Tests/CXXModules: add example for private modules between targets

Adapted from the example in issue #24652 by Ivan Garramona.

Tests/RunCMake/CXXModules/RunCMakeTest.cmake

@@ -155,6 +155,9 @@ endif ()
 # Tests which require collation work.
 if ("collation" IN_LIST CMake_TEST_MODULE_COMPILATION)
   run_cxx_module_test(public-req-private)
+  set(RunCMake_CXXModules_NO_TEST 1)
+  run_cxx_module_test(req-private-other-target)
+  unset(RunCMake_CXXModules_NO_TEST)
 endif ()
 
 # Tests which use named modules in shared libraries.

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

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

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

@@ -0,0 +1 @@
+((Ninja generators)?(Unable to use module 'lib.priv' as it is 'PRIVATE' and therefore not accessible outside of its owning target.))

Tests/RunCMake/CXXModules/examples/req-private-other-target-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/req-private-other-target/CMakeLists.txt

@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.26)
+project(req_private_other_target CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_library(lib)
+target_sources(lib
+  PUBLIC FILE_SET pub TYPE CXX_MODULES FILES lib.cxx
+  PRIVATE FILE_SET priv TYPE CXX_MODULES FILES priv.cxx
+)
+target_compile_features(lib PUBLIC cxx_std_20)
+
+add_executable(exe main.cxx)
+target_link_libraries(exe PRIVATE lib)
+
+add_test(NAME exe COMMAND exe)

Tests/RunCMake/CXXModules/examples/req-private-other-target/lib.cxx

@@ -0,0 +1 @@
+export module lib;

Tests/RunCMake/CXXModules/examples/req-private-other-target/main.cxx

@@ -0,0 +1,7 @@
+import lib;
+import lib.priv;
+
+int main(int argc, char const* argv[])
+{
+  return 0;
+}

Tests/RunCMake/CXXModules/examples/req-private-other-target/priv.cxx

@@ -0,0 +1 @@
+export module lib.priv;