cmNinjaTargetGenerator: do not order-depend on C++ module sources

C++ module sources should not be included by any other TUs, so their
presence cannot matter for order-only dependencies of the entire target.
Exclude them.

Update CMP0154 to take this into consideration and add tests to the
`CXXModules` suite (which already deals with module support detection).

6 files changed, 72 insertions, 1 deletions

diff --git a/Tests/RunCMake/CXXModules/RunCMakeTest.cmake b/Tests/RunCMake/CXXModules/RunCMakeTest.cmake
index 2938fa8..e687e9f 100644
--- a/Tests/RunCMake/CXXModules/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CXXModules/RunCMakeTest.cmake
@@ -133,7 +133,11 @@ function (run_cxx_module_test directory)
     ${ARGN})
   run_cmake("examples/${test_name}")
   set(RunCMake_TEST_NO_CLEAN 1)
-  run_cmake_command("examples/${test_name}-build" "${CMAKE_COMMAND}" --build . --config Debug)
+  if (RunCMake_CXXModules_TARGET)
+    run_cmake_command("examples/${test_name}-build" "${CMAKE_COMMAND}" --build . --config Debug --target "${RunCMake_CXXModules_TARGET}")
+  else ()
+    run_cmake_command("examples/${test_name}-build" "${CMAKE_COMMAND}" --build . --config Debug)
+  endif ()
   if (RunCMake_CXXModules_INSTALL)
     run_cmake_command("examples/${test_name}-install" "${CMAKE_COMMAND}" --build . --target install --config Debug)
   endif ()
@@ -142,8 +146,23 @@ function (run_cxx_module_test directory)
   endif ()
 endfunction ()
 
+function (run_cxx_module_test_target directory target)
+  set(RunCMake_CXXModules_TARGET "${target}")
+  set(RunCMake_CXXModules_NO_TEST 1)
+  run_cxx_module_test("${directory}" ${ARGN})
+endfunction ()
+
 string(REPLACE "," ";" CMake_TEST_MODULE_COMPILATION "${CMake_TEST_MODULE_COMPILATION}")
 
+if (RunCMake_GENERATOR MATCHES "Ninja")
+  if (RunCMake_GENERATOR_IS_MULTI_CONFIG)
+    set(ninja_cmp0154_target "CMakeFiles/ninja_cmp0154.dir/Debug/unrelated.cxx${CMAKE_CXX_OUTPUT_EXTENSION}")
+  else ()
+    set(ninja_cmp0154_target "CMakeFiles/ninja_cmp0154.dir/unrelated.cxx${CMAKE_CXX_OUTPUT_EXTENSION}")
+  endif ()
+  run_cxx_module_test_target(ninja-cmp0154 "${ninja_cmp0154_target}")
+endif ()
+
 # Tests which use named modules.
 if ("named" IN_LIST CMake_TEST_MODULE_COMPILATION)
   run_cxx_module_test(simple)
diff --git a/Tests/RunCMake/CXXModules/examples/ninja-cmp0154-build-check.cmake b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154-build-check.cmake
new file mode 100644
index 0000000..6c4812b
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154-build-check.cmake
@@ -0,0 +1,4 @@
+if (EXISTS "${RunCMake_TEST_BINARY_DIR}/importable.cxx")
+  list(APPEND RunCMake_TEST_FAILED
+    "The `importable.cxx` file should not be generated to compile `unrelated`'s object")
+endif ()
diff --git a/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/CMakeLists.txt
new file mode 100644
index 0000000..1aa36c1
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/CMakeLists.txt
@@ -0,0 +1,31 @@
+cmake_minimum_required(VERSION 3.24...3.28)
+project(cxx_modules_ninja_cmp0154 CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_custom_command(
+  OUTPUT  "${CMAKE_CURRENT_BINARY_DIR}/importable.cxx"
+  DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/importable.cxx.in"
+  COMMAND "${CMAKE_COMMAND}"
+          -E copy_if_different
+          "${CMAKE_CURRENT_SOURCE_DIR}/importable.cxx.in"
+          "${CMAKE_CURRENT_BINARY_DIR}/importable.cxx"
+  COMMENT "Copying 'importable.cxx'")
+
+add_executable(ninja_cmp0154)
+target_sources(ninja_cmp0154
+  PRIVATE
+    main.cxx
+    unrelated.cxx
+  PUBLIC
+    FILE_SET CXX_MODULES
+      BASE_DIRS
+      "${CMAKE_CURRENT_BINARY_DIR}"
+      FILES
+        "${CMAKE_CURRENT_BINARY_DIR}/importable.cxx")
+target_compile_features(ninja_cmp0154 PUBLIC cxx_std_20)
+set_property(SOURCE unrelated.cxx
+  PROPERTY
+    CXX_SCAN_FOR_MODULES 0)
+
+add_test(NAME ninja_cmp0154 COMMAND ninja_cmp0154)
diff --git a/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/importable.cxx.in b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/importable.cxx.in
new file mode 100644
index 0000000..a9287d7
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/importable.cxx.in
@@ -0,0 +1,5 @@
+export module importable;
+
+export int from_import() {
+  return 0;
+}
diff --git a/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/main.cxx b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/main.cxx
new file mode 100644
index 0000000..1ac4850
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/main.cxx
@@ -0,0 +1,8 @@
+import importable;
+
+extern int unrelated();
+
+int main(int argc, char* argv[])
+{
+  return from_import() + unrelated();
+}
diff --git a/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/unrelated.cxx b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/unrelated.cxx
new file mode 100644
index 0000000..d54a47f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/ninja-cmp0154/unrelated.cxx
@@ -0,0 +1,4 @@
+int unrelated()
+{
+  return 0;
+}