Implement export as namespace from

src/compiler/binder.ts

@@ -56,9 +56,10 @@ namespace ts {
                 break;
             // 4. Export alias declarations pointing at only uninstantiated modules or things uninstantiated modules contain
             case SyntaxKind.ExportDeclaration:
-                if (!(node as ExportDeclaration).moduleSpecifier && !!(node as ExportDeclaration).exportClause) {
+                const exportDeclaration = node as ExportDeclaration;
+                if (!exportDeclaration.moduleSpecifier && exportDeclaration.exportClause && exportDeclaration.exportClause.kind === SyntaxKind.NamedExports) {
                     let state = ModuleInstanceState.NonInstantiated;
-                    for (const specifier of (node as ExportDeclaration).exportClause!.elements) {
+                    for (const specifier of exportDeclaration.exportClause.elements) {
                         const specifierState = getModuleInstanceStateForAliasTarget(specifier, visited);
                         if (specifierState > state) {
                             state = specifierState;
@@ -2575,6 +2576,9 @@ namespace ts {
                 // All export * declarations are collected in an __export symbol
                 declareSymbol(container.symbol.exports, container.symbol, node, SymbolFlags.ExportStar, SymbolFlags.None);
             }
+            else if (isNamespaceExport(node.exportClause)) {
+                declareSymbol(container.symbol.exports, container.symbol, node.exportClause, SymbolFlags.Alias, SymbolFlags.AliasExcludes);
+            }
         }
 
         function bindImportClause(node: ImportClause) {
@@ -4111,6 +4115,10 @@ namespace ts {
             case SyntaxKind.SourceFile:
                 break;
 
+            case SyntaxKind.NamespaceExport:
+                transformFlags |= TransformFlags.AssertESNext;
+                break;
+
             case SyntaxKind.ReturnStatement:
                 // Return statements may require an `await` in ES2018.
                 transformFlags |= TransformFlags.ContainsHoistedDeclarationOrCompletion | TransformFlags.AssertES2018;

src/compiler/checker.ts

@@ -1547,7 +1547,7 @@ namespace ts {
                             const moduleExport = moduleExports.get(name);
                             if (moduleExport &&
                                 moduleExport.flags === SymbolFlags.Alias &&
-                                getDeclarationOfKind(moduleExport, SyntaxKind.ExportSpecifier)) {
+                                (getDeclarationOfKind(moduleExport, SyntaxKind.ExportSpecifier) || getDeclarationOfKind(moduleExport, SyntaxKind.NamespaceExport))) {
                                 break;
                             }
                         }
@@ -2217,6 +2217,11 @@ namespace ts {
             return resolveESModuleSymbol(resolveExternalModuleName(node, moduleSpecifier), moduleSpecifier, dontResolveAlias, /*suppressUsageError*/ false);
         }
 
+        function getTargetOfNamespaceExport(node: NamespaceExport, dontResolveAlias: boolean): Symbol | undefined {
+            const moduleSpecifier = node.parent.moduleSpecifier;
+            return moduleSpecifier && resolveESModuleSymbol(resolveExternalModuleName(node, moduleSpecifier), moduleSpecifier, dontResolveAlias, /*suppressUsageError*/ false);
+        }
+
         // This function creates a synthetic symbol that combines the value side of one symbol with the
         // type/namespace side of another symbol. Consider this example:
         //
@@ -2382,6 +2387,8 @@ namespace ts {
                     return getTargetOfImportClause(<ImportClause>node, dontRecursivelyResolve);
                 case SyntaxKind.NamespaceImport:
                     return getTargetOfNamespaceImport(<NamespaceImport>node, dontRecursivelyResolve);
+                case SyntaxKind.NamespaceExport:
+                    return getTargetOfNamespaceExport(<NamespaceExport>node, dontRecursivelyResolve);
                 case SyntaxKind.ImportSpecifier:
                     return getTargetOfImportSpecifier(<ImportSpecifier>node, dontRecursivelyResolve);
                 case SyntaxKind.ExportSpecifier:
@@ -5077,18 +5084,18 @@ namespace ts {
 
                 function mergeExportDeclarations(statements: Statement[]) {
                     // Pass 2: Combine all `export {}` declarations
-                    const exports = filter(statements, d => isExportDeclaration(d) && !d.moduleSpecifier && !!d.exportClause) as ExportDeclaration[];
+                    const exports = filter(statements, d => isExportDeclaration(d) && !d.moduleSpecifier && !!d.exportClause && isNamedExports(d.exportClause)) as ExportDeclaration[];
                     if (length(exports) > 1) {
                         const nonExports = filter(statements, d => !isExportDeclaration(d) || !!d.moduleSpecifier || !d.exportClause);
                         statements = [...nonExports, createExportDeclaration(
                             /*decorators*/ undefined,
                             /*modifiers*/ undefined,
-                            createNamedExports(flatMap(exports, e => e.exportClause!.elements)),
+                            createNamedExports(flatMap(exports, e => cast(e.exportClause, isNamedExports).elements)),
                             /*moduleSpecifier*/ undefined
                         )];
                     }
                     // Pass 2b: Also combine all `export {} from "..."` declarations as needed
-                    const reexports = filter(statements, d => isExportDeclaration(d) && !!d.moduleSpecifier && !!d.exportClause) as ExportDeclaration[];
+                    const reexports = filter(statements, d => isExportDeclaration(d) && !!d.moduleSpecifier && !!d.exportClause && isNamedExports(d.exportClause)) as ExportDeclaration[];
                     if (length(reexports) > 1) {
                         const groups = group(reexports, decl => isStringLiteral(decl.moduleSpecifier!) ? ">" + decl.moduleSpecifier.text : ">");
                         if (groups.length !== reexports.length) {
@@ -5100,7 +5107,7 @@ namespace ts {
                                         createExportDeclaration(
                                             /*decorators*/ undefined,
                                             /*modifiers*/ undefined,
-                                            createNamedExports(flatMap(group, e => e.exportClause!.elements)),
+                                            createNamedExports(flatMap(group, e => cast(e.exportClause, isNamedExports).elements)),
                                             group[0].moduleSpecifier
                                         )
                                     ];
@@ -5114,8 +5121,8 @@ namespace ts {
                 function inlineExportModifiers(statements: Statement[]) {
                     // Pass 3: Move all `export {}`'s to `export` modifiers where possible
                     const exportDecl = find(statements, d => isExportDeclaration(d) && !d.moduleSpecifier && !!d.exportClause) as ExportDeclaration | undefined;
-                    if (exportDecl) {
-                        const replacements = mapDefined(exportDecl.exportClause!.elements, e => {
+                    if (exportDecl && exportDecl.exportClause && isNamedExports(exportDecl.exportClause)) {
+                        const replacements = mapDefined(exportDecl.exportClause.elements, e => {
                             if (!e.propertyName) {
                                 // export {name} - look thru `statements` for `name`, and if all results can take an `export` modifier, do so and filter it
                                 const associated = filter(statements, s => nodeHasName(s, e.name));
@@ -5133,7 +5140,7 @@ namespace ts {
                         else {
                             // some items filtered, others not - update the export declaration
                             // (mutating because why not, we're building a whole new tree here anyway)
-                            exportDecl.exportClause!.elements = createNodeArray(replacements);
+                            exportDecl.exportClause.elements = createNodeArray(replacements);
                         }
                     }
                     return statements;
@@ -5649,6 +5656,14 @@ namespace ts {
                                 createLiteral(getSpecifierForModuleSymbol(target, context))
                             ), ModifierFlags.None);
                             break;
+                        case SyntaxKind.NamespaceExport:
+                            addResult(createExportDeclaration(
+                                /*decorators*/ undefined,
+                                /*modifiers*/ undefined,
+                                createNamespaceExport(createIdentifier(localName)),
+                                createLiteral(getSpecifierForModuleSymbol(target, context))
+                            ), ModifierFlags.None);
+                            break;
                         case SyntaxKind.ImportSpecifier:
                             addResult(createImportDeclaration(
                                 /*decorators*/ undefined,
@@ -32600,7 +32615,7 @@ namespace ts {
             return true;
         }
 
-        function checkAliasSymbol(node: ImportEqualsDeclaration | ImportClause | NamespaceImport | ImportSpecifier | ExportSpecifier) {
+        function checkAliasSymbol(node: ImportEqualsDeclaration | ImportClause | NamespaceImport | ImportSpecifier | ExportSpecifier | NamespaceExport) {
             let symbol = getSymbolOfNode(node);
             const target = resolveAlias(symbol);
 
@@ -32719,7 +32734,12 @@ namespace ts {
                 if (node.exportClause) {
                     // export { x, y }
                     // export { x, y } from "foo"
-                    forEach(node.exportClause.elements, checkExportSpecifier);
+                    if (isNamedExports(node.exportClause)) {
+                        forEach(node.exportClause.elements, checkExportSpecifier);
+                    }
+                    else if(!isNamespaceExport(node.exportClause)) {
+                        checkImportBinding(node.exportClause);
+                    }
 
                     const inAmbientExternalModule = node.parent.kind === SyntaxKind.ModuleBlock && isAmbientModule(node.parent.parent);
                     const inAmbientNamespaceDeclaration = !inAmbientExternalModule && node.parent.kind === SyntaxKind.ModuleBlock &&
@@ -34149,7 +34169,10 @@ namespace ts {
                     return isAliasResolvedToValue(getSymbolOfNode(node) || unknownSymbol);
                 case SyntaxKind.ExportDeclaration:
                     const exportClause = (<ExportDeclaration>node).exportClause;
-                    return !!exportClause && some(exportClause.elements, isValueAliasDeclaration);
+                    return !!exportClause && (
+                        isNamespaceExport(exportClause) ||
+                        some(exportClause.elements, isValueAliasDeclaration)
+                    );
                 case SyntaxKind.ExportAssignment:
                     return (<ExportAssignment>node).expression && (<ExportAssignment>node).expression.kind === SyntaxKind.Identifier ?
                         isAliasResolvedToValue(getSymbolOfNode(node) || unknownSymbol) :

src/compiler/emitter.ts

@@ -1435,6 +1435,8 @@ namespace ts {
                         return emitImportClause(<ImportClause>node);
                     case SyntaxKind.NamespaceImport:
                         return emitNamespaceImport(<NamespaceImport>node);
+                    case SyntaxKind.NamespaceExport:
+                        return emitNamespaceExport(<NamespaceExport>node);
                     case SyntaxKind.NamedImports:
                         return emitNamedImports(<NamedImports>node);
                     case SyntaxKind.ImportSpecifier:
@@ -3104,6 +3106,14 @@ namespace ts {
             writeTrailingSemicolon();
         }
 
+        function emitNamespaceExport(node: NamespaceExport) {
+            const asPos = emitTokenWithComment(SyntaxKind.AsteriskToken, node.pos, writePunctuation, node);
+            writeSpace();
+            emitTokenWithComment(SyntaxKind.AsKeyword, asPos, writeKeyword, node);
+            writeSpace();
+            emit(node.name);
+        }
+
         function emitNamedExports(node: NamedExports) {
             emitNamedImportsOrExports(node);
         }
@@ -4408,6 +4418,9 @@ namespace ts {
                 case SyntaxKind.NamespaceImport:
                     generateNameIfNeeded((<NamespaceImport>node).name);
                     break;
+                case SyntaxKind.NamespaceExport:
+                    generateNameIfNeeded((<NamespaceExport>node).name);
+                    break;
                 case SyntaxKind.NamedImports:
                     forEach((<NamedImports>node).elements, generateNames);
                     break;

src/compiler/factoryPublic.ts

@@ -2278,12 +2278,24 @@ namespace ts {
         return node;
     }
 
+    export function createNamespaceExport(name: Identifier): NamespaceExport {
+        const node = <NamespaceExport>createSynthesizedNode(SyntaxKind.NamespaceExport);
+        node.name = name;
+        return node;
+    }
+
     export function updateNamespaceImport(node: NamespaceImport, name: Identifier) {
         return node.name !== name
             ? updateNode(createNamespaceImport(name), node)
             : node;
     }
 
+    export function updateNamespaceExport(node: NamespaceExport, name: Identifier) {
+        return node.name !== name
+            ? updateNode(createNamespaceExport(name), node)
+            : node;
+    }
+
     export function createNamedImports(elements: readonly ImportSpecifier[]): NamedImports {
         const node = <NamedImports>createSynthesizedNode(SyntaxKind.NamedImports);
         node.elements = createNodeArray(elements);
@@ -2327,7 +2339,7 @@ namespace ts {
             : node;
     }
 
-    export function createExportDeclaration(decorators: readonly Decorator[] | undefined, modifiers: readonly Modifier[] | undefined, exportClause: NamedExports | undefined, moduleSpecifier?: Expression) {
+    export function createExportDeclaration(decorators: readonly Decorator[] | undefined, modifiers: readonly Modifier[] | undefined, exportClause: NamedExportBindings | undefined, moduleSpecifier?: Expression) {
         const node = <ExportDeclaration>createSynthesizedNode(SyntaxKind.ExportDeclaration);
         node.decorators = asNodeArray(decorators);
         node.modifiers = asNodeArray(modifiers);
@@ -2340,7 +2352,7 @@ namespace ts {
         node: ExportDeclaration,
         decorators: readonly Decorator[] | undefined,
         modifiers: readonly Modifier[] | undefined,
-        exportClause: NamedExports | undefined,
+        exportClause: NamedExportBindings | undefined,
         moduleSpecifier: Expression | undefined) {
         return node.decorators !== decorators
             || node.modifiers !== modifiers

src/compiler/parser.ts

@@ -390,6 +390,8 @@ namespace ts {
 
             case SyntaxKind.NamespaceImport:
                 return visitNode(cbNode, (<NamespaceImport>node).name);
+            case SyntaxKind.NamespaceExport:
+                return visitNode(cbNode, (<NamespaceExport>node).name);
             case SyntaxKind.NamedImports:
             case SyntaxKind.NamedExports:
                 return visitNodes(cbNode, cbNodes, (<NamedImportsOrExports>node).elements);
@@ -6470,9 +6472,18 @@ namespace ts {
             return finishNode(node);
         }
 
+        function parseNamespaceExport(): NamespaceExport {
+            const node = <NamespaceExport>createNode(SyntaxKind.NamespaceExport);
+            node.name = parseIdentifier();
+            return finishNode(node);
+        }
+
         function parseExportDeclaration(node: ExportDeclaration): ExportDeclaration {
             node.kind = SyntaxKind.ExportDeclaration;
             if (parseOptional(SyntaxKind.AsteriskToken)) {
+                if (parseOptional(SyntaxKind.AsKeyword)) {
+                    node.exportClause = parseNamespaceExport();
+                }
                 parseExpected(SyntaxKind.FromKeyword);
                 node.moduleSpecifier = parseModuleSpecifier();
             }

src/compiler/transformer.ts

@@ -4,7 +4,7 @@ namespace ts {
         switch (moduleKind) {
             case ModuleKind.ESNext:
             case ModuleKind.ES2015:
-                return transformES2015Module;
+                return transformECMAScriptModule;
             case ModuleKind.System:
                 return transformSystemModule;
             default:

src/compiler/transformers/module/es2015.ts → src/compiler/transformers/module/esnextAnd2015.ts

@@ -1,6 +1,6 @@
 /*@internal*/
 namespace ts {
-    export function transformES2015Module(context: TransformationContext) {
+    export function transformECMAScriptModule(context: TransformationContext) {
         const compilerOptions = context.getCompilerOptions();
         const previousOnEmitNode = context.onEmitNode;
         const previousOnSubstituteNode = context.onSubstituteNode;
@@ -44,6 +44,9 @@ namespace ts {
                     return undefined;
                 case SyntaxKind.ExportAssignment:
                     return visitExportAssignment(<ExportAssignment>node);
+                case SyntaxKind.ExportDeclaration:
+                    const exportDecl = (node as ExportDeclaration);
+                    return visitExportDeclaration(exportDecl);
             }
 
             return node;
@@ -54,6 +57,41 @@ namespace ts {
             return node.isExportEquals ? undefined : node;
         }
 
+        function visitExportDeclaration(node: ExportDeclaration) {
+            // `export * as ns` only needs to be transformed in ES2015
+            if (compilerOptions.module !== undefined && compilerOptions.module > ModuleKind.ES2015) {
+                return node;
+            }
+
+            // Either ill-formed or don't need to be tranformed.
+            if (!node.exportClause || !isNamespaceExport(node.exportClause) || !node.moduleSpecifier) {
+                return node;
+            }
+
+            const oldIdentifier = node.exportClause.name;
+            const synthName = getGeneratedNameForNode(oldIdentifier);
+            const importDecl = createImportDeclaration(
+                /*decorators*/ undefined,
+                /*modifiers*/ undefined,
+                createImportClause(/*name*/ undefined,
+                    createNamespaceImport(
+                        synthName
+                    )
+                ),
+                node.moduleSpecifier,
+            );
+            setOriginalNode(importDecl, node.exportClause);
+
+            const exportDecl = createExportDeclaration(
+                /*decorators*/ undefined,
+                /*modifiers*/ undefined,
+                createNamedExports([createExportSpecifier(synthName, oldIdentifier)]),
+            );
+            setOriginalNode(exportDecl, node);
+
+            return [importDecl, exportDecl];
+        }
+
         //
         // Emit Notification
         //