add a new line if after writing trailing comments (#12894)

src/compiler/comments.ts

@@ -156,6 +156,9 @@ namespace ts {
 
             if (!skipTrailingComments) {
                 emitLeadingComments(detachedRange.end, /*isEmittedNode*/ true);
+                if (hasWrittenComment && !writer.isAtStartOfLine()) {
+                    writer.writeLine();
+                }
             }
 
             if (extendedDiagnostics) {

src/compiler/transformers/module/system.ts

@@ -101,20 +101,21 @@ namespace ts {
             // So the helper will be emit at the correct position instead of at the top of the source-file
             const moduleName = tryGetModuleNameFromFile(node, host, compilerOptions);
             const dependencies = createArrayLiteral(map(dependencyGroups, dependencyGroup => dependencyGroup.name));
-            const updated = updateSourceFileNode(
-                node,
-                createNodeArray([
-                    createStatement(
-                        createCall(
-                            createPropertyAccess(createIdentifier("System"), "register"),
+            const updated = setEmitFlags(
+                updateSourceFileNode(
+                    node,
+                    createNodeArray([
+                        createStatement(
+                            createCall(
+                                createPropertyAccess(createIdentifier("System"), "register"),
                             /*typeArguments*/ undefined,
-                            moduleName
-                                ? [moduleName, dependencies, moduleBodyFunction]
-                                : [dependencies, moduleBodyFunction]
+                                moduleName
+                                    ? [moduleName, dependencies, moduleBodyFunction]
+                                    : [dependencies, moduleBodyFunction]
+                            )
                         )
-                    )
-                ], node.statements)
-            );
+                    ], node.statements)
+                ), EmitFlags.NoTrailingComments);
 
             if (!(compilerOptions.outFile || compilerOptions.out)) {
                 moveEmitHelpers(updated, moduleBodyBlock, helper => !helper.scoped);

tests/baselines/reference/systemModuleTrailingComments.js

@@ -0,0 +1,18 @@
+//// [systemModuleTrailingComments.ts]
+export const test = "TEST";
+
+//some comment
+
+//// [systemModuleTrailingComments.js]
+System.register([], function (exports_1, context_1) {
+    "use strict";
+    var __moduleName = context_1 && context_1.id;
+    var test;
+    return {
+        setters: [],
+        execute: function () {
+            exports_1("test", test = "TEST");
+            //some comment 
+        }
+    };
+});

tests/baselines/reference/systemModuleTrailingComments.symbols

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/systemModuleTrailingComments.ts ===
+export const test = "TEST";
+>test : Symbol(test, Decl(systemModuleTrailingComments.ts, 0, 12))
+
+//some comment

tests/baselines/reference/systemModuleTrailingComments.types

@@ -0,0 +1,6 @@
+=== tests/cases/compiler/systemModuleTrailingComments.ts ===
+export const test = "TEST";
+>test : "TEST"
+>"TEST" : "TEST"
+
+//some comment

tests/cases/compiler/systemModuleTrailingComments.ts

@@ -0,0 +1,4 @@
+// @module: system
+export const test = "TEST";
+
+//some comment