Fix array destructuring elision parsing in TS arrow functions (#13641)

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

@@ -257,7 +257,9 @@ export default class LValParser extends NodeUtils {
         return this.isAssignable(node.argument);
 
       case "ArrayExpression":
-        return node.elements.every(element => this.isAssignable(element));
+        return node.elements.every(
+          element => element === null || this.isAssignable(element),
+        );
 
       case "AssignmentExpression":
         return node.operator === "=";

packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/input.ts

@@ -0,0 +1 @@
+([, a]): b => c;

packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/output.json

@@ -0,0 +1,56 @@
+{
+  "type": "File",
+  "start":0,"end":16,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":16}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":16,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":16}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":16,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":16}},
+        "expression": {
+          "type": "ArrowFunctionExpression",
+          "start":0,"end":15,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":15}},
+          "returnType": {
+            "type": "TSTypeAnnotation",
+            "start":7,"end":10,"loc":{"start":{"line":1,"column":7},"end":{"line":1,"column":10}},
+            "typeAnnotation": {
+              "type": "TSTypeReference",
+              "start":9,"end":10,"loc":{"start":{"line":1,"column":9},"end":{"line":1,"column":10}},
+              "typeName": {
+                "type": "Identifier",
+                "start":9,"end":10,"loc":{"start":{"line":1,"column":9},"end":{"line":1,"column":10},"identifierName":"b"},
+                "name": "b"
+              }
+            }
+          },
+          "id": null,
+          "generator": false,
+          "async": false,
+          "params": [
+            {
+              "type": "ArrayPattern",
+              "start":1,"end":6,"loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":6}},
+              "elements": [
+                null,
+                {
+                  "type": "Identifier",
+                  "start":4,"end":5,"loc":{"start":{"line":1,"column":4},"end":{"line":1,"column":5},"identifierName":"a"},
+                  "name": "a"
+                }
+              ]
+            }
+          ],
+          "body": {
+            "type": "Identifier",
+            "start":14,"end":15,"loc":{"start":{"line":1,"column":14},"end":{"line":1,"column":15},"identifierName":"c"},
+            "name": "c"
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}