Bug 1496852 - Support JavaScript export-ns-from syntax r=jorendorff

Add support for `export * as ns from "a";` syntax. This was added in
ECMAScript 2020.

One wrinkle in the implementation is that the parser decides whether to use a
lexical vs indirect binding before module linking. Instead, we reserve a
hidden environment slot called "*namespace*" for each module that can be
referenced by indirect binding maps as needed.

Spec is a needs-consensus PR at tc39/ecma262#1174

Depends on D80984

Differential Revision: https://phabricator.services.mozilla.com/D80777

Author: moztcampbell

js/src/builtin/Module.js

@@ -136,9 +136,9 @@ function ModuleResolveExport(exportName, resolveSet = new_List())
         if (exportName === e.exportName) {
             let importedModule = CallModuleResolveHook(module, e.moduleRequest,
                                                        MODULE_STATUS_UNLINKED);
-
-            // TODO: Step 7.a.ii
-
+            if (e.importName === "*") {
+                return {module: importedModule, bindingName: "*namespace*"};
+            }
             return callFunction(importedModule.resolveExport, importedModule, e.importName,
                                 resolveSet);
         }
@@ -232,8 +232,18 @@ function ModuleNamespaceCreate(module, exports)
         let name = exports[i];
         let binding = callFunction(module.resolveExport, module, name);
         assert(IsResolvedBinding(binding), "Failed to resolve binding");
-        // TODO: ES2020 9.4.6.7 Module Namespace Exotic Object [[Get]], Step 10.
-        AddModuleNamespaceBinding(ns, name, binding.module, binding.bindingName);
+        // ES2020 9.4.6.7 Module Namespace Exotic Object [[Get]], Step 10.
+        if (binding.bindingName === "*namespace*") {
+            let namespace = GetModuleNamespace(binding.module);
+
+            // The spec uses an immutable binding here but we have already
+            // generated bytecode for an indirect binding. Instead, use an
+            // indirect binding to "*namespace*" slot of the target environment.
+            EnsureModuleEnvironmentNamespace(binding.module, namespace);
+            AddModuleNamespaceBinding(ns, name, binding.module, binding.bindingName);
+        } else {
+            AddModuleNamespaceBinding(ns, name, binding.module, binding.bindingName);
+        }
     }
 
     return ns;
@@ -478,9 +488,21 @@ function InitializeEnvironment()
                                      imp.lineNumber, imp.columnNumber);
             }
 
-            // TODO: Step 9.d.iii
-
-            CreateImportBinding(env, imp.localName, resolution.module, resolution.bindingName);
+            if (resolution.bindingName === "*namespace*") {
+                let namespace = GetModuleNamespace(resolution.module);
+
+                // This should be CreateNamespaceBinding, but we have already
+                // generated bytecode assuming an indirect binding. Instead,
+                // ensure a special "*namespace*"" binding exists on the target
+                // module's environment. We then generate an indirect binding to
+                // this synthetic binding.
+                EnsureModuleEnvironmentNamespace(resolution.module, namespace);
+                CreateImportBinding(env, imp.localName, resolution.module,
+                                    resolution.bindingName);
+            } else {
+                CreateImportBinding(env, imp.localName, resolution.module,
+                                    resolution.bindingName);
+            }
         }
     }
 

js/src/builtin/ModuleObject.cpp

@@ -1300,7 +1300,7 @@ ModuleBuilder::buildTables()
                         return false;
                 }
             }
-        } else if (exp->importName() == cx_->names().star) {
+        } else if (exp->importName() == cx_->names().star && !exp->exportName()) {
             if (!starExportEntries_.append(exp))
                 return false;
         } else {

js/src/builtin/TestingFunctions.cpp

@@ -3876,6 +3876,10 @@ GetModuleEnvironmentNames(JSContext* cx, unsigned argc, Value* vp)
     if (!JS_Enumerate(cx, env, &ids))
         return false;
 
+    // The "*namespace*" binding is a detail of current implementation so hide
+    // it to give stable results in tests.
+    ids.eraseIfEqual(NameToId(cx->names().starNamespaceStar));
+
     uint32_t length = ids.length();
     RootedArrayObject array(cx, NewDenseFullyAllocatedArray(cx, length));
     if (!array)

js/src/frontend/Parser.cpp

@@ -2333,6 +2333,17 @@ Parser<FullParseHandler, char16_t>::moduleBody(ModuleSharedContext* modulesc)
         p->value()->setClosedOver();
     }
 
+    // Reserve an environment slot for a "*namespace*" psuedo-binding and mark as
+    // closed-over. We do not know until module linking if this will be used.
+    if (!noteDeclaredName(context->names().starNamespaceStar, DeclarationKind::Const,
+                          pos())) {
+        return nullptr;
+    }
+    modulepc.varScope()
+        .lookupDeclaredName(context->names().starNamespaceStar)
+        ->value()
+        ->setClosedOver();
+
     if (!FoldConstants(context, &pn, this))
         return null();
 
@@ -5578,13 +5589,44 @@ Parser<ParseHandler, CharT>::exportBatch(uint32_t begin)
     if (!kid)
         return null();
 
-    // Handle the form |export *| by adding a special export batch
-    // specifier to the list.
-    Node exportSpec = handler.newExportBatchSpec(pos());
-    if (!exportSpec)
-        return null();
+    bool foundAs;
+    if (!tokenStream.matchToken(&foundAs, TokenKind::As)) {
+      return null();
+    }
+
+    if (foundAs) {
+        MUST_MATCH_TOKEN_FUNC(TokenKindIsPossibleIdentifierName, JSMSG_NO_EXPORT_NAME);
+
+        Node exportName = newName(anyChars.currentName());
+        if (!exportName) {
+            return null();
+        }
+
+        if (!checkExportedNameForClause(exportName)) {
+            return null();
+        }
 
-    handler.addList(kid, exportSpec);
+        Node importName = newName(context->names().star);
+        if (!importName) {
+            return null();
+        }
+
+        Node exportSpec = handler.newExportSpec(importName, exportName);
+        if (!exportSpec) {
+            return null();
+        }
+
+        handler.addList(kid, exportSpec);
+    } else {
+        // Handle the form |export *| by adding a special export batch
+        // specifier to the list.
+        Node exportSpec = handler.newExportBatchSpec(pos());
+        if (!exportSpec) {
+            return null();
+        }
+
+        handler.addList(kid, exportSpec);
+    }
 
     MUST_MATCH_TOKEN(TokenKind::From, JSMSG_FROM_AFTER_EXPORT_STAR);
 

js/src/jit-test/lib/syntax.js

@@ -451,6 +451,13 @@ function test_syntax(postfixes, check_error, ignore_opts) {
   test("export * from 'a' ", opts);
   test("export * from 'a'; ", opts);
 
+  test("export * ", opts);
+  test("export * as ", opts);
+  test("export * as ns ", opts);
+  test("export * as ns from ", opts);
+  test("export * as ns from 'a' ", opts);
+  test("export * as ns from 'a'; ", opts);
+
   test("export function ", opts);
   test("export function f ", opts);
   test("export function f( ", opts);

js/src/jit-test/modules/export-ns.js

@@ -0,0 +1 @@
+export * as ns from "module1.js";

js/src/jit-test/tests/modules/export-ns-from.js

@@ -0,0 +1,10 @@
+// |jit-test| module
+
+import { ns } from "export-ns.js";
+
+load(libdir + 'asserts.js');
+
+assertEq(isProxy(ns), true);
+assertEq(ns.a, 1);
+assertThrowsInstanceOf(function() { eval("delete ns"); }, SyntaxError);
+assertThrowsInstanceOf(function() { ns = null; }, TypeError);

js/src/vm/CommonPropertyNames.h

@@ -380,6 +380,7 @@
     macro(StarGeneratorNext, StarGeneratorNext, "StarGeneratorNext") \
     macro(StarGeneratorReturn, StarGeneratorReturn, "StarGeneratorReturn") \
     macro(StarGeneratorThrow, StarGeneratorThrow, "StarGeneratorThrow") \
+    macro(starNamespaceStar, starNamespaceStar, "*namespace*") \
     macro(start, start, "start") \
     macro(startTimestamp, startTimestamp, "startTimestamp") \
     macro(state, state, "state") \

js/src/vm/EnvironmentObject.cpp

@@ -736,11 +736,12 @@ static inline bool IsUnscopableDotName(JSContext* cx, HandleId id) {
 #ifdef DEBUG
 static bool IsInternalDotName(JSContext* cx, HandleId id) {
   return JSID_IS_ATOM(id, cx->names().dotThis) ||
-         JSID_IS_ATOM(id, cx->names().dotGenerator); /* || The following aren't currently implemented in Waterfox
+         JSID_IS_ATOM(id, cx->names().dotGenerator) /* || The following aren't currently implemented in Waterfox
          JSID_IS_ATOM(id, cx->names().dotInitializers) ||
          JSID_IS_ATOM(id, cx->names().dotFieldKeys) ||
          JSID_IS_ATOM(id, cx->names().dotStaticInitializers) ||
-         JSID_IS_ATOM(id, cx->names().dotStaticFieldKeys); */
+         JSID_IS_ATOM(id, cx->names().dotStaticFieldKeys) */ ||
+         JSID_IS_ATOM(id, cx->names().starNamespaceStar);
 }
 #endif
 

js/src/vm/SelfHosting.cpp

@@ -2166,6 +2166,23 @@ intrinsic_CreateNamespaceBinding(JSContext* cx, unsigned argc, Value* vp)
     return true;
 }
 
+static bool intrinsic_EnsureModuleEnvironmentNamespace(JSContext* cx,
+                                                       unsigned argc,
+                                                       Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  MOZ_ASSERT(args.length() == 2);
+  RootedModuleObject module(cx, &args[0].toObject().as<ModuleObject>());
+  MOZ_ASSERT(args[1].toObject().is<ModuleNamespaceObject>());
+  RootedModuleEnvironmentObject environment(cx, &module->initialEnvironment());
+  // The property already exists in the evironment but is not writable, so set
+  // the slot directly.
+  RootedShape shape(cx, environment->lookup(cx, cx->names().starNamespaceStar));
+  MOZ_ASSERT(shape);
+  environment->setSlot(shape->slot(), args[1]);
+  args.rval().setUndefined();
+  return true;
+}
+
 static bool
 intrinsic_InstantiateModuleFunctionDeclarations(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -2679,6 +2696,8 @@ static const JSFunctionSpec intrinsic_functions[] = {
     JS_FN("IsModuleEnvironment", intrinsic_IsInstanceOfBuiltin<ModuleEnvironmentObject>, 1, 0),
     JS_FN("CreateImportBinding", intrinsic_CreateImportBinding, 4, 0),
     JS_FN("CreateNamespaceBinding", intrinsic_CreateNamespaceBinding, 3, 0),
+    JS_FN("EnsureModuleEnvironmentNamespace",
+          intrinsic_EnsureModuleEnvironmentNamespace, 1, 0),
     JS_FN("InstantiateModuleFunctionDeclarations",
           intrinsic_InstantiateModuleFunctionDeclarations, 1, 0),
     JS_FN("ExecuteModule", intrinsic_ExecuteModule, 1, 0),