From c32bb74612bc2d5eb463f6bd20b69ed18da53b15 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Thu, 29 Jun 2017 06:43:39 -0700
Subject: [PATCH] Type-check `sum`

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

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 7cb9902b83149..a033cbca67df0 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -84,9 +84,9 @@ namespace ts {
         // extra cost of calling `getParseTreeNode` when calling these functions from inside the
         // checker.
         const checker: TypeChecker = {
-            getNodeCount: () => sum(host.getSourceFiles(), "nodeCount"),
-            getIdentifierCount: () => sum(host.getSourceFiles(), "identifierCount"),
-            getSymbolCount: () => sum(host.getSourceFiles(), "symbolCount") + symbolCount,
+            getNodeCount: () => sum<"nodeCount">(host.getSourceFiles(), "nodeCount"),
+            getIdentifierCount: () => sum<"identifierCount">(host.getSourceFiles(), "identifierCount"),
+            getSymbolCount: () => sum<"symbolCount">(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 86ad483ccc31f..41fa35cf0bcad 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -727,7 +727,7 @@ namespace ts {
         return result;
     }
 
-    export function sum(array: any[], prop: string): number {
+    export function sum<K extends string>(array: { [x in K]: number }[], prop: K): number {
         let result = 0;
         for (const v of array) {
             result += v[prop];