CMake update to find liblz4 using pkg-config instead of cmake.

CMakeLists.txt

@@ -6,12 +6,13 @@
 ##########################################################
 
 # minimum version of CMake, which is determined by Geant4's requirements
-cmake_minimum_required(VERSION 3.14)
+cmake_minimum_required(VERSION 3.20)
 
 project(HIPO VERSION 4.0.1)
 
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
 #
 # Set a default build type if none was specified
 #
@@ -60,25 +61,21 @@ find_package(LZ4 QUIET CONFIG PATHS ${PROJECT_SOURCE_DIR}/cmake )
 
 if(NOT LZ4_FOUND)
     message(STATUS "**LZ4********************************************************************")
-    message(STATUS "* We did not find a system LZ4 package -- We will build this locally.   *")
+    message(STATUS "* We did not find a system (or local build) LZ4 package.                *")
+    message(STATUS "* Please install lz4 (Centos: yum install lz4  MacOS: brew install lz4) *")
+    message(STATUS "* Or build lz4 from the included sources.                               *")
+    message(STATUS "*                                                                       *")
     message(STATUS "* To make this possible, please make sure you initialized the submodule.*")
     message(STATUS "* If you did not include --recurse-submodules at initial clone do:      *")
     message(STATUS "* git submodule init                                                    *")
     message(STATUS "* git submodule update                                                  *")
+    message(STATUS "* Then: 'cd lz4' followed by:                                           *")
+    message(STATUS "* make PREFIX=${CMAKE_INSTALL_PREFIX} CFLAGS='-fPIC' install ")
     message(STATUS "*************************************************************************")
-    message("PROJECT_SOURCE_DIR = ${PROJECT_SOURCE_DIR}")
-    file(MAKE_DIRECTORY ${CMAKE_INSTALL_PREFIX}/include/hipo4)
-    add_custom_target(LZ4 ALL
-                      WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}/lz4/lib
-                      COMMAND make PREFIX=${CMAKE_INSTALL_PREFIX} CFLAGS="-fPIC" install
-                      )
-
-    set(LZ4_INCLUDE_DIRS ${CMAKE_INSTALL_PREFIX}/include)
-    set(LZ4_LIBRARIES  ${CMAKE_INSTALL_PREFIX}/lib/liblz4.a)
+    message(FATAL_ERROR "stop processing until lz4 is available")
 endif()
 
 add_compile_definitions(__LZ4__)
-include_directories(${LZ4_INCLUDE_DIRS})
 
 set(DATAFRAME_IN_MAIN TRUE)
 add_subdirectory(extensions/dataframes)
@@ -129,7 +126,9 @@ set_target_properties(hipo4_static PROPERTIES OUTPUT_NAME hipo4)   # So that the
 
 # Required on Unix OS family to be able to be linked into shared libraries.
 set_target_properties(hipo4_objs PROPERTIES POSITION_INDEPENDENT_CODE ON)
-add_dependencies(hipo4_objs LZ4)
+# Note: Neither add_dependencies(hipo4_objs PkgConfig::LZ4) nor target_include_directories(hipo4_objs PUBLIC PkgConfig::LZ4)
+# work in an Intel Mac.
+target_include_directories(hipo4_objs PUBLIC ${LZ4_INCLUDE_DIRS})
 
 # Include the macros for creating export package.
 include(CMakePackageConfigHelpers)
@@ -144,8 +143,8 @@ target_include_directories(hipo4 PUBLIC
                            $<INSTALL_INTERFACE:include/hipo4>
                            )
 
-target_link_libraries(hipo4 PUBLIC  ${LZ4_LIBRARIES} )
-target_link_libraries(hipo4_static PUBLIC ${LZ4_LIBRARIES})
+target_link_libraries(hipo4 PUBLIC PkgConfig::LZ4 )
+target_link_libraries(hipo4_static PUBLIC PkgConfig::LZ4)
 
 install(TARGETS hipo4
         EXPORT hipo4-export

cmake/LZ4Config.cmake

@@ -1,41 +1,15 @@
 #
 #  Find the LZ4 library and include files and configure target for it.
 #
-get_filename_component(_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
-find_path(LZ4_INCLUDE_DIR NAMES lz4.h)
-find_library(LZ4_LIBRARY NAMES lz4)
-if (LZ4_LIBRARY)
-    include(CheckCSourceRuns)
-    set(CMAKE_REQUIRED_INCLUDES ${LZ4_INCLUDE_DIR})
-    set(CMAKE_REQUIRED_LIBRARIES ${LZ4_LIBRARY})
-    enable_language(C)
-    check_c_source_runs("
-#include <lz4.h>
-int main() {
-  int good = (LZ4_VERSION_MAJOR > 1) ||
-    ((LZ4_VERSION_MAJOR == 1) && (LZ4_VERSION_MINOR >= 8));
-return !good;
-}" LZ4_GOOD_VERSION)
-    set(CMAKE_REQUIRED_INCLUDES)
-    set(CMAKE_REQUIRED_LIBRARIES)
-endif()
-
-include(FindPackageHandleStandardArgs)
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(
-        LZ4 DEFAULT_MSG
-        LZ4_LIBRARY LZ4_INCLUDE_DIR LZ4_GOOD_VERSION)
+set(ENV{PKG_CONFIG_PATH} "${PKG_CONFIG_PATH}:${CMAKE_INSTALL_PREFIX}/lib/pkgconfig")
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(LZ4 IMPORTED_TARGET "liblz4")
 
 if (NOT LZ4_FOUND)
     message(STATUS "No system version of LZ4 found.")
 else()
-    if(NOT TARGET LZ4)
-        add_library(LZ4 INTERFACE IMPORTED)
-        set_target_properties(LZ4 PROPERTIES
-                              INTERFACE_INCLUDE_DIRECTORIES "${LZ4_INCLUDE_DIR}"
-                              )
-    endif()
-    message(STATUS "Found LZ4: ${LZ4_LIBRARY}")
-    set(LZ4_INCLUDE_DIRS ${LZ4_INCLUDE_DIR})
-    set(LZ4_LIBRARIES ${LZ4_LIBRARY})
+    add_library(LZ4 INTERFACE IMPORTED)
+    set_target_properties(LZ4 PROPERTIES INTERFACE_INCLUDE_DIRECTORIES "${LZ4_INCLUDE_DIR}")
+    message(STATUS "Found LZ4: ${LZ4_LIBRARIES}")
     mark_as_advanced(LZ4_INCLUDE_DIRS LZ4_INCLUDE_DIR LZ4_LIBRARIES LZ4_LIBRARY)
 endif (NOT LZ4_FOUND)

cmake/hipo4.pc.in

@@ -5,5 +5,6 @@ libdir=${prefix}/lib
 Name: hipo4
 Description: High Performance Output data format for experimental physics
 Version: @HIPO_VERSION@
+Requires: liblz4 >= @LZ4_VERSION@
 Libs: -L${libdir} -lhipo4
 Cflags: -I${includedir}

extensions/dataframes/README.md

@@ -27,7 +27,7 @@ cd build
 cmake -DCMAKE_INSTALL_PREFIX=/path/to/install/location ..
 make -j8 install
 ```
-This will install the hipo4 library (both .a and .so) in
+This will install the hipo4 and HipoDataFrame libraries in
 `/path/to/install/location/lib`
 
 You can now load the library into root with:
@@ -42,7 +42,7 @@ root [0] .L libHipoDataFrame.so
 and the .so with .dylib)
 
 ***NOTE***: On a system where the default compiler is NOT c++17 compatible, i.e. Linux at JLab,
-you want to specify the compiler to cmake. You can do so with the following lines:
+you have to specify the compiler to cmake. You can do so with the following lines:
 ```bash
 module use /apps/modulefiles
 module load gcc/9.3.0
@@ -58,13 +58,21 @@ currently C++17 compatible, so use the ROOT version installed in `~holtrop/root`
 
 [See the ROOT documentation for RDataFrame](https://root.cern/doc/master/classROOT_1_1RDataFrame.html)
 
+***Note***: The names of the Hipo schema are mangled to avoid :: and . (period) in the name, since
+these indicate C++ namespace and class member. So instead of :: and . we use underscores (_).
+
 The basics:
 
 ```bash
 root 
 root [0] .L libHipoDataFrame.so
 root [1] auto df = MakeHipoDataFrame("rec_clas_016214.evio.00000.hipo")
 root [2] df.GetColumnNames() // Shows what is in the file.
-root [3] auto h_px = df.Histo1D("REC::Particle.px")
+root [3] auto h_px = df.Histo1D("REC_Particle_px")
 root [4] h_px->DrawClone();
 ```
+The result would be a histogram of the REC::Particle.px, i.e the x component of the particle momentum
+for all particles in the events.
+
+The ROOT RDataFrame is very versatile and is intended by the ROOT team as the future of 
+data analysis. [See more details on the ROOT website](https://root.cern/doc/master/classROOT_1_1RDataFrame.html).