cxxmodules: Do not expect collator install scripts with no CXX_MODULES

Calling `install(EXPORT)` with the `CXX_MODULES_DIRECTORY` parameter
leads to installation rules being generated which `include()` CMake
scripts that set the `IMPORTED_CXX_MODULES_[CONFIG]` target property for
relevant targets.  However, these scripts don't get generated for
targets in an export set which don't have any C++20 modules.  When the
installation rules attempt to `include()` the missing scripts, the
install fails.

Co-authored-by: Brad King <brad.king@kitware.com>

12 files changed, 36 insertions, 6 deletions

diff --git a/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-build/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-build/CMakeLists.txt
index a450b7e..62971a3 100644
--- a/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-build/CMakeLists.txt
+++ b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-build/CMakeLists.txt
@@ -21,7 +21,9 @@ target_sources(export_bmi_and_interfaces
         importable.cxx)
 target_compile_features(export_bmi_and_interfaces PUBLIC cxx_std_20)
 
-install(TARGETS export_bmi_and_interfaces
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS export_bmi_and_interfaces no_modules
   EXPORT CXXModules
   FILE_SET modules DESTINATION "lib/cxx/miu"
   CXX_MODULES_BMI DESTINATION "lib/cxx/bmi")
diff --git a/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-build/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-build/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-build/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-install/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-install/CMakeLists.txt
index a5574fe..bc19d93 100644
--- a/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-install/CMakeLists.txt
+++ b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-install/CMakeLists.txt
@@ -21,7 +21,9 @@ target_sources(export_bmi_and_interfaces
         importable.cxx)
 target_compile_features(export_bmi_and_interfaces PUBLIC cxx_std_20)
 
-install(TARGETS export_bmi_and_interfaces
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS export_bmi_and_interfaces no_modules
   EXPORT CXXModules
   FILE_SET modules DESTINATION "lib/cxx/miu"
   CXX_MODULES_BMI DESTINATION "lib/cxx/bmi")
diff --git a/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-install/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-install/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-bmi-and-interface-install/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-build/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-interface-build/CMakeLists.txt
index 8584dce..62352ff 100644
--- a/Tests/RunCMake/CXXModules/examples/export-interface-build/CMakeLists.txt
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-build/CMakeLists.txt
@@ -21,7 +21,9 @@ target_sources(export_interfaces
         importable.cxx)
 target_compile_features(export_interfaces PUBLIC cxx_std_20)
 
-install(TARGETS export_interfaces
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS export_interfaces no_modules
   EXPORT CXXModules
   FILE_SET modules DESTINATION "lib/cxx/miu")
 export(EXPORT CXXModules
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-build/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-interface-build/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-build/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-install/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-interface-install/CMakeLists.txt
index b5c6224..15c91d9 100644
--- a/Tests/RunCMake/CXXModules/examples/export-interface-install/CMakeLists.txt
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-install/CMakeLists.txt
@@ -21,7 +21,9 @@ target_sources(export_interfaces
         importable.cxx)
 target_compile_features(export_interfaces PUBLIC cxx_std_20)
 
-install(TARGETS export_interfaces
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS export_interfaces no_modules
   EXPORT CXXModules
   FILE_SET modules DESTINATION "lib/cxx/miu")
 install(EXPORT CXXModules
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-install/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-interface-install/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-install/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-build/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-build/CMakeLists.txt
index 7633bec..7d04c50 100644
--- a/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-build/CMakeLists.txt
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-build/CMakeLists.txt
@@ -21,7 +21,9 @@ target_sources(export_interfaces_no_properties
         importable.cxx)
 target_compile_features(export_interfaces_no_properties PUBLIC cxx_std_20)
 
-install(TARGETS export_interfaces_no_properties
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS export_interfaces_no_properties no_modules
   EXPORT CXXModules
   FILE_SET modules DESTINATION "lib/cxx/miu")
 export(EXPORT CXXModules
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-build/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-build/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-build/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-install/CMakeLists.txt b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-install/CMakeLists.txt
index 75f2440..c0db766 100644
--- a/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-install/CMakeLists.txt
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-install/CMakeLists.txt
@@ -21,7 +21,9 @@ target_sources(export_interfaces_no_properties
         importable.cxx)
 target_compile_features(export_interfaces_no_properties PUBLIC cxx_std_20)
 
-install(TARGETS export_interfaces_no_properties
+add_library(no_modules STATIC no_modules.cxx)
+
+install(TARGETS export_interfaces_no_properties no_modules
   EXPORT CXXModules
   FILE_SET modules DESTINATION "lib/cxx/miu")
 install(EXPORT CXXModules
diff --git a/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-install/no_modules.cxx b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-install/no_modules.cxx
new file mode 100644
index 0000000..eea854f
--- /dev/null
+++ b/Tests/RunCMake/CXXModules/examples/export-interface-no-properties-install/no_modules.cxx
@@ -0,0 +1,3 @@
+void no_modules()
+{
+}