Use namespaces for exported targets.

There is a major GOTCHA for exported targets. If an imported library is
namespaced (eg `HSPlasma::HSPlasma`), CMake will ensure that the library
exists when it is used in a call to `target_link_libraries()`. If an
imported library is *not* namespaced (eg `HSPlasma`), then, if the
target doesn't exist, CMake will simply pass that library name to the
linker and hope for the best. This can lead to confusing errors where,
when a non-namespaced imported target is used, configuration can
"succeed" but HSPlasma is not actually found correctly. The error
doesn't actually emerge until the downstream project attempts to link
against the nonexistent HSPlasma.

This change allows downstream users to link against `HSPlasma::HSPlasma`
and get a free configure-time check that libHSPlasma has been properly
found. An `ALIAS` has been added for the old exported target names to
ensure backwards compatibility.

core/CMakeLists.txt

@@ -831,7 +831,10 @@ install(TARGETS HSPlasma
         LIBRARY DESTINATION lib
         ARCHIVE DESTINATION lib
 )
-install(EXPORT HSPlasma-targets DESTINATION share/cmake/HSPlasma)
+install(EXPORT HSPlasma-targets
+        DESTINATION share/cmake/HSPlasma
+        NAMESPACE HSPlasma::
+)
 
 include(CMakePackageConfigHelpers)
 configure_package_config_file(HSPlasmaConfig.cmake.in

core/HSPlasmaConfig.cmake.in

@@ -10,3 +10,5 @@ include(${CMAKE_CURRENT_LIST_DIR}/HSPlasma-targets.cmake)
 
 check_required_components("HSPlasma")
 set_and_check(HSPlasma_INCLUDE_DIRS "${PACKAGE_PREFIX_DIR}/include/HSPlasma")
+
+add_library(HSPlasma ALIAS HSPlasma::HSPlasma)

net/CMakeLists.txt

@@ -117,7 +117,10 @@ install(TARGETS HSPlasmaNet
         LIBRARY DESTINATION lib
         ARCHIVE DESTINATION lib
 )
-install(EXPORT HSPlasmaNet-targets DESTINATION share/cmake/HSPlasmaNet)
+install(EXPORT HSPlasmaNet-targets
+        DESTINATION share/cmake/HSPlasmaNet
+        NAMESPACE HSPlasma::
+)
 
 include(CMakePackageConfigHelpers)
 configure_package_config_file(HSPlasmaNetConfig.cmake.in

net/HSPlasmaNetConfig.cmake.in

@@ -10,4 +10,6 @@ check_required_components("HSPlasmaNet")
 set_and_check(HSPlasmaNet_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include/HSPlasmaNet")
 
 set(HSPlasmaNet_INCLUDE_DIRS ${HSPlasmaNet_INCLUDE_DIR} ${HSPlasma_INCLUDE_DIRS})
-set(HSPlasmaNet_LIBRARIES HSPlasmaNet HSPlasma)
+set(HSPlasmaNet_LIBRARIES HSPlasma::HSPlasmaNet HSPlasma::HSPlasma)
+
+add_library(HSPlasmaNet ALIAS HSPlasma::HSPlasmaNet)