function checkTypeRelatedTo(source, target, relation, errorNode, headMessage, containingMessageChain) {
            var errorInfo;
            var sourceStack;
            var targetStack;
            var maybeStack;
            var expandingFlags;
            var depth = 0;
            var overflow = false;
            var elaborateErrors = false;
            ts.Debug.assert(relation !== identityRelation || !errorNode, "no error reporting in identity checking");
            var result = isRelatedTo(source, target, errorNode !== undefined, headMessage);
            if (overflow) {
                error(errorNode, ts.Diagnostics.Excessive_stack_depth_comparing_types_0_and_1, typeToString(source), typeToString(target));
            }
            else if (errorInfo) {
                // If we already computed this relation, but in a context where we didn't want to report errors (e.g. overload resolution),
                // then we'll only have a top-level error (e.g. 'Class X does not implement interface Y') without any details. If this happened,
                // request a recompuation to get a complete error message. This will be skipped if we've already done this computation in a context
                // where errors were being reported.
                if (errorInfo.next === undefined) {
                    errorInfo = undefined;
                    elaborateErrors = true;
                    isRelatedTo(source, target, errorNode !== undefined, headMessage);
                }
                if (containingMessageChain) {
                    errorInfo = ts.concatenateDiagnosticMessageChains(containingMessageChain, errorInfo);
                }
                diagnostics.add(ts.createDiagnosticForNodeFromMessageChain(errorNode, errorInfo));
            }
            return result !== 0 /* False */;
            function reportError(message, arg0, arg1, arg2) {
                errorInfo = ts.chainDiagnosticMessages(errorInfo, message, arg0, arg1, arg2);
            }
            function reportRelationError(message, source, target) {
                var sourceType = typeToString(source);
                var targetType = typeToString(target);
                if (sourceType === targetType) {
                    sourceType = typeToString(source, /*enclosingDeclaration*/ undefined, 128 /* UseFullyQualifiedType */);
                    targetType = typeToString(target, /*enclosingDeclaration*/ undefined, 128 /* UseFullyQualifiedType */);
                }
                reportError(message || ts.Diagnostics.Type_0_is_not_assignable_to_type_1, sourceType, targetType);
            }
            // Compare two types and return
            // Ternary.True if they are related with no assumptions,
            // Ternary.Maybe if they are related with assumptions of other relationships, or
            // Ternary.False if they are not related.
            function isRelatedTo(source, target, reportErrors, headMessage) {
                var result;
                // both types are the same - covers 'they are the same primitive type or both are Any' or the same type parameter cases
                if (source === target)
                    return -1 /* True */;
                if (relation === identityRelation) {
                    return isIdenticalTo(source, target);
                }
                if (isTypeAny(target))
                    return -1 /* True */;
                if (source === undefinedType)
                    return -1 /* True */;
                if (source === nullType && target !== undefinedType)
                    return -1 /* True */;
                if (source.flags & 128 /* Enum */ && target === numberType)
                    return -1 /* True */;
                if (source.flags & 256 /* StringLiteral */ && target === stringType)
                    return -1 /* True */;
                if (relation === assignableRelation) {
                    if (isTypeAny(source))
                        return -1 /* True */;
                    if (source === numberType && target.flags & 128 /* Enum */)
                        return -1 /* True */;
                }
                if (source.flags & 1048576 /* FreshObjectLiteral */) {
                    if (hasExcessProperties(source, target, reportErrors)) {
                        if (reportErrors) {
                            reportRelationError(headMessage, source, target);
                        }
                        return 0 /* False */;
                    }
                    // Above we check for excess properties with respect to the entire target type. When union
                    // and intersection types are further deconstructed on the target side, we don't want to
                    // make the check again (as it might fail for a partial target type). Therefore we obtain
                    // the regular source type and proceed with that.
                    if (target.flags & 49152 /* UnionOrIntersection */) {
                        source = getRegularTypeOfObjectLiteral(source);
                    }
                }
                var saveErrorInfo = errorInfo;
                // Note that the "each" checks must precede the "some" checks to produce the correct results
                if (source.flags & 16384 /* Union */) {
                    if (result = eachTypeRelatedToType(source, target, reportErrors)) {
                        return result;
                    }
                }
                else if (target.flags & 32768 /* Intersection */) {
                    if (result = typeRelatedToEachType(source, target, reportErrors)) {
                        return result;
                    }
                }
                else {
                    // It is necessary to try "some" checks on both sides because there may be nested "each" checks
                    // on either side that need to be prioritized. For example, A | B = (A | B) & (C | D) or
                    // A & B = (A & B) | (C & D).
                    if (source.flags & 32768 /* Intersection */) {
                        // If target is a union type the following check will report errors so we suppress them here
                        if (result = someTypeRelatedToType(source, target, reportErrors && !(target.flags & 16384 /* Union */))) {
                            return result;
                        }
                    }
                    if (target.flags & 16384 /* Union */) {
                        if (result = typeRelatedToSomeType(source, target, reportErrors)) {
                            return result;
                        }
                    }
                }
                if (source.flags & 512 /* TypeParameter */) {
                    var constraint = getConstraintOfTypeParameter(source);
                    if (!constraint || constraint.flags & 1 /* Any */) {
                        constraint = emptyObjectType;
                    }
                    // Report constraint errors only if the constraint is not the empty object type
                    var reportConstraintErrors = reportErrors && constraint !== emptyObjectType;
                    if (result = isRelatedTo(constraint, target, reportConstraintErrors)) {
                        errorInfo = saveErrorInfo;
                        return result;
                    }
                }
                else {
                    if (source.flags & 4096 /* Reference */ && target.flags & 4096 /* Reference */ && source.target === target.target) {
                        // We have type references to same target type, see if relationship holds for all type arguments
                        if (result = typeArgumentsRelatedTo(source, target, reportErrors)) {
                            return result;
                        }
                    }
                    // Even if relationship doesn't hold for unions, intersections, or generic type references,
                    // it may hold in a structural comparison.
                    var apparentType = getApparentType(source);
                    // In a check of the form X = A & B, we will have previously checked if A relates to X or B relates
                    // to X. Failing both of those we want to check if the aggregation of A and B's members structurally
                    // relates to X. Thus, we include intersection types on the source side here.
                    if (apparentType.flags & (80896 /* ObjectType */ | 32768 /* Intersection */) && target.flags & 80896 /* ObjectType */) {
                        // Report structural errors only if we haven't reported any errors yet
                        var reportStructuralErrors = reportErrors && errorInfo === saveErrorInfo;
                        if (result = objectTypeRelatedTo(apparentType, source, target, reportStructuralErrors)) {
                            errorInfo = saveErrorInfo;
                            return result;
                        }
                    }
                }
                if (reportErrors) {
                    reportRelationError(headMessage, source, target);
                }
                return 0 /* False */;
            }
            function isIdenticalTo(source, target) {
                var result;
                if (source.flags & 80896 /* ObjectType */ && target.flags & 80896 /* ObjectType */) {
                    if (source.flags & 4096 /* Reference */ && target.flags & 4096 /* Reference */ && source.target === target.target) {
                        // We have type references to same target type, see if all type arguments are identical
                        if (result = typeArgumentsRelatedTo(source, target, /*reportErrors*/ false)) {
                            return result;
                        }
                    }
                    return objectTypeRelatedTo(source, source, target, /*reportErrors*/ false);
                }
                if (source.flags & 512 /* TypeParameter */ && target.flags & 512 /* TypeParameter */) {
                    return typeParameterIdenticalTo(source, target);
                }
                if (source.flags & 16384 /* Union */ && target.flags & 16384 /* Union */ ||
                    source.flags & 32768 /* Intersection */ && target.flags & 32768 /* Intersection */) {
                    if (result = eachTypeRelatedToSomeType(source, target)) {
                        if (result &= eachTypeRelatedToSomeType(target, source)) {
                            return result;
                        }
                    }
                }
                return 0 /* False */;
            }
            // Check if a property with the given name is known anywhere in the given type. In an object type, a property
            // is considered known if the object type is empty and the check is for assignability, if the object type has
            // index signatures, or if the property is actually declared in the object type. In a union or intersection
            // type, a property is considered known if it is known in any constituent type.
            function isKnownProperty(type, name) {
                if (type.flags & 80896 /* ObjectType */) {
                    var resolved = resolveStructuredTypeMembers(type);
                    if (relation === assignableRelation && (type === globalObjectType || resolved.properties.length === 0) ||
                        resolved.stringIndexType || resolved.numberIndexType || getPropertyOfType(type, name)) {
                        return true;
                    }
                }
                else if (type.flags & 49152 /* UnionOrIntersection */) {
                    for (var _i = 0, _a = type.types; _i < _a.length; _i++) {
                        var t = _a[_i];
                        if (isKnownProperty(t, name)) {
                            return true;
                        }
                    }
                }
                return false;
            }
            function hasExcessProperties(source, target, reportErrors) {
                if (!(target.flags & 67108864 /* ObjectLiteralPatternWithComputedProperties */) && someConstituentTypeHasKind(target, 80896 /* ObjectType */)) {
                    for (var _i = 0, _a = getPropertiesOfObjectType(source); _i < _a.length; _i++) {
                        var prop = _a[_i];
                        if (!isKnownProperty(target, prop.name)) {
                            if (reportErrors) {
                                // We know *exactly* where things went wrong when comparing the types.
                                // Use this property as the error node as this will be more helpful in
                                // reasoning about what went wrong.
                                errorNode = prop.valueDeclaration;
                                reportError(ts.Diagnostics.Object_literal_may_only_specify_known_properties_and_0_does_not_exist_in_type_1, symbolToString(prop), typeToString(target));
                            }
                            return true;
                        }
                    }
                }
                return false;
            }
            function eachTypeRelatedToSomeType(source, target) {
                var result = -1 /* True */;
                var sourceTypes = source.types;
                for (var _i = 0, sourceTypes_1 = sourceTypes; _i < sourceTypes_1.length; _i++) {
                    var sourceType = sourceTypes_1[_i];
                    var related = typeRelatedToSomeType(sourceType, target, false);
                    if (!related) {
                        return 0 /* False */;
                    }
                    result &= related;
                }
                return result;
            }
            function typeRelatedToSomeType(source, target, reportErrors) {
                var targetTypes = target.types;
                for (var i = 0, len = targetTypes.length; i < len; i++) {
                    var related = isRelatedTo(source, targetTypes[i], reportErrors && i === len - 1);
                    if (related) {
                        return related;
                    }
                }
                return 0 /* False */;
            }
            function typeRelatedToEachType(source, target, reportErrors) {
                var result = -1 /* True */;
                var targetTypes = target.types;
                for (var _i = 0, targetTypes_1 = targetTypes; _i < targetTypes_1.length; _i++) {
                    var targetType = targetTypes_1[_i];
                    var related = isRelatedTo(source, targetType, reportErrors);
                    if (!related) {
                        return 0 /* False */;
                    }
                    result &= related;
                }
                return result;
            }
            function someTypeRelatedToType(source, target, reportErrors) {
                var sourceTypes = source.types;
                for (var i = 0, len = sourceTypes.length; i < len; i++) {
                    var related = isRelatedTo(sourceTypes[i], target, reportErrors && i === len - 1);
                    if (related) {
                        return related;
                    }
                }
                return 0 /* False */;
            }
            function eachTypeRelatedToType(source, target, reportErrors) {
                var result = -1 /* True */;
                var sourceTypes = source.types;
                for (var _i = 0, sourceTypes_2 = sourceTypes; _i < sourceTypes_2.length; _i++) {
                    var sourceType = sourceTypes_2[_i];
                    var related = isRelatedTo(sourceType, target, reportErrors);
                    if (!related) {
                        return 0 /* False */;
                    }
                    result &= related;
                }
                return result;
            }
            function typeArgumentsRelatedTo(source, target, reportErrors) {
                var sources = source.typeArguments || emptyArray;
                var targets = target.typeArguments || emptyArray;
                if (sources.length !== targets.length && relation === identityRelation) {
                    return 0 /* False */;
                }
                var result = -1 /* True */;
                for (var i = 0; i < targets.length; i++) {
                    var related = isRelatedTo(sources[i], targets[i], reportErrors);
                    if (!related) {
                        return 0 /* False */;
                    }
                    result &= related;
                }
                return result;
            }
            function typeParameterIdenticalTo(source, target) {
                // covers case when both type parameters does not have constraint (both equal to noConstraintType)
                if (source.constraint === target.constraint) {
                    return -1 /* True */;
                }
                if (source.constraint === noConstraintType || target.constraint === noConstraintType) {
                    return 0 /* False */;
                }
                return isIdenticalTo(source.constraint, target.constraint);
            }
            // Determine if two object types are related by structure. First, check if the result is already available in the global cache.
            // Second, check if we have already started a comparison of the given two types in which case we assume the result to be true.
            // Third, check if both types are part of deeply nested chains of generic type instantiations and if so assume the types are
            // equal and infinitely expanding. Fourth, if we have reached a depth of 100 nested comparisons, assume we have runaway recursion
            // and issue an error. Otherwise, actually compare the structure of the two types.
            function objectTypeRelatedTo(apparentSource, originalSource, target, reportErrors) {
                if (overflow) {
                    return 0 /* False */;
                }
                var id = relation !== identityRelation || apparentSource.id < target.id ? apparentSource.id + "," + target.id : target.id + "," + apparentSource.id;
                var related = relation[id];
                if (related !== undefined) {
                    // If we computed this relation already and it was failed and reported, or if we're not being asked to elaborate
                    // errors, we can use the cached value. Otherwise, recompute the relation
                    if (!elaborateErrors || (related === 3 /* FailedAndReported */)) {
                        return related === 1 /* Succeeded */ ? -1 /* True */ : 0 /* False */;
                    }
                }
                if (depth > 0) {
                    for (var i = 0; i < depth; i++) {
                        // If source and target are already being compared, consider them related with assumptions
                        if (maybeStack[i][id]) {
                            return 1 /* Maybe */;
                        }
                    }
                    if (depth === 100) {
                        overflow = true;
                        return 0 /* False */;
                    }
                }
                else {
                    sourceStack = [];
                    targetStack = [];
                    maybeStack = [];
                    expandingFlags = 0;
                }
                sourceStack[depth] = apparentSource;
                targetStack[depth] = target;
                maybeStack[depth] = {};
                maybeStack[depth][id] = 1 /* Succeeded */;
                depth++;
                var saveExpandingFlags = expandingFlags;
                if (!(expandingFlags & 1) && isDeeplyNestedGeneric(apparentSource, sourceStack, depth))
                    expandingFlags |= 1;
                if (!(expandingFlags & 2) && isDeeplyNestedGeneric(target, targetStack, depth))
                    expandingFlags |= 2;
                var result;
                if (expandingFlags === 3) {
                    result = 1 /* Maybe */;
                }
                else {
                    result = propertiesRelatedTo(apparentSource, target, reportErrors);
                    if (result) {
                        result &= signaturesRelatedTo(apparentSource, target, 0 /* Call */, reportErrors);
                        if (result) {
                            result &= signaturesRelatedTo(apparentSource, target, 1 /* Construct */, reportErrors);
                            if (result) {
                                result &= stringIndexTypesRelatedTo(apparentSource, originalSource, target, reportErrors);
                                if (result) {
                                    result &= numberIndexTypesRelatedTo(apparentSource, originalSource, target, reportErrors);
                                }
                            }
                        }
                    }
                }
                expandingFlags = saveExpandingFlags;
                depth--;
                if (result) {
                    var maybeCache = maybeStack[depth];
                    // If result is definitely true, copy assumptions to global cache, else copy to next level up
                    var destinationCache = (result === -1 /* True */ || depth === 0) ? relation : maybeStack[depth - 1];
                    ts.copyMap(maybeCache, destinationCache);
                }
                else {
                    // A false result goes straight into global cache (when something is false under assumptions it
                    // will also be false without assumptions)
                    relation[id] = reportErrors ? 3 /* FailedAndReported */ : 2 /* Failed */;
                }
                return result;
            }
            function propertiesRelatedTo(source, target, reportErrors) {
                if (relation === identityRelation) {
                    return propertiesIdenticalTo(source, target);
                }
                var result = -1 /* True */;
                var properties = getPropertiesOfObjectType(target);
                var requireOptionalProperties = relation === subtypeRelation && !(source.flags & 524288 /* ObjectLiteral */);
                for (var _i = 0, properties_1 = properties; _i < properties_1.length; _i++) {
                    var targetProp = properties_1[_i];
                    var sourceProp = getPropertyOfType(source, targetProp.name);
                    if (sourceProp !== targetProp) {
                        if (!sourceProp) {
                            if (!(targetProp.flags & 536870912 /* Optional */) || requireOptionalProperties) {
                                if (reportErrors) {
                                    reportError(ts.Diagnostics.Property_0_is_missing_in_type_1, symbolToString(targetProp), typeToString(source));
                                }
                                return 0 /* False */;
                            }
                        }
                        else if (!(targetProp.flags & 134217728 /* Prototype */)) {
                            var sourcePropFlags = getDeclarationFlagsFromSymbol(sourceProp);
                            var targetPropFlags = getDeclarationFlagsFromSymbol(targetProp);
                            if (sourcePropFlags & 16 /* Private */ || targetPropFlags & 16 /* Private */) {
                                if (sourceProp.valueDeclaration !== targetProp.valueDeclaration) {
                                    if (reportErrors) {
                                        if (sourcePropFlags & 16 /* Private */ && targetPropFlags & 16 /* Private */) {
                                            reportError(ts.Diagnostics.Types_have_separate_declarations_of_a_private_property_0, symbolToString(targetProp));
                                        }
                                        else {
                                            reportError(ts.Diagnostics.Property_0_is_private_in_type_1_but_not_in_type_2, symbolToString(targetProp), typeToString(sourcePropFlags & 16 /* Private */ ? source : target), typeToString(sourcePropFlags & 16 /* Private */ ? target : source));
                                        }
                                    }
                                    return 0 /* False */;
                                }
                            }
                            else if (targetPropFlags & 32 /* Protected */) {
                                var sourceDeclaredInClass = sourceProp.parent && sourceProp.parent.flags & 32 /* Class */;
                                var sourceClass = sourceDeclaredInClass ? getDeclaredTypeOfSymbol(sourceProp.parent) : undefined;
                                var targetClass = getDeclaredTypeOfSymbol(targetProp.parent);
                                if (!sourceClass || !hasBaseType(sourceClass, targetClass)) {
                                    if (reportErrors) {
                                        reportError(ts.Diagnostics.Property_0_is_protected_but_type_1_is_not_a_class_derived_from_2, symbolToString(targetProp), typeToString(sourceClass || source), typeToString(targetClass));
                                    }
                                    return 0 /* False */;
                                }
                            }
                            else if (sourcePropFlags & 32 /* Protected */) {
                                if (reportErrors) {
                                    reportError(ts.Diagnostics.Property_0_is_protected_in_type_1_but_public_in_type_2, symbolToString(targetProp), typeToString(source), typeToString(target));
                                }
                                return 0 /* False */;
                            }
                            var related = isRelatedTo(getTypeOfSymbol(sourceProp), getTypeOfSymbol(targetProp), reportErrors);
                            if (!related) {
                                if (reportErrors) {
                                    reportError(ts.Diagnostics.Types_of_property_0_are_incompatible, symbolToString(targetProp));
                                }
                                return 0 /* False */;
                            }
                            result &= related;
                            if (sourceProp.flags & 536870912 /* Optional */ && !(targetProp.flags & 536870912 /* Optional */)) {
                                // TypeScript 1.0 spec (April 2014): 3.8.3
                                // S is a subtype of a type T, and T is a supertype of S if ...
                                // S' and T are object types and, for each member M in T..
                                // M is a property and S' contains a property N where
                                // if M is a required property, N is also a required property
                                // (M - property in T)
                                // (N - property in S)
                                if (reportErrors) {
                                    reportError(ts.Diagnostics.Property_0_is_optional_in_type_1_but_required_in_type_2, symbolToString(targetProp), typeToString(source), typeToString(target));
                                }
                                return 0 /* False */;
                            }
                        }
                    }
                }
                return result;
            }
            function propertiesIdenticalTo(source, target) {
                if (!(source.flags & 80896 /* ObjectType */ && target.flags & 80896 /* ObjectType */)) {
                    return 0 /* False */;
                }
                var sourceProperties = getPropertiesOfObjectType(source);
                var targetProperties = getPropertiesOfObjectType(target);
                if (sourceProperties.length !== targetProperties.length) {
                    return 0 /* False */;
                }
                var result = -1 /* True */;
                for (var _i = 0, sourceProperties_1 = sourceProperties; _i < sourceProperties_1.length; _i++) {
                    var sourceProp = sourceProperties_1[_i];
                    var targetProp = getPropertyOfObjectType(target, sourceProp.name);
                    if (!targetProp) {
                        return 0 /* False */;
                    }
                    var related = compareProperties(sourceProp, targetProp, isRelatedTo);
                    if (!related) {
                        return 0 /* False */;
                    }
                    result &= related;
                }
                return result;
            }
            function signaturesRelatedTo(source, target, kind, reportErrors) {
                if (relation === identityRelation) {
                    return signaturesIdenticalTo(source, target, kind);
                }
                if (target === anyFunctionType || source === anyFunctionType) {
                    return -1 /* True */;
                }
                var sourceSignatures = getSignaturesOfType(source, kind);
                var targetSignatures = getSignaturesOfType(target, kind);
                var result = -1 /* True */;
                var saveErrorInfo = errorInfo;
                if (kind === 1 /* Construct */) {
                    // Only want to compare the construct signatures for abstractness guarantees.
                    // Because the "abstractness" of a class is the same across all construct signatures
                    // (internally we are checking the corresponding declaration), it is enough to perform
                    // the check and report an error once over all pairs of source and target construct signatures.
                    //
                    // sourceSig and targetSig are (possibly) undefined.
                    //
                    // Note that in an extends-clause, targetSignatures is stripped, so the check never proceeds.
                    var sourceSig = sourceSignatures[0];
                    var targetSig = targetSignatures[0];
                    result &= abstractSignatureRelatedTo(source, sourceSig, target, targetSig);
                    if (result !== -1 /* True */) {
                        return result;
                    }
                }
                outer: for (var _i = 0, targetSignatures_1 = targetSignatures; _i < targetSignatures_1.length; _i++) {
                    var t = targetSignatures_1[_i];
                    if (!t.hasStringLiterals || target.flags & 262144 /* FromSignature */) {
                        var localErrors = reportErrors;
                        var checkedAbstractAssignability = false;
                        for (var _a = 0, sourceSignatures_1 = sourceSignatures; _a < sourceSignatures_1.length; _a++) {
                            var s = sourceSignatures_1[_a];
                            if (!s.hasStringLiterals || source.flags & 262144 /* FromSignature */) {
                                var related = signatureRelatedTo(s, t, localErrors);
                                if (related) {
                                    result &= related;
                                    errorInfo = saveErrorInfo;
                                    continue outer;
                                }
                                // Only report errors from the first failure
                                localErrors = false;
                            }
                        }
                        return 0 /* False */;
                    }
                }
                return result;
                function abstractSignatureRelatedTo(source, sourceSig, target, targetSig) {
                    if (sourceSig && targetSig) {
                        var sourceDecl = source.symbol && getClassLikeDeclarationOfSymbol(source.symbol);
                        var targetDecl = target.symbol && getClassLikeDeclarationOfSymbol(target.symbol);
                        if (!sourceDecl) {
                            // If the source object isn't itself a class declaration, it can be freely assigned, regardless
                            // of whether the constructed object is abstract or not.
                            return -1 /* True */;
                        }
                        var sourceErasedSignature = getErasedSignature(sourceSig);
                        var targetErasedSignature = getErasedSignature(targetSig);
                        var sourceReturnType = sourceErasedSignature && getReturnTypeOfSignature(sourceErasedSignature);
                        var targetReturnType = targetErasedSignature && getReturnTypeOfSignature(targetErasedSignature);
                        var sourceReturnDecl = sourceReturnType && sourceReturnType.symbol && getClassLikeDeclarationOfSymbol(sourceReturnType.symbol);
                        var targetReturnDecl = targetReturnType && targetReturnType.symbol && getClassLikeDeclarationOfSymbol(targetReturnType.symbol);
                        var sourceIsAbstract = sourceReturnDecl && sourceReturnDecl.flags & 128 /* Abstract */;
                        var targetIsAbstract = targetReturnDecl && targetReturnDecl.flags & 128 /* Abstract */;
                        if (sourceIsAbstract && !(targetIsAbstract && targetDecl)) {
                            // if target isn't a class-declaration type, then it can be new'd, so we forbid the assignment.
                            if (reportErrors) {
                                reportError(ts.Diagnostics.Cannot_assign_an_abstract_constructor_type_to_a_non_abstract_constructor_type);
                            }
                            return 0 /* False */;
                        }
                    }
                    return -1 /* True */;
                }
            }
            function signatureRelatedTo(source, target, reportErrors) {
                if (source === target) {
                    return -1 /* True */;
                }
                if (!target.hasRestParameter && source.minArgumentCount > target.parameters.length) {
                    return 0 /* False */;
                }
                var sourceMax = source.parameters.length;
                var targetMax = target.parameters.length;
                var checkCount;
                if (source.hasRestParameter && target.hasRestParameter) {
                    checkCount = sourceMax > targetMax ? sourceMax : targetMax;
                    sourceMax--;
                    targetMax--;
                }
                else if (source.hasRestParameter) {
                    sourceMax--;
                    checkCount = targetMax;
                }
                else if (target.hasRestParameter) {
                    targetMax--;
                    checkCount = sourceMax;
                }
                else {
                    checkCount = sourceMax < targetMax ? sourceMax : targetMax;
                }
                // Spec 1.0 Section 3.8.3 & 3.8.4:
                // M and N (the signatures) are instantiated using type Any as the type argument for all type parameters declared by M and N
                source = getErasedSignature(source);
                target = getErasedSignature(target);
                var result = -1 /* True */;
                for (var i = 0; i < checkCount; i++) {
                    var s = i < sourceMax ? getTypeOfSymbol(source.parameters[i]) : getRestTypeOfSignature(source);
                    var t = i < targetMax ? getTypeOfSymbol(target.parameters[i]) : getRestTypeOfSignature(target);
                    var saveErrorInfo = errorInfo;
                    var related = isRelatedTo(s, t, reportErrors);
                    if (!related) {
                        related = isRelatedTo(t, s, false);
                        if (!related) {
                            if (reportErrors) {
                                reportError(ts.Diagnostics.Types_of_parameters_0_and_1_are_incompatible, source.parameters[i < sourceMax ? i : sourceMax].name, target.parameters[i < targetMax ? i : targetMax].name);
                            }
                            return 0 /* False */;
                        }
                        errorInfo = saveErrorInfo;
                    }
                    result &= related;
                }
                if (source.typePredicate && target.typePredicate) {
                    var hasDifferentParameterIndex = source.typePredicate.parameterIndex !== target.typePredicate.parameterIndex;
                    var hasDifferentTypes;
                    if (hasDifferentParameterIndex ||
                        (hasDifferentTypes = !isTypeIdenticalTo(source.typePredicate.type, target.typePredicate.type))) {
                        if (reportErrors) {
                            var sourceParamText = source.typePredicate.parameterName;
                            var targetParamText = target.typePredicate.parameterName;
                            var sourceTypeText = typeToString(source.typePredicate.type);
                            var targetTypeText = typeToString(target.typePredicate.type);
                            if (hasDifferentParameterIndex) {
                                reportError(ts.Diagnostics.Parameter_0_is_not_in_the_same_position_as_parameter_1, sourceParamText, targetParamText);
                            }
                            else if (hasDifferentTypes) {
                                reportError(ts.Diagnostics.Type_0_is_not_assignable_to_type_1, sourceTypeText, targetTypeText);
                            }
                            reportError(ts.Diagnostics.Type_predicate_0_is_not_assignable_to_1, sourceParamText + " is " + sourceTypeText, targetParamText + " is " + targetTypeText);
                        }
                        return 0 /* False */;
                    }
                }
                else if (!source.typePredicate && target.typePredicate) {
                    if (reportErrors) {
                        reportError(ts.Diagnostics.Signature_0_must_have_a_type_predicate, signatureToString(source));
                    }
                    return 0 /* False */;
                }
                var targetReturnType = getReturnTypeOfSignature(target);
                if (targetReturnType === voidType)
                    return result;
                var sourceReturnType = getReturnTypeOfSignature(source);
                return result & isRelatedTo(sourceReturnType, targetReturnType, reportErrors);
            }
            function signaturesIdenticalTo(source, target, kind) {
                var sourceSignatures = getSignaturesOfType(source, kind);
                var targetSignatures = getSignaturesOfType(target, kind);
                if (sourceSignatures.length !== targetSignatures.length) {
                    return 0 /* False */;
                }
                var result = -1 /* True */;
                for (var i = 0, len = sourceSignatures.length; i < len; ++i) {
                    var related = compareSignatures(sourceSignatures[i], targetSignatures[i], /*partialMatch*/ false, /*ignoreReturnTypes*/ false, isRelatedTo);
                    if (!related) {
                        return 0 /* False */;
                    }
                    result &= related;
                }
                return result;
            }
            function stringIndexTypesRelatedTo(source, originalSource, target, reportErrors) {
                if (relation === identityRelation) {
                    return indexTypesIdenticalTo(0 /* String */, source, target);
                }
                var targetType = getIndexTypeOfType(target, 0 /* String */);
                if (targetType) {
                    if ((targetType.flags & 1 /* Any */) && !(originalSource.flags & 16777726 /* Primitive */)) {
                        // non-primitive assignment to any is always allowed, eg
                        //   `var x: { [index: string]: any } = { property: 12 };`
                        return -1 /* True */;
                    }
                    var sourceType = getIndexTypeOfType(source, 0 /* String */);
                    if (!sourceType) {
                        if (reportErrors) {
                            reportError(ts.Diagnostics.Index_signature_is_missing_in_type_0, typeToString(source));
                        }
                        return 0 /* False */;
                    }
                    var related = isRelatedTo(sourceType, targetType, reportErrors);
                    if (!related) {
                        if (reportErrors) {
                            reportError(ts.Diagnostics.Index_signatures_are_incompatible);
                        }
                        return 0 /* False */;
                    }
                    return related;
                }
                return -1 /* True */;
            }
            function numberIndexTypesRelatedTo(source, originalSource, target, reportErrors) {
                if (relation === identityRelation) {
                    return indexTypesIdenticalTo(1 /* Number */, source, target);
                }
                var targetType = getIndexTypeOfType(target, 1 /* Number */);
                if (targetType) {
                    if ((targetType.flags & 1 /* Any */) && !(originalSource.flags & 16777726 /* Primitive */)) {
                        // non-primitive assignment to any is always allowed, eg
                        //   `var x: { [index: number]: any } = { property: 12 };`
                        return -1 /* True */;
                    }
                    var sourceStringType = getIndexTypeOfType(source, 0 /* String */);
                    var sourceNumberType = getIndexTypeOfType(source, 1 /* Number */);
                    if (!(sourceStringType || sourceNumberType)) {
                        if (reportErrors) {
                            reportError(ts.Diagnostics.Index_signature_is_missing_in_type_0, typeToString(source));
                        }
                        return 0 /* False */;
                    }
                    var related;
                    if (sourceStringType && sourceNumberType) {
                        // If we know for sure we're testing both string and numeric index types then only report errors from the second one
                        related = isRelatedTo(sourceStringType, targetType, false) || isRelatedTo(sourceNumberType, targetType, reportErrors);
                    }
                    else {
                        related = isRelatedTo(sourceStringType || sourceNumberType, targetType, reportErrors);
                    }
                    if (!related) {
                        if (reportErrors) {
                            reportError(ts.Diagnostics.Index_signatures_are_incompatible);
                        }
                        return 0 /* False */;
                    }
                    return related;
                }
                return -1 /* True */;
            }
            function indexTypesIdenticalTo(indexKind, source, target) {
                var targetType = getIndexTypeOfType(target, indexKind);
                var sourceType = getIndexTypeOfType(source, indexKind);
                if (!sourceType && !targetType) {
                    return -1 /* True */;
                }
                if (sourceType && targetType) {
                    return isRelatedTo(sourceType, targetType);
                }
                return 0 /* False */;
            }
        }
Checks if 'source' is related to 'target' (e.g.: is a assignable to).
@param source The left-hand-side of the relation.
@param target The right-hand-side of the relation.
@param relation The relation considered. One of 'identityRelation', 'assignableRelation', or 'subTypeRelation'.
Used as both to determine which checks are performed and as a cache of previously computed results.
@param errorNode The suggested node upon which all errors will be reported, if defined. This may or may not be the actual node used.
@param headMessage If the error chain should be prepended by a head message, then headMessage will be used.
@param containingMessageChain A chain of errors to prepend any new errors found.