Don't double-fetch a module specified on the d8 command line

Shell::FetchModuleTree assumes that the module at file_name wasn't
already fetched. Shell::ExecuteModule is calling into
FetchModuleTree without checking if the module is already in the module
map, violating this assumption.

This change fixes this by having Shell::ExecuteModule check for the
existence of the module before calling into Shell::ExecuteModule, the
same way that Shell::DoHostImportModuleDynamically does.

Bug: v8:12530
Change-Id: Ia038cbd1715e85c9c92c4554fd486c657ef952e8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3388130Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78636}

src/d8/d8.cc

@@ -1365,9 +1365,13 @@ bool Shell::ExecuteModule(Isolate* isolate, const char* file_name) {
   // isolate->ReportPendingMessages().
   TryCatch try_catch(isolate);
 
+  ModuleEmbedderData* d = GetModuleDataFromContext(realm);
   Local<Module> root_module;
-
-  if (!FetchModuleTree(Local<Module>(), realm, absolute_path,
+  auto module_it = d->module_map.find(
+      std::make_pair(absolute_path, ModuleType::kJavaScript));
+  if (module_it != d->module_map.end()) {
+    root_module = module_it->second.Get(isolate);
+  } else if (!FetchModuleTree(Local<Module>(), realm, absolute_path,
                               ModuleType::kJavaScript)
                   .ToLocal(&root_module)) {
     CHECK(try_catch.HasCaught());

test/mjsunit/d8/d8-multiple-module-exec.js

+// Copyright 2022 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags:  test/mjsunit/modules-skip-1.mjs test/mjsunit/modules-skip-1.mjs
+
+// Just test that d8 doesn't crash when running the same module on the
+// command line twice.