tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(11,5): error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
  Type 'T' is not assignable to type 'U'.
    'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(16,5): error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
  Type 'T' is not assignable to type 'U'.
    'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(20,5): error TS2536: Type 'keyof U' cannot be used to index type 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(21,12): error TS2536: Type 'keyof U' cannot be used to index type 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(25,5): error TS2536: Type 'K' cannot be used to index type 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(26,12): error TS2536: Type 'K' cannot be used to index type 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(30,5): error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
  Type 'undefined' is not assignable to type 'T[keyof T]'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(35,5): error TS2322: Type 'T[K] | undefined' is not assignable to type 'T[K]'.
  Type 'undefined' is not assignable to type 'T[K]'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(40,5): error TS2322: Type 'U[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
  Type 'undefined' is not assignable to type 'T[keyof T]'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(41,5): error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T] | undefined'.
  Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[keyof T] | undefined'.
    Type 'T[string]' is not assignable to type 'U[keyof T] | undefined'.
      Type 'T[string]' is not assignable to type 'U[keyof T]'.
        Type 'T' is not assignable to type 'U'.
          'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(45,5): error TS2322: Type 'U[K] | undefined' is not assignable to type 'T[K]'.
  Type 'undefined' is not assignable to type 'T[K]'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(46,5): error TS2322: Type 'T[K]' is not assignable to type 'U[K] | undefined'.
  Type 'T[keyof T]' is not assignable to type 'U[K] | undefined'.
    Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[K] | undefined'.
      Type 'T[string]' is not assignable to type 'U[K] | undefined'.
        Type 'T[string]' is not assignable to type 'U[K]'.
          Type 'T' is not assignable to type 'U'.
            'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(51,5): error TS2542: Index signature in type 'Readonly<T>' only permits reading.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(56,5): error TS2542: Index signature in type 'Readonly<T>' only permits reading.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(61,5): error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
  Type 'T' is not assignable to type 'U'.
    'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(61,5): error TS2542: Index signature in type 'Readonly<U>' only permits reading.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(66,5): error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
  Type 'T' is not assignable to type 'U'.
    'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(66,5): error TS2542: Index signature in type 'Readonly<U>' only permits reading.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(72,5): error TS2322: Type 'Partial<T>' is not assignable to type 'T'.
  'T' could be instantiated with an arbitrary type which could be unrelated to 'Partial<T>'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(78,5): error TS2322: Type 'Partial<Thing>' is not assignable to type 'Partial<T>'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(88,5): error TS2322: Type 'Readonly<Thing>' is not assignable to type 'Readonly<T>'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(127,5): error TS2322: Type 'Partial<U>' is not assignable to type 'Identity<U>'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(143,5): error TS2322: Type '{ [P in keyof T]: T[P]; }' is not assignable to type '{ [P in keyof T]: U[P]; }'.
  Type 'T[P]' is not assignable to type 'U[P]'.
    Type 'T' is not assignable to type 'U'.
      'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(148,5): error TS2322: Type '{ [P in keyof T]: T[P]; }' is not assignable to type '{ [P in keyof U]: U[P]; }'.
  Type 'keyof U' is not assignable to type 'keyof T'.
    Type 'string | number | symbol' is not assignable to type 'keyof T'.
      Type 'string' is not assignable to type 'keyof T'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(153,5): error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in keyof T]: T[P]; }'.
  Type 'keyof T' is not assignable to type 'K'.
    'keyof T' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
      Type 'string | number | symbol' is not assignable to type 'K'.
        'string | number | symbol' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
          Type 'string' is not assignable to type 'K'.
            'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(158,5): error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in keyof U]: U[P]; }'.
  Type 'keyof U' is not assignable to type 'K'.
    'keyof U' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
      Type 'string | number | symbol' is not assignable to type 'K'.
        'string | number | symbol' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
          Type 'string' is not assignable to type 'K'.
            'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(163,5): error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in keyof T]: U[P]; }'.
  Type 'keyof T' is not assignable to type 'K'.
    'keyof T' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
      Type 'string | number | symbol' is not assignable to type 'K'.
        'string | number | symbol' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
          Type 'string' is not assignable to type 'K'.
            'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
tests/cases/conformance/types/mapped/mappedTypeRelationships.ts(168,5): error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in K]: U[P]; }'.
  Type 'T[P]' is not assignable to type 'U[P]'.
    Type 'T' is not assignable to type 'U'.
      'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.


==== tests/cases/conformance/types/mapped/mappedTypeRelationships.ts (28 errors) ====
    function f1<T>(x: T, k: keyof T) {
        return x[k];
    }
    
    function f2<T, K extends keyof T>(x: T, k: K) {
        return x[k];
    }
    
    function f3<T, U extends T>(x: T, y: U, k: keyof T) {
        x[k] = y[k];
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
!!! error TS2322:   Type 'T' is not assignable to type 'U'.
!!! error TS2322:     'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
    }
    
    function f4<T, U extends T, K extends keyof T>(x: T, y: U, k: K) {
        x[k] = y[k];
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
!!! error TS2322:   Type 'T' is not assignable to type 'U'.
!!! error TS2322:     'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
    }
    
    function f5<T, U extends T>(x: T, y: U, k: keyof U) {
        x[k] = y[k];  // Error
        ~~~~
!!! error TS2536: Type 'keyof U' cannot be used to index type 'T'.
        y[k] = x[k];  // Error
               ~~~~
!!! error TS2536: Type 'keyof U' cannot be used to index type 'T'.
    }
    
    function f6<T, U extends T, K extends keyof U>(x: T, y: U, k: K) {
        x[k] = y[k];  // Error
        ~~~~
!!! error TS2536: Type 'K' cannot be used to index type 'T'.
        y[k] = x[k];  // Error
               ~~~~
!!! error TS2536: Type 'K' cannot be used to index type 'T'.
    }
    
    function f10<T>(x: T, y: Partial<T>, k: keyof T) {
        x[k] = y[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
!!! error TS2322:   Type 'undefined' is not assignable to type 'T[keyof T]'.
        y[k] = x[k];
    }
    
    function f11<T, K extends keyof T>(x: T, y: Partial<T>, k: K) {
        x[k] = y[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[K] | undefined' is not assignable to type 'T[K]'.
!!! error TS2322:   Type 'undefined' is not assignable to type 'T[K]'.
        y[k] = x[k];
    }
    
    function f12<T, U extends T>(x: T, y: Partial<U>, k: keyof T) {
        x[k] = y[k];  // Error
        ~~~~
!!! error TS2322: Type 'U[keyof T] | undefined' is not assignable to type 'T[keyof T]'.
!!! error TS2322:   Type 'undefined' is not assignable to type 'T[keyof T]'.
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T] | undefined'.
!!! error TS2322:   Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[keyof T] | undefined'.
!!! error TS2322:     Type 'T[string]' is not assignable to type 'U[keyof T] | undefined'.
!!! error TS2322:       Type 'T[string]' is not assignable to type 'U[keyof T]'.
!!! error TS2322:         Type 'T' is not assignable to type 'U'.
!!! error TS2322:           'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
    }
    
    function f13<T, U extends T, K extends keyof T>(x: T, y: Partial<U>, k: K) {
        x[k] = y[k];  // Error
        ~~~~
!!! error TS2322: Type 'U[K] | undefined' is not assignable to type 'T[K]'.
!!! error TS2322:   Type 'undefined' is not assignable to type 'T[K]'.
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[K]' is not assignable to type 'U[K] | undefined'.
!!! error TS2322:   Type 'T[keyof T]' is not assignable to type 'U[K] | undefined'.
!!! error TS2322:     Type 'T[string] | T[number] | T[symbol]' is not assignable to type 'U[K] | undefined'.
!!! error TS2322:       Type 'T[string]' is not assignable to type 'U[K] | undefined'.
!!! error TS2322:         Type 'T[string]' is not assignable to type 'U[K]'.
!!! error TS2322:           Type 'T' is not assignable to type 'U'.
!!! error TS2322:             'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
    }
    
    function f20<T>(x: T, y: Readonly<T>, k: keyof T) {
        x[k] = y[k];
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2542: Index signature in type 'Readonly<T>' only permits reading.
    }
    
    function f21<T, K extends keyof T>(x: T, y: Readonly<T>, k: K) {
        x[k] = y[k];
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2542: Index signature in type 'Readonly<T>' only permits reading.
    }
    
    function f22<T, U extends T>(x: T, y: Readonly<U>, k: keyof T) {
        x[k] = y[k];
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[keyof T]' is not assignable to type 'U[keyof T]'.
!!! error TS2322:   Type 'T' is not assignable to type 'U'.
!!! error TS2322:     'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
        ~~~~
!!! error TS2542: Index signature in type 'Readonly<U>' only permits reading.
    }
    
    function f23<T, U extends T, K extends keyof T>(x: T, y: Readonly<U>, k: K) {
        x[k] = y[k];
        y[k] = x[k];  // Error
        ~~~~
!!! error TS2322: Type 'T[K]' is not assignable to type 'U[K]'.
!!! error TS2322:   Type 'T' is not assignable to type 'U'.
!!! error TS2322:     'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
        ~~~~
!!! error TS2542: Index signature in type 'Readonly<U>' only permits reading.
    }
    
    type Thing = { a: string, b: string };
    
    function f30<T>(x: T, y: Partial<T>) {
        x = y;  // Error
        ~
!!! error TS2322: Type 'Partial<T>' is not assignable to type 'T'.
!!! error TS2322:   'T' could be instantiated with an arbitrary type which could be unrelated to 'Partial<T>'.
        y = x;
    }
    
    function f31<T extends Thing>(x: Partial<Thing>, y: Partial<T>) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type 'Partial<Thing>' is not assignable to type 'Partial<T>'.
    }
    
    function f40<T>(x: T, y: Readonly<T>) {
        x = y;
        y = x;
    }
    
    function f41<T extends Thing>(x: Readonly<Thing>, y: Readonly<T>) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type 'Readonly<Thing>' is not assignable to type 'Readonly<T>'.
    }
    
    type Item = {
        name: string;
    }
    
    type ItemMap = {
        [x: string]: Item;
    }
    
    function f50<T extends ItemMap>(obj: T, key: keyof T) {
        let item: Item = obj[key];
        return obj[key].name;
    }
    
    function f51<T extends ItemMap, K extends keyof T>(obj: T, key: K) {
        let item: Item = obj[key];
        return obj[key].name;
    }
    
    type T1<T> = {
        [P in keyof T]: T[P];
    }
    
    type T2<T> = {
        [P in keyof T]: T[P];
    }
    
    function f60<U>(x: T1<U>, y: T2<U>) {
        x = y;
        y = x;
    }
    
    type Identity<T> = {
        [P in keyof T]: T[P];
    }
    
    function f61<U>(x: Identity<U>, y: Partial<U>) {
        x = y;  // Error
        ~
!!! error TS2322: Type 'Partial<U>' is not assignable to type 'Identity<U>'.
        y = x;
    }
    
    function f62<U>(x: Identity<U>, y: Readonly<U>) {
        x = y;
        y = x;
    }
    
    function f70<T>(x: { [P in keyof T]: T[P] }, y: { [P in keyof T]: T[P] }) {
        x = y;
        y = x;
    }
    
    function f71<T, U extends T>(x: { [P in keyof T]: T[P] }, y: { [P in keyof T]: U[P] }) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type '{ [P in keyof T]: T[P]; }' is not assignable to type '{ [P in keyof T]: U[P]; }'.
!!! error TS2322:   Type 'T[P]' is not assignable to type 'U[P]'.
!!! error TS2322:     Type 'T' is not assignable to type 'U'.
!!! error TS2322:       'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
    }
    
    function f72<T, U extends T>(x: { [P in keyof T]: T[P] }, y: { [P in keyof U]: U[P] }) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type '{ [P in keyof T]: T[P]; }' is not assignable to type '{ [P in keyof U]: U[P]; }'.
!!! error TS2322:   Type 'keyof U' is not assignable to type 'keyof T'.
!!! error TS2322:     Type 'string | number | symbol' is not assignable to type 'keyof T'.
!!! error TS2322:       Type 'string' is not assignable to type 'keyof T'.
    }
    
    function f73<T, K extends keyof T>(x: { [P in K]: T[P] }, y: { [P in keyof T]: T[P] }) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in keyof T]: T[P]; }'.
!!! error TS2322:   Type 'keyof T' is not assignable to type 'K'.
!!! error TS2322:     'keyof T' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
!!! error TS2322:       Type 'string | number | symbol' is not assignable to type 'K'.
!!! error TS2322:         'string | number | symbol' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
!!! error TS2322:           Type 'string' is not assignable to type 'K'.
!!! error TS2322:             'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
    }
    
    function f74<T, U extends T, K extends keyof T>(x: { [P in K]: T[P] }, y: { [P in keyof U]: U[P] }) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in keyof U]: U[P]; }'.
!!! error TS2322:   Type 'keyof U' is not assignable to type 'K'.
!!! error TS2322:     'keyof U' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
!!! error TS2322:       Type 'string | number | symbol' is not assignable to type 'K'.
!!! error TS2322:         'string | number | symbol' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
!!! error TS2322:           Type 'string' is not assignable to type 'K'.
!!! error TS2322:             'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
    }
    
    function f75<T, U extends T, K extends keyof T>(x: { [P in K]: T[P] }, y: { [P in keyof T]: U[P] }) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in keyof T]: U[P]; }'.
!!! error TS2322:   Type 'keyof T' is not assignable to type 'K'.
!!! error TS2322:     'keyof T' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
!!! error TS2322:       Type 'string | number | symbol' is not assignable to type 'K'.
!!! error TS2322:         'string | number | symbol' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
!!! error TS2322:           Type 'string' is not assignable to type 'K'.
!!! error TS2322:             'string' is assignable to the constraint of type 'K', but 'K' could be instantiated with a different subtype of constraint 'string | number | symbol'.
    }
    
    function f76<T, U extends T, K extends keyof T>(x: { [P in K]: T[P] }, y: { [P in K]: U[P] }) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type '{ [P in K]: T[P]; }' is not assignable to type '{ [P in K]: U[P]; }'.
!!! error TS2322:   Type 'T[P]' is not assignable to type 'U[P]'.
!!! error TS2322:     Type 'T' is not assignable to type 'U'.
!!! error TS2322:       'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
    }
    
    function f80<T>(t: T): Partial<T> {
        return t;
    }
    
    function f81<T, K extends keyof T>(t: T, k: K): Partial<T[K]> {
        return t[k];
    }
    
    function f82<T, K1 extends keyof T, K2 extends keyof T[K1]>(t: T, k1: K1, k2: K2): Partial<T[K1][K2]> {
        return t[k1][k2];
    }
    
    // #31070
    type Numeric<T> = { [K in keyof T]?: number };
    function f90<T extends { x: number }>() {
        const n: Numeric<T> = { x: 1 };
    }
    
    function f<T extends { x: {} }>(): Partial<T> {
        return undefined! as T;
    }