From 22cbfe3b1b70d44b1647a7cecaeb5e84ca247b47 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 7 Feb 2018 14:48:13 -0800
Subject: [PATCH] Fix getConstrainedTypeParameter function

---
 src/compiler/checker.ts   | 2 +-
 src/compiler/utilities.ts | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 7cfa484118e..a10bfe1d18c 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7245,7 +7245,7 @@ namespace ts {
 
         function getConstrainedTypeParameter(typeParameter: TypeParameter, node: Node) {
             let constraints: Type[];
-            while (isTypeNode(node)) {
+            while (isPartOfTypeNode(node)) {
                 const parent = node.parent;
                 if (parent.kind === SyntaxKind.ConditionalType && node === (<ConditionalTypeNode>parent).trueType) {
                     if (getTypeFromTypeNode((<ConditionalTypeNode>parent).checkType) === typeParameter) {
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 388ce814cc3..3c76bcf3119 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -771,6 +771,8 @@ namespace ts {
                 return node.parent.kind !== SyntaxKind.VoidExpression;
             case SyntaxKind.ExpressionWithTypeArguments:
                 return !isExpressionWithTypeArgumentsInClassExtendsClause(node);
+            case SyntaxKind.TypeParameter:
+                return node.parent.kind === SyntaxKind.MappedType || node.parent.kind === SyntaxKind.InferType;
 
             // Identifiers and qualified names may be type nodes, depending on their context. Climb
             // above them to find the lowest container