check return type of this type predicates

src/compiler/checker.ts

@@ -736,6 +736,7 @@ import {
     isThisInTypeQuery,
     isThisProperty,
     isThisTypeParameter,
+    isThisTypePredicate,
     isTransientSymbol,
     isTupleTypeNode,
     isTypeAlias,
@@ -21217,7 +21218,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 if (sourceTypePredicate) {
                     result &= compareTypePredicateRelatedTo(sourceTypePredicate, targetTypePredicate, reportErrors, errorReporter, compareTypes);
                 }
-                else if (isIdentifierTypePredicate(targetTypePredicate)) {
+                else if (isIdentifierTypePredicate(targetTypePredicate) || isThisTypePredicate(targetTypePredicate)) {
                     if (reportErrors) {
                         errorReporter!(Diagnostics.Signature_0_must_be_a_type_predicate, signatureToString(source));
                     }

src/server/scriptVersionCache.ts

@@ -591,7 +591,7 @@ export class LineNode implements LineCollection {
         if (children.length) this.updateCounts();
     }
 
-    isLeaf() {
+    isLeaf(): this is LineLeaf {
         return false;
     }
 
@@ -839,7 +839,7 @@ export class LineLeaf implements LineCollection {
     constructor(public text: string) {
     }
 
-    isLeaf() {
+    isLeaf(): this is LineLeaf {
         return true;
     }
 

tests/baselines/reference/implementArrayInterface.errors.txt

@@ -0,0 +1,43 @@
+implementArrayInterface.ts(19,5): error TS2416: Property 'every' in type 'MyArray<T>' is not assignable to the same property in base type 'T[]'.
+  Type '(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any) => boolean' is not assignable to type '{ <S extends T>(predicate: (value: T, index: number, array: T[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: T, index: number, array: T[]) => unknown, thisArg?: any): boolean; }'.
+    Signature '(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): boolean' must be a type predicate.
+
+
+==== implementArrayInterface.ts (1 errors) ====
+    declare class MyArray<T> implements Array<T> {
+        toString(): string;
+        toLocaleString(): string;
+        concat<U extends T[]>(...items: U[]): T[];
+        concat(...items: T[]): T[];
+        join(separator?: string): string;
+        pop(): T;
+        push(...items: T[]): number;
+        reverse(): T[];
+        shift(): T;
+        slice(start?: number, end?: number): T[];
+        sort(compareFn?: (a: T, b: T) => number): this;
+        splice(start: number): T[];
+        splice(start: number, deleteCount: number, ...items: T[]): T[];
+        unshift(...items: T[]): number;
+
+        indexOf(searchElement: T, fromIndex?: number): number;
+        lastIndexOf(searchElement: T, fromIndex?: number): number;
+        every(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): boolean;
+        ~~~~~
+!!! error TS2416: Property 'every' in type 'MyArray<T>' is not assignable to the same property in base type 'T[]'.
+!!! error TS2416:   Type '(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any) => boolean' is not assignable to type '{ <S extends T>(predicate: (value: T, index: number, array: T[]) => value is S, thisArg?: any): this is S[]; (predicate: (value: T, index: number, array: T[]) => unknown, thisArg?: any): boolean; }'.
+!!! error TS2416:     Signature '(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): boolean' must be a type predicate.
+        some(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): boolean;
+        forEach(callbackfn: (value: T, index: number, array: T[]) => void, thisArg?: any): void;
+        map<U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any): U[];
+        filter(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): T[];
+        reduce(callbackfn: (previousValue: T, currentValue: T, currentIndex: number, array: T[]) => T, initialValue?: T): T;
+        reduce<U>(callbackfn: (previousValue: U, currentValue: T, currentIndex: number, array: T[]) => U, initialValue: U): U;
+        reduceRight(callbackfn: (previousValue: T, currentValue: T, currentIndex: number, array: T[]) => T, initialValue?: T): T;
+        reduceRight<U>(callbackfn: (previousValue: U, currentValue: T, currentIndex: number, array: T[]) => U, initialValue: U): U;
+
+        length: number;
+
+        [n: number]: T;
+    }
+

tests/baselines/reference/implementArrayInterface.types

@@ -117,6 +117,7 @@ declare class MyArray<T> implements Array<T> {
 >array : T[]
 >      : ^^^
 >thisArg : any
+>        : ^^^
 
     some(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): boolean;
 >some : (callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any) => boolean
@@ -130,6 +131,7 @@ declare class MyArray<T> implements Array<T> {
 >array : T[]
 >      : ^^^
 >thisArg : any
+>        : ^^^
 
     forEach(callbackfn: (value: T, index: number, array: T[]) => void, thisArg?: any): void;
 >forEach : (callbackfn: (value: T, index: number, array: T[]) => void, thisArg?: any) => void
@@ -143,6 +145,7 @@ declare class MyArray<T> implements Array<T> {
 >array : T[]
 >      : ^^^
 >thisArg : any
+>        : ^^^
 
     map<U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any): U[];
 >map : <U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any) => U[]
@@ -156,6 +159,7 @@ declare class MyArray<T> implements Array<T> {
 >array : T[]
 >      : ^^^
 >thisArg : any
+>        : ^^^
 
     filter(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): T[];
 >filter : (callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any) => T[]
@@ -169,6 +173,7 @@ declare class MyArray<T> implements Array<T> {
 >array : T[]
 >      : ^^^
 >thisArg : any
+>        : ^^^
 
     reduce(callbackfn: (previousValue: T, currentValue: T, currentIndex: number, array: T[]) => T, initialValue?: T): T;
 >reduce : { (callbackfn: (previousValue: T, currentValue: T, currentIndex: number, array: T[]) => T, initialValue?: T): T; <U>(callbackfn: (previousValue: U, currentValue: T, currentIndex: number, array: T[]) => U, initialValue: U): U; }

tests/baselines/reference/typePredicateInherit.errors.txt

@@ -0,0 +1,91 @@
+typePredicateInherit.ts(11,3): error TS2416: Property 'method1' in type 'B' is not assignable to the same property in base type 'A'.
+  Type '() => void' is not assignable to type '() => this is { a: 1; }'.
+    Signature '(): void' must be a type predicate.
+typePredicateInherit.ts(13,3): error TS2416: Property 'method2' in type 'B' is not assignable to the same property in base type 'A'.
+  Type '() => void' is not assignable to type '() => boolean'.
+    Type 'void' is not assignable to type 'boolean'.
+typePredicateInherit.ts(15,3): error TS2416: Property 'method3' in type 'B' is not assignable to the same property in base type 'A'.
+  Type '() => boolean' is not assignable to type '() => this is { a: 1; }'.
+    Signature '(): boolean' must be a type predicate.
+typePredicateInherit.ts(41,3): error TS2416: Property 'method1' in type 'D' is not assignable to the same property in base type 'C'.
+  Type '() => void' is not assignable to type '() => this is { a: 1; }'.
+    Signature '(): void' must be a type predicate.
+typePredicateInherit.ts(50,3): error TS2416: Property 'method3' in type 'D' is not assignable to the same property in base type 'C'.
+  Type '() => boolean' is not assignable to type '() => this is { a: 1; }'.
+    Signature '(): boolean' must be a type predicate.
+
+
+==== typePredicateInherit.ts (5 errors) ====
+    interface A {
+      method1(): this is {
+        a: 1
+      }
+      method2(): boolean;
+      method3(): this is {
+        a: 1
+      };
+    }
+    class B implements A {
+      method1() { }      // should error
+      ~~~~~~~
+!!! error TS2416: Property 'method1' in type 'B' is not assignable to the same property in base type 'A'.
+!!! error TS2416:   Type '() => void' is not assignable to type '() => this is { a: 1; }'.
+!!! error TS2416:     Signature '(): void' must be a type predicate.
+
+      method2() { }   // should error
+      ~~~~~~~
+!!! error TS2416: Property 'method2' in type 'B' is not assignable to the same property in base type 'A'.
+!!! error TS2416:   Type '() => void' is not assignable to type '() => boolean'.
+!!! error TS2416:     Type 'void' is not assignable to type 'boolean'.
+
+      method3() {   // should error
+      ~~~~~~~
+!!! error TS2416: Property 'method3' in type 'B' is not assignable to the same property in base type 'A'.
+!!! error TS2416:   Type '() => boolean' is not assignable to type '() => this is { a: 1; }'.
+!!! error TS2416:     Signature '(): boolean' must be a type predicate.
+        return true
+      }
+    }
+
+    class C {
+      method1(): this is {
+        a: 1
+      } {
+        return true;
+      }
+
+      method2(): this is {
+        a: 1
+      } {
+        return true;
+      }
+
+      method3(): this is {
+        a: 1
+      } {
+        return true;
+      }
+    }
+
+    class D extends C {
+      method1(): void {   // should error
+      ~~~~~~~
+!!! error TS2416: Property 'method1' in type 'D' is not assignable to the same property in base type 'C'.
+!!! error TS2416:   Type '() => void' is not assignable to type '() => this is { a: 1; }'.
+!!! error TS2416:     Signature '(): void' must be a type predicate.
+      }
+
+      method2(): this is {  // should ok
+        a: 1
+      } {
+        return true;
+      }
+
+      method3(): boolean {  // should error
+      ~~~~~~~
+!!! error TS2416: Property 'method3' in type 'D' is not assignable to the same property in base type 'C'.
+!!! error TS2416:   Type '() => boolean' is not assignable to type '() => this is { a: 1; }'.
+!!! error TS2416:     Signature '(): boolean' must be a type predicate.
+        return true;
+      }
+    }

tests/baselines/reference/typePredicateInherit.js

@@ -0,0 +1,112 @@
+//// [tests/cases/compiler/typePredicateInherit.ts] ////
+
+//// [typePredicateInherit.ts]
+interface A {
+  method1(): this is {
+    a: 1
+  }
+  method2(): boolean;
+  method3(): this is {
+    a: 1
+  };
+}
+class B implements A {
+  method1() { }      // should error
+
+  method2() { }   // should error
+
+  method3() {   // should error
+    return true
+  }
+}
+
+class C {
+  method1(): this is {
+    a: 1
+  } {
+    return true;
+  }
+
+  method2(): this is {
+    a: 1
+  } {
+    return true;
+  }
+
+  method3(): this is {
+    a: 1
+  } {
+    return true;
+  }
+}
+
+class D extends C {
+  method1(): void {   // should error
+  }
+
+  method2(): this is {  // should ok
+    a: 1
+  } {
+    return true;
+  }
+
+  method3(): boolean {  // should error
+    return true;
+  }
+}
+
+//// [typePredicateInherit.js]
+var __extends = (this && this.__extends) || (function () {
+    var extendStatics = function (d, b) {
+        extendStatics = Object.setPrototypeOf ||
+            ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
+            function (d, b) { for (var p in b) if (Object.prototype.hasOwnProperty.call(b, p)) d[p] = b[p]; };
+        return extendStatics(d, b);
+    };
+    return function (d, b) {
+        if (typeof b !== "function" && b !== null)
+            throw new TypeError("Class extends value " + String(b) + " is not a constructor or null");
+        extendStatics(d, b);
+        function __() { this.constructor = d; }
+        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+    };
+})();
+var B = /** @class */ (function () {
+    function B() {
+    }
+    B.prototype.method1 = function () { }; // should error
+    B.prototype.method2 = function () { }; // should error
+    B.prototype.method3 = function () {
+        return true;
+    };
+    return B;
+}());
+var C = /** @class */ (function () {
+    function C() {
+    }
+    C.prototype.method1 = function () {
+        return true;
+    };
+    C.prototype.method2 = function () {
+        return true;
+    };
+    C.prototype.method3 = function () {
+        return true;
+    };
+    return C;
+}());
+var D = /** @class */ (function (_super) {
+    __extends(D, _super);
+    function D() {
+        return _super !== null && _super.apply(this, arguments) || this;
+    }
+    D.prototype.method1 = function () {
+    };
+    D.prototype.method2 = function () {
+        return true;
+    };
+    D.prototype.method3 = function () {
+        return true;
+    };
+    return D;
+}(C));