From af606f11d8f8ae0f871db74b8f43febd79094cf7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hu=C3=A1ng=20J=C3=B9nli=C3=A0ng?= <jlhwung@gmail.com>
Date: Mon, 13 Dec 2021 17:15:42 -0500
Subject: [PATCH] fix: check preceding line break before exclamation

---
 .../src/plugins/typescript/index.js           |  6 ++-
 .../variable-declarator/definite-asi/input.ts |  2 +
 .../definite-asi/output.json                  | 54 +++++++++++++++++++
 3 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/input.ts
 create mode 100644 packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/output.json

diff --git a/packages/babel-parser/src/plugins/typescript/index.js b/packages/babel-parser/src/plugins/typescript/index.js
index 8fb93cddda71..d07ad1759b5c 100644
--- a/packages/babel-parser/src/plugins/typescript/index.js
+++ b/packages/babel-parser/src/plugins/typescript/index.js
@@ -2832,7 +2832,11 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       kind: "var" | "let" | "const",
     ): void {
       super.parseVarId(decl, kind);
-      if (decl.id.type === "Identifier" && this.eat(tt.bang)) {
+      if (
+        decl.id.type === "Identifier" &&
+        !this.hasPrecedingLineBreak() &&
+        this.eat(tt.bang)
+      ) {
         decl.definite = true;
       }
 
diff --git a/packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/input.ts b/packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/input.ts
new file mode 100644
index 000000000000..d17851234900
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/input.ts
@@ -0,0 +1,2 @@
+let x
+!function() {};
diff --git a/packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/output.json b/packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/output.json
new file mode 100644
index 000000000000..d777e9b8156c
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/typescript/variable-declarator/definite-asi/output.json
@@ -0,0 +1,54 @@
+{
+  "type": "File",
+  "start":0,"end":21,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":15}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":21,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":15}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "VariableDeclaration",
+        "start":0,"end":5,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":5}},
+        "declarations": [
+          {
+            "type": "VariableDeclarator",
+            "start":4,"end":5,"loc":{"start":{"line":1,"column":4},"end":{"line":1,"column":5}},
+            "id": {
+              "type": "Identifier",
+              "start":4,"end":5,"loc":{"start":{"line":1,"column":4},"end":{"line":1,"column":5},"identifierName":"x"},
+              "name": "x"
+            },
+            "init": null
+          }
+        ],
+        "kind": "let"
+      },
+      {
+        "type": "ExpressionStatement",
+        "start":6,"end":21,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":15}},
+        "expression": {
+          "type": "UnaryExpression",
+          "start":6,"end":20,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":14}},
+          "operator": "!",
+          "prefix": true,
+          "argument": {
+            "type": "FunctionExpression",
+            "start":7,"end":20,"loc":{"start":{"line":2,"column":1},"end":{"line":2,"column":14}},
+            "id": null,
+            "generator": false,
+            "async": false,
+            "params": [],
+            "body": {
+              "type": "BlockStatement",
+              "start":18,"end":20,"loc":{"start":{"line":2,"column":12},"end":{"line":2,"column":14}},
+              "body": [],
+              "directives": []
+            }
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}