Allow override as parameter property

src/compiler/checker.ts

@@ -40609,6 +40609,7 @@ namespace ts {
                         }
                         break;
                     case SyntaxKind.OverrideKeyword:
+                        // If node.kind === SyntaxKind.Parameter, checkParameter reports an error if it's not a parameter property.
                         if (flags & ModifierFlags.Override) {
                             return grammarErrorOnNode(modifier, Diagnostics._0_modifier_already_seen, "override");
                         }
@@ -40621,9 +40622,6 @@ namespace ts {
                         else if (flags & ModifierFlags.Async) {
                             return grammarErrorOnNode(modifier, Diagnostics._0_modifier_must_precede_1_modifier, "override", "async");
                         }
-                        if (node.kind === SyntaxKind.Parameter) {
-                            return grammarErrorOnNode(modifier, Diagnostics._0_modifier_cannot_appear_on_a_parameter, "override");
-                        }
                         flags |= ModifierFlags.Override;
                         lastOverride = modifier;
                         break;
@@ -40696,7 +40694,7 @@ namespace ts {
                             return grammarErrorOnNode(modifier, Diagnostics._0_modifier_already_seen, "readonly");
                         }
                         else if (node.kind !== SyntaxKind.PropertyDeclaration && node.kind !== SyntaxKind.PropertySignature && node.kind !== SyntaxKind.IndexSignature && node.kind !== SyntaxKind.Parameter) {
-                            // If node.kind === SyntaxKind.Parameter, checkParameter report an error if it's not a parameter property.
+                            // If node.kind === SyntaxKind.Parameter, checkParameter reports an error if it's not a parameter property.
                             return grammarErrorOnNode(modifier, Diagnostics.readonly_modifier_can_only_appear_on_a_property_declaration_or_index_signature);
                         }
                         flags |= ModifierFlags.Readonly;

src/compiler/types.ts

@@ -806,7 +806,7 @@ namespace ts {
 
         AccessibilityModifier = Public | Private | Protected,
         // Accessibility modifiers and 'readonly' can be attached to a parameter in a constructor to make it a property.
-        ParameterPropertyModifier = AccessibilityModifier | Readonly,
+        ParameterPropertyModifier = AccessibilityModifier | Readonly | Override,
         NonPublicAccessibilityModifier = Private | Protected,
 
         TypeScriptModifier = Ambient | Public | Private | Protected | Readonly | Abstract | Const | Override,

src/harness/fourslashInterfaceImpl.ts

@@ -1175,7 +1175,7 @@ namespace FourSlashInterface {
         export const classElementInJsKeywords = getInJsKeywords(classElementKeywords);
 
         export const constructorParameterKeywords: readonly ExpectedCompletionEntryObject[] =
-            ["private", "protected", "public", "readonly"].map((name): ExpectedCompletionEntryObject => ({
+            ["private", "protected", "public", "readonly", "override"].map((name): ExpectedCompletionEntryObject => ({
                 name,
                 kind: "keyword",
                 sortText: SortText.GlobalsOrKeywords

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -540,7 +540,7 @@ declare namespace ts {
         Override = 16384,
         HasComputedFlags = 536870912,
         AccessibilityModifier = 28,
-        ParameterPropertyModifier = 92,
+        ParameterPropertyModifier = 16476,
         NonPublicAccessibilityModifier = 24,
         TypeScriptModifier = 18654,
         ExportDefault = 513,

tests/baselines/reference/api/typescript.d.ts

@@ -540,7 +540,7 @@ declare namespace ts {
         Override = 16384,
         HasComputedFlags = 536870912,
         AccessibilityModifier = 28,
-        ParameterPropertyModifier = 92,
+        ParameterPropertyModifier = 16476,
         NonPublicAccessibilityModifier = 24,
         TypeScriptModifier = 18654,
         ExportDefault = 513,

tests/baselines/reference/override11.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/conformance/override/override11.ts(6,18): error TS1090: 'override' modifier cannot appear on a parameter.
+tests/cases/conformance/override/override11.ts(6,27): error TS1029: 'public' modifier must precede 'override' modifier.
 
 
 ==== tests/cases/conformance/override/override11.ts (1 errors) ====
@@ -8,8 +8,8 @@ tests/cases/conformance/override/override11.ts(6,18): error TS1090: 'override' m
 
     class Sub extends Base {
         constructor (override public foo: number) {
-                     ~~~~~~~~
-!!! error TS1090: 'override' modifier cannot appear on a parameter.
+                              ~~~~~~
+!!! error TS1029: 'public' modifier must precede 'override' modifier.
             super();
         }
     }

tests/baselines/reference/overrideParameterProperty.errors.txt

@@ -0,0 +1,36 @@
+tests/cases/conformance/override/overrideParameterProperty.ts(20,24): error TS1029: 'public' modifier must precede 'override' modifier.
+tests/cases/conformance/override/overrideParameterProperty.ts(25,5): error TS2369: A parameter property is only allowed in a constructor implementation.
+
+
+==== tests/cases/conformance/override/overrideParameterProperty.ts (2 errors) ====
+    class Base {
+      p1!: string;
+    }
+
+    class C1 extends Base {
+      constructor(public override p1: "hello") {
+        super();
+        this.p1;
+      }
+    }
+
+    class C2 extends Base {
+      constructor(override p1: "hello") {
+        super();
+        this.p1;
+      }
+    }
+
+    class C3 extends Base {
+      constructor(override public p1: "hello") {
+                           ~~~~~~
+!!! error TS1029: 'public' modifier must precede 'override' modifier.
+        super();
+        this.p1;
+      }
+
+      m(override p1: "hello") {}
+        ~~~~~~~~~~~~~~~~~~~~
+!!! error TS2369: A parameter property is only allowed in a constructor implementation.
+    }
+

tests/baselines/reference/overrideParameterProperty.js

@@ -0,0 +1,81 @@
+//// [overrideParameterProperty.ts]
+class Base {
+  p1!: string;
+}
+
+class C1 extends Base {
+  constructor(public override p1: "hello") {
+    super();
+    this.p1;
+  }
+}
+
+class C2 extends Base {
+  constructor(override p1: "hello") {
+    super();
+    this.p1;
+  }
+}
+
+class C3 extends Base {
+  constructor(override public p1: "hello") {
+    super();
+    this.p1;
+  }
+
+  m(override p1: "hello") {}
+}
+
+
+//// [overrideParameterProperty.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 Base = /** @class */ (function () {
+    function Base() {
+    }
+    return Base;
+}());
+var C1 = /** @class */ (function (_super) {
+    __extends(C1, _super);
+    function C1(p1) {
+        var _this = _super.call(this) || this;
+        _this.p1 = p1;
+        _this.p1;
+        return _this;
+    }
+    return C1;
+}(Base));
+var C2 = /** @class */ (function (_super) {
+    __extends(C2, _super);
+    function C2(p1) {
+        var _this = _super.call(this) || this;
+        _this.p1 = p1;
+        _this.p1;
+        return _this;
+    }
+    return C2;
+}(Base));
+var C3 = /** @class */ (function (_super) {
+    __extends(C3, _super);
+    function C3(p1) {
+        var _this = _super.call(this) || this;
+        _this.p1 = p1;
+        _this.p1;
+        return _this;
+    }
+    C3.prototype.m = function (p1) { };
+    return C3;
+}(Base));

tests/baselines/reference/overrideParameterProperty.symbols

@@ -0,0 +1,63 @@
+=== tests/cases/conformance/override/overrideParameterProperty.ts ===
+class Base {
+>Base : Symbol(Base, Decl(overrideParameterProperty.ts, 0, 0))
+
+  p1!: string;
+>p1 : Symbol(Base.p1, Decl(overrideParameterProperty.ts, 0, 12))
+}
+
+class C1 extends Base {
+>C1 : Symbol(C1, Decl(overrideParameterProperty.ts, 2, 1))
+>Base : Symbol(Base, Decl(overrideParameterProperty.ts, 0, 0))
+
+  constructor(public override p1: "hello") {
+>p1 : Symbol(C1.p1, Decl(overrideParameterProperty.ts, 5, 14))
+
+    super();
+>super : Symbol(Base, Decl(overrideParameterProperty.ts, 0, 0))
+
+    this.p1;
+>this.p1 : Symbol(C1.p1, Decl(overrideParameterProperty.ts, 5, 14))
+>this : Symbol(C1, Decl(overrideParameterProperty.ts, 2, 1))
+>p1 : Symbol(C1.p1, Decl(overrideParameterProperty.ts, 5, 14))
+  }
+}
+
+class C2 extends Base {
+>C2 : Symbol(C2, Decl(overrideParameterProperty.ts, 9, 1))
+>Base : Symbol(Base, Decl(overrideParameterProperty.ts, 0, 0))
+
+  constructor(override p1: "hello") {
+>p1 : Symbol(C2.p1, Decl(overrideParameterProperty.ts, 12, 14))
+
+    super();
+>super : Symbol(Base, Decl(overrideParameterProperty.ts, 0, 0))
+
+    this.p1;
+>this.p1 : Symbol(C2.p1, Decl(overrideParameterProperty.ts, 12, 14))
+>this : Symbol(C2, Decl(overrideParameterProperty.ts, 9, 1))
+>p1 : Symbol(C2.p1, Decl(overrideParameterProperty.ts, 12, 14))
+  }
+}
+
+class C3 extends Base {
+>C3 : Symbol(C3, Decl(overrideParameterProperty.ts, 16, 1))
+>Base : Symbol(Base, Decl(overrideParameterProperty.ts, 0, 0))
+
+  constructor(override public p1: "hello") {
+>p1 : Symbol(C3.p1, Decl(overrideParameterProperty.ts, 19, 14))
+
+    super();
+>super : Symbol(Base, Decl(overrideParameterProperty.ts, 0, 0))
+
+    this.p1;
+>this.p1 : Symbol(C3.p1, Decl(overrideParameterProperty.ts, 19, 14))
+>this : Symbol(C3, Decl(overrideParameterProperty.ts, 16, 1))
+>p1 : Symbol(C3.p1, Decl(overrideParameterProperty.ts, 19, 14))
+  }
+
+  m(override p1: "hello") {}
+>m : Symbol(C3.m, Decl(overrideParameterProperty.ts, 22, 3))
+>p1 : Symbol(p1, Decl(overrideParameterProperty.ts, 24, 4))
+}
+

tests/baselines/reference/overrideParameterProperty.types

@@ -0,0 +1,66 @@
+=== tests/cases/conformance/override/overrideParameterProperty.ts ===
+class Base {
+>Base : Base
+
+  p1!: string;
+>p1 : string
+}
+
+class C1 extends Base {
+>C1 : C1
+>Base : Base
+
+  constructor(public override p1: "hello") {
+>p1 : "hello"
+
+    super();
+>super() : void
+>super : typeof Base
+
+    this.p1;
+>this.p1 : "hello"
+>this : this
+>p1 : "hello"
+  }
+}
+
+class C2 extends Base {
+>C2 : C2
+>Base : Base
+
+  constructor(override p1: "hello") {
+>p1 : "hello"
+
+    super();
+>super() : void
+>super : typeof Base
+
+    this.p1;
+>this.p1 : "hello"
+>this : this
+>p1 : "hello"
+  }
+}
+
+class C3 extends Base {
+>C3 : C3
+>Base : Base
+
+  constructor(override public p1: "hello") {
+>p1 : "hello"
+
+    super();
+>super() : void
+>super : typeof Base
+
+    this.p1;
+>this.p1 : "hello"
+>this : this
+>p1 : "hello"
+  }
+
+  m(override p1: "hello") {}
+>m : (p1: "hello") => void
+>p1 : "hello"
+}
+

tests/cases/conformance/override/overrideParameterProperty.ts

@@ -0,0 +1,28 @@
+// @noImplicitOverride: true
+
+class Base {
+  p1!: string;
+}
+
+class C1 extends Base {
+  constructor(public override p1: "hello") {
+    super();
+    this.p1;
+  }
+}
+
+class C2 extends Base {
+  constructor(override p1: "hello") {
+    super();
+    this.p1;
+  }
+}
+
+class C3 extends Base {
+  constructor(override public p1: "hello") {
+    super();
+    this.p1;
+  }
+
+  m(override p1: "hello") {}
+}