From 171e439bd400143b15e5e4ec057155bde3cef0bc Mon Sep 17 00:00:00 2001
From: Rodrigo Arias <rodrigo.arias@bsc.es>
Date: Fri, 14 Apr 2023 13:14:52 +0200
Subject: [PATCH] Allow builds without MPI with -DUSE_MPI=OFF

---
 .gitlab-ci.yml         |  7 +++++++
 nix/rt.nix             |  6 ++++++
 src/emu/CMakeLists.txt | 23 ++++++++++++++---------
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 7c0106b..5002cca 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -21,6 +21,13 @@ build:rt-tests:
   script:
     - nix build -L --tarball-ttl 0 --file nix/rt.nix bsc.ovni-rt
 
+build:no-mpi:
+  stage: build
+  tags:
+    - nix
+  script:
+    - nix build -L --tarball-ttl 0 --file nix/rt.nix bsc.ovni-nompi
+
 build:old-gcc:
   stage: build
   tags:
diff --git a/nix/rt.nix b/nix/rt.nix
index 681c99e..d5e2780 100644
--- a/nix/rt.nix
+++ b/nix/rt.nix
@@ -155,6 +155,12 @@ let
         export NODES_HOME="${last.nodes}"
       '';
     });
+
+    ovni-nompi = last.ovni.overrideAttrs (old: {
+      buildInputs = pkgs.lib.filter (x: x != last.mpi ) old.buildInputs;
+      cmakeFlags = old.cmakeFlags ++ [ "-DUSE_MPI=OFF" ];
+    });
+
   });
 
 in
diff --git a/src/emu/CMakeLists.txt b/src/emu/CMakeLists.txt
index 5b7a518..29c7762 100644
--- a/src/emu/CMakeLists.txt
+++ b/src/emu/CMakeLists.txt
@@ -66,14 +66,19 @@ target_link_libraries(ovnidump emu parson-static ovni-static)
 add_executable(ovnisort ovnisort.c)
 target_link_libraries(ovnisort emu parson-static ovni-static)
 
-# Use <PackageName>_ROOT variables if available, commonly used by MPI
-# installations
-if(POLICY CMP0074)
-  cmake_policy(SET CMP0074 NEW)
+set(USE_MPI ON CACHE BOOL "Use MPI (required by ovnisync)")
+if(USE_MPI)
+  # Use <PackageName>_ROOT variables if available, commonly used by MPI
+  # installations
+  if(POLICY CMP0074)
+    cmake_policy(SET CMP0074 NEW)
+  endif()
+  find_package(MPI REQUIRED)
+  add_executable(ovnisync ovnisync.c)
+  target_link_libraries(ovnisync m MPI::MPI_C)
+  install(TARGETS ovnisync RUNTIME DESTINATION bin)
+else()
+  message(STATUS "Disabling ovnisync as MPI is disabled")
 endif()
 
-find_package(MPI REQUIRED)
-add_executable(ovnisync ovnisync.c)
-target_link_libraries(ovnisync m MPI::MPI_C)
-
-install(TARGETS ovniemu ovnidump ovnisync ovnisort RUNTIME DESTINATION bin)
+install(TARGETS ovniemu ovnidump ovnisort RUNTIME DESTINATION bin)