Tests/CXXModules: add a test importing from a `Ninja` install

This ensures that consuming from a single configuration generator works
in all generators.

See: #25568

Tests/RunCMake/CXXModules/RunCMakeTest.cmake

@@ -335,3 +335,7 @@ endfunction ()
 
 # Installation happens within `run_cxx_module_test_ninja`.
 set(RunCMake_CXXModules_INSTALL 0)
+
+set(test_set modules-from-ninja)
+run_cxx_module_test_ninja("export-${test_set}")
+run_cxx_module_test(import-modules "import-${test_set}" "-DCMAKE_PREFIX_PATH=${RunCMake_BINARY_DIR}/examples/export-${test_set}-ninja-install" -DFROM_NINJA=1)

Tests/RunCMake/CXXModules/examples/export-modules-from-ninja/CMakeLists.txt

@@ -0,0 +1,41 @@
+cmake_minimum_required(VERSION 3.24...3.28)
+project(cxx_modules_export_from_ninja CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_library(export_from_ninja STATIC)
+target_sources(export_from_ninja
+  PRIVATE
+    forward.cxx
+  PRIVATE
+    FILE_SET modules_private TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        private.cxx
+  PUBLIC
+    FILE_SET modules TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        importable.cxx
+        subdir/importable.cxx
+  )
+target_compile_features(export_from_ninja PUBLIC cxx_std_20)
+
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS export_from_ninja no_modules
+  EXPORT CXXModules
+  FILE_SET modules DESTINATION "lib/cxx/miu")
+install(EXPORT CXXModules
+  NAMESPACE CXXModules::
+  DESTINATION "lib/cmake/export_from_ninja"
+  FILE "export_from_ninja-targets.cmake"
+  CXX_MODULES_DIRECTORY "export_from_ninja-cxx-modules")
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/export_from_ninja-config.cmake"
+  "include(\"\${CMAKE_CURRENT_LIST_DIR}/export_from_ninja-targets.cmake\")
+set(\${CMAKE_FIND_PACKAGE_NAME}_FOUND 1)
+")
+install(FILES "${CMAKE_CURRENT_BINARY_DIR}/export_from_ninja-config.cmake"
+  DESTINATION "lib/cmake/export_from_ninja")

Tests/RunCMake/CXXModules/examples/export-modules-from-ninja/forward.cxx

@@ -0,0 +1,6 @@
+import priv;
+
+int forwarding()
+{
+  return from_private();
+}

Tests/RunCMake/CXXModules/examples/export-modules-from-ninja/importable.cxx

@@ -0,0 +1,10 @@
+export module importable;
+
+extern "C++" {
+int forwarding();
+}
+
+export int from_import()
+{
+  return forwarding();
+}

Tests/RunCMake/CXXModules/examples/export-modules-from-ninja/no_modules.cxx

@@ -0,0 +1,3 @@
+void no_modules()
+{
+}

Tests/RunCMake/CXXModules/examples/export-modules-from-ninja/private.cxx

@@ -0,0 +1,6 @@
+export module priv;
+
+export int from_private()
+{
+  return 0;
+}

Tests/RunCMake/CXXModules/examples/export-modules-from-ninja/subdir/importable.cxx

@@ -0,0 +1,6 @@
+export module subdir_importable;
+
+export int from_subdir()
+{
+  return 0;
+}

Tests/RunCMake/CXXModules/examples/import-modules/CMakeLists.txt

@@ -9,6 +9,8 @@ elseif (WITH_BMIS)
   set(package_name "export_bmi_and_interfaces")
 elseif (INCLUDE_PROPERTIES)
   set(package_name "export_include_directories")
+elseif (FROM_NINJA)
+  set(package_name "export_from_ninja")
 else ()
   set(package_name "export_interfaces")
 endif ()