c++modules: Fix transitive import of object producing BMIs

Fixes: #28185

Source/cmGlobalNinjaGenerator.cxx

@@ -3243,18 +3243,23 @@ bool cmGlobalNinjaGenerator::WriteDyndepFile(
     forward_info(transitiveInterfaceObjects, fmft["interface-objects"]);
   }
 
-  // Compute the set of modules actually imported by sources in this target.
+  // Compute the set of modules imported directly or transitively by sources in
+  // this target.
   std::set<std::string> usedModules;
   for (cmScanDepInfo const& object : objects) {
     for (auto const& r : object.Requires) {
       usedModules.insert(r.LogicalName);
+      auto usage = usages.Usage.find(r.LogicalName);
+      if (usage != usages.Usage.end()) {
+        usedModules.insert(usage->second.begin(), usage->second.end());
+      }
     }
   }
 
-  // Merge direct interface objects into the accumulated set.
-  // Direct objects are filtered: only keep those for modules that are
-  // actually imported by sources in this target. Transitive objects from
-  // linked targets were already filtered in their originating target.
+  // Merge interface objects into the accumulated set.
+  // Objects are filtered: only keep those for modules that are imported
+  // directly or transitively by sources in this target. Transitive objects
+  // from linked targets were already filtered in their originating target.
   if (cxx_interface_objects && cxx_interface_objects->isObject()) {
     Json::Value const& directObjects =
       (*cxx_interface_objects)["module-objects"];

Tests/RunCMake/CXXModulesCompile/RunCMakeTest.cmake

@@ -246,6 +246,7 @@ if ("named" IN_LIST CMake_TEST_MODULE_COMPILATION)
   if ("cxx_std_23" IN_LIST CMAKE_CXX_COMPILE_FEATURES AND
       "import_std23" IN_LIST CMake_TEST_MODULE_COMPILATION)
     run_cxx_module_test(imp-std)
+    run_cxx_module_test(imp-std-compat)
     set(RunCMake_CXXModules_NO_TEST 1)
     run_cxx_module_test(imp-std-no-std-json)
     unset(RunCMake_CXXModules_NO_TEST)

Tests/RunCMake/CXXModulesCompile/imp-std-compat/CMakeLists.txt

@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 3.29)
+project(cxx_modules_import_std_compat CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_executable(main
+  main.cxx)
+target_compile_features(main PRIVATE cxx_std_23)
+
+add_test(NAME main COMMAND main)

Tests/RunCMake/CXXModulesCompile/imp-std-compat/main.cxx

@@ -0,0 +1,15 @@
+import std.compat;
+
+int main(int argc, char* argv[])
+{
+  // std::chrono::current_zone() references _Global_tzdb_list, which is
+  // provided by std.ixx.obj on MSVC. Ensure we get a failed link if this
+  // definition isn't available through the transitive import of std.
+  static_cast<void>(std::chrono::current_zone());
+
+  if (argc > 0 && argv[0]) {
+    std::string argv0 = argv[0];
+    std::cout << "program: " << argv0 << std::endl;
+  }
+  return 0;
+}