From 72884b8f27abb8bfe8d8ec0f4368d09f1a4c80bf Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Wed, 6 Sep 2017 21:59:06 -0700
Subject: [PATCH] Emit comments on system export default expressions on the
 surrounding export call epxression instead (#17970)

---
 src/compiler/emitter.ts                       |  2 +-
 src/compiler/transformers/module/system.ts    |  3 ++-
 .../systemDefaultExportCommentValidity.js     | 20 +++++++++++++++++++
 ...systemDefaultExportCommentValidity.symbols |  8 ++++++++
 .../systemDefaultExportCommentValidity.types  |  9 +++++++++
 .../systemDefaultExportCommentValidity.ts     |  5 +++++
 6 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 tests/baselines/reference/systemDefaultExportCommentValidity.js
 create mode 100644 tests/baselines/reference/systemDefaultExportCommentValidity.symbols
 create mode 100644 tests/baselines/reference/systemDefaultExportCommentValidity.types
 create mode 100644 tests/cases/compiler/systemDefaultExportCommentValidity.ts

diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index 5444c61835..166e475198 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -2519,7 +2519,7 @@ namespace ts {
                 //          2
                 //          /* end of element 2 */
                 //       ];
-                if (previousSibling && delimiter && previousSibling.end !== parentNode.end) {
+                if (previousSibling && delimiter && previousSibling.end !== parentNode.end && !(getEmitFlags(previousSibling) & EmitFlags.NoTrailingComments)) {
                     emitLeadingCommentsOfPosition(previousSibling.end);
                 }
 
diff --git a/src/compiler/transformers/module/system.ts b/src/compiler/transformers/module/system.ts
index e1c239736d..8c47ec82f7 100644
--- a/src/compiler/transformers/module/system.ts
+++ b/src/compiler/transformers/module/system.ts
@@ -1132,7 +1132,8 @@ namespace ts {
          */
         function createExportExpression(name: Identifier | StringLiteral, value: Expression) {
             const exportName = isIdentifier(name) ? createLiteral(name) : name;
-            return createCall(exportFunction, /*typeArguments*/ undefined, [exportName, value]);
+            setEmitFlags(value, getEmitFlags(value) | EmitFlags.NoComments);
+            return setCommentRange(createCall(exportFunction, /*typeArguments*/ undefined, [exportName, value]), value);
         }
 
         //
diff --git a/tests/baselines/reference/systemDefaultExportCommentValidity.js b/tests/baselines/reference/systemDefaultExportCommentValidity.js
new file mode 100644
index 0000000000..a56110b0de
--- /dev/null
+++ b/tests/baselines/reference/systemDefaultExportCommentValidity.js
@@ -0,0 +1,20 @@
+//// [systemDefaultExportCommentValidity.ts]
+const Home = {}
+
+export default Home
+// There is intentionally no semicolon on the prior line, this comment should not break emit
+
+//// [systemDefaultExportCommentValidity.js]
+System.register([], function (exports_1, context_1) {
+    "use strict";
+    var __moduleName = context_1 && context_1.id;
+    var Home;
+    return {
+        setters: [],
+        execute: function () {
+            Home = {};
+            exports_1("default", Home);
+            // There is intentionally no semicolon on the prior line, this comment should not break emit 
+        }
+    };
+});
diff --git a/tests/baselines/reference/systemDefaultExportCommentValidity.symbols b/tests/baselines/reference/systemDefaultExportCommentValidity.symbols
new file mode 100644
index 0000000000..39abe3a668
--- /dev/null
+++ b/tests/baselines/reference/systemDefaultExportCommentValidity.symbols
@@ -0,0 +1,8 @@
+=== tests/cases/compiler/systemDefaultExportCommentValidity.ts ===
+const Home = {}
+>Home : Symbol(Home, Decl(systemDefaultExportCommentValidity.ts, 0, 5))
+
+export default Home
+>Home : Symbol(Home, Decl(systemDefaultExportCommentValidity.ts, 0, 5))
+
+// There is intentionally no semicolon on the prior line, this comment should not break emit
diff --git a/tests/baselines/reference/systemDefaultExportCommentValidity.types b/tests/baselines/reference/systemDefaultExportCommentValidity.types
new file mode 100644
index 0000000000..d8b89394ed
--- /dev/null
+++ b/tests/baselines/reference/systemDefaultExportCommentValidity.types
@@ -0,0 +1,9 @@
+=== tests/cases/compiler/systemDefaultExportCommentValidity.ts ===
+const Home = {}
+>Home : {}
+>{} : {}
+
+export default Home
+>Home : {}
+
+// There is intentionally no semicolon on the prior line, this comment should not break emit
diff --git a/tests/cases/compiler/systemDefaultExportCommentValidity.ts b/tests/cases/compiler/systemDefaultExportCommentValidity.ts
new file mode 100644
index 0000000000..df1d028397
--- /dev/null
+++ b/tests/cases/compiler/systemDefaultExportCommentValidity.ts
@@ -0,0 +1,5 @@
+// @module: system
+const Home = {}
+
+export default Home
+// There is intentionally no semicolon on the prior line, this comment should not break emit
\ No newline at end of file