Array.isArray for readonly array

Author: graphemecluster

src/harness/fourslashInterfaceImpl.ts

@@ -1173,6 +1173,7 @@ namespace FourSlashInterface {
             typeEntry("Record"),
             typeEntry("Exclude"),
             typeEntry("Extract"),
+            typeEntry("Cast"),
             typeEntry("Omit"),
             typeEntry("NonNullable"),
             typeEntry("Parameters"),

src/lib/es2015.iterable.d.ts

@@ -56,6 +56,20 @@ interface Array<T> {
 }
 
 interface ArrayConstructor {
+    /**
+     * Determines whether an object is an array.
+     * @param arg The object to test.
+     */
+    isArray<T>(arg: T): arg is Cast<
+        0 extends (1 & T) ? any[] :
+        T extends readonly unknown[] ? T :
+        T extends string ? never :
+        T extends Iterable<infer U> | ArrayLike<infer U> ? U[] :
+        unknown extends T ? unknown[] :
+        never,
+        T
+    >;
+
     /**
      * Creates an array from an array-like or iterable object.
      * @param source An array-like or iterable object to convert to an array.

src/lib/es2017.object.d.ts

@@ -27,5 +27,5 @@ interface ObjectConstructor {
      * Returns an object containing all own property descriptors of an object
      * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
      */
-    getOwnPropertyDescriptors<T extends {}>(o: T): { [P in keyof T]: TypedPropertyDescriptor<T[P]> } & { [x: string]: PropertyDescriptor };
+    getOwnPropertyDescriptors<T extends {}>(o: T): { [P in keyof T]: TypedPropertyDescriptor<T[P]> } & PropertyDescriptorMap;
 }

src/lib/es5.d.ts

@@ -1495,7 +1495,19 @@ interface ArrayConstructor {
     (arrayLength?: number): any[];
     <T>(arrayLength: number): T[];
     <T>(...items: T[]): T[];
-    isArray(arg: any): arg is any[];
+    /**
+     * Determines whether an object is an array.
+     * @param arg The object to test.
+     */
+    isArray<T>(arg: T): arg is Cast<
+        0 extends (1 & T) ? any[] :
+        T extends readonly unknown[] ? T :
+        T extends string ? never :
+        T extends ArrayLike<infer U> ? U[] :
+        unknown extends T ? unknown[] :
+        never,
+        T
+    >;
     readonly prototype: any[];
 }
 
@@ -1615,6 +1627,11 @@ type Exclude<T, U> = T extends U ? never : T;
  */
 type Extract<T, U> = T extends U ? T : never;
 
+/**
+ * Make sure T is at least assignable to U
+ */
+type Cast<T, U> = T extends U ? T : U;
+
 /**
  * Construct a type with the properties of T except for those in type K.
  */

tests/baselines/reference/arrayDestructuringInSwitch1.types

@@ -11,9 +11,9 @@ export function evaluate(expression: Expression): boolean {
 
   if (Array.isArray(expression)) {
 >Array.isArray(expression) : boolean
->Array.isArray : (arg: any) => arg is any[]
+>Array.isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >Array : ArrayConstructor
->isArray : (arg: any) => arg is any[]
+>isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >expression : Expression
 
     const [operator, ...operands] = expression;

tests/baselines/reference/arrayTypeOfTypeOf.types

@@ -14,11 +14,11 @@ var xs2: typeof Array;
 >Array : ArrayConstructor
 
 var xs3: typeof Array<number>;
->xs3 : { (arrayLength: number): number[]; (...items: number[]): number[]; new (arrayLength: number): number[]; new (...items: number[]): number[]; isArray(arg: any): arg is any[]; readonly prototype: any[]; }
+>xs3 : { (arrayLength: number): number[]; (...items: number[]): number[]; new (arrayLength: number): number[]; new (...items: number[]): number[]; isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
 >Array : ArrayConstructor
 
 var xs4: typeof Array<typeof x>;
->xs4 : { (arrayLength: number): number[]; (...items: number[]): number[]; new (arrayLength: number): number[]; new (...items: number[]): number[]; isArray(arg: any): arg is any[]; readonly prototype: any[]; }
+>xs4 : { (arrayLength: number): number[]; (...items: number[]): number[]; new (arrayLength: number): number[]; new (...items: number[]): number[]; isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
 >Array : ArrayConstructor
 >x : number
 

tests/baselines/reference/declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.symbols

@@ -79,9 +79,9 @@ export const updateIfChanged = <T>(t: T) => {
 >Object.assign : Symbol(ObjectConstructor.assign, Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
 >Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >assign : Symbol(ObjectConstructor.assign, Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --))
->Array.isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
+>Array.isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --))
 >Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
->isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --))
+>isArray : Symbol(ArrayConstructor.isArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --))
 >u : Symbol(u, Decl(declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.ts, 7, 23))
 >u : Symbol(u, Decl(declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.ts, 7, 23))
 >[key] : Symbol([key], Decl(declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.ts, 12, 80))

tests/baselines/reference/declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.types

@@ -67,9 +67,9 @@ export const updateIfChanged = <T>(t: T) => {
 >assign : { <T extends {}>(target: T): T; <T extends {}, U>(target: T, source: U): T & Writable<U>; <T extends {}, U, V>(target: T, source1: U, source2: V): T & Writable<U> & Writable<V>; <T extends {}, U, V, W>(target: T, source1: U, source2: V, source3: W): T & Writable<U> & Writable<V> & Writable<W>; (target: {}, ...sources: any[]): any; }
 >Array.isArray(u) ? [] : {} : undefined[] | {}
 >Array.isArray(u) : boolean
->Array.isArray : (arg: any) => arg is any[]
+>Array.isArray : { <T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; <T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends Iterable<infer U> | ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; }
 >Array : ArrayConstructor
->isArray : (arg: any) => arg is any[]
+>isArray : { <T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; <T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends Iterable<infer U> | ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; }
 >u : U
 >[] : undefined[]
 >{} : {}

tests/baselines/reference/destructuringParameterDeclaration4.errors.txt

@@ -41,7 +41,7 @@ tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration4.ts(
     a1(...array2);            // Error parameter type is (number|string)[]
           ~~~~~~
 !!! error TS2552: Cannot find name 'array2'. Did you mean 'Array'?
-!!! related TS2728 /.ts/lib.es5.d.ts:1522:13: 'Array' is declared here.
+!!! related TS2728 /.ts/lib.es5.d.ts:1534:13: 'Array' is declared here.
     a5([1, 2, "string", false, true]);       // Error, parameter type is [any, any, [[any]]]
               ~~~~~~~~
 !!! error TS2322: Type 'string' is not assignable to type '[[any]]'.

tests/baselines/reference/fixSignatureCaching.types

@@ -1109,9 +1109,9 @@ define(function () {
 >Array : ArrayConstructor
 
         Array.isArray : function (value) { return Object.prototype.toString.call(value) === '[object Array]'; };
->Array.isArray : (arg: any) => arg is any[]
+>Array.isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >Array : ArrayConstructor
->isArray : (arg: any) => arg is any[]
+>isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >function (value) { return Object.prototype.toString.call(value) === '[object Array]'; } : (value: any) => boolean
 >value : any
 >Object.prototype.toString.call(value) === '[object Array]' : boolean
@@ -1150,9 +1150,9 @@ define(function () {
 >'[object Array]' : "[object Array]"
 
         : Array.isArray;
->Array.isArray : (arg: any) => arg is any[]
+>Array.isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >Array : ArrayConstructor
->isArray : (arg: any) => arg is any[]
+>isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 
     function equalIC(a, b) {
 >equalIC : (a: any, b: any) => boolean

tests/baselines/reference/instantiationExpressions.types

@@ -61,13 +61,13 @@ function f2() {
 >Array : ArrayConstructor
 
     const A1 = Array<string>;  // new (...) => string[]
->A1 : { (arrayLength: number): string[]; (...items: string[]): string[]; new (arrayLength: number): string[]; new (...items: string[]): string[]; isArray(arg: any): arg is any[]; readonly prototype: any[]; }
->Array<string> : { (arrayLength: number): string[]; (...items: string[]): string[]; new (arrayLength: number): string[]; new (...items: string[]): string[]; isArray(arg: any): arg is any[]; readonly prototype: any[]; }
+>A1 : { (arrayLength: number): string[]; (...items: string[]): string[]; new (arrayLength: number): string[]; new (...items: string[]): string[]; isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
+>Array<string> : { (arrayLength: number): string[]; (...items: string[]): string[]; new (arrayLength: number): string[]; new (...items: string[]): string[]; isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
 >Array : ArrayConstructor
 
     const A2 = Array<string, number>;  // Error
->A2 : { isArray(arg: any): arg is any[]; readonly prototype: any[]; }
->Array<string, number> : { isArray(arg: any): arg is any[]; readonly prototype: any[]; }
+>A2 : { isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
+>Array<string, number> : { isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
 >Array : ArrayConstructor
 }
 
@@ -76,11 +76,11 @@ type T20 = typeof Array<>;  // Error
 >Array : ArrayConstructor
 
 type T21 = typeof Array<string>;  // new (...) => string[]
->T21 : { (arrayLength: number): string[]; (...items: string[]): string[]; new (arrayLength: number): string[]; new (...items: string[]): string[]; isArray(arg: any): arg is any[]; readonly prototype: any[]; }
+>T21 : { (arrayLength: number): string[]; (...items: string[]): string[]; new (arrayLength: number): string[]; new (...items: string[]): string[]; isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
 >Array : ArrayConstructor
 
 type T22 = typeof Array<string, number>;  // Error
->T22 : { isArray(arg: any): arg is any[]; readonly prototype: any[]; }
+>T22 : { isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }
 >Array : ArrayConstructor
 
 declare class C<T> {

tests/baselines/reference/isArray.js

@@ -1,5 +1,5 @@
 //// [isArray.ts]
-var maybeArray: number | number[];
+var maybeArray: number | number[] | readonly string[];
 
 
 if (Array.isArray(maybeArray)) {

tests/baselines/reference/isArray.symbols

@@ -1,5 +1,5 @@
 === tests/cases/compiler/isArray.ts ===
-var maybeArray: number | number[];
+var maybeArray: number | number[] | readonly string[];
 >maybeArray : Symbol(maybeArray, Decl(isArray.ts, 0, 3))
 
 
@@ -10,9 +10,9 @@ if (Array.isArray(maybeArray)) {
 >maybeArray : Symbol(maybeArray, Decl(isArray.ts, 0, 3))
 
     maybeArray.length; // OK
->maybeArray.length : Symbol(Array.length, Decl(lib.es5.d.ts, --, --))
+>maybeArray.length : Symbol(length, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >maybeArray : Symbol(maybeArray, Decl(isArray.ts, 0, 3))
->length : Symbol(Array.length, Decl(lib.es5.d.ts, --, --))
+>length : Symbol(length, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 }
 else {
     maybeArray.toFixed(); // OK

tests/baselines/reference/isArray.types

@@ -1,18 +1,18 @@
 === tests/cases/compiler/isArray.ts ===
-var maybeArray: number | number[];
->maybeArray : number | number[]
+var maybeArray: number | number[] | readonly string[];
+>maybeArray : number | number[] | readonly string[]
 
 
 if (Array.isArray(maybeArray)) {
 >Array.isArray(maybeArray) : boolean
->Array.isArray : (arg: any) => arg is any[]
+>Array.isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >Array : ArrayConstructor
->isArray : (arg: any) => arg is any[]
->maybeArray : number | number[]
+>isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
+>maybeArray : number | number[] | readonly string[]
 
     maybeArray.length; // OK
 >maybeArray.length : number
->maybeArray : number[]
+>maybeArray : number[] | readonly string[]
 >length : number
 }
 else {

tests/baselines/reference/javascriptThisAssignmentInStaticBlock.errors.txt

@@ -1,6 +1,6 @@
-/src/a.js(10,7): error TS2417: Class static side 'typeof ElementsArray' incorrectly extends base class static side '{ isArray(arg: any): arg is any[]; readonly prototype: any[]; }'.
+/src/a.js(10,7): error TS2417: Class static side 'typeof ElementsArray' incorrectly extends base class static side '{ isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }'.
   Types of property 'isArray' are incompatible.
-    Type '(arg: any) => boolean' is not assignable to type '(arg: any) => arg is any[]'.
+    Type '(arg: any) => boolean' is not assignable to type '<T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>'.
       Signature '(arg: any): boolean' must be a type predicate.
 
 
@@ -16,9 +16,9 @@
     // GH#46468
     class ElementsArray extends Array {
           ~~~~~~~~~~~~~
-!!! error TS2417: Class static side 'typeof ElementsArray' incorrectly extends base class static side '{ isArray(arg: any): arg is any[]; readonly prototype: any[]; }'.
+!!! error TS2417: Class static side 'typeof ElementsArray' incorrectly extends base class static side '{ isArray<T>(arg: T): arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>; readonly prototype: any[]; }'.
 !!! error TS2417:   Types of property 'isArray' are incompatible.
-!!! error TS2417:     Type '(arg: any) => boolean' is not assignable to type '(arg: any) => arg is any[]'.
+!!! error TS2417:     Type '(arg: any) => boolean' is not assignable to type '<T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>'.
 !!! error TS2417:       Signature '(arg: any): boolean' must be a type predicate.
         static {
             const superisArray = super.isArray;

tests/baselines/reference/javascriptThisAssignmentInStaticBlock.types

@@ -25,17 +25,17 @@ class ElementsArray extends Array {
 
     static {
         const superisArray = super.isArray;
->superisArray : (arg: any) => arg is any[]
->super.isArray : (arg: any) => arg is any[]
+>superisArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
+>super.isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >super : ArrayConstructor
->isArray : (arg: any) => arg is any[]
+>isArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 
         const customIsArray = (arg)=> superisArray(arg);
 >customIsArray : (arg: any) => boolean
 >(arg)=> superisArray(arg) : (arg: any) => boolean
 >arg : any
 >superisArray(arg) : boolean
->superisArray : (arg: any) => arg is any[]
+>superisArray : <T>(arg: T) => arg is Cast<0 extends 1 & T ? any[] : T extends readonly unknown[] ? T : T extends string ? never : T extends ArrayLike<infer U> ? U[] : unknown extends T ? unknown[] : never, T>
 >arg : any
 
         this.isArray = customIsArray;