support generic variant setter

src/compiler/checker.ts

@@ -18760,7 +18760,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function instantiateSymbol(symbol: Symbol, mapper: TypeMapper): Symbol {
         const links = getSymbolLinks(symbol);
-        if (links.type && !couldContainTypeVariables(links.type)) {
+        if (links.type && !couldContainTypeVariables(links.type) && !(getDeclarationOfKind(symbol, SyntaxKind.SetAccessor) && couldContainTypeVariables(getWriteTypeOfSymbol(symbol)))) {
             // If the type of the symbol is already resolved, and if that type could not possibly
             // be affected by instantiation, simply return the symbol itself.
             return symbol;

tests/baselines/reference/divergentAccessorsTypes7.js

@@ -0,0 +1,44 @@
+//// [tests/cases/compiler/divergentAccessorsTypes7.ts] ////
+
+//// [divergentAccessorsTypes7.ts]
+class Test<S> {
+    constructor() {}
+
+    set value(value: string | ((item: S) => string)) {}
+
+    get value(): string {
+        return null!;
+    }
+
+    // -- Replacing the getter such that the getter/setter types match, removes the error:
+    // get value(): string | ((item: S) => string) {
+    //     return null!;
+    // }
+
+    // -- Or, replacing the setter such that a concrete type is used, removes the error:
+    // set value(value: string | ((item: { property: string }) => string)) {}
+}
+
+const a = new Test<{
+    property: string
+}>();
+
+a.value = (item) => item.property
+
+
+//// [divergentAccessorsTypes7.js]
+var Test = /** @class */ (function () {
+    function Test() {
+    }
+    Object.defineProperty(Test.prototype, "value", {
+        get: function () {
+            return null;
+        },
+        set: function (value) { },
+        enumerable: false,
+        configurable: true
+    });
+    return Test;
+}());
+var a = new Test();
+a.value = function (item) { return item.property; };

tests/baselines/reference/divergentAccessorsTypes7.symbols

@@ -0,0 +1,48 @@
+//// [tests/cases/compiler/divergentAccessorsTypes7.ts] ////
+
+=== divergentAccessorsTypes7.ts ===
+class Test<S> {
+>Test : Symbol(Test, Decl(divergentAccessorsTypes7.ts, 0, 0))
+>S : Symbol(S, Decl(divergentAccessorsTypes7.ts, 0, 11))
+
+    constructor() {}
+
+    set value(value: string | ((item: S) => string)) {}
+>value : Symbol(Test.value, Decl(divergentAccessorsTypes7.ts, 1, 20), Decl(divergentAccessorsTypes7.ts, 3, 55))
+>value : Symbol(value, Decl(divergentAccessorsTypes7.ts, 3, 14))
+>item : Symbol(item, Decl(divergentAccessorsTypes7.ts, 3, 32))
+>S : Symbol(S, Decl(divergentAccessorsTypes7.ts, 0, 11))
+
+    get value(): string {
+>value : Symbol(Test.value, Decl(divergentAccessorsTypes7.ts, 1, 20), Decl(divergentAccessorsTypes7.ts, 3, 55))
+
+        return null!;
+    }
+
+    // -- Replacing the getter such that the getter/setter types match, removes the error:
+    // get value(): string | ((item: S) => string) {
+    //     return null!;
+    // }
+
+    // -- Or, replacing the setter such that a concrete type is used, removes the error:
+    // set value(value: string | ((item: { property: string }) => string)) {}
+}
+
+const a = new Test<{
+>a : Symbol(a, Decl(divergentAccessorsTypes7.ts, 18, 5))
+>Test : Symbol(Test, Decl(divergentAccessorsTypes7.ts, 0, 0))
+
+    property: string
+>property : Symbol(property, Decl(divergentAccessorsTypes7.ts, 18, 20))
+
+}>();
+
+a.value = (item) => item.property
+>a.value : Symbol(Test.value, Decl(divergentAccessorsTypes7.ts, 1, 20), Decl(divergentAccessorsTypes7.ts, 3, 55))
+>a : Symbol(a, Decl(divergentAccessorsTypes7.ts, 18, 5))
+>value : Symbol(Test.value, Decl(divergentAccessorsTypes7.ts, 1, 20), Decl(divergentAccessorsTypes7.ts, 3, 55))
+>item : Symbol(item, Decl(divergentAccessorsTypes7.ts, 22, 11))
+>item.property : Symbol(property, Decl(divergentAccessorsTypes7.ts, 18, 20))
+>item : Symbol(item, Decl(divergentAccessorsTypes7.ts, 22, 11))
+>property : Symbol(property, Decl(divergentAccessorsTypes7.ts, 18, 20))
+

tests/baselines/reference/divergentAccessorsTypes7.types

@@ -0,0 +1,50 @@
+//// [tests/cases/compiler/divergentAccessorsTypes7.ts] ////
+
+=== divergentAccessorsTypes7.ts ===
+class Test<S> {
+>Test : Test<S>
+
+    constructor() {}
+
+    set value(value: string | ((item: S) => string)) {}
+>value : string
+>value : string | ((item: S) => string)
+>item : S
+
+    get value(): string {
+>value : string
+
+        return null!;
+>null! : null
+    }
+
+    // -- Replacing the getter such that the getter/setter types match, removes the error:
+    // get value(): string | ((item: S) => string) {
+    //     return null!;
+    // }
+
+    // -- Or, replacing the setter such that a concrete type is used, removes the error:
+    // set value(value: string | ((item: { property: string }) => string)) {}
+}
+
+const a = new Test<{
+>a : Test<{ property: string; }>
+>new Test<{    property: string}>() : Test<{ property: string; }>
+>Test : typeof Test
+
+    property: string
+>property : string
+
+}>();
+
+a.value = (item) => item.property
+>a.value = (item) => item.property : (item: { property: string; }) => string
+>a.value : string | ((item: { property: string; }) => string)
+>a : Test<{ property: string; }>
+>value : string | ((item: { property: string; }) => string)
+>(item) => item.property : (item: { property: string; }) => string
+>item : { property: string; }
+>item.property : string
+>item : { property: string; }
+>property : string
+

tests/cases/compiler/divergentAccessorsTypes7.ts

@@ -0,0 +1,23 @@
+class Test<S> {
+    constructor() {}
+
+    set value(value: string | ((item: S) => string)) {}
+
+    get value(): string {
+        return null!;
+    }
+
+    // -- Replacing the getter such that the getter/setter types match, removes the error:
+    // get value(): string | ((item: S) => string) {
+    //     return null!;
+    // }
+
+    // -- Or, replacing the setter such that a concrete type is used, removes the error:
+    // set value(value: string | ((item: { property: string }) => string)) {}
+}
+
+const a = new Test<{
+    property: string
+}>();
+
+a.value = (item) => item.property