Disallow "let" as name at lexical bindings (#10099)

* Disallow "let" as name at lexical bindings

* Simplify

* Clean up

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

@@ -16,7 +16,7 @@ import type {
 import type { Pos, Position } from "../util/location";
 import { isStrictBindReservedWord } from "../util/identifier";
 import { NodeUtils } from "./node";
-import { type BindingTypes, BIND_NONE } from "../util/scopeflags";
+import { type BindingTypes, BIND_NONE, BIND_LEXICAL } from "../util/scopeflags";
 
 export default class LValParser extends NodeUtils {
   // Forward-declaration: defined in expression.js
@@ -363,6 +363,12 @@ export default class LValParser extends NodeUtils {
             checkClashes[key] = true;
           }
         }
+        if (bindingType === BIND_LEXICAL && expr.name === "let") {
+          this.raise(
+            expr.start,
+            "'let' is not allowed to be used as a name in 'let' or 'const' declarations.",
+          );
+        }
         if (!(bindingType & BIND_NONE)) {
           this.scope.declareName(expr.name, bindingType, expr.start);
         }

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

@@ -1010,9 +1010,6 @@ export default class StatementParser extends ExpressionParser {
   }
 
   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,