Tests/CXXModules: test Visual Studio synthetic target error

Tests/RunCMake/CXXModules/RunCMakeTest.cmake

@@ -95,7 +95,7 @@ if (RunCMake_GENERATOR MATCHES "Ninja")
   run_cmake(NinjaDependInfoExport)
   run_cmake(NinjaDependInfoBMIInstall)
 elseif (RunCMake_GENERATOR MATCHES "Visual Studio")
-  # Not supported yet.
+  run_cmake(VisualStudioNoSyntheticTargets)
 else ()
   message(FATAL_ERROR
     "Please add 'DependInfo' tests for the '${RunCMake_GENERATOR}' generator.")

Tests/RunCMake/CXXModules/VisualStudioNoSyntheticTargets-result.txt

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

Tests/RunCMake/CXXModules/VisualStudioNoSyntheticTargets-stderr.txt

@@ -0,0 +1,6 @@
+^(CMake Error in CMakeLists.txt:
+  Target "imported-cxx-modules@synth_[0-9a-f]+" contains C\+\+ modules
+  intended for BMI-only compilation.  This is not yet supported by the Visual
+  Studio generator.
+*
+)+CMake Generate step failed.  Build files cannot be regenerated correctly.

Tests/RunCMake/CXXModules/VisualStudioNoSyntheticTargets.cmake

@@ -0,0 +1,27 @@
+enable_language(CXX)
+
+if (NOT CMAKE_GENERATOR MATCHES "Visual Studio")
+  message(FATAL_ERROR
+    "This test requires a 'Visual Studio' generator to be used.")
+endif ()
+
+add_library(imported-cxx-modules IMPORTED INTERFACE)
+target_sources(imported-cxx-modules
+  INTERFACE
+    FILE_SET modules TYPE CXX_MODULES
+    BASE_DIRS
+      "${CMAKE_CURRENT_SOURCE_DIR}/sources"
+    FILES
+      sources/module-simple.cxx)
+set_target_properties(imported-cxx-modules PROPERTIES
+  IMPORTED_CONFIGURATIONS DEBUG
+  IMPORTED_LINK_INTERFACE_LANGUAGES_DEBUG "CXX"
+  IMPORTED_CXX_MODULES_COMPILE_FEATURES "cxx_std_20"
+  INTERFACE_COMPILE_FEATURES "cxx_std_20"
+  IMPORTED_CXX_MODULES_DEBUG "simple=${CMAKE_CURRENT_SOURCE_DIR}/sources/module-simple.cxx")
+
+add_executable(vs-use-imported-cxx-modules
+  sources/module-simple-use.cxx)
+target_link_libraries(vs-use-imported-cxx-modules
+  PRIVATE
+    imported-cxx-modules)

Tests/RunCMake/CXXModules/sources/module-simple-use.cxx

@@ -0,0 +1,6 @@
+import simple;
+
+int main(int argc, char* argv[])
+{
+  return g();
+}

Tests/RunCMake/CXXModules/sources/module-simple.cxx

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