allow extends type to be supertype of constraint types

2026-06-17 21:09:09 -05:00 · 2025-02-04 13:22:26 -08:00
parent c50b5e718a
commit a668b6b19b
6 changed files with 309 additions and 9 deletions
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -46082,7 +46082,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
    // (0) The conditional type is distributive;
    // (1) The conditional type has no `infer` type parameters;
    // (2) The conditional type's check type is a narrowable type parameter (i.e. a type parameter with a union constraint);
-    // (3) The extends type `A` is a type or a union of types belonging to the union constraint of the type parameter;
+    // (3) The extends type `A` is a type or a union of types that are supertypes of the union constraint of the type parameter;
    // (4) `TrueBranch<T>` and `FalseBranch<T>` must be valid, recursively.
    //      In particular, the false-most branch of the conditional type must be `never`.
    function isNarrowableConditionalTypeWorker(type: ConditionalType): boolean {
@@ -46111,7 +46111,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
            !everyType(type.extendsType, extendsType =>
                some(
                    (constraintType as UnionType).types,
-                    constraintType => isTypeIdenticalTo(constraintType, extendsType),
+                    constraintType => isTypeAssignableTo(constraintType, extendsType),
                ))
        ) {
            return false;
--- a/tests/baselines/reference/dependentReturnType1.errors.txt
+++ b/tests/baselines/reference/dependentReturnType1.errors.txt
@@ -26,8 +26,6 @@ dependentReturnType1.ts(275,9): error TS2322: Type '1' is not assignable to type
 dependentReturnType1.ts(278,9): error TS2322: Type '2' is not assignable to type 'HelperCond<{ x: U; y: V; }, { x: string; y: true; }, 1, { x: number; y: false; }, 2>'.
 dependentReturnType1.ts(280,5): error TS2322: Type '0' is not assignable to type 'HelperCond<{ x: U; y: V; }, { x: string; y: true; }, 1, { x: number; y: false; }, 2>'.
 dependentReturnType1.ts(302,9): error TS2322: Type 'string' is not assignable to type 'string[]'.
-dependentReturnType1.ts(311,9): error TS2322: Type 'undefined' is not assignable to type 'T extends {} ? void : T extends undefined ? number : never'.
-dependentReturnType1.ts(313,5): error TS2322: Type 'number' is not assignable to type 'T extends {} ? void : T extends undefined ? number : never'.
 dependentReturnType1.ts(334,9): error TS2322: Type '1' is not assignable to type '4'.
 dependentReturnType1.ts(367,13): error TS2322: Type 'number' is not assignable to type 'T extends 1 ? number : T extends 2 ? string : never'.
 dependentReturnType1.ts(369,9): error TS2322: Type 'string' is not assignable to type 'T extends 1 ? number : T extends 2 ? string : never'.
@@ -44,7 +42,7 @@ dependentReturnType1.ts(488,9): error TS2322: Type 'R' is not assignable to type
 dependentReturnType1.ts(514,5): error TS2322: Type '1' is not assignable to type 'never'.


-==== dependentReturnType1.ts (39 errors) ====
+==== dependentReturnType1.ts (37 errors) ====
    interface A {
        1: number;
        2: string;
@@ -407,12 +405,8 @@ dependentReturnType1.ts(514,5): error TS2322: Type '1' is not assignable to type
    ): T extends {} ? void : T extends undefined ? number : never {
        if (x) {
            return;
-            ~~~~~~
-!!! error TS2322: Type 'undefined' is not assignable to type 'T extends {} ? void : T extends undefined ? number : never'.
        }
        return 1;
-        ~~~~~~
-!!! error TS2322: Type 'number' is not assignable to type 'T extends {} ? void : T extends undefined ? number : never'.
    }
    
    // Multiple type parameters at once
--- a/tests/baselines/reference/dependentReturnType10.errors.txt
+++ b/tests/baselines/reference/dependentReturnType10.errors.txt
@@ -0,0 +1,41 @@
+dependentReturnType10.ts(29,9): error TS2322: Type 'number' is not assignable to type 'void'.
+
+
+==== dependentReturnType10.ts (1 errors) ====
+    interface Animal {
+        name: string;
+        species: string;
+    }
+    
+    interface Dog extends Animal {
+        breed: string;
+    }
+    
+    type GreetRet<T> =
+        T extends string ? string :
+        T extends { name: string } ? { greeting: string, breed: string } :
+        never;
+    
+    function greet<T extends string | Dog>(animal: T): GreetRet<T> {
+        if (typeof animal === "string") {
+            return `hello, ${animal}`
+        }
+        return { greeting: `woof, ${animal.name}`, breed: animal.breed }
+    }
+    
+    type BadRet<T> =
+        T extends {} ? void :
+        T extends string ? number :
+        never;
+    
+    function badFun<T extends { a: string } | string>(x: T): BadRet<T> {
+        if (typeof x === "string") {
+            return 1
+            ~~~~~~
+!!! error TS2322: Type 'number' is not assignable to type 'void'.
+        }
+        return;
+    }
+    
+    declare let arg2: { a: string } | string;
+    const badRet = badFun(arg2);
--- a/tests/baselines/reference/dependentReturnType10.symbols
+++ b/tests/baselines/reference/dependentReturnType10.symbols
@@ -0,0 +1,100 @@
+//// [tests/cases/compiler/dependentReturnType10.ts] ////
+
+=== dependentReturnType10.ts ===
+interface Animal {
+>Animal : Symbol(Animal, Decl(dependentReturnType10.ts, 0, 0))
+
+    name: string;
+>name : Symbol(Animal.name, Decl(dependentReturnType10.ts, 0, 18))
+
+    species: string;
+>species : Symbol(Animal.species, Decl(dependentReturnType10.ts, 1, 17))
+}
+
+interface Dog extends Animal {
+>Dog : Symbol(Dog, Decl(dependentReturnType10.ts, 3, 1))
+>Animal : Symbol(Animal, Decl(dependentReturnType10.ts, 0, 0))
+
+    breed: string;
+>breed : Symbol(Dog.breed, Decl(dependentReturnType10.ts, 5, 30))
+}
+
+type GreetRet<T> =
+>GreetRet : Symbol(GreetRet, Decl(dependentReturnType10.ts, 7, 1))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 9, 14))
+
+    T extends string ? string :
+>T : Symbol(T, Decl(dependentReturnType10.ts, 9, 14))
+
+    T extends { name: string } ? { greeting: string, breed: string } :
+>T : Symbol(T, Decl(dependentReturnType10.ts, 9, 14))
+>name : Symbol(name, Decl(dependentReturnType10.ts, 11, 15))
+>greeting : Symbol(greeting, Decl(dependentReturnType10.ts, 11, 34))
+>breed : Symbol(breed, Decl(dependentReturnType10.ts, 11, 52))
+
+    never;
+
+function greet<T extends string | Dog>(animal: T): GreetRet<T> {
+>greet : Symbol(greet, Decl(dependentReturnType10.ts, 12, 10))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 14, 15))
+>Dog : Symbol(Dog, Decl(dependentReturnType10.ts, 3, 1))
+>animal : Symbol(animal, Decl(dependentReturnType10.ts, 14, 39))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 14, 15))
+>GreetRet : Symbol(GreetRet, Decl(dependentReturnType10.ts, 7, 1))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 14, 15))
+
+    if (typeof animal === "string") {
+>animal : Symbol(animal, Decl(dependentReturnType10.ts, 14, 39))
+
+        return `hello, ${animal}`
+>animal : Symbol(animal, Decl(dependentReturnType10.ts, 14, 39))
+    }
+    return { greeting: `woof, ${animal.name}`, breed: animal.breed }
+>greeting : Symbol(greeting, Decl(dependentReturnType10.ts, 18, 12))
+>animal.name : Symbol(Animal.name, Decl(dependentReturnType10.ts, 0, 18))
+>animal : Symbol(animal, Decl(dependentReturnType10.ts, 14, 39))
+>name : Symbol(Animal.name, Decl(dependentReturnType10.ts, 0, 18))
+>breed : Symbol(breed, Decl(dependentReturnType10.ts, 18, 46))
+>animal.breed : Symbol(Dog.breed, Decl(dependentReturnType10.ts, 5, 30))
+>animal : Symbol(animal, Decl(dependentReturnType10.ts, 14, 39))
+>breed : Symbol(Dog.breed, Decl(dependentReturnType10.ts, 5, 30))
+}
+
+type BadRet<T> =
+>BadRet : Symbol(BadRet, Decl(dependentReturnType10.ts, 19, 1))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 21, 12))
+
+    T extends {} ? void :
+>T : Symbol(T, Decl(dependentReturnType10.ts, 21, 12))
+
+    T extends string ? number :
+>T : Symbol(T, Decl(dependentReturnType10.ts, 21, 12))
+
+    never;
+
+function badFun<T extends { a: string } | string>(x: T): BadRet<T> {
+>badFun : Symbol(badFun, Decl(dependentReturnType10.ts, 24, 10))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 26, 16))
+>a : Symbol(a, Decl(dependentReturnType10.ts, 26, 27))
+>x : Symbol(x, Decl(dependentReturnType10.ts, 26, 50))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 26, 16))
+>BadRet : Symbol(BadRet, Decl(dependentReturnType10.ts, 19, 1))
+>T : Symbol(T, Decl(dependentReturnType10.ts, 26, 16))
+
+    if (typeof x === "string") {
+>x : Symbol(x, Decl(dependentReturnType10.ts, 26, 50))
+
+        return 1
+    }
+    return;
+}
+
+declare let arg2: { a: string } | string;
+>arg2 : Symbol(arg2, Decl(dependentReturnType10.ts, 33, 11))
+>a : Symbol(a, Decl(dependentReturnType10.ts, 33, 19))
+
+const badRet = badFun(arg2);
+>badRet : Symbol(badRet, Decl(dependentReturnType10.ts, 34, 5))
+>badFun : Symbol(badFun, Decl(dependentReturnType10.ts, 24, 10))
+>arg2 : Symbol(arg2, Decl(dependentReturnType10.ts, 33, 11))
+
--- a/tests/baselines/reference/dependentReturnType10.types
+++ b/tests/baselines/reference/dependentReturnType10.types
@@ -0,0 +1,128 @@
+//// [tests/cases/compiler/dependentReturnType10.ts] ////
+
+=== dependentReturnType10.ts ===
+interface Animal {
+    name: string;
+>name : string
+>     : ^^^^^^
+
+    species: string;
+>species : string
+>        : ^^^^^^
+}
+
+interface Dog extends Animal {
+    breed: string;
+>breed : string
+>      : ^^^^^^
+}
+
+type GreetRet<T> =
+>GreetRet : GreetRet<T>
+>         : ^^^^^^^^^^^
+
+    T extends string ? string :
+    T extends { name: string } ? { greeting: string, breed: string } :
+>name : string
+>     : ^^^^^^
+>greeting : string
+>         : ^^^^^^
+>breed : string
+>      : ^^^^^^
+
+    never;
+
+function greet<T extends string | Dog>(animal: T): GreetRet<T> {
+>greet : <T extends string | Dog>(animal: T) => GreetRet<T>
+>      : ^ ^^^^^^^^^            ^^      ^^ ^^^^^           
+>animal : T
+>       : ^
+
+    if (typeof animal === "string") {
+>typeof animal === "string" : boolean
+>                           : ^^^^^^^
+>typeof animal : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>              : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>animal : T
+>       : ^
+>"string" : "string"
+>         : ^^^^^^^^
+
+        return `hello, ${animal}`
+>`hello, ${animal}` : string
+>                   : ^^^^^^
+>animal : T & string
+>       : ^^^^^^^^^^
+    }
+    return { greeting: `woof, ${animal.name}`, breed: animal.breed }
+>{ greeting: `woof, ${animal.name}`, breed: animal.breed } : { greeting: string; breed: string; }
+>                                                          : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>greeting : string
+>         : ^^^^^^
+>`woof, ${animal.name}` : string
+>                       : ^^^^^^
+>animal.name : string
+>            : ^^^^^^
+>animal : Dog
+>       : ^^^
+>name : string
+>     : ^^^^^^
+>breed : string
+>      : ^^^^^^
+>animal.breed : string
+>             : ^^^^^^
+>animal : Dog
+>       : ^^^
+>breed : string
+>      : ^^^^^^
+}
+
+type BadRet<T> =
+>BadRet : BadRet<T>
+>       : ^^^^^^^^^
+
+    T extends {} ? void :
+    T extends string ? number :
+    never;
+
+function badFun<T extends { a: string } | string>(x: T): BadRet<T> {
+>badFun : <T extends { a: string; } | string>(x: T) => BadRet<T>
+>       : ^ ^^^^^^^^^                       ^^ ^^ ^^^^^         
+>a : string
+>  : ^^^^^^
+>x : T
+>  : ^
+
+    if (typeof x === "string") {
+>typeof x === "string" : boolean
+>                      : ^^^^^^^
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>         : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>x : T
+>  : ^
+>"string" : "string"
+>         : ^^^^^^^^
+
+        return 1
+>1 : 1
+>  : ^
+    }
+    return;
+}
+
+declare let arg2: { a: string } | string;
+>arg2 : string | { a: string; }
+>     : ^^^^^^^^^^^^^^      ^^^
+>a : string
+>  : ^^^^^^
+
+const badRet = badFun(arg2);
+>badRet : void
+>       : ^^^^
+>badFun(arg2) : void
+>             : ^^^^
+>badFun : <T extends { a: string; } | string>(x: T) => BadRet<T>
+>       : ^ ^^^^^^^^^                       ^^ ^^ ^^^^^         
+>arg2 : string | { a: string; }
+>     : ^^^^^^^^^^^^^^      ^^^
+
--- a/tests/cases/compiler/dependentReturnType10.ts
+++ b/tests/cases/compiler/dependentReturnType10.ts
@@ -0,0 +1,37 @@
+// @noEmit: true
+
+interface Animal {
+    name: string;
+    species: string;
+}
+
+interface Dog extends Animal {
+    breed: string;
+}
+
+type GreetRet<T> =
+    T extends string ? string :
+    T extends { name: string } ? { greeting: string, breed: string } :
+    never;
+
+function greet<T extends string | Dog>(animal: T): GreetRet<T> {
+    if (typeof animal === "string") {
+        return `hello, ${animal}`
+    }
+    return { greeting: `woof, ${animal.name}`, breed: animal.breed }
+}
+
+type BadRet<T> =
+    T extends {} ? void :
+    T extends string ? number :
+    never;
+
+function badFun<T extends { a: string } | string>(x: T): BadRet<T> {
+    if (typeof x === "string") {
+        return 1
+    }
+    return;
+}
+
+declare let arg2: { a: string } | string;
+const badRet = badFun(arg2);