resolve TypeReference in class decorator at parent of class

Fixes: #28603

Author: ajafff

src/compiler/checker.ts

@@ -1459,7 +1459,14 @@ namespace ts {
                         //       @y method(x, y) {} // <-- decorator y should be resolved at the class declaration, not the method.
                         //   }
                         //
-                        if (location.parent && isClassElement(location.parent)) {
+
+                        // class Decorators are resolved outside of the class to avoid referencing type parameters of that class.
+                        //
+                        //   type T = number;
+                        //   declare function y(x: T): any;
+                        //   @param(1 as T) // <-- T should resolve to the type alias outside of class C
+                        //   class C<T> {}
+                        if (location.parent && (isClassElement(location.parent) || location.parent.kind === SyntaxKind.ClassDeclaration)) {
                             location = location.parent;
                         }
                         break;

tests/baselines/reference/decoratorReferences.js

@@ -0,0 +1,35 @@
+//// [decoratorReferences.ts]
+declare function y(...args: any[]): any;
+type T = number;
+@y(1 as T, C) // <-- T should be resolved to the type alias, not the type parameter of the class; C should resolve to the class
+class C<T> {
+    @y(null as T) // <-- y should resolve to the function declaration, not the parameter; T should resolve to the type parameter of the class
+    method(@y x, y) {} // <-- decorator y should be resolved at the class declaration, not the parameter.
+}
+
+//// [decoratorReferences.js]
+var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
+    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
+    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
+    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
+    return c > 3 && r && Object.defineProperty(target, key, r), r;
+};
+var __param = (this && this.__param) || function (paramIndex, decorator) {
+    return function (target, key) { decorator(target, key, paramIndex); }
+};
+var C = /** @class */ (function () {
+    function C() {
+    }
+    C_1 = C;
+    C.prototype.method = function (x, y) { }; // <-- decorator y should be resolved at the class declaration, not the parameter.
+    var C_1;
+    __decorate([
+        y(null) // <-- y should resolve to the function declaration, not the parameter; T should resolve to the type parameter of the class
+        ,
+        __param(0, y)
+    ], C.prototype, "method");
+    C = C_1 = __decorate([
+        y(1, C_1) // <-- T should be resolved to the type alias, not the type parameter of the class; C should resolve to the class
+    ], C);
+    return C;
+}());

tests/baselines/reference/decoratorReferences.symbols

@@ -0,0 +1,27 @@
+=== tests/cases/compiler/decoratorReferences.ts ===
+declare function y(...args: any[]): any;
+>y : Symbol(y, Decl(decoratorReferences.ts, 0, 0))
+>args : Symbol(args, Decl(decoratorReferences.ts, 0, 19))
+
+type T = number;
+>T : Symbol(T, Decl(decoratorReferences.ts, 0, 40))
+
+@y(1 as T, C) // <-- T should be resolved to the type alias, not the type parameter of the class; C should resolve to the class
+>y : Symbol(y, Decl(decoratorReferences.ts, 0, 0))
+>T : Symbol(T, Decl(decoratorReferences.ts, 0, 40))
+>C : Symbol(C, Decl(decoratorReferences.ts, 1, 16))
+
+class C<T> {
+>C : Symbol(C, Decl(decoratorReferences.ts, 1, 16))
+>T : Symbol(T, Decl(decoratorReferences.ts, 3, 8))
+
+    @y(null as T) // <-- y should resolve to the function declaration, not the parameter; T should resolve to the type parameter of the class
+>y : Symbol(y, Decl(decoratorReferences.ts, 0, 0))
+>T : Symbol(T, Decl(decoratorReferences.ts, 3, 8))
+
+    method(@y x, y) {} // <-- decorator y should be resolved at the class declaration, not the parameter.
+>method : Symbol(C.method, Decl(decoratorReferences.ts, 3, 12))
+>y : Symbol(y, Decl(decoratorReferences.ts, 0, 0))
+>x : Symbol(x, Decl(decoratorReferences.ts, 5, 11))
+>y : Symbol(y, Decl(decoratorReferences.ts, 5, 16))
+}

tests/baselines/reference/decoratorReferences.types

@@ -0,0 +1,30 @@
+=== tests/cases/compiler/decoratorReferences.ts ===
+declare function y(...args: any[]): any;
+>y : (...args: any[]) => any
+>args : any[]
+
+type T = number;
+>T : number
+
+@y(1 as T, C) // <-- T should be resolved to the type alias, not the type parameter of the class; C should resolve to the class
+>y(1 as T, C) : any
+>y : (...args: any[]) => any
+>1 as T : number
+>1 : 1
+>C : typeof C
+
+class C<T> {
+>C : C<T>
+
+    @y(null as T) // <-- y should resolve to the function declaration, not the parameter; T should resolve to the type parameter of the class
+>y(null as T) : any
+>y : (...args: any[]) => any
+>null as T : T
+>null : null
+
+    method(@y x, y) {} // <-- decorator y should be resolved at the class declaration, not the parameter.
+>method : (x: any, y: any) => void
+>y : (...args: any[]) => any
+>x : any
+>y : any
+}

tests/cases/compiler/decoratorReferences.ts

@@ -0,0 +1,9 @@
+// @experimentalDecorators: true
+
+declare function y(...args: any[]): any;
+type T = number;
+@y(1 as T, C) // <-- T should be resolved to the type alias, not the type parameter of the class; C should resolve to the class
+class C<T> {
+    @y(null as T) // <-- y should resolve to the function declaration, not the parameter; T should resolve to the type parameter of the class
+    method(@y x, y) {} // <-- decorator y should be resolved at the class declaration, not the parameter.
+}