From f9dcc4e4bbf159a2658dcad8d329f38214f8d749 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=B2=20Ribaudo?= <nicolo.ribaudo@gmail.com>
Date: Thu, 5 Aug 2021 21:47:30 +0200
Subject: [PATCH] Fix array destructuring elision parsing in TS arrow functions
 (#13641)

---
 packages/babel-parser/src/parser/lval.js      |  4 +-
 .../input.ts                                  |  1 +
 .../output.json                               | 56 +++++++++++++++++++
 3 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/input.ts
 create mode 100644 packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/output.json

diff --git a/packages/babel-parser/src/parser/lval.js b/packages/babel-parser/src/parser/lval.js
index c6a87facf3..440e8396fa 100644
--- a/packages/babel-parser/src/parser/lval.js
+++ b/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 === "=";
diff --git a/packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/input.ts b/packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/input.ts
new file mode 100644
index 0000000000..a7878618ab
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/input.ts
@@ -0,0 +1 @@
+([, a]): b => c;
diff --git a/packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/output.json b/packages/babel-parser/test/fixtures/typescript/regression/elision-arrow-destructuring-13636/output.json
new file mode 100644
index 0000000000..5a87bda59b
--- /dev/null
+++ b/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": []
+  }
+}
\ No newline at end of file