From ce936ca88f97f5aa52bea586657cb3d6d1c04a2d Mon Sep 17 00:00:00 2001
From: Ryan Cavanaugh <RyanCavanaugh@users.noreply.github.com>
Date: Wed, 13 Jun 2018 10:44:05 -0700
Subject: [PATCH] Don't believe prepend projects are UTUTD

---
 src/compiler/tsbuild.ts | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/compiler/tsbuild.ts b/src/compiler/tsbuild.ts
index 79306cc5d06..bbee1f09dad 100644
--- a/src/compiler/tsbuild.ts
+++ b/src/compiler/tsbuild.ts
@@ -773,8 +773,10 @@ namespace ts {
             }
 
             let pseudoUpToDate = false;
+            let usesPrepend = false;
             if (project.projectReferences) {
                 for (const ref of project.projectReferences) {
+                    usesPrepend = usesPrepend || ref.prepend;
                     const resolvedRef = resolveProjectReferencePath(compilerHost, ref) as ResolvedConfigFileName;
                     const refStatus = getUpToDateStatus(configFileCache.parseConfigFile(resolvedRef));
 
@@ -832,6 +834,10 @@ namespace ts {
                 };
             }
 
+            if (usesPrepend) {
+                psuedoUpToDate = false;
+            }
+
             // Up to date
             return {
                 type: pseudoUpToDate ? UpToDateStatusType.UpToDateWithUpstreamTypes : UpToDateStatusType.UpToDate,