fix(es/parser): Allow using async as the first one in parameters (#2386)

Cargo.lock

@@ -2687,7 +2687,7 @@ dependencies = [
 
 [[package]]
 name = "swc_ecma_parser"
-version = "0.73.4"
+version = "0.73.5"
 dependencies = [
  "either",
  "enum_kind",

ecmascript/parser/Cargo.toml

@@ -7,7 +7,7 @@ include = ["Cargo.toml", "src/**/*.rs", "examples/**/*.rs"]
 license = "Apache-2.0/MIT"
 name = "swc_ecma_parser"
 repository = "https://github.com/swc-project/swc.git"
-version = "0.73.4"
+version = "0.73.5"
 
 [package.metadata.docs.rs]
 all-features = true

ecmascript/parser/src/parser/expr.rs

@@ -1266,7 +1266,7 @@ impl<'a, I: Tokens> Parser<I> {
         // as a pattern instead of reparsing)
         while !eof!(self) && !is!(self, ')') {
             if first {
-                if is!(self, "async") {
+                if is!(self, "async") && !peeked_is!(self, ',') {
                     // https://github.com/swc-project/swc/issues/410
                     self.state.potential_arrow_start = Some(cur_pos!(self));
                     let expr = self.parse_assignment_expr()?;

ecmascript/parser/tests/typescript/arrow-function/async-param/input.ts

@@ -0,0 +1 @@
+let fn = (async, x) => {};

ecmascript/parser/tests/typescript/arrow-function/async-param/input.ts.json

@@ -0,0 +1,88 @@
+{
+  "type": "Script",
+  "span": {
+    "start": 0,
+    "end": 26,
+    "ctxt": 0
+  },
+  "body": [
+    {
+      "type": "VariableDeclaration",
+      "span": {
+        "start": 0,
+        "end": 26,
+        "ctxt": 0
+      },
+      "kind": "let",
+      "declare": false,
+      "declarations": [
+        {
+          "type": "VariableDeclarator",
+          "span": {
+            "start": 4,
+            "end": 25,
+            "ctxt": 0
+          },
+          "id": {
+            "type": "Identifier",
+            "span": {
+              "start": 4,
+              "end": 6,
+              "ctxt": 0
+            },
+            "value": "fn",
+            "optional": false,
+            "typeAnnotation": null
+          },
+          "init": {
+            "type": "ArrowFunctionExpression",
+            "span": {
+              "start": 9,
+              "end": 25,
+              "ctxt": 0
+            },
+            "params": [
+              {
+                "type": "Identifier",
+                "span": {
+                  "start": 10,
+                  "end": 15,
+                  "ctxt": 0
+                },
+                "value": "async",
+                "optional": false,
+                "typeAnnotation": null
+              },
+              {
+                "type": "Identifier",
+                "span": {
+                  "start": 17,
+                  "end": 18,
+                  "ctxt": 0
+                },
+                "value": "x",
+                "optional": false,
+                "typeAnnotation": null
+              }
+            ],
+            "body": {
+              "type": "BlockStatement",
+              "span": {
+                "start": 23,
+                "end": 25,
+                "ctxt": 0
+              },
+              "stmts": []
+            },
+            "async": false,
+            "generator": false,
+            "typeParameters": null,
+            "returnType": null
+          },
+          "definite": false
+        }
+      ]
+    }
+  ],
+  "interpreter": null
+}