From 477cba539b1da025c3fb27fe6aa99a7772f7fd29 Mon Sep 17 00:00:00 2001
From: Andy <anhans@microsoft.com>
Date: Thu, 1 Feb 2018 10:51:28 -0800
Subject: [PATCH] Improve debug failure for failed node cast (#21539)

---
 src/compiler/core.ts | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 2966582cb39..c2ede12345f 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1454,7 +1454,13 @@ namespace ts {
 
     export function cast<TOut extends TIn, TIn = any>(value: TIn | undefined, test: (value: TIn) => value is TOut): TOut {
         if (value !== undefined && test(value)) return value;
-        Debug.fail(`Invalid cast. The supplied value did not pass the test '${Debug.getFunctionName(test)}'.`);
+
+        if (value && typeof (value as any).kind === "number") {
+            Debug.fail(`Invalid cast. The supplied ${(ts as any).SyntaxKind[(value as any).kind]} did not pass the test '${Debug.getFunctionName(test)}'.`);
+        }
+        else {
+            Debug.fail(`Invalid cast. The supplied value did not pass the test '${Debug.getFunctionName(test)}'.`);
+        }
     }
 
     /** Does nothing. */