Merge pull request cburstedde#301 from jmark/cmake-conditional-libsc-…

…registration

Check if libsc is already a known target.

CMakeLists.txt

@@ -18,9 +18,13 @@ message(STATUS "p4est ${PROJECT_VERSION} "
 
 # --- external libs
 
-include(cmake/GitSubmodule.cmake)
-git_submodule("${PROJECT_SOURCE_DIR}/sc")
-add_subdirectory(sc)
+# Skip `libsc` if already registered. This is useful when `p4est` is added as a
+# dependency by another software project which in turn already registered `libsc`.
+if(NOT TARGET SC::SC)
+  include(cmake/GitSubmodule.cmake)
+  git_submodule("${PROJECT_SOURCE_DIR}/sc")
+  add_subdirectory(sc)
+endif()
 
 # --- configure p4est