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 = [])
         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;
@@ -477,9 +487,21 @@ 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

@@ -1246,7 +1246,7 @@ bool ModuleBuilder::buildTables(frontend::StencilModuleMetadata& metadata) {
           }
         }
       }
-    } else if (exp.importName == cx_->names().star) {
+    } else if (exp.importName == cx_->names().star && !exp.exportName) {
       if (!metadata.starExportEntries.append(exp)) {
         return false;
       }

js/src/builtin/TestingFunctions.cpp

@@ -5054,6 +5054,10 @@ static bool GetModuleEnvironmentNames(JSContext* cx, unsigned argc, Value* vp) {
     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

@@ -1649,6 +1649,17 @@ ModuleNode* Parser<FullParseHandler, Unit>::moduleBody(
     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(cx_->names().starNamespaceStar, DeclarationKind::Const,
+                        pos())) {
+    return nullptr;
+  }
+  modulepc.varScope()
+      .lookupDeclaredName(cx_->names().starNamespaceStar)
+      ->value()
+      ->setClosedOver();
+
   if (!CheckParseTree(cx_, alloc_, stmtList)) {
     return null();
   }
@@ -5150,14 +5161,47 @@ GeneralParser<ParseHandler, Unit>::exportBatch(uint32_t begin) {
     return null();
   }
 
-  // Handle the form |export *| by adding a special export batch
-  // specifier to the list.
-  NullaryNodeType exportSpec = handler_.newExportBatchSpec(pos());
-  if (!exportSpec) {
+  bool foundAs;
+  if (!tokenStream.matchToken(&foundAs, TokenKind::As)) {
     return null();
   }
 
-  handler_.addList(kid, exportSpec);
+  if (foundAs) {
+    if (!mustMatchToken(TokenKindIsPossibleIdentifierName,
+                        JSMSG_NO_EXPORT_NAME)) {
+      return null();
+    }
+
+    NameNodeType exportName = newName(anyChars.currentName());
+    if (!exportName) {
+      return null();
+    }
+
+    if (!checkExportedNameForClause(exportName)) {
+      return null();
+    }
+
+    NameNodeType importName = newName(cx_->names().star);
+    if (!importName) {
+      return null();
+    }
+
+    BinaryNodeType 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.
+    NullaryNodeType exportSpec = handler_.newExportBatchSpec(pos());
+    if (!exportSpec) {
+      return null();
+    }
+
+    handler_.addList(kid, exportSpec);
+  }
 
   if (!mustMatchToken(TokenKind::From, JSMSG_FROM_AFTER_EXPORT_STAR)) {
     return null();

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

@@ -443,6 +443,13 @@ 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/tests/test262-update.py

@@ -24,7 +24,6 @@
     "class-methods-private",
     "class-static-methods-private",
     "regexp-match-indices",
-    "export-star-as-namespace-from-module",
     "Intl.DateTimeFormat-quarter",
     "Intl.Segmenter",
     "top-level-await",

js/src/tests/test262/language/expressions/dynamic-import/namespace/await-ns-get-nested-namespace-dflt-direct.js

@@ -1,4 +1,4 @@
-// |reftest| skip async -- export-star-as-namespace-from-module is not supported
+// |reftest| async
 // This file was procedurally generated from the following sources:
 // - src/dynamic-import/ns-get-nested-namespace-dflt-direct.case
 // - src/dynamic-import/namespace/await.template

js/src/tests/test262/language/expressions/dynamic-import/namespace/await-ns-get-nested-namespace-dflt-indirect.js

@@ -1,4 +1,4 @@
-// |reftest| skip module async -- export-star-as-namespace-from-module is not supported
+// |reftest| module async
 // This file was procedurally generated from the following sources:
 // - src/dynamic-import/ns-get-nested-namespace-dflt-indirect.case
 // - src/dynamic-import/namespace/await.template