Enable usage of fmtlib on the system.

If fmtlib is present on the system we used that one
in the normal mode (not header only). Otherwise we
fallback to the embedded one header only.

CMakeLists.txt

@@ -64,6 +64,20 @@ include(Findopm-tests)
 # with the find module
 include (${project}-prereqs)
 
+if(ENABLE_ECL_INPUT)
+  # source_hook runs before config_hook and the former needs fmt, hence this
+  # needs to be here.
+  if(fmt_FOUND)
+    # OpmSatellites will not add the library, do it here.
+    list(APPEND opm-common_LIBRARIES fmt::fmt)
+  else()
+    add_definitions(-DFMT_HEADER_ONLY)
+    include_directories(SYSTEM ${PROJECT_SOURCE_DIR}/external/fmtlib/include)
+    # Not sure why this is needed.
+    list(APPEND EXTRA_INCLUDES ${PROJECT_SOURCE_DIR}/external/fmtlib/include)
+  endif()
+endif()
+
 # read the list of components from this file (in the project directory);
 # it should set various lists with the names of the files to include
 include (CMakeLists_files.cmake)
@@ -75,11 +89,7 @@ macro (config_hook)
     endif()
 
     # For this project
-    add_definitions(-DFMT_HEADER_ONLY)
-    include_directories(SYSTEM ${PROJECT_SOURCE_DIR}/external/fmtlib/include)
     include_directories(${EXTRA_INCLUDES} ${PROJECT_BINARY_DIR}/include)
-    list(APPEND EXTRA_INCLUDES ${PROJECT_SOURCE_DIR}/external/fmtlib/include)
-
     # For downstreams
     list(APPEND EXTRA_INCLUDES ${PROJECT_BINARY_DIR}/include)
     set(OPM_PROJECT_EXTRA_CODE_INTREE "${OPM_PROJECT_EXTRA_CODE_INTREE}

opm-common-prereqs.cmake

@@ -17,6 +17,10 @@ list(APPEND opm-common_DEPS
       "Boost 1.44.0 COMPONENTS system unit_test_framework REQUIRED"
       "OpenMP QUIET"
       "cjson"
+      # Still it produces compile errors complaining that it
+      # cannot format UDQVarType. Hence we use the same version
+      # as the embedded one.
+      "fmt 7.0.3"
 )
 
 find_package_deps(opm-common)