From 11341a5b6651cbdab242a6ea1a195fc3357fe55b Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 10 Feb 2021 08:57:14 -0500
Subject: [PATCH] enforce documented Python version requirement for MLIAP with
 Python

---
 cmake/Modules/Packages/MLIAP.cmake | 11 ++++++++++-
 doc/src/Packages_details.rst       |  4 ++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/cmake/Modules/Packages/MLIAP.cmake b/cmake/Modules/Packages/MLIAP.cmake
index d3f601a1e1..81bb10cb8f 100644
--- a/cmake/Modules/Packages/MLIAP.cmake
+++ b/cmake/Modules/Packages/MLIAP.cmake
@@ -1,7 +1,7 @@
 # if PYTHON package is included we may also include Python support in MLIAP
 set(MLIAP_ENABLE_PYTHON_DEFAULT OFF)
 if(PKG_PYTHON)
-  find_package(Cythonize)
+  find_package(Cythonize QUIET)
   if(Cythonize_FOUND)
     set(MLIAP_ENABLE_PYTHON_DEFAULT ON)
   endif()
@@ -14,6 +14,15 @@ if(MLIAP_ENABLE_PYTHON)
   if(NOT PKG_PYTHON)
     message(FATAL_ERROR "Must enable PYTHON package for including Python support in MLIAP")
   endif()
+  if(CMAKE_VERSION VERSION_LESS 3.12)
+    if(PYTHONLIBS_VERSION_STRING VERSION_LESS 3.6)
+      message(FATAL_ERROR "Python support in MLIAP requires Python 3.6 or later")
+    endif()
+  else()
+    if(Python_VERSION VERSION_LESS 3.6)
+      message(FATAL_ERROR "Python support in MLIAP requires Python 3.6 or later")
+    endif()
+  endif()
 
   set(MLIAP_BINARY_DIR ${CMAKE_BINARY_DIR}/cython)
   set(MLIAP_CYTHON_SRC ${LAMMPS_SOURCE_DIR}/MLIAP/mliap_model_python_couple.pyx)
diff --git a/doc/src/Packages_details.rst b/doc/src/Packages_details.rst
index e044adfcb3..455df083e4 100644
--- a/doc/src/Packages_details.rst
+++ b/doc/src/Packages_details.rst
@@ -668,8 +668,8 @@ A general interface for machine-learning interatomic potentials, including PyTor
 
 To use this package, also the :ref:`SNAP package <PKG-SNAP>` package needs
 to be installed.  To make the *mliappy* model available, also the
-:ref:`PYTHON package <PKG-PYTHON>` package needs to be installed, the version of
-Python must be 3.6 or later, and the `cython <https://cython.org/>`_ software
+:ref:`PYTHON package <PKG-PYTHON>` package needs to be installed, the version
+of Python must be 3.6 or later, and the `cython <https://cython.org/>`_ software
 must be installed.
 
 **Author:** Aidan Thompson (Sandia), Nicholas Lubbers (LANL).