boolean allArgumentsInferred = true;
for (TypeParameterDescriptor variable : variables) {
TypeProjection value = substitution.get(variable.getTypeConstructor());
if (value == null) {
substitution.put(
variable.getTypeConstructor(), SubstitutionUtils.makeStarProjection(variable));
allArgumentsInferred = false;
}
}
// At this point we have values for all type parameters of List
// Let's make a type by substituting them: List<T> -> List<Foo>
JetType substituted =
TypeSubstitutor.create(substitution).substitute(subtypeWithVariables, Variance.INVARIANT);
return new TypeReconstructionResult(substituted, allArgumentsInferred);
}