From d85df9e9faa807f8481c88d4babb77e1e7d9ed72 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Tue, 22 Jul 2014 10:54:20 -0700
Subject: [PATCH] Addressing CR feedback. Adding comment to explain source type
 instantiation. Adding a test case.

---
 src/compiler/checker.ts                       |  1 +
 .../contextualSignatureInstantiation3.js      | 42 +++++++++++++++++++
 .../contextualSignatureInstantiation3.ts      | 22 ++++++++++
 3 files changed, 65 insertions(+)
 create mode 100644 tests/baselines/reference/contextualSignatureInstantiation3.js
 create mode 100644 tests/cases/compiler/contextualSignatureInstantiation3.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 792dc64a1b9..aa457833175 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -3675,6 +3675,7 @@ module ts {
         function instantiateSignatureInContextOf(signature: Signature, contextualSignature: Signature, contextualMapper: TypeMapper): Signature {
             var context = createInferenceContext(signature.typeParameters);
             forEachMatchingParameterType(contextualSignature, signature, (source, target) => {
+                // Type parameters from outer context referenced by source type are fixed by instantiation of the source type
                 inferTypes(context, instantiateType(source, contextualMapper), target);
             });
             return getSignatureInstantiation(signature, getInferredTypes(context));
diff --git a/tests/baselines/reference/contextualSignatureInstantiation3.js b/tests/baselines/reference/contextualSignatureInstantiation3.js
new file mode 100644
index 00000000000..44737476482
--- /dev/null
+++ b/tests/baselines/reference/contextualSignatureInstantiation3.js
@@ -0,0 +1,42 @@
+//// [contextualSignatureInstantiation3.ts]
+function map<T, U>(items: T[], f: (x: T) => U): U[]{
+    return items.map(f);
+}
+
+function identity<T>(x: T) {
+    return x;
+}
+
+function singleton<T>(x: T) {
+    return [x];
+}
+
+var xs = [1, 2, 3];
+
+// Have compiler check that we get the correct types
+var v1: number[];
+var v1 = xs.map(identity);      // Error if not number[]
+var v1 = map(xs, identity);     // Error if not number[]
+
+var v2: number[][];         
+var v2 = xs.map(singleton);     // Error if not number[][]
+var v2 = map(xs, singleton);    // Error if not number[][]
+
+
+//// [contextualSignatureInstantiation3.js]
+function map(items, f) {
+    return items.map(f);
+}
+function identity(x) {
+    return x;
+}
+function singleton(x) {
+    return [x];
+}
+var xs = [1, 2, 3];
+var v1;
+var v1 = xs.map(identity);
+var v1 = map(xs, identity);
+var v2;
+var v2 = xs.map(singleton);
+var v2 = map(xs, singleton);
diff --git a/tests/cases/compiler/contextualSignatureInstantiation3.ts b/tests/cases/compiler/contextualSignatureInstantiation3.ts
new file mode 100644
index 00000000000..a71f08d209d
--- /dev/null
+++ b/tests/cases/compiler/contextualSignatureInstantiation3.ts
@@ -0,0 +1,22 @@
+function map<T, U>(items: T[], f: (x: T) => U): U[]{
+    return items.map(f);
+}
+
+function identity<T>(x: T) {
+    return x;
+}
+
+function singleton<T>(x: T) {
+    return [x];
+}
+
+var xs = [1, 2, 3];
+
+// Have compiler check that we get the correct types
+var v1: number[];
+var v1 = xs.map(identity);      // Error if not number[]
+var v1 = map(xs, identity);     // Error if not number[]
+
+var v2: number[][];         
+var v2 = xs.map(singleton);     // Error if not number[][]
+var v2 = map(xs, singleton);    // Error if not number[][]