Tests/CXXModules: add a test with transitive targets
diff --git a/Tests/RunCMake/CXXModules/RunCMakeTest.cmake b/Tests/RunCMake/CXXModules/RunCMakeTest.cmake
index aaf289c..2f91d6a 100644
--- a/Tests/RunCMake/CXXModules/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CXXModules/RunCMakeTest.cmake
@@ -262,6 +262,7 @@
   run_cxx_module_test(export-include-directories-build)
   run_cxx_module_test(export-usage-build)
   run_cxx_module_test(export-bmi-and-interface-build)
+  run_cxx_module_test(export-transitive-targets-build)
 
   if ("collation" IN_LIST CMake_TEST_MODULE_COMPILATION AND
       "bmionly" IN_LIST CMake_TEST_MODULE_COMPILATION)
@@ -276,6 +277,9 @@
 
     set(test_suffix export-bmi-and-interface-build)
     run_cxx_module_test(import-modules "import-modules-${test_suffix}" "-DCMAKE_PREFIX_PATH=${RunCMake_BINARY_DIR}/examples/${test_suffix}-build" -DWITH_BMIS=1)
+
+    set(test_suffix export-transitive-targets-build)
+    run_cxx_module_test(import-modules "import-modules-${test_suffix}" "-DCMAKE_PREFIX_PATH=${RunCMake_BINARY_DIR}/examples/${test_suffix}-build" -DTRANSITIVE_TARGETS=1)
   endif ()
 endif ()
 
@@ -293,6 +297,7 @@
     run_cxx_module_test(export-include-directories-install)
     run_cxx_module_test(export-usage-install)
     run_cxx_module_test(export-bmi-and-interface-install)
+    run_cxx_module_test(export-transitive-targets-install)
 
     if ("collation" IN_LIST CMake_TEST_MODULE_COMPILATION AND
         "bmionly" IN_LIST CMake_TEST_MODULE_COMPILATION)
@@ -308,6 +313,9 @@
 
       set(test_suffix export-bmi-and-interface-install)
       run_cxx_module_test(import-modules "import-modules-${test_suffix}" "-DCMAKE_PREFIX_PATH=${RunCMake_BINARY_DIR}/examples/${test_suffix}-install" -DWITH_BMIS=1)
+
+      set(test_suffix export-transitive-targets-install)
+      run_cxx_module_test(import-modules "import-modules-${test_suffix}" "-DCMAKE_PREFIX_PATH=${RunCMake_BINARY_DIR}/examples/${test_suffix}-install" -DTRANSITIVE_TARGETS=1)
       set(RunCMake_CXXModules_INSTALL 1)
     endif ()
   endif ()
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/CMakeLists.txt
new file mode 100644
index 0000000..99ec585
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/CMakeLists.txt
@@ -0,0 +1,71 @@
+cmake_minimum_required(VERSION 3.24...3.28)
+project(cxx_modules_export_transitive_targets CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_library(usage_reqs INTERFACE
+  include/include.h
+  includes/includes.h)
+target_compile_definitions(usage_reqs
+  INTERFACE
+    FROM_USAGE_REQS)
+target_include_directories(usage_reqs
+  INTERFACE
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>"
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/includes>")
+
+add_library(export_transitive_targets STATIC)
+target_sources(export_transitive_targets
+  PRIVATE
+    forward.cxx
+  PRIVATE
+    FILE_SET modules_private TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        private.cxx
+  PUBLIC
+    FILE_SET modules TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        importable.cxx
+        subdir/importable.cxx
+  )
+target_compile_features(export_transitive_targets PUBLIC cxx_std_20)
+target_link_libraries(export_transitive_targets PRIVATE usage_reqs)
+
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS usage_reqs export_transitive_targets no_modules
+  EXPORT CXXModules
+  FILE_SET modules DESTINATION "lib/cxx/miu")
+export(EXPORT CXXModules
+  NAMESPACE CXXModules::
+  FILE "${CMAKE_CURRENT_BINARY_DIR}/export_transitive_targets-targets.cmake"
+  CXX_MODULES_DIRECTORY "export_transitive_targets-cxx-modules")
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/export_transitive_targets-config.cmake"
+  "include(\"\${CMAKE_CURRENT_LIST_DIR}/export_transitive_targets-targets.cmake\")
+set(\${CMAKE_FIND_PACKAGE_NAME}_FOUND 1)
+")
+
+set(generator
+  -G "${CMAKE_GENERATOR}")
+if (CMAKE_GENERATOR_TOOLSET)
+  list(APPEND generator
+    -T "${CMAKE_GENERATOR_TOOLSET}")
+endif ()
+if (CMAKE_GENERATOR_PLATFORM)
+  list(APPEND generator
+    -A "${CMAKE_GENERATOR_PLATFORM}")
+endif ()
+
+add_test(NAME export_transitive_targets_build
+  COMMAND
+    "${CMAKE_COMMAND}"
+    "-Dexpected_source_dir=${CMAKE_CURRENT_SOURCE_DIR}"
+    "-Dexpected_binary_dir=${CMAKE_CURRENT_BINARY_DIR}"
+    "-Dexport_transitive_targets_DIR=${CMAKE_CURRENT_BINARY_DIR}"
+    ${generator}
+    -S "${CMAKE_CURRENT_SOURCE_DIR}/test"
+    -B "${CMAKE_CURRENT_BINARY_DIR}/test")
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/forward.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/forward.cxx
new file mode 100644
index 0000000..7f53271
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/forward.cxx
@@ -0,0 +1,6 @@
+import priv;
+
+int forwarding()
+{
+  return from_private();
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/importable.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/importable.cxx
new file mode 100644
index 0000000..77210ef
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/importable.cxx
@@ -0,0 +1,28 @@
+module;
+
+#include "include/include.h"
+
+#ifndef include_h_included
+#  error "include define not found"
+#endif
+
+#include "includes/includes.h"
+
+#ifndef includes_h_included
+#  error "includes define not found"
+#endif
+
+#ifndef FROM_USAGE_REQS
+#  error "missing `FROM_USAGE_REQS` define"
+#endif
+
+export module importable;
+
+extern "C++" {
+int forwarding();
+}
+
+export int from_import()
+{
+  return forwarding();
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/include/include.h b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/include/include.h
new file mode 100644
index 0000000..e3eee34
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/include/include.h
@@ -0,0 +1,3 @@
+#pragma once
+
+#define include_h_included
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/includes/includes.h b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/includes/includes.h
new file mode 100644
index 0000000..96bf33b
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/includes/includes.h
@@ -0,0 +1,3 @@
+#pragma once
+
+#define includes_h_included
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/private.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/private.cxx
new file mode 100644
index 0000000..c5b719a
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/private.cxx
@@ -0,0 +1,6 @@
+export module priv;
+
+export int from_private()
+{
+  return 0;
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/subdir/importable.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/subdir/importable.cxx
new file mode 100644
index 0000000..07d6af6
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/subdir/importable.cxx
@@ -0,0 +1,6 @@
+export module subdir_importable;
+
+export int from_subdir()
+{
+  return 0;
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/test/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/test/CMakeLists.txt
new file mode 100644
index 0000000..8e70576
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-build/test/CMakeLists.txt
@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.28)
+project(cxx_modules_library NONE)
+
+find_package(export_transitive_targets REQUIRED)
+
+if (NOT TARGET CXXModules::export_transitive_targets)
+  message(FATAL_ERROR
+    "Missing imported target")
+endif ()
+
+get_property(transitive_targets TARGET CXXModules::export_transitive_targets
+  PROPERTY IMPORTED_CXX_MODULES_LINK_LIBRARIES)
+if (NOT transitive_targets STREQUAL "$<COMPILE_ONLY:CXXModules::usage_reqs>")
+  message(FATAL_ERROR
+    "Incorrect transitive link library in C++ module interface CXXModules::export_transitive_targets:\n  ${transitive_targets}")
+endif ()
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/CMakeLists.txt
new file mode 100644
index 0000000..dd1eb01
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/CMakeLists.txt
@@ -0,0 +1,80 @@
+cmake_minimum_required(VERSION 3.24...3.28)
+project(cxx_modules_export_transitive_targets CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_library(usage_reqs INTERFACE
+  include/include.h
+  includes/includes.h)
+target_compile_definitions(usage_reqs
+  INTERFACE
+    FROM_USAGE_REQS)
+target_include_directories(usage_reqs
+  INTERFACE
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>"
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/includes>"
+    "$<INSTALL_INTERFACE:include>")
+
+add_library(export_transitive_targets STATIC)
+target_sources(export_transitive_targets
+  PRIVATE
+    forward.cxx
+  PRIVATE
+    FILE_SET modules_private TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        private.cxx
+  PUBLIC
+    FILE_SET modules TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        importable.cxx
+        subdir/importable.cxx
+  )
+target_compile_features(export_transitive_targets PUBLIC cxx_std_20)
+target_link_libraries(export_transitive_targets PRIVATE usage_reqs)
+
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS usage_reqs export_transitive_targets no_modules
+  EXPORT CXXModules
+  FILE_SET modules DESTINATION "lib/cxx/miu"
+  INCLUDES DESTINATION "elsewhere")
+install(DIRECTORY include
+  DESTINATION "include")
+install(DIRECTORY includes
+  DESTINATION "elsewhere")
+install(EXPORT CXXModules
+  NAMESPACE CXXModules::
+  DESTINATION "lib/cmake/export_transitive_targets"
+  FILE "export_transitive_targets-targets.cmake"
+  CXX_MODULES_DIRECTORY "export_transitive_targets-cxx-modules")
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/export_transitive_targets-config.cmake"
+  "include(\"\${CMAKE_CURRENT_LIST_DIR}/export_transitive_targets-targets.cmake\")
+set(\${CMAKE_FIND_PACKAGE_NAME}_FOUND 1)
+")
+install(FILES "${CMAKE_CURRENT_BINARY_DIR}/export_transitive_targets-config.cmake"
+  DESTINATION "lib/cmake/export_transitive_targets")
+
+set(generator
+  -G "${CMAKE_GENERATOR}")
+if (CMAKE_GENERATOR_TOOLSET)
+  list(APPEND generator
+    -T "${CMAKE_GENERATOR_TOOLSET}")
+endif ()
+if (CMAKE_GENERATOR_PLATFORM)
+  list(APPEND generator
+    -A "${CMAKE_GENERATOR_PLATFORM}")
+endif ()
+
+add_test(NAME export_transitive_targets_build
+  COMMAND
+    "${CMAKE_COMMAND}"
+    "-Dexpected_source_dir=${CMAKE_INSTALL_PREFIX}/lib/cxx/miu"
+    "-Dexpected_binary_dir=${CMAKE_INSTALL_PREFIX}/lib/cxx/bmi"
+    "-Dexport_transitive_targets_DIR=${CMAKE_INSTALL_PREFIX}/lib/cmake/export_transitive_targets"
+    ${generator}
+    -S "${CMAKE_CURRENT_SOURCE_DIR}/test"
+    -B "${CMAKE_CURRENT_BINARY_DIR}/test")
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/forward.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/forward.cxx
new file mode 100644
index 0000000..7f53271
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/forward.cxx
@@ -0,0 +1,6 @@
+import priv;
+
+int forwarding()
+{
+  return from_private();
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/importable.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/importable.cxx
new file mode 100644
index 0000000..77210ef
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/importable.cxx
@@ -0,0 +1,28 @@
+module;
+
+#include "include/include.h"
+
+#ifndef include_h_included
+#  error "include define not found"
+#endif
+
+#include "includes/includes.h"
+
+#ifndef includes_h_included
+#  error "includes define not found"
+#endif
+
+#ifndef FROM_USAGE_REQS
+#  error "missing `FROM_USAGE_REQS` define"
+#endif
+
+export module importable;
+
+extern "C++" {
+int forwarding();
+}
+
+export int from_import()
+{
+  return forwarding();
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/include/include.h b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/include/include.h
new file mode 100644
index 0000000..e3eee34
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/include/include.h
@@ -0,0 +1,3 @@
+#pragma once
+
+#define include_h_included
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/includes/includes.h b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/includes/includes.h
new file mode 100644
index 0000000..96bf33b
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/includes/includes.h
@@ -0,0 +1,3 @@
+#pragma once
+
+#define includes_h_included
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/private.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/private.cxx
new file mode 100644
index 0000000..c5b719a
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/private.cxx
@@ -0,0 +1,6 @@
+export module priv;
+
+export int from_private()
+{
+  return 0;
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/subdir/importable.cxx b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/subdir/importable.cxx
new file mode 100644
index 0000000..07d6af6
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/subdir/importable.cxx
@@ -0,0 +1,6 @@
+export module subdir_importable;
+
+export int from_subdir()
+{
+  return 0;
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/test/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/test/CMakeLists.txt
new file mode 100644
index 0000000..8e70576
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-transitive-targets-install/test/CMakeLists.txt
@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.28)
+project(cxx_modules_library NONE)
+
+find_package(export_transitive_targets REQUIRED)
+
+if (NOT TARGET CXXModules::export_transitive_targets)
+  message(FATAL_ERROR
+    "Missing imported target")
+endif ()
+
+get_property(transitive_targets TARGET CXXModules::export_transitive_targets
+  PROPERTY IMPORTED_CXX_MODULES_LINK_LIBRARIES)
+if (NOT transitive_targets STREQUAL "$<COMPILE_ONLY:CXXModules::usage_reqs>")
+  message(FATAL_ERROR
+    "Incorrect transitive link library in C++ module interface CXXModules::export_transitive_targets:\n  ${transitive_targets}")
+endif ()
diff --git a/Tests/RunCMake/CXXModules/examples/import-modules/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/import-modules/CMakeLists.txt
index 16bc6d8..0b125ba 100644
--- a/Tests/RunCMake/CXXModules/examples/import-modules/CMakeLists.txt
+++ b/Tests/RunCMake/CXXModules/examples/import-modules/CMakeLists.txt
@@ -11,6 +11,8 @@
   set(package_name "export_include_directories")
 elseif (FROM_NINJA)
   set(package_name "export_from_ninja")
+elseif (TRANSITIVE_TARGETS)
+  set(package_name "export_transitive_targets")
 else ()
   set(package_name "export_interfaces")
 endif ()
diff --git a/Tests/RunCMake/CXXModules/examples/import-modules/use.cxx b/Tests/RunCMake/CXXModules/examples/import-modules/use.cxx
index 2da1913..a012f38 100644
--- a/Tests/RunCMake/CXXModules/examples/import-modules/use.cxx
+++ b/Tests/RunCMake/CXXModules/examples/import-modules/use.cxx
@@ -4,6 +4,10 @@
 #  endif
 #endif
 
+#ifdef FROM_USAGE_REQS
+#  error "compile definitions leaked from private module requirements"
+#endif
+
 import importable;
 
 int main(int argc, char* argv[])