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Adds Subset type for true subsets of interfaces
The subset type will allow creating true subsets of models to model things like partial DTOs and the like. Resolves microsoft#12936 (and microsoft#28586 to some extent)
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‎lib/lib.es5.d.ts

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@@ -1432,6 +1432,11 @@ type Required<T> = {
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[P in keyof T]-?: T[P];
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};
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/**
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* Construct a true subset of T as defined by U
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*/
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type Subset<T extends U, U> = U;
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/**
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* Make all properties in T readonly
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*/

‎tests/baselines/reference/subsetTests.errors.txt

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tests/cases/compiler/subsetTests.ts(16,28): error TS2304: Cannot find name 'Subset'.
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tests/cases/compiler/subsetTests.ts(27,40): error TS2304: Cannot find name 'Subset'.
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tests/cases/compiler/subsetTests.ts(32,34): error TS2304: Cannot find name 'Subset'.
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tests/cases/compiler/subsetTests.ts(39,28): error TS2304: Cannot find name 'Subset'.
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tests/cases/compiler/subsetTests.ts(49,40): error TS2304: Cannot find name 'Subset'.
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tests/cases/compiler/subsetTests.ts(62,34): error TS2304: Cannot find name 'Subset'.
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==== tests/cases/compiler/subsetTests.ts (6 errors) ====
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interface User {
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name: string;
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age: number;
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contact: {
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email: string;
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phone: string;
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address: {
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street: string;
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country: string;
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zipcode: number;
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}
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};
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password: string;
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}
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type PersonalInformation = Subset<User, {
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~~~~~~
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!!! error TS2304: Cannot find name 'Subset'.
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name: string;
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age: number;
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}>; // Fine
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const test: PersonalInformation = {
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name: 'Hans',
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age: 21,
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password: 'string' // Error: password does not exist in type
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};
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type WronglyTypedPersonalInformation = Subset<User, {
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~~~~~~
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!!! error TS2304: Cannot find name 'Subset'.
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name: string;
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age: string; // Error: Types of property age are incompatible
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}>;
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type ExcessPersonalInformation = Subset<User, {
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~~~~~~
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!!! error TS2304: Cannot find name 'Subset'.
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name: string;
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favoriteColor: string; // Error: Property favoriteColor is missing in type User
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}>;
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// This also works for "deep" properties
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type ShippingInformation = Subset<User, {
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~~~~~~
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!!! error TS2304: Cannot find name 'Subset'.
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name: string;
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contact: {
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address: {
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street: string;
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zipcode: number;
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}
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}
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}>; // Fine (Omitting properties of nested properties is ok too)
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type WronglyTypedShippingInformation = Subset<User, {
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~~~~~~
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!!! error TS2304: Cannot find name 'Subset'.
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name: string;
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contact: {
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address: {
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street: {
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name: string;
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nr: number;
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}; // Error: Types of property street are incompatible
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zipcode: number;
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}
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}
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}>;
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type ExcessShippingInformation = Subset<User, {
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~~~~~~
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!!! error TS2304: Cannot find name 'Subset'.
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name: string;
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contact: {
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address: {
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street: string;
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zipcode: number;
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state: string; // Error: Property state is missing in type User
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}
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}
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}>;
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‎tests/baselines/reference/subsetTests.js

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//// [subsetTests.ts]
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interface User {
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name: string;
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age: number;
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contact: {
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email: string;
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phone: string;
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address: {
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street: string;
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country: string;
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zipcode: number;
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}
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};
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password: string;
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}
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type PersonalInformation = Subset<User, {
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name: string;
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age: number;
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}>; // Fine
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const test: PersonalInformation = {
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name: 'Hans',
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age: 21,
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password: 'string' // Error: password does not exist in type
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};
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type WronglyTypedPersonalInformation = Subset<User, {
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name: string;
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age: string; // Error: Types of property age are incompatible
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}>;
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type ExcessPersonalInformation = Subset<User, {
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name: string;
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favoriteColor: string; // Error: Property favoriteColor is missing in type User
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}>;
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// This also works for "deep" properties
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type ShippingInformation = Subset<User, {
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name: string;
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contact: {
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address: {
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street: string;
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zipcode: number;
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}
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}
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}>; // Fine (Omitting properties of nested properties is ok too)
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type WronglyTypedShippingInformation = Subset<User, {
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name: string;
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contact: {
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address: {
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street: {
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name: string;
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nr: number;
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}; // Error: Types of property street are incompatible
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zipcode: number;
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}
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}
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}>;
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type ExcessShippingInformation = Subset<User, {
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name: string;
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contact: {
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address: {
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street: string;
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zipcode: number;
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state: string; // Error: Property state is missing in type User
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}
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}
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}>;
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//// [subsetTests.js]
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var test = {
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name: 'Hans',
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age: 21,
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password: 'string' // Error: password does not exist in type
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};

‎tests/baselines/reference/subsetTests.symbols

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=== tests/cases/compiler/subsetTests.ts ===
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interface User {
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>User : Symbol(User, Decl(subsetTests.ts, 0, 0))
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name: string;
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>name : Symbol(User.name, Decl(subsetTests.ts, 0, 16))
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age: number;
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>age : Symbol(User.age, Decl(subsetTests.ts, 1, 17))
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contact: {
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>contact : Symbol(User.contact, Decl(subsetTests.ts, 2, 16))
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email: string;
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>email : Symbol(email, Decl(subsetTests.ts, 3, 14))
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phone: string;
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>phone : Symbol(phone, Decl(subsetTests.ts, 4, 22))
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address: {
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>address : Symbol(address, Decl(subsetTests.ts, 5, 22))
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street: string;
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>street : Symbol(street, Decl(subsetTests.ts, 6, 18))
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country: string;
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>country : Symbol(country, Decl(subsetTests.ts, 7, 27))
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zipcode: number;
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>zipcode : Symbol(zipcode, Decl(subsetTests.ts, 8, 28))
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}
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};
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password: string;
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>password : Symbol(User.password, Decl(subsetTests.ts, 11, 6))
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}
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type PersonalInformation = Subset<User, {
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>PersonalInformation : Symbol(PersonalInformation, Decl(subsetTests.ts, 13, 1))
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>User : Symbol(User, Decl(subsetTests.ts, 0, 0))
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name: string;
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>name : Symbol(name, Decl(subsetTests.ts, 15, 41))
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age: number;
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>age : Symbol(age, Decl(subsetTests.ts, 16, 17))
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}>; // Fine
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const test: PersonalInformation = {
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>test : Symbol(test, Decl(subsetTests.ts, 20, 5))
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>PersonalInformation : Symbol(PersonalInformation, Decl(subsetTests.ts, 13, 1))
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name: 'Hans',
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>name : Symbol(name, Decl(subsetTests.ts, 20, 35))
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age: 21,
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>age : Symbol(age, Decl(subsetTests.ts, 21, 17))
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password: 'string' // Error: password does not exist in type
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>password : Symbol(password, Decl(subsetTests.ts, 22, 12))
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};
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type WronglyTypedPersonalInformation = Subset<User, {
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>WronglyTypedPersonalInformation : Symbol(WronglyTypedPersonalInformation, Decl(subsetTests.ts, 24, 2))
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>User : Symbol(User, Decl(subsetTests.ts, 0, 0))
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name: string;
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>name : Symbol(name, Decl(subsetTests.ts, 26, 53))
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age: string; // Error: Types of property age are incompatible
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>age : Symbol(age, Decl(subsetTests.ts, 27, 17))
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}>;
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type ExcessPersonalInformation = Subset<User, {
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>ExcessPersonalInformation : Symbol(ExcessPersonalInformation, Decl(subsetTests.ts, 29, 3))
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>User : Symbol(User, Decl(subsetTests.ts, 0, 0))
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name: string;
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>name : Symbol(name, Decl(subsetTests.ts, 31, 47))
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favoriteColor: string; // Error: Property favoriteColor is missing in type User
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>favoriteColor : Symbol(favoriteColor, Decl(subsetTests.ts, 32, 17))
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}>;
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// This also works for "deep" properties
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type ShippingInformation = Subset<User, {
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>ShippingInformation : Symbol(ShippingInformation, Decl(subsetTests.ts, 34, 3))
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>User : Symbol(User, Decl(subsetTests.ts, 0, 0))
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name: string;
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>name : Symbol(name, Decl(subsetTests.ts, 38, 41))
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contact: {
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>contact : Symbol(contact, Decl(subsetTests.ts, 39, 17))
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address: {
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>address : Symbol(address, Decl(subsetTests.ts, 40, 14))
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street: string;
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>street : Symbol(street, Decl(subsetTests.ts, 41, 18))
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zipcode: number;
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>zipcode : Symbol(zipcode, Decl(subsetTests.ts, 42, 27))
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}
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}
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}>; // Fine (Omitting properties of nested properties is ok too)
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type WronglyTypedShippingInformation = Subset<User, {
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>WronglyTypedShippingInformation : Symbol(WronglyTypedShippingInformation, Decl(subsetTests.ts, 46, 3))
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>User : Symbol(User, Decl(subsetTests.ts, 0, 0))
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name: string;
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>name : Symbol(name, Decl(subsetTests.ts, 48, 53))
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contact: {
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>contact : Symbol(contact, Decl(subsetTests.ts, 49, 17))
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address: {
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>address : Symbol(address, Decl(subsetTests.ts, 50, 14))
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street: {
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>street : Symbol(street, Decl(subsetTests.ts, 51, 18))
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name: string;
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>name : Symbol(name, Decl(subsetTests.ts, 52, 21))
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nr: number;
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>nr : Symbol(nr, Decl(subsetTests.ts, 53, 29))
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}; // Error: Types of property street are incompatible
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zipcode: number;
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>zipcode : Symbol(zipcode, Decl(subsetTests.ts, 55, 14))
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}
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}
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}>;
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type ExcessShippingInformation = Subset<User, {
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>ExcessShippingInformation : Symbol(ExcessShippingInformation, Decl(subsetTests.ts, 59, 3))
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>User : Symbol(User, Decl(subsetTests.ts, 0, 0))
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name: string;
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>name : Symbol(name, Decl(subsetTests.ts, 61, 47))
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contact: {
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>contact : Symbol(contact, Decl(subsetTests.ts, 62, 17))
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address: {
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>address : Symbol(address, Decl(subsetTests.ts, 63, 14))
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street: string;
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>street : Symbol(street, Decl(subsetTests.ts, 64, 18))
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zipcode: number;
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>zipcode : Symbol(zipcode, Decl(subsetTests.ts, 65, 27))
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state: string; // Error: Property state is missing in type User
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>state : Symbol(state, Decl(subsetTests.ts, 66, 28))
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}
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}
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}>;
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