RunCMake/CXXModules: test public modules requiring private modules

Tests/RunCMake/CXXModules/RunCMakeTest.cmake

@@ -130,6 +130,7 @@ if ("named" IN_LIST CMake_TEST_MODULE_COMPILATION)
   run_cxx_module_test(simple)
   run_cxx_module_test(library library-static -DBUILD_SHARED_LIBS=OFF)
   run_cxx_module_test(generated)
+  run_cxx_module_test(public-req-private)
 endif ()
 
 # Tests which use named modules in shared libraries.

Tests/RunCMake/CXXModules/examples/public-req-private-build-result.txt

@@ -0,0 +1 @@
+1

Tests/RunCMake/CXXModules/examples/public-req-private-build-stdout.txt

@@ -0,0 +1 @@
+CMake Error: Public C\+\+ module source `.*/Tests/RunCMake/CXXModules/examples/public-req-private/pub.cxx` requires the `priv` C\+\+ module which is provided by a private source

Tests/RunCMake/CXXModules/examples/public-req-private-stderr.txt

@@ -0,0 +1,9 @@
+CMake Warning \(dev\) at CMakeLists.txt:7 \(target_sources\):
+  CMake's C\+\+ module support is experimental.  It is meant only for
+  experimentation and feedback to CMake developers.
+This warning is for project developers.  Use -Wno-dev to suppress it.
+
+CMake Warning \(dev\):
+  C\+\+20 modules support via CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP is
+  experimental.  It is meant only for compiler developers to try.
+This warning is for project developers.  Use -Wno-dev to suppress it.

Tests/RunCMake/CXXModules/examples/public-req-private/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.24)
+project(cxx_modules_public_req_private CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_library(public_req_private)
+target_sources(public_req_private
+  PRIVATE
+    FILE_SET private TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        priv.cxx
+  PUBLIC
+    FILE_SET public TYPE CXX_MODULES
+      BASE_DIRS
+        "${CMAKE_CURRENT_SOURCE_DIR}"
+      FILES
+        pub.cxx)
+target_compile_features(public_req_private PUBLIC cxx_std_20)
+
+add_test(NAME cmake-version COMMAND "${CMAKE_COMMAND}" --version)

Tests/RunCMake/CXXModules/examples/public-req-private/priv.cxx

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

Tests/RunCMake/CXXModules/examples/public-req-private/pub.cxx

@@ -0,0 +1,8 @@
+export module pub;
+
+import priv;
+
+export int f()
+{
+  return g();
+}