🤖 Pick PR #52984 (Check for strict subtypes and then ...) into releas…

…e-5.0 (#53085)

Co-authored-by: Anders Hejlsberg <andersh@microsoft.com>

src/compiler/checker.ts

@@ -19108,6 +19108,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return isTypeRelatedTo(source, target, subtypeRelation);
     }
 
+    function isTypeStrictSubtypeOf(source: Type, target: Type): boolean {
+        return isTypeRelatedTo(source, target, strictSubtypeRelation);
+    }
+
     function isTypeAssignableTo(source: Type, target: Type): boolean {
         return isTypeRelatedTo(source, target, assignableRelation);
     }
@@ -27262,7 +27266,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 // prototype object types.
                 const directlyRelated = mapType(matching || type, checkDerived ?
                     t => isTypeDerivedFrom(t, c) ? t : isTypeDerivedFrom(c, t) ? c : neverType :
-                    t => isTypeSubtypeOf(c, t) && !isTypeIdenticalTo(c, t) ? c : isTypeSubtypeOf(t, c) ? t : neverType);
+                    t => isTypeStrictSubtypeOf(t, c) ? t : isTypeStrictSubtypeOf(c, t) ? c : isTypeSubtypeOf(t, c) ? t : isTypeSubtypeOf(c, t) ? c : neverType);
                 // If no constituents are directly related, create intersections for any generic constituents that
                 // are related by constraint.
                 return directlyRelated.flags & TypeFlags.Never ?

tests/baselines/reference/controlFlowFavorAssertedTypeThroughTypePredicate.types

@@ -58,11 +58,11 @@ if (isObject2(obj3)) {
 >obj3 : Record<string, unknown>
 
     obj3;
->obj3 : {}
+>obj3 : Record<string, unknown>
 
     obj3['attr'];
->obj3['attr'] : any
->obj3 : {}
+>obj3['attr'] : unknown
+>obj3 : Record<string, unknown>
 >'attr' : "attr"
 }
 // check type after conditional block
@@ -78,11 +78,11 @@ if (isObject2(obj4)) {
 >obj4 : Record<string, unknown> | undefined
 
     obj4;
->obj4 : {}
+>obj4 : Record<string, unknown>
 
     obj4['attr'];
->obj4['attr'] : any
->obj4 : {}
+>obj4['attr'] : unknown
+>obj4 : Record<string, unknown>
 >'attr' : "attr"
 }
 // check type after conditional block

tests/baselines/reference/narrowingMutualSubtypes.types

@@ -123,11 +123,11 @@ function gg2(x: Record<string, unknown>) {
 >x : Record<string, unknown>
 
         x;  // {}
->x : {}
+>x : Record<string, unknown>
     }
     else {
         x;  // Record<string, unknown>
->x : Record<string, unknown>
+>x : never
     }
     x;  // Record<string, unknown>
 >x : Record<string, unknown>

tests/baselines/reference/strictSubtypeAndNarrowing.errors.txt

@@ -146,4 +146,104 @@ tests/cases/compiler/strictSubtypeAndNarrowing.ts(129,26): error TS2322: Type '{
 !!! error TS2322: Type '{ x: number; y: number; }' is not assignable to type '{ x?: number | undefined; }'.
 !!! error TS2322:   Object literal may only specify known properties, and 'y' does not exist in type '{ x?: number | undefined; }'.
     }
+
+    // Repros from #52827
+
+    declare function isArrayLike(value: any): value is { length: number };
+
+    function ff1(value: { [index: number]: boolean, length: number } | undefined) {
+        if (isArrayLike(value)) {
+            value;
+        } else {
+            value;
+        }
+        value;
+    }
+
+    function ff2(value: { [index: number]: boolean, length: number } | string) {
+        if (isArrayLike(value)) {
+            value;
+        } else {
+            value;
+        }
+        value;
+    }
+
+    function ff3(value: string | string[] | { [index: number]: boolean, length: number } | [number, boolean] | number | { length: string } | { a: string } | null | undefined) {
+        if (isArrayLike(value)) {
+            value;
+        } else {
+            value;
+        }
+        value;
+    }
+
+    // Repro from comment in #52984
+
+    type DistributedKeyOf<T> = T extends unknown ? keyof T : never;
+
+    type NarrowByKeyValue<ObjT, KeyT extends PropertyKey, ValueT> = ObjT extends unknown
+        ? KeyT extends keyof ObjT
+            ? ValueT extends ObjT[KeyT]
+                ? ObjT & Readonly<Record<KeyT, ValueT>>
+                : never
+            : never
+        : never;
+
+    type NarrowByDeepValue<ObjT, DeepPathT, ValueT> = DeepPathT extends readonly [
+        infer Head extends DistributedKeyOf<ObjT>,
+    ]
+        ? NarrowByKeyValue<ObjT, Head, ValueT>
+        : DeepPathT extends readonly [infer Head extends DistributedKeyOf<ObjT>, ...infer Rest]
+        ? NarrowByKeyValue<ObjT, Head, NarrowByDeepValue<NonNullable<ObjT[Head]>, Rest, ValueT>>
+        : never;
+
+
+    declare function doesValueAtDeepPathSatisfy<
+        ObjT extends object,
+        const DeepPathT extends ReadonlyArray<number | string>,
+        ValueT,
+    >(
+        obj: ObjT,
+        deepPath: DeepPathT,
+        predicate: (arg: unknown) => arg is ValueT,
+    ): obj is NarrowByDeepValue<ObjT, DeepPathT, ValueT>;
+
+
+    type Foo = {value: {type: 'A'}; a?: number} | {value: {type: 'B'}; b?: number};
+
+    declare function isA(arg: unknown): arg is 'A';
+    declare function isB(arg: unknown): arg is 'B';
+
+    declare function assert(condition: boolean): asserts condition;
+
+    function test1(foo: Foo): {value: {type: 'A'}; a?: number} {
+        assert(doesValueAtDeepPathSatisfy(foo, ['value', 'type'], isA));
+        return foo;
+    }
+
+    function test2(foo: Foo): {value: {type: 'A'}; a?: number} {
+        assert(!doesValueAtDeepPathSatisfy(foo, ['value', 'type'], isB));
+        return foo;
+    }
+
+    // Repro from #53063
+
+    interface Free {
+        premium: false;
+    }
+
+    interface Premium {
+        premium: true;
+    }
+
+    type Union = { premium: false } | { premium: true };
+
+    declare const checkIsPremium: (a: Union) => a is Union & Premium;
+
+    const f = (value: Union) => {
+        if (!checkIsPremium(value)) {
+            value.premium;
+        }
+    };
 

tests/baselines/reference/strictSubtypeAndNarrowing.js

@@ -129,6 +129,106 @@ function fx11(): { x?: number } {
     let obj: { x?: number, y?: number };
     return obj = { x: 1, y: 2 };
 }
+
+// Repros from #52827
+
+declare function isArrayLike(value: any): value is { length: number };
+
+function ff1(value: { [index: number]: boolean, length: number } | undefined) {
+    if (isArrayLike(value)) {
+        value;
+    } else {
+        value;
+    }
+    value;
+}
+
+function ff2(value: { [index: number]: boolean, length: number } | string) {
+    if (isArrayLike(value)) {
+        value;
+    } else {
+        value;
+    }
+    value;
+}
+
+function ff3(value: string | string[] | { [index: number]: boolean, length: number } | [number, boolean] | number | { length: string } | { a: string } | null | undefined) {
+    if (isArrayLike(value)) {
+        value;
+    } else {
+        value;
+    }
+    value;
+}
+
+// Repro from comment in #52984
+
+type DistributedKeyOf<T> = T extends unknown ? keyof T : never;
+
+type NarrowByKeyValue<ObjT, KeyT extends PropertyKey, ValueT> = ObjT extends unknown
+    ? KeyT extends keyof ObjT
+        ? ValueT extends ObjT[KeyT]
+            ? ObjT & Readonly<Record<KeyT, ValueT>>
+            : never
+        : never
+    : never;
+
+type NarrowByDeepValue<ObjT, DeepPathT, ValueT> = DeepPathT extends readonly [
+    infer Head extends DistributedKeyOf<ObjT>,
+]
+    ? NarrowByKeyValue<ObjT, Head, ValueT>
+    : DeepPathT extends readonly [infer Head extends DistributedKeyOf<ObjT>, ...infer Rest]
+    ? NarrowByKeyValue<ObjT, Head, NarrowByDeepValue<NonNullable<ObjT[Head]>, Rest, ValueT>>
+    : never;
+
+
+declare function doesValueAtDeepPathSatisfy<
+    ObjT extends object,
+    const DeepPathT extends ReadonlyArray<number | string>,
+    ValueT,
+>(
+    obj: ObjT,
+    deepPath: DeepPathT,
+    predicate: (arg: unknown) => arg is ValueT,
+): obj is NarrowByDeepValue<ObjT, DeepPathT, ValueT>;
+
+
+type Foo = {value: {type: 'A'}; a?: number} | {value: {type: 'B'}; b?: number};
+
+declare function isA(arg: unknown): arg is 'A';
+declare function isB(arg: unknown): arg is 'B';
+
+declare function assert(condition: boolean): asserts condition;
+
+function test1(foo: Foo): {value: {type: 'A'}; a?: number} {
+    assert(doesValueAtDeepPathSatisfy(foo, ['value', 'type'], isA));
+    return foo;
+}
+
+function test2(foo: Foo): {value: {type: 'A'}; a?: number} {
+    assert(!doesValueAtDeepPathSatisfy(foo, ['value', 'type'], isB));
+    return foo;
+}
+
+// Repro from #53063
+
+interface Free {
+    premium: false;
+}
+
+interface Premium {
+    premium: true;
+}
+
+type Union = { premium: false } | { premium: true };
+
+declare const checkIsPremium: (a: Union) => a is Union & Premium;
+
+const f = (value: Union) => {
+    if (!checkIsPremium(value)) {
+        value.premium;
+    }
+};
 
 
 //// [strictSubtypeAndNarrowing.js]
@@ -226,3 +326,43 @@ function fx11() {
     var obj;
     return obj = { x: 1, y: 2 };
 }
+function ff1(value) {
+    if (isArrayLike(value)) {
+        value;
+    }
+    else {
+        value;
+    }
+    value;
+}
+function ff2(value) {
+    if (isArrayLike(value)) {
+        value;
+    }
+    else {
+        value;
+    }
+    value;
+}
+function ff3(value) {
+    if (isArrayLike(value)) {
+        value;
+    }
+    else {
+        value;
+    }
+    value;
+}
+function test1(foo) {
+    assert(doesValueAtDeepPathSatisfy(foo, ['value', 'type'], isA));
+    return foo;
+}
+function test2(foo) {
+    assert(!doesValueAtDeepPathSatisfy(foo, ['value', 'type'], isB));
+    return foo;
+}
+var f = function (value) {
+    if (!checkIsPremium(value)) {
+        value.premium;
+    }
+};