Add missing emitter for NamespaceExportDeclaration (#16025)

src/compiler/binder.ts

@@ -3398,6 +3398,7 @@ namespace ts {
             case SyntaxKind.IndexedAccessType:
             case SyntaxKind.MappedType:
             case SyntaxKind.LiteralType:
+            case SyntaxKind.NamespaceExportDeclaration:
                 // Types and signatures are TypeScript syntax, and exclude all other facts.
                 transformFlags = TransformFlags.AssertTypeScript;
                 excludeFlags = TransformFlags.TypeExcludes;

src/compiler/emitter.ts

@@ -571,6 +571,8 @@ namespace ts {
                     return emitModuleBlock(<ModuleBlock>node);
                 case SyntaxKind.CaseBlock:
                     return emitCaseBlock(<CaseBlock>node);
+                case SyntaxKind.NamespaceExportDeclaration:
+                    return emitNamespaceExportDeclaration(<NamespaceExportDeclaration>node);
                 case SyntaxKind.ImportEqualsDeclaration:
                     return emitImportEqualsDeclaration(<ImportEqualsDeclaration>node);
                 case SyntaxKind.ImportDeclaration:
@@ -1886,6 +1888,12 @@ namespace ts {
             write(";");
         }
 
+        function emitNamespaceExportDeclaration(node: NamespaceExportDeclaration) {
+            write("export as namespace ");
+            emit(node.name);
+            write(";");
+        }
+
         function emitNamedExports(node: NamedExports) {
             emitNamedImportsOrExports(node);
         }

src/compiler/transformers/ts.ts

@@ -345,6 +345,9 @@ namespace ts {
 
                 case SyntaxKind.PropertyDeclaration:
                     // TypeScript property declarations are elided.
+
+                case SyntaxKind.NamespaceExportDeclaration:
+                    // TypeScript namespace export declarations are elided.
                     return undefined;
 
                 case SyntaxKind.Constructor:

src/harness/unittests/printer.ts

@@ -131,6 +131,9 @@ namespace ts {
 
             // tslint:enable boolean-trivia
             printsCorrectly("class", {}, printer => printer.printNode(EmitHint.Unspecified, syntheticNode, sourceFile));
+
+            printsCorrectly("namespaceExportDeclaration", {}, printer => printer.printNode(EmitHint.Unspecified, createNamespaceExportDeclaration("B"), sourceFile));
+
             printsCorrectly("classWithOptionalMethodAndProperty", {}, printer => printer.printNode(EmitHint.Unspecified, classWithOptionalMethodAndProperty, sourceFile));
         });
     });

tests/baselines/reference/printerApi/printsNodeCorrectly.namespaceExportDeclaration.js

@@ -0,0 +1 @@
+export as namespace B;