Support TS 4.3 override syntax in class (#13097)

* support TS 4.3 `override` syntax in class

* fix types

* fix types

* tweak error message

* update TypeScript commit

* split tests

* add more tests

* update allowlist

* disallow `override` with `declare`

* disallow `override` in non-sub class

* update TypeScript allowlist

* rename error message key

* add more tests

packages/babel-parser/src/parser/error-message.js

@@ -128,6 +128,8 @@ export const ErrorMessages = makeErrorTemplates(
       "constructors in/after an Optional Chain are not allowed",
     OptionalChainingNoTemplate:
       "Tagged Template Literals are not allowed in optionalChain",
+    OverrideOnConstructor:
+      "'override' modifier cannot appear on a constructor declaration.",
     ParamDupe: "Argument name clash",
     PatternHasAccessor: "Object pattern can't contain getter or setter",
     PatternHasMethod: "Object pattern can't contain methods",

packages/babel-parser/src/parser/statement.js

@@ -1205,15 +1205,12 @@ export default class StatementParser extends ExpressionParser {
   }
 
   // https://tc39.es/ecma262/#prod-ClassBody
-  parseClassBody(
-    constructorAllowsSuper: boolean,
-    oldStrict: boolean,
-  ): N.ClassBody {
+  parseClassBody(hadSuperClass: boolean, oldStrict: boolean): N.ClassBody {
     this.classScope.enter();
 
     const state: N.ParseClassMemberState = {
-      constructorAllowsSuper,
       hadConstructor: false,
+      hadSuperClass,
     };
     let decorators: N.Decorator[] = [];
     const classBody: N.ClassBody = this.startNode();
@@ -1400,8 +1397,11 @@ export default class StatementParser extends ExpressionParser {
         if (state.hadConstructor && !this.hasPlugin("typescript")) {
           this.raise(key.start, Errors.DuplicateConstructor);
         }
+        if (isConstructor && this.hasPlugin("typescript") && member.override) {
+          this.raise(key.start, Errors.OverrideOnConstructor);
+        }
         state.hadConstructor = true;
-        allowsDirectSuper = state.constructorAllowsSuper;
+        allowsDirectSuper = state.hadSuperClass;
       }
 
       this.pushClassMethod(

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

@@ -41,6 +41,7 @@ type TsModifier =
   | "abstract"
   | "declare"
   | "static"
+  | "override"
   | N.Accessibility;
 
 function nonNull<T>(x: ?T): T {
@@ -86,12 +87,15 @@ const TSErrors = makeErrorTemplates(
     ExpectedAmbientAfterExportDeclare:
       "'export declare' must be followed by an ambient declaration.",
     ImportAliasHasImportType: "An import alias can not use 'import type'",
+    IncompatibleModifiers: "'%0' modifier cannot be used with '%1' modifier.",
     IndexSignatureHasAbstract:
       "Index signatures cannot have the 'abstract' modifier",
     IndexSignatureHasAccessibility:
       "Index signatures cannot have an accessibility modifier ('%0')",
     IndexSignatureHasDeclare:
       "Index signatures cannot have the 'declare' modifier",
+    IndexSignatureHasOverride:
+      "'override' modifier cannot appear on an index signature.",
     IndexSignatureHasStatic:
       "Index signatures cannot have the 'static' modifier",
     InvalidModifierOnTypeMember:
@@ -107,6 +111,8 @@ const TSErrors = makeErrorTemplates(
       "'abstract' modifier can only appear on a class, method, or property declaration.",
     OptionalTypeBeforeRequired:
       "A required element cannot follow an optional element.",
+    OverrideNotInSubClass:
+      "This member cannot have an 'override' modifier because its containing class does not extend another class.",
     PatternIsOptional:
       "A binding pattern parameter cannot be optional in an implementation signature.",
     PrivateElementHasAbstract:
@@ -257,6 +263,16 @@ export default (superClass: Class<Parser>): Class<Parser> =>
               "static",
               "readonly",
             );
+          } else if (
+            (modified.declare && modifier === "override") ||
+            (modified.override && modifier === "declare")
+          ) {
+            this.raise(
+              startPos,
+              TSErrors.IncompatibleModifiers,
+              "declare",
+              "override",
+            );
           }
           modified[modifier] = true;
         }
@@ -622,7 +638,15 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       this.tsParseModifiers(
         node,
         ["readonly"],
-        ["declare", "abstract", "private", "protected", "public", "static"],
+        [
+          "declare",
+          "abstract",
+          "private",
+          "protected",
+          "public",
+          "static",
+          "override",
+        ],
         TSErrors.InvalidModifierOnTypeMember,
       );
 
@@ -2223,6 +2247,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         "private",
         "public",
         "protected",
+        "override",
       ]);
 
       const callParseClassMember = () => {
@@ -2246,6 +2271,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         "readonly",
         "declare",
         "static",
+        "override",
       ]);
 
       if (isStatic) {
@@ -2269,6 +2295,9 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         if ((member: any).declare) {
           this.raise(member.start, TSErrors.IndexSignatureHasDeclare);
         }
+        if ((member: any).override) {
+          this.raise(member.start, TSErrors.IndexSignatureHasOverride);
+        }
 
         return;
       }
@@ -2277,6 +2306,19 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         this.raise(member.start, TSErrors.NonAbstractClassHasAbstractMethod);
       }
 
+      if ((member: any).override) {
+        if (isStatic) {
+          this.raise(
+            member.start,
+            TSErrors.IncompatibleModifiers,
+            "static",
+            "override",
+          );
+        } else if (!state.hadSuperClass) {
+          this.raise(member.start, TSErrors.OverrideNotInSubClass);
+        }
+      }
+
       /*:: invariant(member.type !== "TSIndexSignature") */
 
       super.parseClassMemberWithIsStatic(classBody, member, state, isStatic);

packages/babel-parser/src/types.js

@@ -730,6 +730,7 @@ export type ClassMemberBase = NodeBase &
     computed: boolean,
     // TypeScript only:
     accessibility?: ?Accessibility,
+    override?: ?true,
     abstract?: ?true,
     optional?: ?true,
   };
@@ -807,6 +808,7 @@ export type ClassPrivateProperty = NodeBase & {
   optional?: true,
   definite?: true,
   readonly?: true,
+  override?: true,
 };
 
 export type OptClassDeclaration = ClassBase &
@@ -1536,5 +1538,5 @@ export type ParseSubscriptState = {
 
 export type ParseClassMemberState = {|
   hadConstructor: boolean,
-  constructorAllowsSuper: boolean,
+  hadSuperClass: boolean,
 |};