Bug Description
If a project foo and its dependency bar have a diamond dependency on HighFive, and both export HighFive cmake files (as is default), then you run into the following error:

CMake Error at /path/to/test/install/lib/cmake/HighFive/HighFiveConfig.cmake:18 (add_library):
  add_library cannot create ALIAS target "HighFive" because another target
  with the same name already exists.
Call Stack (most recent call first):
  /opt/homebrew/Cellar/cmake/3.30.5/share/cmake/Modules/CMakeFindDependencyMacro.cmake:76 (find_package)
  /path/to/test/install/lib/cmake/foo/foo-dependencies.cmake:45 (find_dependency)
  /path/to/test/install/lib/cmake/foo/foo-config.cmake:72 (include)
  ...

Because:

1. In foo-config.cmake it goes to load bar-config.cmake.
2. bar-config.cmake successfully loads and loads HighFive.
3. HighFive loads and creates its targets.
4. Now foo-config.cmake goes on to also load HighFive.
5. HighFive now re-loads. HighFiveTargets.cmake is idempotent, and early-returns before re-creating HighFive::HighFive.
6. HighFiveConfig.cmake is not, and attempts to create the targets again.
7. Error.

The fix is

diff --git a/cmake/HighFiveConfig.cmake b/cmake/HighFiveConfig.cmake
index 33ce7b7..a270d4c 100644
--- a/cmake/HighFiveConfig.cmake
+++ b/cmake/HighFiveConfig.cmake
@@ -14,6 +14,9 @@ if(HDF5_IS_PARALLEL)
   find_dependency(MPI)
   target_link_libraries(HighFive::HighFive INTERFACE MPI::MPI_C MPI::MPI_CXX)
 endif()
-
-add_library(HighFive ALIAS HighFive::HighFive)
-add_library(HighFiveInclude ALIAS HighFive::Include)
+if(NOT TARGET HighFive)
+  add_library(HighFive ALIAS HighFive::HighFive)
+endif()
+if(NOT TARGET HighFiveInclude)
+  add_library(HighFiveInclude ALIAS HighFive::Include)
+endif()

Version Information

• HighFive: 2.9.0
• CMake: 3.30.5