fix(es/parser): Correctly parse the keyword (#8483)

**Related issue:**

 - Closes #8482.

crates/swc/tests/fixture/issues-8xxx/8482/input/.swcrc

@@ -0,0 +1,24 @@
+{
+  "jsc": {
+    "parser": {
+      "syntax": "ecmascript",
+      "jsx": false
+    },
+    "externalHelpers": true,
+    "minify": {
+      "compress": false,
+      "mangle": false
+    },
+    "keepClassNames": true,
+    "loose": true
+  },
+  "minify": false,
+  "isModule": true,
+  "module": {
+    "type": "umd"
+  },
+  "env": {
+    "targets": "",
+    "bugfixes": true
+  }
+}

crates/swc/tests/fixture/issues-8xxx/8482/input/index.js

@@ -0,0 +1 @@
+export let a = ''

crates/swc/tests/fixture/issues-8xxx/8482/output/index.js

@@ -0,0 +1,19 @@
+(function(global, factory) {
+    if (typeof module === "object" && typeof module.exports === "object") factory(exports);
+    else if (typeof define === "function" && define.amd) define([
+        "exports"
+    ], factory);
+    else if (global = typeof globalThis !== "undefined" ? globalThis : global || self) factory(global.index = {});
+})(this, function(exports) {
+    "use strict";
+    Object.defineProperty(exports, "__esModule", {
+        value: true
+    });
+    Object.defineProperty(exports, "a", {
+        enumerable: true,
+        get: function() {
+            return a;
+        }
+    });
+    let a = "";
+});

crates/swc_ecma_parser/src/lexer/mod.rs

@@ -824,12 +824,16 @@ impl<'a> Lexer<'a> {
                 // Optimization
                 {
                     let s = l.input.uncons_while(|c| {
+                        if !c.is_ident_part() {
+                            return false;
+                        }
+
                         // Performance optimization
                         if c.is_ascii_uppercase() || c.is_ascii_digit() || !c.is_ascii() {
                             can_be_keyword = false;
                         }
 
-                        c.is_ident_part()
+                        true
                     });
                     if !s.is_empty() {
                         first = false;

crates/swc_ecma_parser/src/lexer/table.rs

@@ -153,12 +153,7 @@ const L_I: ByteHandler = Some(|lexer| {
     })
 });
 
-const L_J: ByteHandler = Some(|lexer| {
-    lexer.read_word_with(|s| match s {
-        "let" => Some(Word::Keyword(Keyword::Let)),
-        _ => None,
-    })
-});
+const L_J: ByteHandler = IDN;
 
 const L_K: ByteHandler = Some(|lexer| {
     lexer.read_word_with(|s| match s {

crates/swc_ecma_parser/tests/js/issue-8482/input.js

@@ -0,0 +1 @@
+export let a = ''

crates/swc_ecma_parser/tests/js/issue-8482/input.js.json

@@ -0,0 +1,61 @@
+{
+  "type": "Module",
+  "span": {
+    "start": 1,
+    "end": 19,
+    "ctxt": 0
+  },
+  "body": [
+    {
+      "type": "ExportDeclaration",
+      "span": {
+        "start": 1,
+        "end": 19,
+        "ctxt": 0
+      },
+      "declaration": {
+        "type": "VariableDeclaration",
+        "span": {
+          "start": 8,
+          "end": 19,
+          "ctxt": 0
+        },
+        "kind": "let",
+        "declare": false,
+        "declarations": [
+          {
+            "type": "VariableDeclarator",
+            "span": {
+              "start": 13,
+              "end": 19,
+              "ctxt": 0
+            },
+            "id": {
+              "type": "Identifier",
+              "span": {
+                "start": 13,
+                "end": 14,
+                "ctxt": 0
+              },
+              "value": "a",
+              "optional": false,
+              "typeAnnotation": null
+            },
+            "init": {
+              "type": "StringLiteral",
+              "span": {
+                "start": 17,
+                "end": 19,
+                "ctxt": 0
+              },
+              "value": "",
+              "raw": "''"
+            },
+            "definite": false
+          }
+        ]
+      }
+    }
+  ],
+  "interpreter": null
+}