From d25fd23e042be44026677466cadedbf36f160933 Mon Sep 17 00:00:00 2001
From: Daniel Rosenwasser <Daniel.Rosenwasser@microsoft.com>
Date: Mon, 10 Jul 2017 14:35:09 -0700
Subject: [PATCH 1/2] Declare 'sum' so that it doesn't require type arguments.

---
 src/compiler/checker.ts | 6 +++---
 src/compiler/core.ts    | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ee0a3a90d7e99..5fac69156eb5d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -83,9 +83,9 @@ namespace ts {
         // extra cost of calling `getParseTreeNode` when calling these functions from inside the
         // checker.
         const checker: TypeChecker = {
-            getNodeCount: () => sum<"nodeCount">(host.getSourceFiles(), "nodeCount"),
-            getIdentifierCount: () => sum<"identifierCount">(host.getSourceFiles(), "identifierCount"),
-            getSymbolCount: () => sum<"symbolCount">(host.getSourceFiles(), "symbolCount") + symbolCount,
+            getNodeCount: () => sum(host.getSourceFiles(), "nodeCount"),
+            getIdentifierCount: () => sum(host.getSourceFiles(), "identifierCount"),
+            getSymbolCount: () => sum(host.getSourceFiles(), "symbolCount") + symbolCount,
             getTypeCount: () => typeCount,
             isUndefinedSymbol: symbol => symbol === undefinedSymbol,
             isArgumentsSymbol: symbol => symbol === argumentsSymbol,
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 745cce8a6cd9d..42faf0b062e22 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -700,10 +700,10 @@ namespace ts {
         return result;
     }
 
-    export function sum<K extends string>(array: { [x in K]: number }[], prop: K): number {
+    export function sum<T extends Record<K, number>, K extends string>(array: T[], prop: K): number {
         let result = 0;
         for (const v of array) {
-            result += v[prop];
+            result += (v[prop] as number);
         }
         return result;
     }

From 325f4b84cf6cc6f88aa023db91ffb4f3e3fada4e Mon Sep 17 00:00:00 2001
From: Daniel Rosenwasser <Daniel.Rosenwasser@microsoft.com>
Date: Tue, 11 Jul 2017 15:32:31 -0700
Subject: [PATCH 2/2] Addressed feedback.

---
 src/compiler/core.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 42faf0b062e22..97b642d8920df 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -703,7 +703,8 @@ namespace ts {
     export function sum<T extends Record<K, number>, K extends string>(array: T[], prop: K): number {
         let result = 0;
         for (const v of array) {
-            result += (v[prop] as number);
+            // Note: we need the following type assertion because of GH #17069
+            result += v[prop] as number;
         }
         return result;
     }