From 71b48253e871caa753aaadb63566d552759565da Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Fri, 30 Jun 2023 23:15:37 -0400
Subject: [PATCH] remove special case CMake code for versions before 3.16

---
 cmake/CMakeLists.txt                 | 41 +++++++---------------------
 cmake/Modules/CodingStandard.cmake   | 18 ++++--------
 cmake/Modules/Documentation.cmake    | 24 ++++++----------
 cmake/Modules/FindCythonize.cmake    | 10 +------
 cmake/Modules/Packages/KIM.cmake     |  7 +----
 cmake/Modules/Packages/MDI.cmake     | 34 ++++-------------------
 cmake/Modules/Packages/ML-IAP.cmake  | 21 +++-----------
 cmake/Modules/Packages/PYTHON.cmake  | 34 ++++++-----------------
 cmake/Modules/Testing.cmake          | 26 ++++--------------
 examples/kim/plugin/CMakeLists.txt   |  9 ++----
 unittest/CMakeLists.txt              |  6 +---
 unittest/force-styles/CMakeLists.txt | 17 ++----------
 unittest/python/CMakeLists.txt       | 10 +------
 unittest/tools/CMakeLists.txt        | 10 ++-----
 14 files changed, 57 insertions(+), 210 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 24b08ae667..3393a56682 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -22,13 +22,8 @@ endif()
 if(POLICY CMP0135)
   cmake_policy(SET CMP0135 OLD)
 endif()
-########################################
-# Use CONFIGURE_DEPENDS as option for file(GLOB...) when available
-if(CMAKE_VERSION VERSION_LESS 3.12)
-  unset(CONFIGURE_DEPENDS)
-else()
-  set(CONFIGURE_DEPENDS CONFIGURE_DEPENDS)
-endif()
+
+set(CONFIGURE_DEPENDS CONFIGURE_DEPENDS)
 ########################################
 
 project(lammps CXX)
@@ -466,12 +461,7 @@ option(WITH_JPEG "Enable JPEG support" ${JPEG_FOUND})
 if(WITH_JPEG)
   find_package(JPEG REQUIRED)
   target_compile_definitions(lammps PRIVATE -DLAMMPS_JPEG)
-  if(CMAKE_VERSION VERSION_LESS 3.12)
-    target_include_directories(lammps PRIVATE ${JPEG_INCLUDE_DIRS})
-    target_link_libraries(lammps PRIVATE ${JPEG_LIBRARIES})
-  else()
-    target_link_libraries(lammps PRIVATE JPEG::JPEG)
-  endif()
+  target_link_libraries(lammps PRIVATE JPEG::JPEG)
 endif()
 
 find_package(PNG QUIET)
@@ -819,20 +809,11 @@ install(
 # This is primarily for people that only want to use the Python wrapper.
 ###############################################################################
 if(BUILD_SHARED_LIBS)
-  if(CMAKE_VERSION VERSION_LESS 3.12)
-    # adjust so we find Python 3 versions before Python 2 on old systems with old CMake
-    set(Python_ADDITIONAL_VERSIONS 3.12 3.11 3.10 3.9 3.8 3.7 3.6)
-    find_package(PythonInterp) # Deprecated since version 3.12
-    if(PYTHONINTERP_FOUND)
-      set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-    endif()
-  else()
-    # backward compatibility
-    if(PYTHON_EXECUTABLE)
-      set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-    endif()
-    find_package(Python COMPONENTS Interpreter)
+  # backward compatibility
+  if(PYTHON_EXECUTABLE)
+    set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
   endif()
+  find_package(Python COMPONENTS Interpreter)
   if(BUILD_IS_MULTI_CONFIG)
     set(MY_BUILD_DIR ${CMAKE_BINARY_DIR}/$<CONFIG>)
   else()
@@ -941,11 +922,9 @@ if(_index GREATER -1)
 endif()
 message(STATUS "<<< Linker flags: >>>")
 message(STATUS "Executable name:  ${LAMMPS_BINARY}")
-if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
-  get_target_property(OPTIONS lammps LINK_OPTIONS)
-  if(OPTIONS)
-    message(STATUS "Linker options:   ${OPTIONS}")
-  endif()
+get_target_property(OPTIONS lammps LINK_OPTIONS)
+if(OPTIONS)
+  message(STATUS "Linker options:   ${OPTIONS}")
 endif()
 if(CMAKE_EXE_LINKER_FLAGS)
   message(STATUS "Executable linker flags: ${CMAKE_EXE_LINKER_FLAGS}")
diff --git a/cmake/Modules/CodingStandard.cmake b/cmake/Modules/CodingStandard.cmake
index 4efd373d22..94639c7771 100644
--- a/cmake/Modules/CodingStandard.cmake
+++ b/cmake/Modules/CodingStandard.cmake
@@ -1,19 +1,11 @@
-if(CMAKE_VERSION VERSION_LESS 3.12)
-    find_package(PythonInterp 3.5 QUIET) # Deprecated since version 3.12
-    if(PYTHONINTERP_FOUND)
-        set(Python3_EXECUTABLE ${PYTHON_EXECUTABLE})
-        set(Python3_VERSION ${PYTHON_VERSION_STRING})
-    endif()
-else()
-    # use default (or custom) Python executable, if version is sufficient
-    if(Python_VERSION VERSION_GREATER_EQUAL 3.5)
-      set(Python3_EXECUTABLE ${Python_EXECUTABLE})
-    endif()
-    find_package(Python3 COMPONENTS Interpreter QUIET)
+# use default (or custom) Python executable, if version is sufficient
+if(Python_VERSION VERSION_GREATER_EQUAL 3.6)
+  set(Python3_EXECUTABLE ${Python_EXECUTABLE})
 endif()
+find_package(Python3 COMPONENTS Interpreter)
 
 if(Python3_EXECUTABLE)
-    if(Python3_VERSION VERSION_GREATER_EQUAL 3.5)
+    if(Python3_VERSION VERSION_GREATER_EQUAL 3.6)
         add_custom_target(
           check-whitespace
           ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/whitespace.py .
diff --git a/cmake/Modules/Documentation.cmake b/cmake/Modules/Documentation.cmake
index 0b01407cd9..df9bf2b449 100644
--- a/cmake/Modules/Documentation.cmake
+++ b/cmake/Modules/Documentation.cmake
@@ -5,25 +5,19 @@ option(BUILD_DOC "Build LAMMPS HTML documentation" OFF)
 
 if(BUILD_DOC)
   # Current Sphinx versions require at least Python 3.8
-  if(CMAKE_VERSION VERSION_LESS 3.12)
-    find_package(PythonInterp 3.8 REQUIRED)
-    set(VIRTUALENV ${PYTHON_EXECUTABLE} -m venv)
-  else()
-    # use default (or custom) Python executable, if version is sufficient
-    if(Python_VERSION VERSION_GREATER_EQUAL 3.8)
-      set(Python3_EXECUTABLE ${Python_EXECUTABLE})
-    endif()
-    find_package(Python3 REQUIRED COMPONENTS Interpreter)
-    if(Python3_VERSION VERSION_LESS 3.8)
-      message(FATAL_ERROR "Python 3.8 and up is required to build the HTML documentation")
-    endif()
-    set(VIRTUALENV ${Python3_EXECUTABLE} -m venv)
+  # use default (or custom) Python executable, if version is sufficient
+  if(Python_VERSION VERSION_GREATER_EQUAL 3.8)
+    set(Python3_EXECUTABLE ${Python_EXECUTABLE})
   endif()
+  find_package(Python3 REQUIRED COMPONENTS Interpreter)
+  if(Python3_VERSION VERSION_LESS 3.8)
+    message(FATAL_ERROR "Python 3.8 and up is required to build the HTML documentation")
+  endif()
+  set(VIRTUALENV ${Python3_EXECUTABLE} -m venv)
+
   find_package(Doxygen 1.8.10 REQUIRED)
-
   file(GLOB DOC_SOURCES ${CONFIGURE_DEPENDS} ${LAMMPS_DOC_DIR}/src/[^.]*.rst)
 
-
   add_custom_command(
     OUTPUT docenv
     COMMAND ${VIRTUALENV} docenv
diff --git a/cmake/Modules/FindCythonize.cmake b/cmake/Modules/FindCythonize.cmake
index 97f0304279..fe436aef28 100644
--- a/cmake/Modules/FindCythonize.cmake
+++ b/cmake/Modules/FindCythonize.cmake
@@ -7,15 +7,7 @@
 # adapted from https://github.com/cmarshall108/cython-cmake-example/blob/master/cmake/FindCython.cmake
 #=============================================================================
 
-if(CMAKE_VERSION VERSION_LESS 3.12)
-    set(Python_ADDITIONAL_VERSIONS 3.12 3.11 3.10 3.9 3.8 3.7 3.6)
-    find_package(PythonInterp 3.6 QUIET) # Deprecated since version 3.12
-    if(PYTHONINTERP_FOUND)
-        set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-    endif()
-else()
-    find_package(Python 3.6 COMPONENTS Interpreter QUIET)
-endif()
+find_package(Python 3.6 COMPONENTS Interpreter QUIET)
 
 # Use the Cython executable that lives next to the Python executable
 # if it is a local installation.
diff --git a/cmake/Modules/Packages/KIM.cmake b/cmake/Modules/Packages/KIM.cmake
index 995d2d9490..d724ec18fc 100644
--- a/cmake/Modules/Packages/KIM.cmake
+++ b/cmake/Modules/Packages/KIM.cmake
@@ -1,12 +1,7 @@
 set(KIM-API_MIN_VERSION 2.1.3)
 find_package(CURL)
 if(CURL_FOUND)
-  if(CMAKE_VERSION VERSION_LESS 3.12)
-    target_include_directories(lammps PRIVATE ${CURL_INCLUDE_DIRS})
-    target_link_libraries(lammps PRIVATE ${CURL_LIBRARIES})
-  else()
-    target_link_libraries(lammps PRIVATE CURL::libcurl)
-  endif()
+  target_link_libraries(lammps PRIVATE CURL::libcurl)
   target_compile_definitions(lammps PRIVATE -DLMP_KIM_CURL)
   set(LMP_DEBUG_CURL OFF CACHE STRING "Set libcurl verbose mode on/off. If on, it displays a lot of verbose information about its operations.")
   mark_as_advanced(LMP_DEBUG_CURL)
diff --git a/cmake/Modules/Packages/MDI.cmake b/cmake/Modules/Packages/MDI.cmake
index dc3af94a0a..447b941d99 100644
--- a/cmake/Modules/Packages/MDI.cmake
+++ b/cmake/Modules/Packages/MDI.cmake
@@ -26,29 +26,9 @@ if(DOWNLOAD_MDI)
 
   # detect if we have python development support and thus can enable python plugins
   set(MDI_USE_PYTHON_PLUGINS OFF)
-  if(CMAKE_VERSION VERSION_LESS 3.12)
-    if(NOT PYTHON_VERSION_STRING)
-      set(Python_ADDITIONAL_VERSIONS 3.12 3.11 3.10 3.9 3.8 3.7 3.6)
-      # search for interpreter first, so we have a consistent library
-      find_package(PythonInterp) # Deprecated since version 3.12
-      if(PYTHONINTERP_FOUND)
-        set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-      endif()
-    endif()
-    # search for the library matching the selected interpreter
-    set(Python_ADDITIONAL_VERSIONS ${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR})
-    find_package(PythonLibs QUIET) # Deprecated since version 3.12
-    if(PYTHONLIBS_FOUND)
-      if(NOT (PYTHON_VERSION_STRING STREQUAL PYTHONLIBS_VERSION_STRING))
-        message(FATAL_ERROR "Python Library version ${PYTHONLIBS_VERSION_STRING} does not match Interpreter version ${PYTHON_VERSION_STRING}")
-      endif()
-      set(MDI_USE_PYTHON_PLUGINS ON)
-    endif()
-  else()
-    find_package(Python QUIET COMPONENTS Development)
-    if(Python_Development_FOUND)
-      set(MDI_USE_PYTHON_PLUGINS ON)
-    endif()
+  find_package(Python QUIET COMPONENTS Development)
+  if(Python_Development_FOUND)
+    set(MDI_USE_PYTHON_PLUGINS ON)
   endif()
   # python plugins are not supported and thus must be always off on Windows
   if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
@@ -102,13 +82,9 @@ if(DOWNLOAD_MDI)
   # if compiling with python plugins we need
   # to add python libraries as dependency.
   if(MDI_USE_PYTHON_PLUGINS)
-    if(CMAKE_VERSION VERSION_LESS 3.12)
-      list(APPEND MDI_DEP_LIBS ${PYTHON_LIBRARIES})
-    else()
-      list(APPEND MDI_DEP_LIBS Python::Python)
-    endif()
-
+    list(APPEND MDI_DEP_LIBS Python::Python)
   endif()
+
   # need to add support for dlopen/dlsym, except when compiling for Windows.
   if(NOT (CMAKE_SYSTEM_NAME STREQUAL "Windows"))
     list(APPEND MDI_DEP_LIBS "${CMAKE_DL_LIBS}")
diff --git a/cmake/Modules/Packages/ML-IAP.cmake b/cmake/Modules/Packages/ML-IAP.cmake
index f8439be538..2e9a02977d 100644
--- a/cmake/Modules/Packages/ML-IAP.cmake
+++ b/cmake/Modules/Packages/ML-IAP.cmake
@@ -2,12 +2,7 @@
 set(MLIAP_ENABLE_PYTHON_DEFAULT OFF)
 if(PKG_PYTHON)
   find_package(Cythonize QUIET)
-  if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.14)
-    find_package(Python COMPONENTS NumPy QUIET)
-  else()
-    # assume we have NumPy
-    set(Python_NumPy_FOUND ON)
-  endif()
+  find_package(Python COMPONENTS NumPy QUIET)
   if(Cythonize_FOUND AND Python_NumPy_FOUND)
     set(MLIAP_ENABLE_PYTHON_DEFAULT ON)
   endif()
@@ -17,20 +12,12 @@ option(MLIAP_ENABLE_PYTHON "Build ML-IAP package with Python support" ${MLIAP_EN
 
 if(MLIAP_ENABLE_PYTHON)
   find_package(Cythonize REQUIRED)
-  if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.14)
-    find_package(Python COMPONENTS NumPy REQUIRED)
-  endif()
+  find_package(Python COMPONENTS NumPy REQUIRED)
   if(NOT PKG_PYTHON)
     message(FATAL_ERROR "Must enable PYTHON package for including Python support in ML-IAP")
   endif()
-  if(CMAKE_VERSION VERSION_LESS 3.12)
-    if(PYTHONLIBS_VERSION_STRING VERSION_LESS 3.6)
-      message(FATAL_ERROR "Python support in ML-IAP requires Python 3.6 or later")
-    endif()
-  else()
-    if(Python_VERSION VERSION_LESS 3.6)
-      message(FATAL_ERROR "Python support in ML-IAP requires Python 3.6 or later")
-    endif()
+  if(Python_VERSION VERSION_LESS 3.6)
+    message(FATAL_ERROR "Python support in ML-IAP requires Python 3.6 or later")
   endif()
 
   set(MLIAP_BINARY_DIR ${CMAKE_BINARY_DIR}/cython)
diff --git a/cmake/Modules/Packages/PYTHON.cmake b/cmake/Modules/Packages/PYTHON.cmake
index 4a2925fe31..59260e39d5 100644
--- a/cmake/Modules/Packages/PYTHON.cmake
+++ b/cmake/Modules/Packages/PYTHON.cmake
@@ -1,29 +1,11 @@
-if(CMAKE_VERSION VERSION_LESS 3.12)
-  if(NOT PYTHON_VERSION_STRING)
-    set(Python_ADDITIONAL_VERSIONS 3.12 3.11 3.10 3.9 3.8 3.7 3.6)
-    # search for interpreter first, so we have a consistent library
-    find_package(PythonInterp) # Deprecated since version 3.12
-    if(PYTHONINTERP_FOUND)
-      set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-    endif()
+
+if(NOT Python_INTERPRETER)
+  # backward compatibility
+  if(PYTHON_EXECUTABLE)
+    set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
   endif()
-  # search for the library matching the selected interpreter
-  set(Python_ADDITIONAL_VERSIONS ${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR})
-  find_package(PythonLibs REQUIRED) # Deprecated since version 3.12
-  if(NOT (PYTHON_VERSION_STRING STREQUAL PYTHONLIBS_VERSION_STRING))
-    message(FATAL_ERROR "Python Library version ${PYTHONLIBS_VERSION_STRING} does not match Interpreter version ${PYTHON_VERSION_STRING}")
-  endif()
-  target_include_directories(lammps PRIVATE ${PYTHON_INCLUDE_DIRS})
-  target_link_libraries(lammps PRIVATE ${PYTHON_LIBRARIES})
-else()
-  if(NOT Python_INTERPRETER)
-    # backward compatibility
-    if(PYTHON_EXECUTABLE)
-      set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-    endif()
-    find_package(Python COMPONENTS Interpreter)
-  endif()
-  find_package(Python REQUIRED COMPONENTS Interpreter Development)
-  target_link_libraries(lammps PRIVATE Python::Python)
+  find_package(Python COMPONENTS Interpreter)
 endif()
+find_package(Python REQUIRED COMPONENTS Interpreter Development)
+target_link_libraries(lammps PRIVATE Python::Python)
 target_compile_definitions(lammps PRIVATE -DLMP_PYTHON)
diff --git a/cmake/Modules/Testing.cmake b/cmake/Modules/Testing.cmake
index 5345211178..5bb8b512d3 100644
--- a/cmake/Modules/Testing.cmake
+++ b/cmake/Modules/Testing.cmake
@@ -19,7 +19,7 @@ if(ENABLE_TESTING)
   # we need to build and link a LOT of tester executables, so it is worth checking if
   # a faster linker is available. requires GNU or Clang compiler, newer CMake.
   # also only verified with Fedora Linux > 30 and Ubuntu 18.04 or 22.04+(Ubuntu 20.04 fails)
-  if((CMAKE_SYSTEM_NAME STREQUAL "Linux") AND (CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
+  if((CMAKE_SYSTEM_NAME STREQUAL "Linux")
       AND ((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") OR (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")))
     if(((CMAKE_LINUX_DISTRO STREQUAL "Ubuntu") AND
           ((CMAKE_DISTRO_VERSION VERSION_LESS_EQUAL 18.04) OR (CMAKE_DISTRO_VERSION VERSION_GREATER_EQUAL 22.04)))
@@ -66,16 +66,8 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   option(ENABLE_COVERAGE "Enable collecting code coverage data" OFF)
   mark_as_advanced(ENABLE_COVERAGE)
   if(ENABLE_COVERAGE)
-    if(CMAKE_VERSION VERSION_LESS 3.13)
-      if(CMAKE_CXX_FLAGS)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --coverage")
-      else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_${CMAKE_BUILD_TYPE}_FLAGS} --coverage")
-      endif()
-    else()
-      target_compile_options(lammps PUBLIC --coverage)
-      target_link_options(lammps PUBLIC --coverage)
-    endif()
+    target_compile_options(lammps PUBLIC --coverage)
+    target_link_options(lammps PUBLIC --coverage)
   endif()
 endif()
 
@@ -118,16 +110,8 @@ validate_option(ENABLE_SANITIZER ENABLE_SANITIZER_VALUES)
 string(TOLOWER ${ENABLE_SANITIZER} ENABLE_SANITIZER)
 if(NOT ENABLE_SANITIZER STREQUAL "none")
   if((${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU") OR (${CMAKE_CXX_COMPILER_ID} STREQUAL "Clang"))
-    if(CMAKE_VERSION VERSION_LESS 3.13)
-      if(CMAKE_CXX_FLAGS)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=${ENABLE_SANITIZER}")
-      else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_${CMAKE_BUILD_TYPE}_FLAGS} -fsanitize=${ENABLE_SANITIZER}")
-      endif()
-    else()
-      target_compile_options(lammps PUBLIC -fsanitize=${ENABLE_SANITIZER})
-      target_link_options(lammps PUBLIC -fsanitize=${ENABLE_SANITIZER})
-    endif()
+    target_compile_options(lammps PUBLIC -fsanitize=${ENABLE_SANITIZER})
+    target_link_options(lammps PUBLIC -fsanitize=${ENABLE_SANITIZER})
   else()
     message(WARNING "ENABLE_SANITIZER option not supported by ${CMAKE_CXX_COMPILER_ID} compilers. Ignoring.")
     set(ENABLE_SANITIZER "none")
diff --git a/examples/kim/plugin/CMakeLists.txt b/examples/kim/plugin/CMakeLists.txt
index 367c0b5b78..999214f9b8 100644
--- a/examples/kim/plugin/CMakeLists.txt
+++ b/examples/kim/plugin/CMakeLists.txt
@@ -3,7 +3,7 @@
 # distributed independent from the LAMMPS package.
 ##########################################
 
-cmake_minimum_required(VERSION 3.10)
+cmake_minimum_required(VERSION 3.16)
 
 project(kimplugin VERSION 1.0 LANGUAGES CXX)
 
@@ -30,12 +30,7 @@ target_link_libraries(kimplugin PRIVATE KIM-API::kim-api)
 # need libcurl
 find_package(CURL)
 if(CURL_FOUND)
-  if(CMAKE_VERSION VERSION_LESS 3.12)
-    target_include_directories(kimplugin PRIVATE ${CURL_INCLUDE_DIRS})
-    target_link_libraries(kimplugin PRIVATE ${CURL_LIBRARIES})
-  else()
-    target_link_libraries(kimplugin PRIVATE CURL::libcurl)
-  endif()
+  target_link_libraries(kimplugin PRIVATE CURL::libcurl)
   target_compile_definitions(kimplugin PRIVATE -DLMP_KIM_CURL)
   set(LMP_DEBUG_CURL OFF CACHE STRING "Set libcurl verbose mode on/off. If on, it displays a lot of verbose information about its operations.")
   mark_as_advanced(LMP_DEBUG_CURL)
diff --git a/unittest/CMakeLists.txt b/unittest/CMakeLists.txt
index cad6c3213c..ba80e654bb 100644
--- a/unittest/CMakeLists.txt
+++ b/unittest/CMakeLists.txt
@@ -35,11 +35,7 @@ endforeach()
 
 # must repeat handling coverage for older CMake
 if((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") AND ENABLE_COVERAGE)
-  if(CMAKE_VERSION VERSION_LESS 3.13)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --coverage")
-  else()
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_${CMAKE_BUILD_TYPE}_FLAGS} --coverage")
-  endif()
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_${CMAKE_BUILD_TYPE}_FLAGS} --coverage")
 endif()
 
 ########################################
diff --git a/unittest/force-styles/CMakeLists.txt b/unittest/force-styles/CMakeLists.txt
index 5742bb6436..21a1bd3eda 100644
--- a/unittest/force-styles/CMakeLists.txt
+++ b/unittest/force-styles/CMakeLists.txt
@@ -20,16 +20,7 @@ function(extract_tags out yaml_file)
   set(${out} "${TAGS}" PARENT_SCOPE)
 endfunction()
 
-if(CMAKE_VERSION VERSION_LESS 3.12)
-  # adjust so we find Python 3 versions before Python 2 on old systems with old CMake
-  set(Python_ADDITIONAL_VERSIONS 3.8 3.7 3.6 3.5)
-  find_package(PythonInterp) # Deprecated since version 3.12
-  if(PYTHONINTERP_FOUND)
-    set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-  endif()
-else()
-  find_package(Python COMPONENTS Interpreter)
-endif()
+find_package(Python COMPONENTS Interpreter)
 if(Python_EXECUTABLE)
   add_custom_target(check-tests
     ${Python_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/check_tests.py
@@ -54,10 +45,8 @@ target_link_libraries(style_tests PUBLIC GTest::GMock Yaml::Yaml lammps)
 
 # propagate sanitizer options to test tools
 if(ENABLE_SANITIZER AND (NOT (ENABLE_SANITIZER STREQUAL "none")))
-  if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
-    target_compile_options(style_tests PUBLIC -fsanitize=${ENABLE_SANITIZER})
-    target_link_options(style_tests PUBLIC -fsanitize=${ENABLE_SANITIZER})
-  endif()
+  target_compile_options(style_tests PUBLIC -fsanitize=${ENABLE_SANITIZER})
+  target_link_options(style_tests PUBLIC -fsanitize=${ENABLE_SANITIZER})
 endif()
 
 # unit test for error stats class
diff --git a/unittest/python/CMakeLists.txt b/unittest/python/CMakeLists.txt
index fd18d7463d..ed56841733 100644
--- a/unittest/python/CMakeLists.txt
+++ b/unittest/python/CMakeLists.txt
@@ -12,20 +12,12 @@ if(NOT BUILD_SHARED_LIBS)
   return()
 endif()
 
-if(CMAKE_VERSION VERSION_LESS 3.12)
-  find_package(PythonInterp 3.6) # Deprecated since version 3.12
-  if(PYTHONINTERP_FOUND)
-    set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-  endif()
-else()
-  find_package(Python COMPONENTS Interpreter Development)
-endif()
+find_package(Python 3.6 COMPONENTS Interpreter Development)
 
 if(PKG_PYTHON)
   add_executable(test_python_package test_python_package.cpp)
   target_link_libraries(test_python_package PRIVATE lammps GTest::GMock)
   target_compile_definitions(test_python_package PRIVATE -DTEST_INPUT_FOLDER=${TEST_INPUT_FOLDER})
-  # this requires CMake 3.12. don't care to add backward compatibility for this.
   if(Python_Development_FOUND)
     target_compile_definitions(test_python_package PRIVATE -DTEST_HAVE_PYTHON_DEVELOPMENT=1)
     target_link_libraries(test_python_package PRIVATE Python::Python)
diff --git a/unittest/tools/CMakeLists.txt b/unittest/tools/CMakeLists.txt
index 15576c60c1..7a496722d2 100644
--- a/unittest/tools/CMakeLists.txt
+++ b/unittest/tools/CMakeLists.txt
@@ -1,14 +1,8 @@
 # -*- CMake -*- file for tests of utily functions and classes in LAMMPS
 
 # we use python 3's subprocess module to run the tools and check the output
-if(CMAKE_VERSION VERSION_LESS 3.12)
-  find_package(PythonInterp 3.5) # Deprecated since version 3.12
-  if(PYTHONINTERP_FOUND)
-    set(Python_EXECUTABLE ${PYTHON_EXECUTABLE})
-  endif()
-else()
-  find_package(Python 3.5 COMPONENTS Interpreter)
-endif()
+find_package(Python 3.6 COMPONENTS Interpreter)
+
 get_property(BUILD_IS_MULTI_CONFIG GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
 if(BUILD_IS_MULTI_CONFIG)
   set(LAMMPS_SHELL_EXE_DIR ${CMAKE_BINARY_DIR}/$<CONFIG>)