Conditional use of Minuit2 (#320)

If AARE_FETCH_MINUIT is set to OFF we first look for a standalone
Minuit2 and if that is not found we try to find Minuit2 as a part of
ROOT.

In both cases we make an alias to allow for simpler use of the target
later.

It still doesn't solve the issue that we install Minuit to when we fetch
it but that can be addressed in a separate PR.

closes #316

CMakeLists.txt

@@ -150,6 +150,8 @@ else()
 endif()
 
 if(AARE_FETCH_MINUIT2)
+  # We are building Minuit2 from sources.
+
   # Patch minuit2 to avoid messing with cmake policies
   set(MINUIT2_PATCH_COMMAND git apply
                             ${CMAKE_CURRENT_SOURCE_DIR}/patches/minuit2.patch)
@@ -176,8 +178,21 @@ if(AARE_FETCH_MINUIT2)
 
   set_property(TARGET Minuit2Math PROPERTY POSITION_INDEPENDENT_CODE ON)
   set_property(TARGET Minuit2 PROPERTY POSITION_INDEPENDENT_CODE ON)
+
+  add_library(aare::Minuit2 ALIAS Minuit2)
 else()
-  find_package(Minuit2 REQUIRED)
+  find_package(Minuit2 CONFIG QUIET)
+  if(NOT Minuit2_FOUND)
+    message(
+      STATUS
+        "Stand alone Minuit2 not found. Trying to find it as a part of ROOT")
+    find_package(
+      ROOT
+      COMPONENTS Minuit2
+      REQUIRED)
+    add_library(aare::Minuit2 ALIAS ROOT::Minuit2)
+    message(STATUS "Found Minuit2 as a part of ROOT: ${ROOT_DIR}")
+  endif()
 endif()
 
 if(AARE_FETCH_ZMQ)
@@ -436,12 +451,12 @@ target_link_libraries(
   aare_core
   PUBLIC fmt::fmt nlohmann_json::nlohmann_json ${STD_FS_LIB} # from
                                                              # helpers.cmake
-         Minuit2::Minuit2
+         aare::Minuit2
   PRIVATE aare_compiler_flags Threads::Threads $<BUILD_INTERFACE:lmfit>)
 
 target_include_directories(
   aare_core SYSTEM
-  PRIVATE $<TARGET_PROPERTY:Minuit2::Minuit2,INTERFACE_INCLUDE_DIRECTORIES>)
+  PRIVATE $<TARGET_PROPERTY:aare::Minuit2,INTERFACE_INCLUDE_DIRECTORIES>)
 
 set_property(TARGET aare_core PROPERTY POSITION_INDEPENDENT_CODE ON)
 

python/CMakeLists.txt

@@ -29,7 +29,7 @@ target_link_libraries(_aare PRIVATE aare_core aare_compiler_flags)
 
 target_include_directories(
   _aare SYSTEM
-  PRIVATE $<TARGET_PROPERTY:Minuit2::Minuit2,INTERFACE_INCLUDE_DIRECTORIES>)
+  PRIVATE $<TARGET_PROPERTY:aare::Minuit2,INTERFACE_INCLUDE_DIRECTORIES>)
 
 # List of python files to be copied to the build directory
 set(PYTHON_FILES