Issue #618 - Align module instantiation/errors with the updated spec.

Store and re-throw module instantiation and evaluation errors.
Ref: BZ 1374239, 1394492

1 files changed, 431 insertions, 102 deletions

diff --git a/js/src/builtin/Module.js b/js/src/builtin/Module.js
index 5c3d5e147..064293670 100644
--- a/js/src/builtin/Module.js
+++ b/js/src/builtin/Module.js
@@ -2,11 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-function CallModuleResolveHook(module, specifier, expectedMinimumState)
+function CallModuleResolveHook(module, specifier, expectedMinimumStatus)
 {
     let requestedModule = HostResolveImportedModule(module, specifier);
-    if (requestedModule.state < expectedMinimumState)
-        ThrowInternalError(JSMSG_BAD_MODULE_STATE);
+    if (requestedModule.state < expectedMinimumStatus)
+        ThrowInternalError(JSMSG_BAD_MODULE_STATUS);
 
     return requestedModule;
 }
@@ -65,7 +65,36 @@ function ModuleGetExportedNames(exportStarSet = [])
     return exportedNames;
 }
 
+function ModuleSetStatus(module, newStatus)
+{
+    assert(newStatus >= MODULE_STATUS_ERRORED && newStatus <= MODULE_STATUS_EVALUATED,
+           "Bad new module status in ModuleSetStatus");
+    if (newStatus !== MODULE_STATUS_ERRORED)
+        assert(newStatus > module.status, "New module status inconsistent with current status");
+
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_STATUS_SLOT, newStatus);
+}
+
 // 15.2.1.16.3 ResolveExport(exportName, resolveSet)
+//
+// Returns an object describing the location of the resolved export or
+// indicating a failure.
+//
+// On success this returns: { resolved: true, module, bindingName }
+//
+// There are three failure cases:
+//
+//  - The resolution failure can be blamed on a particular module.
+//    Returns: { resolved: false, module, ambiguous: false }
+//
+//  - No culprit can be determined and the resolution failure was due to star
+//    export ambiguity.
+//    Returns: { resolved: false, module: null, ambiguous: true }
+//
+//  - No culprit can be determined and the resolution failure was not due to
+//    star export ambiguity.
+//    Returns: { resolved: false, module: null, ambiguous: false }
+//
 function ModuleResolveExport(exportName, resolveSet = [])
 {
     if (!IsObject(this) || !IsModule(this)) {
@@ -77,88 +106,104 @@ function ModuleResolveExport(exportName, resolveSet = [])
     let module = this;
 
     // Step 2
+    assert(module.status !== MODULE_STATUS_ERRORED, "Bad module status in ResolveExport");
+    
+    // Step 3
     for (let i = 0; i < resolveSet.length; i++) {
         let r = resolveSet[i];
-        if (r.module === module && r.exportName === exportName)
-            return null;
+        if (r.module === module && r.exportName === exportName) {
+            // This is a circular import request.
+            return {resolved: false, module: null, ambiguous: false};
+        }
     }
 
-    // Step 3
+    // Step 4
     _DefineDataProperty(resolveSet, resolveSet.length, {module: module, exportName: exportName});
 
-    // Step 4
+    // Step 5
     let localExportEntries = module.localExportEntries;
     for (let i = 0; i < localExportEntries.length; i++) {
         let e = localExportEntries[i];
         if (exportName === e.exportName)
-            return {module: module, bindingName: e.localName};
+            return {resolved: true, module, bindingName: e.localName};
     }
 
-    // Step 5
+    // Step 6
     let indirectExportEntries = module.indirectExportEntries;
     for (let i = 0; i < indirectExportEntries.length; i++) {
         let e = indirectExportEntries[i];
         if (exportName === e.exportName) {
             let importedModule = CallModuleResolveHook(module, e.moduleRequest,
-                                                       MODULE_STATE_PARSED);
-            return callFunction(importedModule.resolveExport, importedModule, e.importName,
-                                resolveSet);
+                                                       MODULE_STATUS_UNINSTANTIATED);
+            let resolution = callFunction(importedModule.resolveExport, importedModule, e.importName,
+                                          resolveSet);
+            if (!resolution.resolved && !resolution.module)
+                resolution.module = module;
+            return resolution;
         }
     }
 
-    // Step 6
+    // Step 7
     if (exportName === "default") {
         // A default export cannot be provided by an export *.
-        return null;
+        return {resolved: false, module: null, ambiguous: false};
     }
 
-    // Step 7
+    // Step 8
     let starResolution = null;
 
-    // Step 8
+    // Step 9
     let starExportEntries = module.starExportEntries;
     for (let i = 0; i < starExportEntries.length; i++) {
         let e = starExportEntries[i];
         let importedModule = CallModuleResolveHook(module, e.moduleRequest,
-                                                   MODULE_STATE_PARSED);
-        let resolution = callFunction(importedModule.resolveExport, importedModule,
-                                      exportName, resolveSet);
-        if (resolution === "ambiguous")
+                                                   MODULE_STATUS_UNINSTANTIATED);
+        let resolution = callFunction(importedModule.resolveExport, importedModule, exportName,
+                                      resolveSet);
+        if (!resolution.resolved && (resolution.module || resolution.ambiguous))
             return resolution;
 
-        if (resolution !== null) {
+        if (resolution.resolved) {
             if (starResolution === null) {
                 starResolution = resolution;
             } else {
                 if (resolution.module !== starResolution.module ||
-                    resolution.exportName !== starResolution.exportName)
+                    resolution.bindingName !== starResolution.bindingName)
                 {
-                    return "ambiguous";
+                    return {resolved: false, module: null, ambiguous: true};
                 }
             }
         }
     }
 
-    // Step 9
-    return starResolution;
+    // Step 10
+    if (starResolution !== null)
+        return starResolution;
+
+    return {resolved: false, module: null, ambiguous: false};
 }
 
 // 15.2.1.18 GetModuleNamespace(module)
 function GetModuleNamespace(module)
 {
+    // Step 1
+    assert(IsModule(module), "GetModuleNamespace called with non-module");
+
     // Step 2
-    let namespace = module.namespace;
+    assert(module.status !== MODULE_STATUS_UNINSTANTIATED &&
+           module.status !== MODULE_STATUS_ERRORED,
+           "Bad module status in GetModuleNamespace");
 
     // Step 3
+    let namespace = module.namespace;
+
     if (typeof namespace === "undefined") {
         let exportedNames = callFunction(module.getExportedNames, module);
         let unambiguousNames = [];
         for (let i = 0; i < exportedNames.length; i++) {
             let name = exportedNames[i];
             let resolution = callFunction(module.resolveExport, module, name);
-            if (resolution === null)
-                ThrowSyntaxError(JSMSG_MISSING_NAMESPACE_EXPORT);
-            if (resolution !== "ambiguous")
+            if (resolution.resolved)
                 _DefineDataProperty(unambiguousNames, unambiguousNames.length, name);
         }
         namespace = ModuleNamespaceCreate(module, unambiguousNames);
@@ -180,7 +225,7 @@ function ModuleNamespaceCreate(module, exports)
     for (let i = 0; i < exports.length; i++) {
         let name = exports[i];
         let binding = callFunction(module.resolveExport, module, name);
-        assert(binding !== null && binding !== "ambiguous", "Failed to resolve binding");
+        assert(binding.resolved, "Failed to resolve binding");
         AddModuleNamespaceBinding(ns, name, binding.module, binding.bindingName);
     }
 
@@ -193,8 +238,8 @@ function GetModuleEnvironment(module)
 
     // Check for a previous failed attempt to instantiate this module. This can
     // only happen due to a bug in the module loader.
-    if (module.state == MODULE_STATE_FAILED)
-        ThrowInternalError(JSMSG_MODULE_INSTANTIATE_FAILED);
+    if (module.status === MODULE_STATUS_ERRORED)
+        ThrowInternalError(JSMSG_MODULE_INSTANTIATE_FAILED, module.status);
 
     let env = UnsafeGetReservedSlot(module, MODULE_OBJECT_ENVIRONMENT_SLOT);
     assert(env === undefined || IsModuleEnvironment(env),
@@ -203,112 +248,396 @@ function GetModuleEnvironment(module)
     return env;
 }
 
-function RecordInstantationFailure(module)
+function RecordModuleError(module, error)
 {
-    // Set the module's state to 'failed' to indicate a failed module
-    // instantiation and reset the environment slot to 'undefined'.
-    assert(IsModule(module), "Non-module passed to RecordInstantationFailure");
-    SetModuleState(module, MODULE_STATE_FAILED);
+    // Set the module's status to 'errored' to indicate a failed module
+    // instantiation and record the exception. The environment slot is also
+    // reset to 'undefined'.
+
+    assert(IsObject(module) && IsModule(module), "Non-module passed to RecordModuleError");
+
+    ModuleSetStatus(module, MODULE_STATUS_ERRORED);
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT, error);
     UnsafeSetReservedSlot(module, MODULE_OBJECT_ENVIRONMENT_SLOT, undefined);
 }
 
-// 15.2.1.16.4 ModuleDeclarationInstantiation()
-function ModuleDeclarationInstantiation()
+function CountArrayValues(array, value)
+{
+    let count = 0;
+    for (let i = 0; i < array.length; i++) {
+        if (array[i] === value)
+            count++;
+    }
+    return count;
+}
+
+function ArrayContains(array, value)
+{
+    for (let i = 0; i < array.length; i++) {
+        if (array[i] === value)
+            return true;
+    }
+    return false;
+}
+
+// 15.2.1.16.4 ModuleInstantiate()
+function ModuleInstantiate()
 {
     if (!IsObject(this) || !IsModule(this))
-        return callFunction(CallModuleMethodIfWrapped, this, "ModuleDeclarationInstantiation");
+        return callFunction(CallModuleMethodIfWrapped, this, "ModuleInstantiate");
 
     // Step 1
     let module = this;
 
-    // Step 5
-    if (GetModuleEnvironment(module) !== undefined)
-        return;
-
-    // Step 7
-    CreateModuleEnvironment(module);
-    let env = GetModuleEnvironment(module);
+    // Step 2
+    if (module.status === MODULE_STATUS_INSTANTIATING ||
+        module.status === MODULE_STATUS_EVALUATING)
+    {
+        ThrowInternalError(JSMSG_BAD_MODULE_STATUS);
+    }
 
-    SetModuleState(this, MODULE_STATE_INSTANTIATED);
+    // Step 3
+    let stack = [];
 
+    // Steps 4-5
     try {
-        // Step 8
-        let requestedModules = module.requestedModules;
-        for (let i = 0; i < requestedModules.length; i++) {
-            let required = requestedModules[i];
-            let requiredModule = CallModuleResolveHook(module, required, MODULE_STATE_PARSED);
-            callFunction(requiredModule.declarationInstantiation, requiredModule);
+        InnerModuleDeclarationInstantiation(module, stack, 0);
+    } catch (error) {
+        for (let i = 0; i < stack.length; i++) {
+            let m = stack[i];
+
+            assert(m.status === MODULE_STATUS_INSTANTIATING ||
+                   m.status === MODULE_STATUS_ERRORED,
+                   "Bad module status after failed instantiation");
+
+            RecordModuleError(m, error);
         }
 
-        // Step 9
-        let indirectExportEntries = module.indirectExportEntries;
-        for (let i = 0; i < indirectExportEntries.length; i++) {
-            let e = indirectExportEntries[i];
-            let resolution = callFunction(module.resolveExport, module, e.exportName);
-            if (resolution === null)
-                ThrowSyntaxError(JSMSG_MISSING_INDIRECT_EXPORT, e.exportName);
-            if (resolution === "ambiguous")
-                ThrowSyntaxError(JSMSG_AMBIGUOUS_INDIRECT_EXPORT, e.exportName);
+        if (stack.length === 0 &&
+            typeof(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT)) === "undefined")
+        {
+            // This can happen due to OOM when appending to the stack.
+            assert(error === "out of memory",
+                   "Stack must contain module unless we hit OOM");
+            RecordModuleError(module, error);
         }
 
-        // Step 12
-        let importEntries = module.importEntries;
-        for (let i = 0; i < importEntries.length; i++) {
-            let imp = importEntries[i];
-            let importedModule = CallModuleResolveHook(module, imp.moduleRequest,
-                                                       MODULE_STATE_INSTANTIATED);
-            if (imp.importName === "*") {
-                let namespace = GetModuleNamespace(importedModule);
-                CreateNamespaceBinding(env, imp.localName, namespace);
-            } else {
-                let resolution = callFunction(importedModule.resolveExport, importedModule,
-                                              imp.importName);
-                if (resolution === null)
-                    ThrowSyntaxError(JSMSG_MISSING_IMPORT, imp.importName);
-                if (resolution === "ambiguous")
-                    ThrowSyntaxError(JSMSG_AMBIGUOUS_IMPORT, imp.importName);
-                if (resolution.module.state < MODULE_STATE_INSTANTIATED)
-                    ThrowInternalError(JSMSG_BAD_MODULE_STATE);
-                CreateImportBinding(env, imp.localName, resolution.module, resolution.bindingName);
-            }
+        assert(module.status === MODULE_STATUS_ERRORED,
+               "Bad module status after failed instantiation");
+        assert(SameValue(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT), error),
+               "Module has different error set after failed instantiation");
+
+        throw error;
+    }
+
+    // Step 6
+    assert(module.status == MODULE_STATUS_INSTANTIATED ||
+           module.status == MODULE_STATUS_EVALUATED,
+           "Bad module status after successful instantiation");
+
+    // Step 7
+    assert(stack.length === 0,
+           "Stack should be empty after successful instantiation");
+
+    // Step 8
+    return undefined;
+}
+_SetCanonicalName(ModuleInstantiate, "ModuleInstantiate");
+
+// 15.2.1.16.4.1 InnerModuleDeclarationInstantiation(module, stack, index)
+function InnerModuleDeclarationInstantiation(module, stack, index)
+{
+    // Step 1
+    // TODO: Support module records other than source text module records.
+
+    // Step 2
+    if (module.status === MODULE_STATUS_INSTANTIATING ||
+        module.status === MODULE_STATUS_INSTANTIATED ||
+        module.status === MODULE_STATUS_EVALUATED)
+    {
+        return index;
+    }
+
+    // Step 3
+    if (module.status === MODULE_STATUS_ERRORED)
+        throw module.error;
+
+    // Step 4
+    assert(module.status === MODULE_STATUS_UNINSTANTIATED,
+          "Bad module status in ModuleDeclarationInstantiation");
+
+    // Steps 5
+    ModuleSetStatus(module, MODULE_STATUS_INSTANTIATING);
+
+    // Step 6-8
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_INDEX_SLOT, index);
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT, index);
+    index++;
+
+    // Step 9
+    _DefineDataProperty(stack, stack.length, module);
+
+    // Step 10
+    let requestedModules = module.requestedModules;
+    for (let i = 0; i < requestedModules.length; i++) {
+        let required = requestedModules[i];
+        let requiredModule = CallModuleResolveHook(module, required, MODULE_STATUS_ERRORED);
+
+        index = InnerModuleDeclarationInstantiation(requiredModule, stack, index);
+
+        assert(requiredModule.status === MODULE_STATUS_INSTANTIATING ||
+               requiredModule.status === MODULE_STATUS_INSTANTIATED ||
+               requiredModule.status === MODULE_STATUS_EVALUATED,
+               "Bad required module status after InnerModuleDeclarationInstantiation");
+
+        assert((requiredModule.status === MODULE_STATUS_INSTANTIATING) ===
+               ArrayContains(stack, requiredModule),
+              "Required module should be in the stack iff it is currently being instantiated");
+
+        assert(typeof requiredModule.dfsIndex === "number", "Bad dfsIndex");
+        assert(typeof requiredModule.dfsAncestorIndex === "number", "Bad dfsAncestorIndex");
+
+        if (requiredModule.status === MODULE_STATUS_INSTANTIATING) {
+            UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT,
+                                  std_Math_min(module.dfsAncestorIndex,
+                                               requiredModule.dfsAncestorIndex));
+        }
+    }
+
+    // Step 11
+    ModuleDeclarationEnvironmentSetup(module);
+
+    // Steps 12-13
+    assert(CountArrayValues(stack, module) === 1,
+           "Current module should appear exactly once in the stack");
+    assert(module.dfsAncestorIndex <= module.dfsIndex,
+           "Bad DFS ancestor index");
+
+    // Step 14
+    if (module.dfsAncestorIndex === module.dfsIndex) {
+        let requiredModule;
+        do {
+            requiredModule = callFunction(std_Array_pop, stack);
+            ModuleSetStatus(requiredModule, MODULE_STATUS_INSTANTIATED);
+        } while (requiredModule !== module);
+    }
+
+    // Step 15
+    return index;
+}
+
+// 15.2.1.16.4.2 ModuleDeclarationEnvironmentSetup(module)
+function ModuleDeclarationEnvironmentSetup(module)
+{
+    // Step 1
+    let indirectExportEntries = module.indirectExportEntries;
+    for (let i = 0; i < indirectExportEntries.length; i++) {
+        let e = indirectExportEntries[i];
+        let resolution = callFunction(module.resolveExport, module, e.exportName);
+        assert(resolution.resolved || resolution.module,
+               "Unexpected failure to resolve export in ModuleDeclarationEnvironmentSetup");
+        if (!resolution.resolved)
+            return ResolutionError(resolution, "indirectExport", e.exportName)
+    }
+
+    // Steps 5-6
+    CreateModuleEnvironment(module);
+    let env = GetModuleEnvironment(module);
+
+    // Step 8
+    let importEntries = module.importEntries;
+    for (let i = 0; i < importEntries.length; i++) {
+        let imp = importEntries[i];
+        let importedModule = CallModuleResolveHook(module, imp.moduleRequest,
+                                                   MODULE_STATUS_INSTANTIATING);
+        if (imp.importName === "*") {
+            let namespace = GetModuleNamespace(importedModule);
+            CreateNamespaceBinding(env, imp.localName, namespace);
+        } else {
+            let resolution = callFunction(importedModule.resolveExport, importedModule,
+                                          imp.importName);
+            if (!resolution.resolved && !resolution.module)
+                resolution.module = module;
+
+            if (!resolution.resolved)
+                return ResolutionError(resolution, "import", imp.importName);
+
+            CreateImportBinding(env, imp.localName, resolution.module, resolution.bindingName);
         }
+    }
+
+    InstantiateModuleFunctionDeclarations(module);
+}
 
-        // Step 17.a.iii
-        InstantiateModuleFunctionDeclarations(module);
-    } catch (e) {
-        RecordInstantationFailure(module);
-        throw e;
+// 15.2.1.16.4.3 ResolutionError(module)
+function ResolutionError(resolution, kind, name)
+{
+    let module = resolution.module;
+    assert(module !== null,
+           "Null module passed to ResolutionError");
+
+    assert(module.status === MODULE_STATUS_UNINSTANTIATED ||
+           module.status === MODULE_STATUS_INSTANTIATING,
+           "Unexpected module status in ResolutionError");
+
+    assert(kind === "import" || kind === "indirectExport",
+           "Unexpected kind in ResolutionError");
+
+    let message;
+    if (kind === "import") {
+        message = resolution.ambiguous ? JSMSG_AMBIGUOUS_IMPORT
+                                       : JSMSG_MISSING_IMPORT;
+    } else {
+        message = resolution.ambiguous ? JSMSG_AMBIGUOUS_INDIRECT_EXPORT
+                                       : JSMSG_MISSING_INDIRECT_EXPORT;
+    }
+
+    try {
+        ThrowSyntaxError(message, name);
+    } catch (error) {
+        RecordModuleError(module, error);
+        throw error;
     }
 }
-_SetCanonicalName(ModuleDeclarationInstantiation, "ModuleDeclarationInstantiation");
 
-// 15.2.1.16.5 ModuleEvaluation()
-function ModuleEvaluation()
+// 15.2.1.16.5 ModuleEvaluate()
+function ModuleEvaluate()
 {
     if (!IsObject(this) || !IsModule(this))
-        return callFunction(CallModuleMethodIfWrapped, this, "ModuleEvaluation");
+        return callFunction(CallModuleMethodIfWrapped, this, "ModuleEvaluatie");
 
     // Step 1
     let module = this;
 
-    if (module.state < MODULE_STATE_INSTANTIATED)
-        ThrowInternalError(JSMSG_BAD_MODULE_STATE);
+    // Step 2
+    if (module.status !== MODULE_STATUS_ERRORED &&
+        module.status !== MODULE_STATUS_INSTANTIATED &&
+        module.status !== MODULE_STATUS_EVALUATED)
+    {
+        ThrowInternalError(JSMSG_BAD_MODULE_STATUS);
+    }
+
+    // Step 3
+    let stack = [];
+
+    // Steps 4-5
+    try {
+        InnerModuleEvaluation(module, stack, 0);
+    } catch (error) {
+        for (let i = 0; i < stack.length; i++) {
+            let m = stack[i];
+
+            assert(m.status === MODULE_STATUS_EVALUATING,
+                   "Bad module status after failed evaluation");
+
+            RecordModuleError(m, error);
+        }
+
+        if (stack.length === 0 &&
+            typeof(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT)) === "undefined")
+        {
+            // This can happen due to OOM when appending to the stack.
+            assert(error === "out of memory",
+                  "Stack must contain module unless we hit OOM");
+            RecordModuleError(module, error);
+        }
+
+        assert(module.status === MODULE_STATUS_ERRORED,
+               "Bad module status after failed evaluation");
+        assert(SameValue(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT), error),
+               "Module has different error set after failed evaluation");
+
+        throw error;
+    }
+
+    assert(module.status == MODULE_STATUS_EVALUATED,
+           "Bad module status after successful evaluation");
+    assert(stack.length === 0,
+           "Stack should be empty after successful evaluation");
+
+    return undefined;
+}
+_SetCanonicalName(ModuleEvaluate, "ModuleEvaluate");
+
+// 15.2.1.16.5.1 InnerModuleEvaluation(module, stack, index)
+function InnerModuleEvaluation(module, stack, index)
+{
+    // Step 1
+    // TODO: Support module records other than source text module records.
+
+    // Step 2
+    if (module.status === MODULE_STATUS_EVALUATING ||
+        module.status === MODULE_STATUS_EVALUATED)
+    {
+        return index;
+    }
+
+    // Step 3
+    if (module.status === MODULE_STATUS_ERRORED)
+        throw module.error;
 
     // Step 4
-    if (module.state == MODULE_STATE_EVALUATED)
-        return undefined;
+    assert(module.status === MODULE_STATUS_INSTANTIATED,
+          "Bad module status in ModuleEvaluation");
 
     // Step 5
-    SetModuleState(this, MODULE_STATE_EVALUATED);
+    ModuleSetStatus(module, MODULE_STATUS_EVALUATING);
 
-    // Step 6
+    // Steps 6-8
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_INDEX_SLOT, index);
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT, index);
+    index++;
+
+    // Step 9
+    _DefineDataProperty(stack, stack.length, module);
+
+    // Step 10
     let requestedModules = module.requestedModules;
     for (let i = 0; i < requestedModules.length; i++) {
         let required = requestedModules[i];
-        let requiredModule = CallModuleResolveHook(module, required, MODULE_STATE_INSTANTIATED);
-        callFunction(requiredModule.evaluation, requiredModule);
+        let requiredModule =
+            CallModuleResolveHook(module, required, MODULE_STATUS_INSTANTIATED);
+
+        index = InnerModuleEvaluation(requiredModule, stack, index);
+
+        assert(requiredModule.status == MODULE_STATUS_EVALUATING ||
+               requiredModule.status == MODULE_STATUS_EVALUATED,
+              "Bad module status after InnerModuleEvaluation");
+
+        assert((requiredModule.status === MODULE_STATUS_EVALUATING) ===
+               ArrayContains(stack, requiredModule),
+               "Required module should be in the stack iff it is currently being evaluated");
+
+        assert(typeof requiredModule.dfsIndex === "number", "Bad dfsIndex");
+        assert(typeof requiredModule.dfsAncestorIndex === "number", "Bad dfsAncestorIndex");
+
+        if (requiredModule.status === MODULE_STATUS_EVALUATING) {
+            UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT,
+                                  std_Math_min(module.dfsAncestorIndex,
+                                               requiredModule.dfsAncestorIndex));
+        }
+    }
+
+    // Step 11
+    ExecuteModule(module);
+
+    // Step 12
+    assert(CountArrayValues(stack, module) === 1,
+           "Current module should appear exactly once in the stack");
+
+    // Step 13
+    assert(module.dfsAncestorIndex <= module.dfsIndex,
+           "Bad DFS ancestor index");
+
+    // Step 14
+    if (module.dfsAncestorIndex === module.dfsIndex) {
+        let requiredModule;
+        do {
+            requiredModule = callFunction(std_Array_pop, stack);
+            ModuleSetStatus(requiredModule, MODULE_STATUS_EVALUATED);
+        } while (requiredModule !== module);
     }
 
-    return EvaluateModule(module);
+    // Step 15
+    return index;
 }
-_SetCanonicalName(ModuleEvaluation, "ModuleEvaluation");