feat: export samurai CMake options (#224)

## Description
samurai options are exported so that calling projects can enable/disable
them

-  through the `ccmake` command,
- in the `cmake` command line:
```bash
cmake -DSAMURAI_[OPTIONNAME]=ON ..
```
- or in the project's `CMakeLists.txt`:
```cmake
set(SAMURAI_[OPTIONNAME] On)
```
Examples of options: `SAMURAI_WITH_MPI`, `SAMURAI_WITH_OPENMP`,
`SAMURAI_CHECK_NAN`.

## Code of Conduct
By submitting this PR, you agree to follow our [Code of
Conduct](https://github.com/hpc-maths/samurai/blob/master/docs/CODE_OF_CONDUCT.md)
- [x] I agree to follow this project's Code of Conduct

CMakeLists.txt

@@ -135,6 +135,9 @@ if(${WITH_OPENMP})
 endif()
 
 if(${WITH_MPI})
+  if (NOT HDF5_IS_PARALLEL)
+    message(FATAL_ERROR "HDF5 is not parallel. Please install a parallel version.")
+  endif()
   find_package(Boost REQUIRED COMPONENTS serialization mpi)
   target_link_system_libraries(
     samurai
@@ -193,3 +196,7 @@ package_project(
   INTERFACE_DEPENDENCIES_CONFIGURED ${DEPENDENCIES_CONFIGURED}
   INTERFACE_INCLUDES ${INCLUDE_DIR}
 )
+
+# Append the content of the file cmake/samuraiConfig.cmake.in to the samurai.Config.cmake generated by the function `package_project`
+file(READ ${CMAKE_CURRENT_SOURCE_DIR}/cmake/samuraiConfig.cmake.in CONFIG_TO_APPEND)
+file(APPEND "${CMAKE_BINARY_DIR}/CMakeFiles/samuraiConfig.cmake.install" ${CONFIG_TO_APPEND})

README.md

@@ -222,18 +222,24 @@ The [tutorial](./demos/tutorial/) directory is a good first step followed by the
 mamba install samurai
 ```
 
-If you want to compile your scripts, you also have to install a C++ compiler and cmake.
+For compiling purposes, you have to install a C++ compiler, `cmake`, and (optionaly) `make`:
 
 ```bash
-mamba install cxx-compiler cmake
+mamba install cxx-compiler cmake [make]
 ```
 
-And finally, if you have to use PETSc to assemble the matrix of your problem, you need to install it
+If you have to use PETSc to assemble the matrix of your problem, you need to install it:
 
 ```bash
 mamba install petsc pkg-config
 ```
 
+For parallel computation,
+
+```bash
+mamba install libboost-mpi libboost-devel libboost-headers 'hdf5=*=mpi*'
+```
+
 ### From Conan Center
 
 If you want to install samurai from Conan, you can use the following command:
@@ -248,13 +254,24 @@ Run the cmake configuration
 
 - With mamba or conda
 
-    First, you need to create the environment with all the dependencies installed
+    First, you need to create the environment with all the dependencies
+    installed, run
 
     ```bash
     mamba env create --file conda/environment.yml
-    mamba activate samurai-env
     ```
 
+    for sequential computation, or
+
+    ```bash
+    mamba env create --file conda/mpi-environment.yml
+    ```
+
+    for parallel computation. Then
+
+    ```bash
+    mamba activate samurai-env
+    ```
 
     ```bash
     cmake . -B build -DCMAKE_BUILD_TYPE=Release -DBUILD_DEMOS=ON
@@ -278,6 +295,22 @@ Build the demos
 cmake --build ./build --config Release
 ```
 
+## CMake configuration
+
+Here is a minimal example of `CMakeLists.txt`:
+
+```cmake
+cmake_minimum_required(VERSION 3.15)
+set(CMAKE_CXX_STANDARD 17)
+
+project(my_samurai_project CXX)
+
+find_package(samurai CONFIG REQUIRED)
+
+add_executable(my_samurai_project main.cpp)
+target_link_libraries(my_samurai_project PRIVATE samurai::samurai samurai::libdeps)
+```
+
 ## Get help
 
 For a better understanding of all the components of samurai, you can consult the documentation https://hpc-math-samurai.readthedocs.io.

cmake/samuraiConfig.cmake.in

@@ -0,0 +1,38 @@
+
+option(SAMURAI_WITH_OPENMP "Enable OpenMP" OFF)
+if(${SAMURAI_WITH_OPENMP})
+    find_dependency(OpenMP)
+    if(OpenMP_CXX_FOUND)
+        target_link_libraries(samurai::samurai INTERFACE OpenMP::OpenMP_CXX)
+        target_compile_definitions(samurai::samurai INTERFACE SAMURAI_WITH_OPENMP)
+    else()
+        message(FATAL_ERROR "OpenMP not found")
+    endif()
+endif()
+
+
+option(SAMURAI_WITH_MPI "Enable MPI" OFF)
+if(SAMURAI_WITH_MPI)
+  if (NOT HDF5_IS_PARALLEL)
+    message(FATAL_ERROR "HDF5 is not parallel. Please install a parallel version.")
+  endif()
+  find_dependency(Boost COMPONENTS serialization mpi)
+  target_link_libraries(samurai::samurai INTERFACE Boost::serialization Boost::mpi)
+  target_compile_definitions(samurai::samurai INTERFACE SAMURAI_WITH_MPI)
+endif()
+
+
+option(SAMURAI_CHECK_NAN "Check NaN in computations" OFF)
+if(SAMURAI_CHECK_NAN)
+  target_compile_definitions(samurai::samurai INTERFACE SAMURAI_CHECK_NAN)
+endif()
+
+
+set(FLUX_CONTAINER_LIST array xtensor)
+set(SAMURAI_FLUX_CONTAINER "xtensor" CACHE STRING "Container to store fluxes: ${FLUX_CONTAINER_LIST}")
+set_property(CACHE SAMURAI_FLUX_CONTAINER PROPERTY STRINGS ${FLUX_CONTAINER_LIST})
+if(NOT SAMURAI_FLUX_CONTAINER IN_LIST FLUX_CONTAINER_LIST)
+    message(FATAL_ERROR "SAMURAI_FLUX_CONTAINER must be one of: ${FLUX_CONTAINER_LIST}")
+else()
+    target_compile_definitions(samurai::samurai INTERFACE FLUX_CONTAINER_${FLUX_CONTAINER})
+endif()