[ts] Support override modifiers for parameter properties (#13428)

packages/babel-parser/src/plugins/typescript/index.js

@@ -283,6 +283,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
           } else {
             enforceOrder(startPos, modifier, modifier, "override");
             enforceOrder(startPos, modifier, modifier, "static");
+            enforceOrder(startPos, modifier, modifier, "readonly");
 
             modified.accessibility = modifier;
           }
@@ -1927,10 +1928,23 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
       let accessibility: ?N.Accessibility;
       let readonly = false;
+      let override = false;
       if (allowModifiers !== undefined) {
-        accessibility = this.parseAccessModifier();
-        readonly = !!this.tsParseModifier(["readonly"]);
-        if (allowModifiers === false && (accessibility || readonly)) {
+        const modified = {};
+        this.tsParseModifiers(modified, [
+          "public",
+          "private",
+          "protected",
+          "override",
+          "readonly",
+        ]);
+        accessibility = modified.accessibility;
+        override = modified.override;
+        readonly = modified.readonly;
+        if (
+          allowModifiers === false &&
+          (accessibility || readonly || override)
+        ) {
           this.raise(startPos, TSErrors.UnexpectedParameterModifier);
         }
       }
@@ -1938,13 +1952,14 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       const left = this.parseMaybeDefault();
       this.parseAssignableListItemTypes(left);
       const elt = this.parseMaybeDefault(left.start, left.loc.start, left);
-      if (accessibility || readonly) {
+      if (accessibility || readonly || override) {
         const pp: N.TSParameterProperty = this.startNodeAt(startPos, startLoc);
         if (decorators.length) {
           pp.decorators = decorators;
         }
         if (accessibility) pp.accessibility = accessibility;
         if (readonly) pp.readonly = readonly;
+        if (override) pp.override = override;
         if (elt.type !== "Identifier" && elt.type !== "AssignmentPattern") {
           this.raise(pp.start, TSErrors.UnsupportedParameterPropertyKind);
         }

packages/babel-parser/src/types.js

@@ -1178,6 +1178,7 @@ export type TSParameterProperty = HasDecorators & {
   // At least one of `accessibility` or `readonly` must be set.
   accessibility?: ?Accessibility,
   readonly?: ?true,
+  override?: ?true,
   parameter: Identifier | AssignmentPattern,
 };