From 69580c4561b75db1cf8eae53593abe4d27189f2c Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 28 Feb 2018 16:57:25 -0800
Subject: [PATCH] Filter outer type parameters (similar to anonymous types)

---
 src/compiler/checker.ts | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0be1c8438b4..520b477da0b 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -8278,7 +8278,9 @@ namespace ts {
             const links = getNodeLinks(node);
             if (!links.resolvedType) {
                 const checkType = getTypeFromTypeNode(node.checkType);
-                const outerTypeParameters = getOuterTypeParameters(node, /*includeThisTypes*/ true);
+                const aliasTypeArguments = getAliasTypeArgumentsForTypeNode(node);
+                const allOuterTypeParameters = getOuterTypeParameters(node, /*includeThisTypes*/ true);
+                const outerTypeParameters = aliasTypeArguments ? allOuterTypeParameters : filter(allOuterTypeParameters, tp => isTypeParameterPossiblyReferenced(tp, node));
                 const root: ConditionalRoot = {
                     node,
                     checkType,
@@ -8290,7 +8292,7 @@ namespace ts {
                     outerTypeParameters,
                     instantiations: undefined,
                     aliasSymbol: getAliasSymbolForTypeNode(node),
-                    aliasTypeArguments: getAliasTypeArgumentsForTypeNode(node)
+                    aliasTypeArguments
                 };
                 links.resolvedType = getConditionalType(root, /*mapper*/ undefined);
                 if (outerTypeParameters) {