From b188cdc0444a5167a1329c34af81a51fe71be327 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Fri, 7 Feb 2025 20:51:50 -0500
Subject: [PATCH] add check for Python version. Require minimum of Python 3.6
 (Sphinx requires 3.8)

---
 cmake/CMakeLists.txt                |  6 +++
 cmake/Modules/CodingStandard.cmake  | 67 ++++++++++++++---------------
 cmake/Modules/Packages/ML-IAP.cmake |  4 +-
 3 files changed, 40 insertions(+), 37 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index ff0d69e316..63dc1a08a4 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -225,6 +225,12 @@ if(DEFINED ENV{VIRTUAL_ENV} AND NOT Python_EXECUTABLE)
     "   Setting Python interpreter to: ${Python_EXECUTABLE}")
 endif()
 
+find_package(Python COMPONENTS Interpreter QUIET)
+# NOTE: RHEL 8.0 and Ubuntu 18.04LTS ship with Python 3.6, Python 3.8 was EOL in 2024
+if(Python_VERSION VERSION_LESS 3.6)
+  message(FATAL_ERROR "LAMMPS requires Python 3.6 or later")
+endif()
+
 set(LAMMPS_MACHINE "" CACHE STRING "Suffix to append to lmp binary (WON'T enable any features automatically")
 mark_as_advanced(LAMMPS_MACHINE)
 if(LAMMPS_MACHINE)
diff --git a/cmake/Modules/CodingStandard.cmake b/cmake/Modules/CodingStandard.cmake
index 94639c7771..4e99c2e39c 100644
--- a/cmake/Modules/CodingStandard.cmake
+++ b/cmake/Modules/CodingStandard.cmake
@@ -1,40 +1,39 @@
-# use default (or custom) Python executable, if version is sufficient
-if(Python_VERSION VERSION_GREATER_EQUAL 3.6)
+# use default (or custom) Python executable.
+# Python version check is in main CMakeLists.txt file
+if(Python_EXECUTABLE)
   set(Python3_EXECUTABLE ${Python_EXECUTABLE})
 endif()
 find_package(Python3 COMPONENTS Interpreter)
 
 if(Python3_EXECUTABLE)
-    if(Python3_VERSION VERSION_GREATER_EQUAL 3.6)
-        add_custom_target(
-          check-whitespace
-          ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/whitespace.py .
-          WORKING_DIRECTORY  ${LAMMPS_DIR}
-          COMMENT "Check for whitespace errors")
-        add_custom_target(
-          check-homepage
-          ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/homepage.py .
-          WORKING_DIRECTORY  ${LAMMPS_DIR}
-          COMMENT "Check for homepage URL errors")
-        add_custom_target(
-          check-permissions
-          ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/permissions.py .
-          WORKING_DIRECTORY  ${LAMMPS_DIR}
-          COMMENT "Check for permission errors")
-        add_custom_target(
-          fix-whitespace
-          ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/whitespace.py -f .
-          WORKING_DIRECTORY  ${LAMMPS_DIR}
-          COMMENT "Fix whitespace errors")
-        add_custom_target(
-          fix-homepage
-          ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/homepage.py -f .
-          WORKING_DIRECTORY  ${LAMMPS_DIR}
-          COMMENT "Fix homepage URL errors")
-        add_custom_target(
-          fix-permissions
-          ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/permissions.py -f .
-          WORKING_DIRECTORY  ${LAMMPS_DIR}
-          COMMENT "Fix permission errors")
-    endif()
+  add_custom_target(
+    check-whitespace
+    ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/whitespace.py .
+    WORKING_DIRECTORY  ${LAMMPS_DIR}
+    COMMENT "Check for whitespace errors")
+  add_custom_target(
+    check-homepage
+    ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/homepage.py .
+    WORKING_DIRECTORY  ${LAMMPS_DIR}
+    COMMENT "Check for homepage URL errors")
+  add_custom_target(
+    check-permissions
+    ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/permissions.py .
+    WORKING_DIRECTORY  ${LAMMPS_DIR}
+    COMMENT "Check for permission errors")
+  add_custom_target(
+    fix-whitespace
+    ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/whitespace.py -f .
+    WORKING_DIRECTORY  ${LAMMPS_DIR}
+    COMMENT "Fix whitespace errors")
+  add_custom_target(
+    fix-homepage
+    ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/homepage.py -f .
+    WORKING_DIRECTORY  ${LAMMPS_DIR}
+    COMMENT "Fix homepage URL errors")
+  add_custom_target(
+    fix-permissions
+    ${Python3_EXECUTABLE} ${LAMMPS_TOOLS_DIR}/coding_standard/permissions.py -f .
+    WORKING_DIRECTORY  ${LAMMPS_DIR}
+    COMMENT "Fix permission errors")
 endif()
diff --git a/cmake/Modules/Packages/ML-IAP.cmake b/cmake/Modules/Packages/ML-IAP.cmake
index 91b772efb5..1691af8d95 100644
--- a/cmake/Modules/Packages/ML-IAP.cmake
+++ b/cmake/Modules/Packages/ML-IAP.cmake
@@ -24,9 +24,7 @@ if(MLIAP_ENABLE_PYTHON)
   if(NOT PKG_PYTHON)
     message(FATAL_ERROR "Must enable PYTHON package for including Python support in ML-IAP")
   endif()
-  if(Python_VERSION VERSION_LESS 3.6)
-    message(FATAL_ERROR "Python support in ML-IAP requires Python 3.6 or later")
-  endif()
+  # Python version check is in main CMakeLists.txt file
 
   set(MLIAP_BINARY_DIR ${CMAKE_BINARY_DIR}/cython)
   file(GLOB MLIAP_CYTHON_SRC CONFIGURE_DEPENDS ${LAMMPS_SOURCE_DIR}/ML-IAP/*.pyx)