@Nullable
public static PsiType getExpectedClosureReturnType(GrClosableBlock closure) {
final Set<PsiType> expectedTypes = getDefaultExpectedTypes(closure);
List<PsiType> expectedReturnTypes = new ArrayList<PsiType>();
for (PsiType expectedType : expectedTypes) {
if (!(expectedType instanceof PsiClassType)) return null;
final PsiClassType.ClassResolveResult resolveResult =
((PsiClassType) expectedType).resolveGenerics();
final PsiClass resolved = resolveResult.getElement();
if (resolved == null
|| !(GroovyCommonClassNames.GROOVY_LANG_CLOSURE.equals(resolved.getQualifiedName())))
return null;
final PsiTypeParameter[] typeParameters = resolved.getTypeParameters();
if (typeParameters.length != 1) return null;
final PsiTypeParameter expected = typeParameters[0];
final PsiType expectedReturnType = resolveResult.getSubstitutor().substitute(expected);
if (expectedReturnType == PsiType.VOID || expectedReturnType == null) return null;
expectedReturnTypes.add(expectedReturnType);
}
return TypesUtil.getLeastUpperBoundNullable(expectedReturnTypes, closure.getManager());
}
