build: integrate CVMix via FetchContent instead of download script

.gitignore

@@ -14,6 +14,5 @@ lib/*.so
 /work_*
 Makefile.in
 mesh_part/build
-test/output_pi 
-src/cvmix_driver/CVMix-*
+test/output_pi
 .claude/

src/CMakeLists.txt

@@ -201,65 +201,30 @@ target_include_directories(${PROJECT_NAME} PUBLIC $<BUILD_INTERFACE:${CMAKE_Fort
 target_include_directories(${PROJECT_NAME} PUBLIC $<INSTALL_INTERFACE:module/fesom>)
 target_link_libraries(${PROJECT_NAME} PRIVATE MPI::MPI_Fortran)
 
-# build CVMix library if CVMIX is ON
-if (CVMIX)
+# Pull CVMix in via FetchContent and build it as part of FESOM's build tree.
+# Offline workflow:
+#   - point at a manually placed checkout: -DFETCHCONTENT_SOURCE_DIR_CVMIX=/path/to/CVMix-src
+#   - or pre-populate <build>/_deps/cvmix-src and pass -DFETCHCONTENT_FULLY_DISCONNECTED=ON
+if(CVMIX)
    message(STATUS "CVMIX: ${CVMIX}")
-
-   # read CVMix install and src directories from the download script, so that there
-   # is only one place where they are defined
-   execute_process(COMMAND bash ${src_home}/cvmix_driver/download_cvmix.sh --print-src_dir
-                   OUTPUT_VARIABLE CVMIX_DIR_src OUTPUT_STRIP_TRAILING_WHITESPACE)
-   execute_process(COMMAND bash ${src_home}/cvmix_driver/download_cvmix.sh --print-prefix
-                   OUTPUT_VARIABLE CVMIX_DIR_install OUTPUT_STRIP_TRAILING_WHITESPACE)  
-
-   # set default CVMix installation path
-   set(CVMIX_ROOT "${src_home}/cvmix_driver/${CVMIX_DIR_install}_${CMAKE_Fortran_COMPILER_ID}") 
-   message(STATUS "set default CVMIX_ROOT=${CVMIX_ROOT}")
-
-   # Where library is located --> fix in download_cvmix.sh that it as always installed 
-   # in /lib and not in /lib64
-   set(CVMIX_LIB "${CVMIX_ROOT}/lib/libcvmix.a")
-
-   # Create parent directory early so CMake does not fail on missing include paths
-   file(MAKE_DIRECTORY ${CVMIX_ROOT})
-   file(MAKE_DIRECTORY ${CVMIX_ROOT}/include/cvmix)
-
-   # Collect CVMix source files so that CMake knows what changes triggers a 
-   # possible rebuild of the CVMix library
-   file(GLOB_RECURSE CVMIX_SOURCES
-         "${src_home}/cvmix_driver/${CVMIX_DIR_src}/src/*.F90"
-         "${src_home}/cvmix_driver/${CVMIX_DIR_src}/src/*/*.F90")
-
-   # Add script dependency (rebuild if script changes)
-   set(CVMIX_DOWNLOAD "${src_home}/cvmix_driver/download_cvmix.sh")
-
-   # Custom command: build CVMix if not yet built
-   add_custom_command(
-         OUTPUT ${CVMIX_LIB}
-         COMMAND bash ${src_home}/cvmix_driver/download_cvmix.sh --prefix ${CVMIX_ROOT}
-         WORKING_DIRECTORY ${src_home}/cvmix_driver
-         DEPENDS ${CVMIX_SOURCES} ${CVMIX_DOWNLOAD} # trigger rebuild if source or download script change
-         COMMENT "Downloading and building CVMix into ${CVMIX_ROOT}"
-         VERBATIM)
-
-   # check if ${CVMIX_ROOT}/lib/libcvmix.a exist or not, only if it does not 
-   # exist build library
-   add_custom_target(cvmix_autobuild DEPENDS ${CVMIX_LIB})
-
-   # build cvmix external libray
-   add_library(cvmix_external STATIC IMPORTED GLOBAL)
-   set_target_properties(cvmix_external PROPERTIES
-         IMPORTED_LOCATION ${CVMIX_LIB}
-         INTERFACE_INCLUDE_DIRECTORIES "${CVMIX_ROOT}/include/cvmix")
-
-   # cvmix_autobuild is a custom target that runs your download_cvmix.sh script 
-   # and produces libcvmix.a. cvmix_external is an imported library, meaning CMake 
-   # doesn’t build it — it just points to an existing file (libcvmix.a).
-   add_dependencies(cvmix_external  cvmix_autobuild)
-
-   # Link CVMix library to fesom, build chain becomes: fesom → cvmix_external → cvmix_autobuild
-   target_link_libraries(${PROJECT_NAME} PRIVATE cvmix_external)
-
+
+   include(FetchContent)
+   set(CVMIX_BUILD_SHARED_LIBS OFF CACHE BOOL "" FORCE)
+   set(CVMIX_BUILD_DRIVER      OFF CACHE BOOL "" FORCE)
+   FetchContent_Declare(cvmix
+      GIT_REPOSITORY https://github.com/CVMix/CVMix-src.git
+      GIT_TAG        v1.0.0
+   )
+   FetchContent_MakeAvailable(cvmix)
+
+   # CVMix's own CMakeLists exposes its module dir only via INSTALL_INTERFACE and
+   # writes .mod files to ${CMAKE_BINARY_DIR}/modules (top-level build dir, set
+   # in the subdirectory scope). Expose that path on the BUILD_INTERFACE so
+   # FESOM's wrapper sources in cvmix_driver/ can find the CVMix .mod files.
+   target_include_directories(cvmix_static INTERFACE
+      $<BUILD_INTERFACE:${CMAKE_BINARY_DIR}/modules>)
+
+   target_link_libraries(${PROJECT_NAME} PRIVATE cvmix_static)
 endif()
 
 set_target_properties(${PROJECT_NAME} PROPERTIES LINKER_LANGUAGE Fortran)