From e6a6ed33f9840e54fd1136f4d3cf7a9eb78cec91 Mon Sep 17 00:00:00 2001
From: Daniel Tschinder <daniel@tschinder.de>
Date: Wed, 31 Oct 2018 16:36:45 -0700
Subject: [PATCH] fix: Do not allow TypeCastExpressions w/o parens inside of
 SequenceExpressions

---
 packages/babel-parser/src/plugins/flow.js       | 17 ++++++++++++++++-
 .../flow/typecasts/fail-without-parens/input.js |  1 +
 .../typecasts/fail-without-parens/options.json  |  8 ++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/input.js
 create mode 100644 packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/options.json

diff --git a/packages/babel-parser/src/plugins/flow.js b/packages/babel-parser/src/plugins/flow.js
index 6382c1f6f3c2..3c0a588a18f3 100644
--- a/packages/babel-parser/src/plugins/flow.js
+++ b/packages/babel-parser/src/plugins/flow.js
@@ -2494,9 +2494,24 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     }
 
     parseParenAndDistinguishExpression(canBeArrow: boolean): N.Expression {
-      return super.parseParenAndDistinguishExpression(
+      const list = super.parseParenAndDistinguishExpression(
         canBeArrow && this.state.noArrowAt.indexOf(this.state.start) === -1,
       );
+
+      // Ensure that TypeCastExpressions without parens are not allowed inside SequenceExpressions
+      // e.g. (A, B: T)
+      if (list.type === "SequenceExpression") {
+        const firstTypeCast = list.expressions.find(
+          ({ type, extra }) =>
+            type === "TypeCastExpression" &&
+            (!extra || extra.parenthesized !== true),
+        );
+        if (firstTypeCast) {
+          this.unexpected(firstTypeCast.typeAnnotation.start);
+        }
+      }
+
+      return list;
     }
 
     parseSubscripts(
diff --git a/packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/input.js b/packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/input.js
new file mode 100644
index 000000000000..767b0cba53b8
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/input.js
@@ -0,0 +1 @@
+(A, B: T)
diff --git a/packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/options.json b/packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/options.json
new file mode 100644
index 000000000000..d904a92181b9
--- /dev/null
+++ b/packages/babel-parser/test/fixtures/flow/typecasts/fail-without-parens/options.json
@@ -0,0 +1,8 @@
+{
+  "sourceType": "module",
+  "plugins": [
+    "jsx",
+    "flow"
+  ],
+  "throws": "Unexpected token (1:5)"
+}
\ No newline at end of file