From 7721cc45c8189d9323ae97549a6bfadfa41d875b Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Thu, 22 Mar 2018 11:46:52 -0700
Subject: [PATCH] Improve assertion violation message (#22522)

---
 src/compiler/binder.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index db8c390da85..2b66e92cdc3 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -297,7 +297,7 @@ namespace ts {
                 case SyntaxKind.Parameter:
                     // Parameters with names are handled at the top of this function.  Parameters
                     // without names can only come from JSDocFunctionTypes.
-                    Debug.assert(node.parent.kind === SyntaxKind.JSDocFunctionType);
+                    Debug.assert(node.parent.kind === SyntaxKind.JSDocFunctionType, "Impossible parameter parent kind", () => `parent is: ${(ts as any).SyntaxKind ? (ts as any).SyntaxKind[node.parent.kind] : node.parent.kind}, expected JSDocFunctionType`);
                     const functionType = <JSDocFunctionType>node.parent;
                     const index = functionType.parameters.indexOf(node as ParameterDeclaration);
                     return "arg" + index as __String;