From b0c6843f3ec0ac57d1348e6b81d902ced954d6cc Mon Sep 17 00:00:00 2001
From: Sheetal Nandi <shkamat@microsoft.com>
Date: Mon, 29 Jan 2018 15:41:21 -0800
Subject: [PATCH] Simplify isEmittedFile check instead of iterating through all
 source files. Fixes #21459

---
 src/compiler/program.ts | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index bd45857fc51..0c9f5765605 100755
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -2351,9 +2351,30 @@ namespace ts {
                 return false;
             }
 
-            return forEachEmittedFile(getEmitHost(), ({ jsFilePath, declarationFilePath }) =>
-                isSameFile(jsFilePath, file) ||
-                (declarationFilePath && isSameFile(declarationFilePath, file)));
+            // If this is source file, its not emitted file
+            const filePath = toPath(file);
+            if (getSourceFileByPath(filePath)) {
+                return false;
+            }
+
+            // If options have --outFile or --out just check that
+            const out = options.outFile || options.out;
+            if (out) {
+                return isSameFile(filePath, out) || isSameFile(filePath, removeFileExtension(out) + Extension.Dts);
+            }
+
+            // If --outDir, check if file is in that directory
+            if (options.outDir) {
+                return containsPath(options.outDir, filePath, currentDirectory, !host.useCaseSensitiveFileNames());
+            }
+
+            if (fileExtensionIsOneOf(filePath, supportedJavascriptExtensions) || fileExtensionIs(filePath, Extension.Dts)) {
+                // Otherwise just check if sourceFile with the name exists
+                const filePathWithoutExtension = removeFileExtension(filePath);
+                return !!getSourceFileByPath(combinePaths(filePathWithoutExtension, Extension.Ts) as Path) ||
+                    !!getSourceFileByPath(combinePaths(filePathWithoutExtension, Extension.Tsx) as Path);
+            }
+            return false;
         }
 
         function isSameFile(file1: string, file2: string) {