move download and extract code into function

cmake/Modules/ExternalCMakeProject.cmake

@@ -0,0 +1,35 @@
+# Build a CMake based external library as subdirectory.
+# The sources will be unpacked to ${CMAKE_BINARY_DIR}/_deps/${target}-src
+# The binaries will be built in ${CMAKE_BINARY_DIR}/_deps/${target}-build
+#
+function(ExternalCMakeProject target url hash basedir cmakedir)
+  # change settings locally
+  set(BUILD_SHARED_LIBS OFF)
+  set(CMAKE_POSITION_INDEPENDENT_CODE ON)
+
+  if(CMAKE_VERSION VERSION_LESS 3.14)
+    get_filename_component(archive ${url} NAME)
+    file(MAKE_DIRECTORY ${CMAKE_BINARY_DIR}/_deps/src)
+    message(STATUS "Downloading ${url}")
+    file(DOWNLOAD ${url} ${CMAKE_BINARY_DIR}/_deps/${archive} EXPECTED_HASH MD5=${hash} SHOW_PROGRESS)
+    message(STATUS "Unpacking and configuring ${archive}")
+    execute_process(COMMAND ${CMAKE_COMMAND} -E tar xzf ${CMAKE_BINARY_DIR}/_deps/${archive}
+      WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/_deps/src)
+    file(GLOB TARGET_SOURCE "${CMAKE_BINARY_DIR}/_deps/src/${basedir}*")
+    list(LENGTH TARGET_SOURCE _num)
+    if(_num GREATER 1)
+      message(FATAL_ERROR "Inconsistent ${target} library sources. "
+        "Please delete ${CMAKE_BINARY_DIR}/_deps/src and re-run cmake")
+    endif()
+    file(REMOVE_RECURSE ${CMAKE_BINARY_DIR}/_deps/${target}-src)
+    file(RENAME ${TARGET_SOURCE} ${CMAKE_BINARY_DIR}/_deps/${target}-src)
+    add_subdirectory("${CMAKE_BINARY_DIR}/_deps/${target}-src/${cmakedir}"
+      "${CMAKE_BINARY_DIR}/_deps/${target}-build")
+  else()
+    include(FetchContent)
+    message(STATUS "Downloading ${url}")
+    FetchContent_Declare(${target} URL ${url} URL_HASH MD5=${hash} SOURCE_SUBDIR ${cmakedir})
+    message(STATUS "Unpacking and configuring ${archive}")
+    FetchContent_MakeAvailable(${target})
+  endif()
+endfunction(ExternalCMakeProject)

cmake/Modules/Packages/MSCG.cmake

@@ -12,47 +12,11 @@ if(DOWNLOAD_MSCG)
   mark_as_advanced(MSCG_URL)
   mark_as_advanced(MSCG_MD5)
 
-  # always compile a static lib but with position independent code
+  include(ExternalCMakeProject)
-  # make a copy of current settings for later use
+  ExternalCMakeProject(mscg ${MSCG_URL} ${MSCG_MD5} MSCG-release src/CMake)
-  set(OLD_SHARED_LIBS ${BUILD_SHARED_LIBS})
-  set(OLD_POSITION_INDEPENDENT_CODE ${CMAKE_POSITION_INDEPENDENT_CODE})
-  set(BUILD_SHARED_LIBS OFF)
-  set(CMAKE_POSITION_INDEPENDENT_CODE ON)
-
-  if(CMAKE_VERSION VERSION_LESS 3.14)
-    file(MAKE_DIRECTORY ${CMAKE_BINARY_DIR}/_deps)
-    file(DOWNLOAD ${MSCG_URL} ${CMAKE_BINARY_DIR}/_deps/mscg.tar.gz EXPECTED_HASH MD5=${MSCG_MD5})
-    execute_process(COMMAND ${CMAKE_COMMAND} -E tar xzf ${CMAKE_BINARY_DIR}/_deps/mscg.tar.gz
-      WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/_deps)
-
-    file(GLOB MSCG_SOURCE "${CMAKE_BINARY_DIR}/_deps/MSCG-release-*")
-    # sanity check. do not allow to have multiple downloaded and extracted versions of the source
-    list(LENGTH MSCG_SOURCE _num)
-    if(_num GREATER 1)
-      message(FATAL_ERROR "Inconsistent MSCG library sources. Please delete ${CMAKE_BINARY_DIR}/_deps and re-run cmake")
-    endif()
-    add_subdirectory(${MSCG_SOURCE}/src/CMake ${CMAKE_BINARY_DIR}/_deps/mscg-build)
-  else()
-    include(FetchContent)
-    FetchContent_Declare(mscg URL ${MSCG_URL} URL_HASH MD5=${MSCG_MD5} SOURCE_SUBDIR src/CMake)
-    FetchContent_MakeAvailable(mscg)
-    set(MSCG_SOURCE ${CMAKE_BINARY_DIR}/_deps/mscg-src)
-  endif()
-
-  # restore previous settings
-  if(OLD_POSITION_INDEPENDENT_CODE)
-    set(CMAKE_POSITON_INDEPENDENT_CODE ${OLD_POSITION_INDEPENDENT_CODE})
-  else()
-    unset(CMAKE_POSITION_INDEPENDENT_CODE)
-  endif()
-  if (OLD_SHARED_LIBS)
-    set(BUILD_SHARED_LIBS ${OLD_SHARED_LIBS})
-  else()
-    unset(BUILD_SHARED_LIBS)
-  endif()
 
   # set include and link library
-  target_include_directories(lammps PRIVATE "${MSCG_SOURCE}/src")
+  target_include_directories(lammps PRIVATE "${CMAKE_BINARY_DIR}/_deps/mscg-src/src")
   target_link_libraries(lammps PRIVATE mscg)
 else()
   find_package(MSCG)

unittest/CMakeLists.txt

@@ -11,24 +11,8 @@ mark_as_advanced(GTEST_URL)
 mark_as_advanced(GTEST_MD5)
 set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 
-# workaround for older CMake versions (tested on Ubuntu 18.04 with CMake 3.10)
+include(ExternalCMakeProject)
-if(CMAKE_VERSION VERSION_LESS 3.14)
+ExternalCMakeProject(googletest ${GTEST_URL} ${GTEST_MD5} googletest .)
-  file(MAKE_DIRECTORY ${CMAKE_BINARY_DIR}/_deps)
-  file(DOWNLOAD ${GTEST_URL} ${CMAKE_BINARY_DIR}/_deps/googletest.tar.gz EXPECTED_HASH MD5=${GTEST_MD5})
-  execute_process(COMMAND ${CMAKE_COMMAND} -E tar xzf ${CMAKE_BINARY_DIR}/_deps/googletest.tar.gz
-    WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/_deps)
-  file(GLOB GTEST_SOURCE "${CMAKE_BINARY_DIR}/_deps/googletest-*")
-  # sanity check. do not allow to have multiple downloaded and extracted versions of the source
-  list(LENGTH GTEST_SOURCE _num)
-  if(_num GREATER 1)
-    message(FATAL_ERROR "Inconsistent googletest sources. Please delete ${CMAKE_BINARY_DIR}/_deps and re-run cmake")
-  endif()
-  add_subdirectory(${GTEST_SOURCE} ${CMAKE_BINARY_DIR}/googletest)
-else()
-  include(FetchContent)
-  FetchContent_Declare(googletest URL ${GTEST_URL} URL_HASH MD5=${GTEST_MD5})
-  FetchContent_MakeAvailable(googletest)
-endif()
 
 ########################################
 # General tests using the LAMMPS executable itself