From de9ff1b0046a66f3d3d0d84fbe063af254be91be Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <293473+sandersn@users.noreply.github.com>
Date: Fri, 11 May 2018 09:12:25 -0700
Subject: [PATCH] Assert:only merge into transient symbols

---
 src/compiler/checker.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0f1ee7e62d9..caa75a45eb9 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -892,6 +892,7 @@ namespace ts {
         function mergeSymbol(target: Symbol, source: Symbol) {
             if (!(target.flags & getExcludedSymbolFlags(source.flags)) ||
                 (source.flags | target.flags) & SymbolFlags.JSContainer) {
+                Debug.assert(!!(target.flags & SymbolFlags.Transient));
                 // Javascript static-property-assignment declarations always merge, even though they are also values
                 if (source.flags & SymbolFlags.ValueModule && target.flags & SymbolFlags.ValueModule && target.constEnumOnlyModule && !source.constEnumOnlyModule) {
                     // reset flag when merging instantiated module into value module that has only const enums