Allow trailing comma after rest parameter in TSDeclareFunction (#13101)

* fix(ts): allow trailing comma after rest parameter in `TSDeclareFunction`

* Apply code review changes

Co-Authored-By: Nicolò Ribaudo <7000710+nicolo-ribaudo@users.noreply.github.com>

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

@@ -2789,6 +2789,18 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return super.parseMaybeDecoratorArguments(expr);
     }
 
+    checkCommaAfterRest(close) {
+      if (
+        this.state.isDeclareContext &&
+        this.match(tt.comma) &&
+        this.lookaheadCharCode() === close
+      ) {
+        this.next();
+      } else {
+        super.checkCommaAfterRest(close);
+      }
+    }
+
     // === === === === === === === === === === === === === === === ===
     // Note: All below methods are duplicates of something in flow.js.
     // Not sure what the best way to combine these is.

packages/babel-parser/test/fixtures/typescript/declare/function-rest-trailing-comma/input.ts

@@ -0,0 +1 @@
+declare function foo(...args: any[], )

packages/babel-parser/test/fixtures/typescript/declare/function-rest-trailing-comma/output.json

@@ -0,0 +1,48 @@
+{
+  "type": "File",
+  "start":0,"end":38,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":38}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":38,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":38}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "TSDeclareFunction",
+        "start":0,"end":38,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":38}},
+        "declare": true,
+        "id": {
+          "type": "Identifier",
+          "start":17,"end":20,"loc":{"start":{"line":1,"column":17},"end":{"line":1,"column":20},"identifierName":"foo"},
+          "name": "foo"
+        },
+        "generator": false,
+        "async": false,
+        "params": [
+          {
+            "type": "RestElement",
+            "start":21,"end":35,"loc":{"start":{"line":1,"column":21},"end":{"line":1,"column":35}},
+            "argument": {
+              "type": "Identifier",
+              "start":24,"end":28,"loc":{"start":{"line":1,"column":24},"end":{"line":1,"column":28},"identifierName":"args"},
+              "name": "args"
+            },
+            "typeAnnotation": {
+              "type": "TSTypeAnnotation",
+              "start":28,"end":35,"loc":{"start":{"line":1,"column":28},"end":{"line":1,"column":35}},
+              "typeAnnotation": {
+                "type": "TSArrayType",
+                "start":30,"end":35,"loc":{"start":{"line":1,"column":30},"end":{"line":1,"column":35}},
+                "elementType": {
+                  "type": "TSAnyKeyword",
+                  "start":30,"end":33,"loc":{"start":{"line":1,"column":30},"end":{"line":1,"column":33}}
+                }
+              }
+            }
+          }
+        ]
+      }
+    ],
+    "directives": []
+  }
+}