Disallow const let or let let

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

@@ -907,7 +907,7 @@ export default class StatementParser extends ExpressionParser {
     node.kind = kind;
     for (;;) {
       const decl = this.startNode();
-      this.parseVarHead(decl);
+      this.parseVarId(decl, kind);
       if (this.eat(tt.eq)) {
         decl.init = this.parseMaybeAssign(isFor);
       } else {
@@ -937,7 +937,10 @@ export default class StatementParser extends ExpressionParser {
     return node;
   }
 
-  parseVarHead(decl: N.VariableDeclarator): void {
+  parseVarId(decl: N.VariableDeclarator, kind: "var" | "let" | "const"): void {
+    if ((kind === "const" || kind === "let") && this.isContextual("let")) {
+      this.unexpected(null, "let is disallowed as a lexically bound name");
+    }
     decl.id = this.parseBindingAtom();
     this.checkLVal(decl.id, true, undefined, "variable declaration");
   }

packages/babel-parser/src/plugins/flow.js

@@ -2344,8 +2344,11 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     }
 
     // parse flow type annotations on variable declarator heads - let foo: string = bar
-    parseVarHead(decl: N.VariableDeclarator): void {
-      super.parseVarHead(decl);
+    parseVarId(
+      decl: N.VariableDeclarator,
+      kind: "var" | "let" | "const",
+    ): void {
+      super.parseVarId(decl, kind);
       if (this.match(tt.colon)) {
         decl.id.typeAnnotation = this.flowParseTypeAnnotation();
         this.finishNode(decl.id, decl.id.type);

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

@@ -1948,8 +1948,11 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     }
 
     // `let x: number;`
-    parseVarHead(decl: N.VariableDeclarator): void {
-      super.parseVarHead(decl);
+    parseVarId(
+      decl: N.VariableDeclarator,
+      kind: "var" | "let" | "const",
+    ): void {
+      super.parseVarId(decl, kind);
       if (decl.id.type === "Identifier" && this.eat(tt.bang)) {
         decl.definite = true;
       }