From c0f187a4e81bf3c29d29a733a5483b0deceb2263 Mon Sep 17 00:00:00 2001
From: Ben Lichtman <belichtm@microsoft.com>
Date: Tue, 6 Aug 2019 13:39:18 -0700
Subject: [PATCH] Allow compile on save with decorator emit

---
 src/server/session.ts                              | 8 ++++++--
 src/testRunner/unittests/tsserver/compileOnSave.ts | 9 +++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/server/session.ts b/src/server/session.ts
index 66f21e88a76..2db58d67460 100644
--- a/src/server/session.ts
+++ b/src/server/session.ts
@@ -1599,6 +1599,10 @@ namespace ts.server {
                 return emptyArray;
             }
 
+            function dtsChangeCanAffectEmit(compilationSettings: CompilerOptions) {
+                return getEmitDeclarations(compilationSettings) || !!compilationSettings.emitDecoratorMetadata;
+            }
+
             return combineProjectOutput(
                 info,
                 path => this.projectService.getScriptInfoForPath(path)!,
@@ -1610,8 +1614,8 @@ namespace ts.server {
 
                     const compilationSettings = project.getCompilationSettings();
 
-                    if (!!compilationSettings.noEmit || fileExtensionIs(info.fileName, Extension.Dts) && !getEmitDeclarations(compilationSettings)) {
-                        // avoid triggering emit when a change is made in a .d.ts when declaration emit is disabled
+                    if (!!compilationSettings.noEmit || fileExtensionIs(info.fileName, Extension.Dts) && !dtsChangeCanAffectEmit(compilationSettings)) {
+                        // avoid triggering emit when a change is made in a .d.ts when declaration emit and decorator metadata emit are disabled
                         return undefined;
                     }
 
diff --git a/src/testRunner/unittests/tsserver/compileOnSave.ts b/src/testRunner/unittests/tsserver/compileOnSave.ts
index 2773edb7d8d..b129c8ecdfc 100644
--- a/src/testRunner/unittests/tsserver/compileOnSave.ts
+++ b/src/testRunner/unittests/tsserver/compileOnSave.ts
@@ -598,6 +598,15 @@ namespace ts.projectSystem {
                 /*expectDTSEmit*/ true
                 );
             });
+
+            it("should return results if change is made in a global declaration file with decorator emit enabled", () => {
+                testDTS(
+                /*dtsFileContents*/ "declare const x: string;",
+                /*tsFileContents*/ "var y = 1;",
+                /*opts*/ { experimentalDecorators: true, emitDecoratorMetadata: true },
+                /*expectDTSEmit*/ true
+                );
+            });
         });
 
         describe("tsserverProjectSystem emit with outFile or out setting", () => {