From 80fab7c5a41534e3c506a90b7375a3cb753aae05 Mon Sep 17 00:00:00 2001
From: Vladimir Matveev <vladima@microsoft.com>
Date: Tue, 12 Apr 2016 15:19:05 -0700
Subject: [PATCH] elide exports with no value side

---
 src/compiler/transformers/module/es6.ts | 36 ++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/compiler/transformers/module/es6.ts b/src/compiler/transformers/module/es6.ts
index 9355b476247..d2f4ca4f224 100644
--- a/src/compiler/transformers/module/es6.ts
+++ b/src/compiler/transformers/module/es6.ts
@@ -34,12 +34,18 @@ namespace ts {
                     return visitImportSpecifier(<ImportSpecifier>node);
                 case SyntaxKind.ExportAssignment:
                     return visitExportAssignment(<ExportAssignment>node);
+                case SyntaxKind.ExportDeclaration:
+                    return visitExportDeclaration(<ExportDeclaration>node);
+                case SyntaxKind.NamedExports:
+                    return visitNamedExports(<NamedExports>node);
+                case SyntaxKind.ExportSpecifier:
+                    return visitExportSpecifier(<ExportSpecifier>node);
             }
 
             return node;
         }
 
-        function visitExportAssignment(node: ExportAssignment): ExportDeclaration {
+        function visitExportAssignment(node: ExportAssignment): ExportAssignment {
             if (node.isExportEquals) {
                 return undefined; // do not emit export equals for ES6
             }
@@ -47,6 +53,34 @@ namespace ts {
             return nodeIsSynthesized(original) || resolver.isValueAliasDeclaration(original) ? node: undefined;
         }
 
+        function visitExportDeclaration(node: ExportDeclaration): ExportDeclaration {
+            if (!node.exportClause) {
+                return node; // export * is always emitted
+            }
+            if (!resolver.isValueAliasDeclaration(node)) {
+                return undefined;
+            }
+            const newExportClause = visitNode(node.exportClause, visitor, isNamedExports, /*optional*/ true);
+            if (node.exportClause === newExportClause) {
+                return node;
+            }
+            return newExportClause 
+                ? createExportDeclaration(newExportClause, node.moduleSpecifier)
+                : undefined;
+        }
+
+        function visitNamedExports(node: NamedExports): NamedExports {
+            const newExports = visitNodes(node.elements, visitor, isExportSpecifier);
+            if (node.elements === newExports) {
+                return node;
+            }
+            return newExports.length ? createNamedExports(newExports) : undefined;
+        }
+
+        function visitExportSpecifier(node: ExportSpecifier): ExportSpecifier {
+            return resolver.isValueAliasDeclaration(node) ? node : undefined;
+        }
+
         function visitImportEqualsDeclaration(node: ImportEqualsDeclaration): ImportEqualsDeclaration {
             return !isExternalModuleImportEqualsDeclaration(node) || resolver.isReferencedAliasDeclaration(node) ? node : undefined;
         }