From 2bf633b973bd71426b5d243d250a18559113a00f Mon Sep 17 00:00:00 2001
From: Rupert Nash <r.nash@epcc.ed.ac.uk>
Date: Tue, 19 Dec 2023 21:27:33 +0000
Subject: [PATCH] Tidy MPI CMake

---
 Code/CMakeLists.txt  |  7 ++++++-
 Code/cmake/mpi.cmake | 12 ------------
 2 files changed, 6 insertions(+), 13 deletions(-)
 delete mode 100644 Code/cmake/mpi.cmake

diff --git a/Code/CMakeLists.txt b/Code/CMakeLists.txt
index 8d13e45f1..f08dc2c71 100644
--- a/Code/CMakeLists.txt
+++ b/Code/CMakeLists.txt
@@ -55,8 +55,11 @@ include(platform_checks)
 include(codesign)
 include(HemeLbDependency)
 
+# We do NOT want the removed MPI 2 C++ bindings
+# Requesting MPI 3 should be enough, but some configurations of
+# e.g. OpenMPI enable them for C++ by default to be "helpful".
 set(MPI_CXX_SKIP_MPICXX ON)
-find_package(MPI REQUIRED CXX)
+find_package(MPI 3 REQUIRED CXX)
 
 find_hemelb_dependency(Boost REQUIRED)
 find_hemelb_dependency(tinyxml2 REQUIRED)
@@ -65,6 +68,8 @@ find_hemelb_dependency(CTemplate REQUIRED)
 find_hemelb_dependency(ZLIB REQUIRED)
 
 # MPI and boost should always be available
+# Note this is NOT the C++ bindings, this is the C bindings from C++
+# (ensures helpful MPI implementations do not sneak the MPI 2 C++ bindings back in)
 link_libraries(MPI::MPI_CXX)
 link_libraries(Boost::headers)
 
diff --git a/Code/cmake/mpi.cmake b/Code/cmake/mpi.cmake
deleted file mode 100644
index c4d57f6de..000000000
--- a/Code/cmake/mpi.cmake
+++ /dev/null
@@ -1,12 +0,0 @@
-# This file is part of HemeLB and is Copyright (C)
-# the HemeLB team and/or their institutions, as detailed in the
-# file AUTHORS. This software is provided under the terms of the
-# license in the file LICENSE.
-include_guard()
-
-# ------MPI------------------
-# Require MPI for this project:
-find_package(MPI REQUIRED)
-set(CMAKE_CXX_COMPILE_FLAGS "${CMAKE_CXX_COMPILE_FLAGS} ${MPI_COMPILE_FLAGS}")
-set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} ${CMAKE_CXX_LINK_FLAGS}")
-include_directories(${MPI_INCLUDE_PATH})