From 3e93461fc84108bdcd8abafbcbf96b5c8bbcc284 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Thu, 20 Dec 2018 07:21:49 -0800
Subject: [PATCH] Add regression test

---
 .../compiler/discriminantPropertyCheck.ts     | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tests/cases/compiler/discriminantPropertyCheck.ts b/tests/cases/compiler/discriminantPropertyCheck.ts
index 16fb847bdf0..a24fe07973b 100644
--- a/tests/cases/compiler/discriminantPropertyCheck.ts
+++ b/tests/cases/compiler/discriminantPropertyCheck.ts
@@ -99,3 +99,25 @@ function func2(inst: Instance) {
         }
     }
 }
+
+// Repro from #29106
+
+const f = (_a: string, _b: string): void => {};
+
+interface A {
+  a?: string;
+  b?: string;
+}
+
+interface B {
+  a: string;
+  b: string;
+}
+
+type U = A | B;
+
+const u: U = {} as any;
+
+u.a && u.b && f(u.a, u.b);
+
+u.b && u.a && f(u.a, u.b);