Allow getter and setter types to be unrelated

src/compiler/checker.ts

@@ -38443,12 +38443,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         error(getter.name, Diagnostics.A_get_accessor_must_be_at_least_as_accessible_as_the_setter);
                         error(setter.name, Diagnostics.A_get_accessor_must_be_at_least_as_accessible_as_the_setter);
                     }
-
-                    const getterType = getAnnotatedAccessorType(getter);
-                    const setterType = getAnnotatedAccessorType(setter);
-                    if (getterType && setterType) {
-                        checkTypeAssignableTo(getterType, setterType, getter, Diagnostics.The_return_type_of_a_get_accessor_must_be_assignable_to_its_set_accessor_type);
-                    }
                 }
             }
             const returnType = getTypeOfAccessors(getSymbolOfDeclaration(node));

src/compiler/diagnosticMessages.json

@@ -1964,10 +1964,6 @@
         "category": "Error",
         "code": 2379
     },
-    "The return type of a 'get' accessor must be assignable to its 'set' accessor type": {
-        "category": "Error",
-        "code": 2380
-    },
     "Overload signatures must all be exported or non-exported.": {
         "category": "Error",
         "code": 2383

tests/baselines/reference/abstractPropertyNegative.errors.txt

@@ -1,4 +1,3 @@
-tests/cases/compiler/abstractPropertyNegative.ts(10,18): error TS2380: The return type of a 'get' accessor must be assignable to its 'set' accessor type
 tests/cases/compiler/abstractPropertyNegative.ts(13,7): error TS2515: Non-abstract class 'C' does not implement inherited abstract member 'm' from class 'B'.
 tests/cases/compiler/abstractPropertyNegative.ts(13,7): error TS2515: Non-abstract class 'C' does not implement inherited abstract member 'mismatch' from class 'B'.
 tests/cases/compiler/abstractPropertyNegative.ts(13,7): error TS2515: Non-abstract class 'C' does not implement inherited abstract member 'prop' from class 'B'.
@@ -18,7 +17,7 @@ tests/cases/compiler/abstractPropertyNegative.ts(40,9): error TS2676: Accessors
 tests/cases/compiler/abstractPropertyNegative.ts(41,18): error TS2676: Accessors must both be abstract or non-abstract.
 
 
-==== tests/cases/compiler/abstractPropertyNegative.ts (15 errors) ====
+==== tests/cases/compiler/abstractPropertyNegative.ts (14 errors) ====
     interface A {
         prop: string;
         m(): string;
@@ -29,9 +28,7 @@ tests/cases/compiler/abstractPropertyNegative.ts(41,18): error TS2676: Accessors
         abstract get readonlyProp(): string;
         abstract m(): string;
         abstract get mismatch(): string;
-                     ~~~~~~~~
-!!! error TS2380: The return type of a 'get' accessor must be assignable to its 'set' accessor type
-        abstract set mismatch(val: number); // error, not same type
+        abstract set mismatch(val: number);
     }
     class C extends B {
           ~

tests/baselines/reference/divergentAccessorsTypes6.errors.txt

@@ -0,0 +1,50 @@
+tests/cases/compiler/divergentAccessorsTypes6.ts(11,1): error TS2322: Type 'CSSStyleDeclaration' is not assignable to type 'string'.
+tests/cases/compiler/divergentAccessorsTypes6.ts(19,23): error TS2344: Type 'string' does not satisfy the constraint 'never'.
+tests/cases/compiler/divergentAccessorsTypes6.ts(23,23): error TS2344: Type 'string' does not satisfy the constraint 'never'.
+tests/cases/compiler/divergentAccessorsTypes6.ts(29,16): error TS2322: Type 'number' is not assignable to type 'string'.
+
+
+==== tests/cases/compiler/divergentAccessorsTypes6.ts (4 errors) ====
+    export {};
+
+    interface Element {
+        get style(): CSSStyleDeclaration;
+        set style(cssText: string);
+    }
+
+    declare const element: Element;
+    element.style = "color: red";
+    element.style.animationTimingFunction;
+    element.style = element.style; // error
+    ~~~~~~~~~~~~~
+!!! error TS2322: Type 'CSSStyleDeclaration' is not assignable to type 'string'.
+
+    // Now that we don't check for getter/setter assignability, we should
+    // ensure the setter annotation is actually checked even if it's never observed.
+
+    type Fail<T extends never> = T;
+    interface I1 {
+        get x(): number;
+        set x(value: Fail<string>);
+                          ~~~~~~
+!!! error TS2344: Type 'string' does not satisfy the constraint 'never'.
+    }
+    const o1 = {
+        get x(): number { return 0; },
+        set x(value: Fail<string>) {}
+                          ~~~~~~
+!!! error TS2344: Type 'string' does not satisfy the constraint 'never'.
+    }
+
+    // A setter annotation still implies the getter return type.
+
+    const o2 = {
+        get p1() { return 0; }, // error - no annotation means type is implied from the setter annotation
+                   ~~~~~~
+!!! error TS2322: Type 'number' is not assignable to type 'string'.
+        set p1(value: string) {},
+
+        get p2(): number { return 0; }, // ok - explicit annotation
+        set p2(value: string) {},
+    };
+

tests/baselines/reference/divergentAccessorsTypes6.js

@@ -0,0 +1,58 @@
+//// [divergentAccessorsTypes6.ts]
+export {};
+
+interface Element {
+    get style(): CSSStyleDeclaration;
+    set style(cssText: string);
+}
+
+declare const element: Element;
+element.style = "color: red";
+element.style.animationTimingFunction;
+element.style = element.style; // error
+
+// Now that we don't check for getter/setter assignability, we should
+// ensure the setter annotation is actually checked even if it's never observed.
+
+type Fail<T extends never> = T;
+interface I1 {
+    get x(): number;
+    set x(value: Fail<string>);
+}
+const o1 = {
+    get x(): number { return 0; },
+    set x(value: Fail<string>) {}
+}
+
+// A setter annotation still implies the getter return type.
+
+const o2 = {
+    get p1() { return 0; }, // error - no annotation means type is implied from the setter annotation
+    set p1(value: string) {},
+
+    get p2(): number { return 0; }, // ok - explicit annotation
+    set p2(value: string) {},
+};
+
+
+//// [divergentAccessorsTypes6.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+element.style = "color: red";
+element.style.animationTimingFunction;
+element.style = element.style; // error
+var o1 = {
+    get x() { return 0; },
+    set x(value) { }
+};
+// A setter annotation still implies the getter return type.
+var o2 = {
+    get p1() { return 0; },
+    set p1(value) { },
+    get p2() { return 0; },
+    set p2(value) { },
+};
+
+
+//// [divergentAccessorsTypes6.d.ts]
+export {};

tests/baselines/reference/divergentAccessorsTypes6.symbols

@@ -0,0 +1,91 @@
+=== tests/cases/compiler/divergentAccessorsTypes6.ts ===
+export {};
+
+interface Element {
+>Element : Symbol(Element, Decl(divergentAccessorsTypes6.ts, 0, 10))
+
+    get style(): CSSStyleDeclaration;
+>style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>CSSStyleDeclaration : Symbol(CSSStyleDeclaration, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+
+    set style(cssText: string);
+>style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>cssText : Symbol(cssText, Decl(divergentAccessorsTypes6.ts, 4, 14))
+}
+
+declare const element: Element;
+>element : Symbol(element, Decl(divergentAccessorsTypes6.ts, 7, 13))
+>Element : Symbol(Element, Decl(divergentAccessorsTypes6.ts, 0, 10))
+
+element.style = "color: red";
+>element.style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>element : Symbol(element, Decl(divergentAccessorsTypes6.ts, 7, 13))
+>style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+
+element.style.animationTimingFunction;
+>element.style.animationTimingFunction : Symbol(CSSStyleDeclaration.animationTimingFunction, Decl(lib.dom.d.ts, --, --))
+>element.style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>element : Symbol(element, Decl(divergentAccessorsTypes6.ts, 7, 13))
+>style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>animationTimingFunction : Symbol(CSSStyleDeclaration.animationTimingFunction, Decl(lib.dom.d.ts, --, --))
+
+element.style = element.style; // error
+>element.style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>element : Symbol(element, Decl(divergentAccessorsTypes6.ts, 7, 13))
+>style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>element.style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+>element : Symbol(element, Decl(divergentAccessorsTypes6.ts, 7, 13))
+>style : Symbol(Element.style, Decl(divergentAccessorsTypes6.ts, 2, 19), Decl(divergentAccessorsTypes6.ts, 3, 37))
+
+// Now that we don't check for getter/setter assignability, we should
+// ensure the setter annotation is actually checked even if it's never observed.
+
+type Fail<T extends never> = T;
+>Fail : Symbol(Fail, Decl(divergentAccessorsTypes6.ts, 10, 30))
+>T : Symbol(T, Decl(divergentAccessorsTypes6.ts, 15, 10))
+>T : Symbol(T, Decl(divergentAccessorsTypes6.ts, 15, 10))
+
+interface I1 {
+>I1 : Symbol(I1, Decl(divergentAccessorsTypes6.ts, 15, 31))
+
+    get x(): number;
+>x : Symbol(I1.x, Decl(divergentAccessorsTypes6.ts, 16, 14), Decl(divergentAccessorsTypes6.ts, 17, 20))
+
+    set x(value: Fail<string>);
+>x : Symbol(I1.x, Decl(divergentAccessorsTypes6.ts, 16, 14), Decl(divergentAccessorsTypes6.ts, 17, 20))
+>value : Symbol(value, Decl(divergentAccessorsTypes6.ts, 18, 10))
+>Fail : Symbol(Fail, Decl(divergentAccessorsTypes6.ts, 10, 30))
+}
+const o1 = {
+>o1 : Symbol(o1, Decl(divergentAccessorsTypes6.ts, 20, 5))
+
+    get x(): number { return 0; },
+>x : Symbol(x, Decl(divergentAccessorsTypes6.ts, 20, 12), Decl(divergentAccessorsTypes6.ts, 21, 34))
+
+    set x(value: Fail<string>) {}
+>x : Symbol(x, Decl(divergentAccessorsTypes6.ts, 20, 12), Decl(divergentAccessorsTypes6.ts, 21, 34))
+>value : Symbol(value, Decl(divergentAccessorsTypes6.ts, 22, 10))
+>Fail : Symbol(Fail, Decl(divergentAccessorsTypes6.ts, 10, 30))
+}
+
+// A setter annotation still implies the getter return type.
+
+const o2 = {
+>o2 : Symbol(o2, Decl(divergentAccessorsTypes6.ts, 27, 5))
+
+    get p1() { return 0; }, // error - no annotation means type is implied from the setter annotation
+>p1 : Symbol(p1, Decl(divergentAccessorsTypes6.ts, 27, 12), Decl(divergentAccessorsTypes6.ts, 28, 27))
+
+    set p1(value: string) {},
+>p1 : Symbol(p1, Decl(divergentAccessorsTypes6.ts, 27, 12), Decl(divergentAccessorsTypes6.ts, 28, 27))
+>value : Symbol(value, Decl(divergentAccessorsTypes6.ts, 29, 11))
+
+    get p2(): number { return 0; }, // ok - explicit annotation
+>p2 : Symbol(p2, Decl(divergentAccessorsTypes6.ts, 29, 29), Decl(divergentAccessorsTypes6.ts, 31, 35))
+
+    set p2(value: string) {},
+>p2 : Symbol(p2, Decl(divergentAccessorsTypes6.ts, 29, 29), Decl(divergentAccessorsTypes6.ts, 31, 35))
+>value : Symbol(value, Decl(divergentAccessorsTypes6.ts, 32, 11))
+
+};
+

tests/baselines/reference/divergentAccessorsTypes6.types

@@ -0,0 +1,89 @@
+=== tests/cases/compiler/divergentAccessorsTypes6.ts ===
+export {};
+
+interface Element {
+    get style(): CSSStyleDeclaration;
+>style : CSSStyleDeclaration
+
+    set style(cssText: string);
+>style : CSSStyleDeclaration
+>cssText : string
+}
+
+declare const element: Element;
+>element : Element
+
+element.style = "color: red";
+>element.style = "color: red" : "color: red"
+>element.style : string
+>element : Element
+>style : string
+>"color: red" : "color: red"
+
+element.style.animationTimingFunction;
+>element.style.animationTimingFunction : string
+>element.style : CSSStyleDeclaration
+>element : Element
+>style : CSSStyleDeclaration
+>animationTimingFunction : string
+
+element.style = element.style; // error
+>element.style = element.style : CSSStyleDeclaration
+>element.style : string
+>element : Element
+>style : string
+>element.style : CSSStyleDeclaration
+>element : Element
+>style : CSSStyleDeclaration
+
+// Now that we don't check for getter/setter assignability, we should
+// ensure the setter annotation is actually checked even if it's never observed.
+
+type Fail<T extends never> = T;
+>Fail : T
+
+interface I1 {
+    get x(): number;
+>x : number
+
+    set x(value: Fail<string>);
+>x : number
+>value : string
+}
+const o1 = {
+>o1 : { x: number; }
+>{    get x(): number { return 0; },    set x(value: Fail<string>) {}} : { x: number; }
+
+    get x(): number { return 0; },
+>x : number
+>0 : 0
+
+    set x(value: Fail<string>) {}
+>x : number
+>value : string
+}
+
+// A setter annotation still implies the getter return type.
+
+const o2 = {
+>o2 : { p1: string; p2: number; }
+>{    get p1() { return 0; }, // error - no annotation means type is implied from the setter annotation    set p1(value: string) {},    get p2(): number { return 0; }, // ok - explicit annotation    set p2(value: string) {},} : { p1: string; p2: number; }
+
+    get p1() { return 0; }, // error - no annotation means type is implied from the setter annotation
+>p1 : string
+>0 : 0
+
+    set p1(value: string) {},
+>p1 : string
+>value : string
+
+    get p2(): number { return 0; }, // ok - explicit annotation
+>p2 : number
+>0 : 0
+
+    set p2(value: string) {},
+>p2 : number
+>value : string
+
+};
+

tests/baselines/reference/getAndSetNotIdenticalType2.errors.txt

@@ -1,22 +1,16 @@
-tests/cases/compiler/getAndSetNotIdenticalType2.ts(5,9): error TS2380: The return type of a 'get' accessor must be assignable to its 'set' accessor type
-  Type 'T' is not assignable to type 'string'.
 tests/cases/compiler/getAndSetNotIdenticalType2.ts(9,9): error TS2322: Type 'A<string>' is not assignable to type 'A<T>'.
   Type 'string' is not assignable to type 'T'.
     'T' could be instantiated with an arbitrary type which could be unrelated to 'string'.
 tests/cases/compiler/getAndSetNotIdenticalType2.ts(15,1): error TS2322: Type 'A<unknown>' is not assignable to type 'A<string>'.
   Type 'unknown' is not assignable to type 'string'.
 
 
-==== tests/cases/compiler/getAndSetNotIdenticalType2.ts (3 errors) ====
+==== tests/cases/compiler/getAndSetNotIdenticalType2.ts (2 errors) ====
     class A<T> { foo: T; }
 
     class C<T> {
         data: A<T>;
         get x(): A<T> {
-            ~
-!!! error TS2380: The return type of a 'get' accessor must be assignable to its 'set' accessor type
-!!! error TS2380:   Type 'T' is not assignable to type 'string'.
-!!! related TS2208 tests/cases/compiler/getAndSetNotIdenticalType2.ts:3:9: This type parameter might need an `extends string` constraint.
             return this.data;
         }
         set x(v: A<string>) {