From cdd10b09b19797647cffe0996bd3dc846a14b6aa Mon Sep 17 00:00:00 2001
From: Daniel Rosenwasser <drosen@microsoft.com>
Date: Sun, 28 Feb 2016 20:08:55 -0800
Subject: [PATCH] Instantiate type parameters with themselves as their 'this'
 type when relating.

---
 src/compiler/checker.ts | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index c2a14e5b9a0..b5526e204ca 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5595,9 +5595,14 @@ namespace ts {
 
                 if (source.flags & TypeFlags.TypeParameter) {
                     let constraint = getConstraintOfTypeParameter(<TypeParameter>source);
+
                     if (!constraint || constraint.flags & TypeFlags.Any) {
                         constraint = emptyObjectType;
                     }
+
+                    // The constraint may need to be further instantiated with its 'this' type.
+                    constraint = getTypeWithThisArgument(constraint);
+
                     // Report constraint errors only if the constraint is not the empty object type
                     const reportConstraintErrors = reportErrors && constraint !== emptyObjectType;
                     if (result = isRelatedTo(constraint, target, reportConstraintErrors)) {