Function inferToMappedType

test/fixtures/snapshot/typescript.js:68857–68905

(source, target, constraintType)

                }
            }
            function inferToMappedType(source, target, constraintType) {
                if (constraintType.flags & 1048576 /* TypeFlags.Union */) {
                    var result = false;
                    for (var _i = 0, _a = constraintType.types; _i < _a.length; _i++) {
                        var type = _a[_i];
                        result = inferToMappedType(source, target, type) || result;
                    }
                    return result;
                }
                if (constraintType.flags & 4194304 /* TypeFlags.Index */) {
                    // We're inferring from some source type S to a homomorphic mapped type { [P in keyof T]: X },
                    // where T is a type variable. Use inferTypeForHomomorphicMappedType to infer a suitable source
                    // type and then make a secondary inference from that type to T. We make a secondary inference
                    // such that direct inferences to T get priority over inferences to Partial<T>, for example.
                    var inference = getInferenceInfoForType(constraintType.type);
                    if (inference && !inference.isFixed && !isFromInferenceBlockedSource(source)) {
                        var inferredType = inferTypeForHomomorphicMappedType(source, target, constraintType);
                        if (inferredType) {
                            // We assign a lower priority to inferences made from types containing non-inferrable
                            // types because we may only have a partial result (i.e. we may have failed to make
                            // reverse inferences for some properties).
                            inferWithPriority(inferredType, inference.typeParameter, ts.getObjectFlags(source) & 262144 /* ObjectFlags.NonInferrableType */ ?
                                16 /* InferencePriority.PartialHomomorphicMappedType */ :
                                8 /* InferencePriority.HomomorphicMappedType */);
                        }
                    }
                    return true;
                }
                if (constraintType.flags & 262144 /* TypeFlags.TypeParameter */) {
                    // We're inferring from some source type S to a mapped type { [P in K]: X }, where K is a type
                    // parameter. First infer from 'keyof S' to K.
                    inferWithPriority(getIndexType(source), constraintType, 32 /* InferencePriority.MappedTypeConstraint */);
                    // If K is constrained to a type C, also infer to C. Thus, for a mapped type { [P in K]: X },
                    // where K extends keyof T, we make the same inferences as for a homomorphic mapped type
                    // { [P in keyof T]: X }. This enables us to make meaningful inferences when the target is a
                    // Pick<T, K>.
                    var extendedConstraint = getConstraintOfType(constraintType);
                    if (extendedConstraint && inferToMappedType(source, target, extendedConstraint)) {
                        return true;
                    }
                    // If no inferences can be made to K's constraint, infer from a union of the property types
                    // in the source to the template type X.
                    var propTypes = ts.map(getPropertiesOfType(source), getTypeOfSymbol);
                    var indexTypes = ts.map(getIndexInfosOfType(source), function (info) { return info !== enumNumberIndexInfo ? info.type : neverType; });
                    inferFromTypes(getUnionType(ts.concatenate(propTypes, indexTypes)), getTemplateTypeFromMappedType(target));
                    return true;
                }
                return false;
            }
            function inferToConditionalType(source, target) {
                if (source.flags & 16777216 /* TypeFlags.Conditional */) {
                    inferFromTypes(source.checkType, target.checkType);