From 26f73d4dc89191fdc317f9e359a5035761413495 Mon Sep 17 00:00:00 2001
From: Jason Freeman <jfreeman@microsoft.com>
Date: Thu, 14 May 2015 13:20:09 -0700
Subject: [PATCH] Add a comment in getTypeOfAlias

---
 src/compiler/checker.ts | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index cb5bcbf0b7e..7a4ba23ca2a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2415,6 +2415,12 @@ module ts {
             let links = getSymbolLinks(symbol);
             if (!links.type) {
                 let targetSymbol = resolveAlias(symbol);
+
+                // It only makes sense to get the type of a value symbol. If the result of resolving
+                // the alias is not a value, then it has no type. To get the type associated with a
+                // type symbol, call getDeclaredTypeOfSymbol.
+                // This check is important because without it, a call to getTypeOfSymbol could end
+                // up recursively calling getTypeOfAlias, causing a stack overflow.
                 links.type = targetSymbol.flags & SymbolFlags.Value
                     ? getTypeOfSymbol(targetSymbol)
                     : unknownType;