From bb29a1087ed5f2ef294e26b449e661812f81d0c7 Mon Sep 17 00:00:00 2001
From: Ryan Cavanaugh <RyanCavanaugh@users.noreply.github.com>
Date: Mon, 18 Jun 2018 11:11:03 -0700
Subject: [PATCH] Fixes downstream prepend projects not being built correctly
 on upstream changes

---
 Jakefile.js             |  2 +-
 src/compiler/tsbuild.ts | 10 ++++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/Jakefile.js b/Jakefile.js
index 633e4f45cb6..7a16c681b6e 100644
--- a/Jakefile.js
+++ b/Jakefile.js
@@ -204,7 +204,7 @@ task(TaskNames.lint, [TaskNames.buildRules], () => {
         if (fold.isTravis()) console.log(fold.end("lint"));
         complete();
     }));
-});
+}, { async: true });
 
 desc("Diffs the compiler baselines using the diff tool specified by the 'DIFF' environment variable");
 task('diff', function () {
diff --git a/src/compiler/tsbuild.ts b/src/compiler/tsbuild.ts
index 80f6d1c1cc8..97b7c0afad7 100644
--- a/src/compiler/tsbuild.ts
+++ b/src/compiler/tsbuild.ts
@@ -777,6 +777,7 @@ namespace ts {
 
             let pseudoUpToDate = false;
             let usesPrepend = false;
+            let upstreamChangedProject: string | undefined;
             if (project.projectReferences) {
                 for (const ref of project.projectReferences) {
                     usesPrepend = usesPrepend || !!(ref.prepend);
@@ -809,6 +810,7 @@ namespace ts {
                     // *after* those files, then we're "psuedo up to date" and eligible for a fast rebuild
                     if (refStatus.newestDeclarationFileContentChangedTime <= oldestOutputFileTime) {
                         pseudoUpToDate = true;
+                        upstreamChangedProject = ref.path;
                         continue;
                     }
 
@@ -837,8 +839,12 @@ namespace ts {
                 };
             }
 
-            if (usesPrepend) {
-                pseudoUpToDate = false;
+            if (usesPrepend && pseudoUpToDate) {
+                return {
+                    type: UpToDateStatusType.OutOfDateWithUpstream,
+                    outOfDateOutputFileName: oldestOutputFileName,
+                    newerProjectName: upstreamChangedProject!
+                };
             }
 
             // Up to date