From 0dc42fea743f5ca50a667a6e604fa85832492df0 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Mon, 30 Apr 2018 10:43:55 -0700
Subject: [PATCH] Add regression tests

---
 .../compiler/controlFlowNullTypeAndLiteral.ts | 25 +++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 tests/cases/compiler/controlFlowNullTypeAndLiteral.ts

diff --git a/tests/cases/compiler/controlFlowNullTypeAndLiteral.ts b/tests/cases/compiler/controlFlowNullTypeAndLiteral.ts
new file mode 100644
index 00000000000..ee66f441f14
--- /dev/null
+++ b/tests/cases/compiler/controlFlowNullTypeAndLiteral.ts
@@ -0,0 +1,25 @@
+// @strict: true
+
+// Repros from #23771
+
+const myNull: null = null;
+const objWithValMaybeNull: { val: number | null } = { val: 1 };
+const addOne = function (num: number) {
+    return num + 1;
+}
+
+if (objWithValMaybeNull.val !== null)
+    addOne(objWithValMaybeNull.val);
+if (objWithValMaybeNull.val !== myNull)
+    addOne(objWithValMaybeNull.val);
+
+if (objWithValMaybeNull.val === null)
+    addOne(objWithValMaybeNull.val);    // Error
+if (objWithValMaybeNull.val === myNull)
+    addOne(objWithValMaybeNull.val);    // Error
+
+function f(x: number | null) {
+    if(x === myNull) {
+        const s: string = x;  // Error
+    }
+}