Function getNarrowedType

test/fixtures/snapshot/typescript.js:71281–71302

(type, candidate, assumeTrue, isRelated)

                return getNarrowedType(type, targetType, assumeTrue, isTypeDerivedFrom);
            }
            function getNarrowedType(type, candidate, assumeTrue, isRelated) {
                if (!assumeTrue) {
                    return filterType(type, function (t) { return !isRelated(t, candidate); });
                }
                // If the current type is a union type, remove all constituents that couldn't be instances of
                // the candidate type. If one or more constituents remain, return a union of those.
                if (type.flags & 1048576 /* TypeFlags.Union */) {
                    var assignableType = filterType(type, function (t) { return isRelated(t, candidate); });
                    if (!(assignableType.flags & 131072 /* TypeFlags.Never */)) {
                        return assignableType;
                    }
                }
                // If the candidate type is a subtype of the target type, narrow to the candidate type.
                // Otherwise, if the target type is assignable to the candidate type, keep the target type.
                // Otherwise, if the candidate type is assignable to the target type, narrow to the candidate
                // type. Otherwise, the types are completely unrelated, so narrow to an intersection of the
                // two types.
                return isTypeSubtypeOf(candidate, type) ? candidate :
                    isTypeAssignableTo(type, candidate) ? type :
                        isTypeAssignableTo(candidate, type) ? candidate :
                            getIntersectionType([type, candidate]);
            }
            function narrowTypeByCallExpression(type, callExpression, assumeTrue) {
                if (hasMatchingArgument(callExpression, reference)) {
                    var signature = assumeTrue || !ts.isCallChain(callExpression) ? getEffectsSignature(callExpression) : undefined;