Allow this in constructor parameter defaults when legal (#57682)

Author: RyanCavanaugh

src/compiler/checker.ts

@@ -29815,12 +29815,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     error(node, Diagnostics.this_cannot_be_referenced_in_current_location);
                     // do not return here so in case if lexical this is captured - it will be reflected in flags on NodeLinks
                     break;
-                case SyntaxKind.Constructor:
-                    if (isInConstructorArgumentInitializer(node, container)) {
-                        error(node, Diagnostics.this_cannot_be_referenced_in_constructor_arguments);
-                        // do not return here so in case if lexical this is captured - it will be reflected in flags on NodeLinks
-                    }
-                    break;
             }
         }
 

src/compiler/diagnosticMessages.json

@@ -1836,10 +1836,6 @@
         "category": "Error",
         "code": 2332
     },
-    "'this' cannot be referenced in constructor arguments.": {
-        "category": "Error",
-        "code": 2333
-    },
     "'this' cannot be referenced in a static property initializer.": {
         "category": "Error",
         "code": 2334

tests/baselines/reference/constructorDefaultValuesReferencingThis.errors.txt

@@ -1,23 +1,25 @@
-constructorDefaultValuesReferencingThis.ts(2,21): error TS2333: 'this' cannot be referenced in constructor arguments.
-constructorDefaultValuesReferencingThis.ts(6,21): error TS2333: 'this' cannot be referenced in constructor arguments.
-constructorDefaultValuesReferencingThis.ts(10,28): error TS2333: 'this' cannot be referenced in constructor arguments.
+constructorDefaultValuesReferencingThis.ts(15,21): error TS17009: 'super' must be called before accessing 'this' in the constructor of a derived class.
 
 
-==== constructorDefaultValuesReferencingThis.ts (3 errors) ====
+==== constructorDefaultValuesReferencingThis.ts (1 errors) ====
     class C {
+        public baseProp = 1;
         constructor(x = this) { }
-                        ~~~~
-!!! error TS2333: 'this' cannot be referenced in constructor arguments.
     }
 
     class D<T> {
         constructor(x = this) { }
-                        ~~~~
-!!! error TS2333: 'this' cannot be referenced in constructor arguments.
     }
 
     class E<T> {
         constructor(public x = this) { }
-                               ~~~~
-!!! error TS2333: 'this' cannot be referenced in constructor arguments.
-    }
+    }
+    
+    class F extends C {
+        constructor(y = this.baseProp) {
+                        ~~~~
+!!! error TS17009: 'super' must be called before accessing 'this' in the constructor of a derived class.
+            super();
+        }
+    }
+    

tests/baselines/reference/constructorDefaultValuesReferencingThis.js

@@ -2,6 +2,7 @@
 
 //// [constructorDefaultValuesReferencingThis.ts]
 class C {
+    public baseProp = 1;
     constructor(x = this) { }
 }
 
@@ -11,12 +12,35 @@ class D<T> {
 
 class E<T> {
     constructor(public x = this) { }
-}
+}
+
+class F extends C {
+    constructor(y = this.baseProp) {
+        super();
+    }
+}
+
 
 //// [constructorDefaultValuesReferencingThis.js]
+var __extends = (this && this.__extends) || (function () {
+    var extendStatics = function (d, b) {
+        extendStatics = Object.setPrototypeOf ||
+            ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
+            function (d, b) { for (var p in b) if (Object.prototype.hasOwnProperty.call(b, p)) d[p] = b[p]; };
+        return extendStatics(d, b);
+    };
+    return function (d, b) {
+        if (typeof b !== "function" && b !== null)
+            throw new TypeError("Class extends value " + String(b) + " is not a constructor or null");
+        extendStatics(d, b);
+        function __() { this.constructor = d; }
+        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+    };
+})();
 var C = /** @class */ (function () {
     function C(x) {
         if (x === void 0) { x = this; }
+        this.baseProp = 1;
     }
     return C;
 }());
@@ -33,3 +57,11 @@ var E = /** @class */ (function () {
     }
     return E;
 }());
+var F = /** @class */ (function (_super) {
+    __extends(F, _super);
+    function F(y) {
+        if (y === void 0) { y = _this.baseProp; }
+        return _super.call(this) || this;
+    }
+    return F;
+}(C));

tests/baselines/reference/constructorDefaultValuesReferencingThis.symbols

@@ -4,25 +4,44 @@
 class C {
 >C : Symbol(C, Decl(constructorDefaultValuesReferencingThis.ts, 0, 0))
 
+    public baseProp = 1;
+>baseProp : Symbol(C.baseProp, Decl(constructorDefaultValuesReferencingThis.ts, 0, 9))
+
     constructor(x = this) { }
->x : Symbol(x, Decl(constructorDefaultValuesReferencingThis.ts, 1, 16))
+>x : Symbol(x, Decl(constructorDefaultValuesReferencingThis.ts, 2, 16))
 >this : Symbol(C, Decl(constructorDefaultValuesReferencingThis.ts, 0, 0))
 }
 
 class D<T> {
->D : Symbol(D, Decl(constructorDefaultValuesReferencingThis.ts, 2, 1))
->T : Symbol(T, Decl(constructorDefaultValuesReferencingThis.ts, 4, 8))
+>D : Symbol(D, Decl(constructorDefaultValuesReferencingThis.ts, 3, 1))
+>T : Symbol(T, Decl(constructorDefaultValuesReferencingThis.ts, 5, 8))
 
     constructor(x = this) { }
->x : Symbol(x, Decl(constructorDefaultValuesReferencingThis.ts, 5, 16))
->this : Symbol(D, Decl(constructorDefaultValuesReferencingThis.ts, 2, 1))
+>x : Symbol(x, Decl(constructorDefaultValuesReferencingThis.ts, 6, 16))
+>this : Symbol(D, Decl(constructorDefaultValuesReferencingThis.ts, 3, 1))
 }
 
 class E<T> {
->E : Symbol(E, Decl(constructorDefaultValuesReferencingThis.ts, 6, 1))
->T : Symbol(T, Decl(constructorDefaultValuesReferencingThis.ts, 8, 8))
+>E : Symbol(E, Decl(constructorDefaultValuesReferencingThis.ts, 7, 1))
+>T : Symbol(T, Decl(constructorDefaultValuesReferencingThis.ts, 9, 8))
 
     constructor(public x = this) { }
->x : Symbol(E.x, Decl(constructorDefaultValuesReferencingThis.ts, 9, 16))
->this : Symbol(E, Decl(constructorDefaultValuesReferencingThis.ts, 6, 1))
+>x : Symbol(E.x, Decl(constructorDefaultValuesReferencingThis.ts, 10, 16))
+>this : Symbol(E, Decl(constructorDefaultValuesReferencingThis.ts, 7, 1))
 }
+
+class F extends C {
+>F : Symbol(F, Decl(constructorDefaultValuesReferencingThis.ts, 11, 1))
+>C : Symbol(C, Decl(constructorDefaultValuesReferencingThis.ts, 0, 0))
+
+    constructor(y = this.baseProp) {
+>y : Symbol(y, Decl(constructorDefaultValuesReferencingThis.ts, 14, 16))
+>this.baseProp : Symbol(C.baseProp, Decl(constructorDefaultValuesReferencingThis.ts, 0, 9))
+>this : Symbol(F, Decl(constructorDefaultValuesReferencingThis.ts, 11, 1))
+>baseProp : Symbol(C.baseProp, Decl(constructorDefaultValuesReferencingThis.ts, 0, 9))
+
+        super();
+>super : Symbol(C, Decl(constructorDefaultValuesReferencingThis.ts, 0, 0))
+    }
+}
+

tests/baselines/reference/constructorDefaultValuesReferencingThis.types

@@ -4,6 +4,10 @@
 class C {
 >C : C
 
+    public baseProp = 1;
+>baseProp : number
+>1 : 1
+
     constructor(x = this) { }
 >x : this
 >this : this
@@ -24,3 +28,20 @@ class E<T> {
 >x : this
 >this : this
 }
+
+class F extends C {
+>F : F
+>C : C
+
+    constructor(y = this.baseProp) {
+>y : number
+>this.baseProp : number
+>this : this
+>baseProp : number
+
+        super();
+>super() : void
+>super : typeof C
+    }
+}
+

tests/baselines/reference/thisInConstructorParameter1.errors.txt

@@ -1,4 +1,5 @@
 class C {
+    public baseProp = 1;
     constructor(x = this) { }
 }
 
@@ -8,4 +9,10 @@ class D<T> {
 
 class E<T> {
     constructor(public x = this) { }
-}
+}
+
+class F extends C {
+    constructor(y = this.baseProp) {
+        super();
+    }
+}