fix: Use proper cmake package config for relocatable CMake config

The CMake config used absolute paths which doesn't allow to move the installed cmake files. This is the case, e.g., if you create a conan package and distribute the binaries to other users.

Fixes: gazebosim#2755
Fixes: gazebosim#2782

CMakeLists.txt

@@ -456,9 +456,14 @@ else (build_errors)
     set(PKG_LIBRARIES ${PKG_LIBRARIES} gazebo_ccd)
   endif()
 
+  include(CMakePackageConfigHelpers)
   set(cmake_conf_file "cmake/gazebo-config.cmake")
   set(cmake_conf_version_file "cmake/gazebo-config-version.cmake")
-  configure_file("${CMAKE_CURRENT_SOURCE_DIR}/${cmake_conf_file}.in" "${CMAKE_CURRENT_BINARY_DIR}/${cmake_conf_file}" @ONLY)
+  set(DATAROOT_INSTALL_DIR ${CMAKE_INSTALL_DATAROOTDIR})
+  configure_package_config_file("${CMAKE_CURRENT_SOURCE_DIR}/${cmake_conf_file}.in" "${CMAKE_CURRENT_BINARY_DIR}/${cmake_conf_file}"
+          INSTALL_DESTINATION ${LIB_INSTALL_DIR}/cmake/${PROJECT_NAME_LOWER}/
+          PATH_VARS INCLUDE_INSTALL_DIR LIB_INSTALL_DIR DATAROOT_INSTALL_DIR
+          )
   # Use write_basic_package_version_file to generate a ConfigVersion file that
   # allow users of gazebo to specify the API or version to depend on
   # TODO: keep this instruction until deprecate Ubuntu/Precise and update with

cmake/gazebo-config.cmake.in

@@ -5,14 +5,21 @@ set(@PKG_NAME@_CONFIG_INCLUDED TRUE)
 set(@PKG_NAME@_VERSION @GAZEBO_VERSION@)
 set(@PKG_NAME@_MAJOR_VERSION @GAZEBO_MAJOR_VERSION@)
 
-set(@PKG_NAME@_PLUGIN_PATH "@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@/gazebo-@GAZEBO_MAJOR_VERSION@/plugins")
+@PACKAGE_INIT@
+
+# Includeing Dartsim will overwrite the PACKAGE_PREFIX_PATH, therefore make gazebo-specific vars
+set(GAZEBO_INSTALL_DATAROOT_DIR @PACKAGE_DATAROOT_INSTALL_DIR@)
+set(GAZEBO_INSTALL_LIB_DIR @PACKAGE_LIB_INSTALL_DIR@)
+set(GAZEBO_INSTALL_INCLUDE_DIR @PACKAGE_INCLUDE_INSTALL_DIR@)
+
+set(@PKG_NAME@_PLUGIN_PATH "${GAZEBO_INSTALL_LIB_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/plugins")
 
 # The media path contains the location on disk where images,
 # materials scripts, shaders, and other related resources are stored.
-set(@PKG_NAME@_MEDIA_PATH "@CMAKE_INSTALL_PREFIX@/share/gazebo-@GAZEBO_MAJOR_VERSION@/media")
+set(@PKG_NAME@_MEDIA_PATH "${GAZEBO_INSTALL_DATAROOT_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/media")
 
 # The model path contains the location on disk where models are stored.
-set(@PKG_NAME@_MODEL_PATH "@CMAKE_INSTALL_PREFIX@/share/gazebo-@GAZEBO_MAJOR_VERSION@/models")
+set(@PKG_NAME@_MODEL_PATH "${GAZEBO_INSTALL_DATAROOT_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/models")
 
 # Set whether Gazebo was built with Bullet support
 set (GAZEBO_HAS_BULLET @HAVE_BULLET@)
@@ -72,23 +79,23 @@ include (FindPkgConfig)
 # target_link_libraries(your_package @PKG_NAME@_PROTO_LIBRARIES)
 #
 set(@PKG_NAME@_PROTO_PATH
-  "@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@/gazebo-@GAZEBO_MAJOR_VERSION@/gazebo/msgs/proto")
+  "${GAZEBO_INSTALL_INCLUDE_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/gazebo/msgs/proto")
 find_library(gazebo_proto_msgs_lib gazebo_msgs
-  PATHS "@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@" NO_DEFAULT_PATH)
+  PATHS "${GAZEBO_INSTALL_LIB_DIR}" NO_DEFAULT_PATH)
 list(APPEND @PKG_NAME@_PROTO_LIBRARIES ${gazebo_proto_msgs_lib})
 list(APPEND @PKG_NAME@_PROTO_INCLUDE_DIRS
-  "@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@/gazebo-@GAZEBO_MAJOR_VERSION@/gazebo/msgs")
+  "${GAZEBO_INSTALL_INCLUDE_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/gazebo/msgs")
 # End @PKG_NAME@_PROTO_PATH, @PKG_NAME@_PROTO_INCLUDE_DIRS, and
 # @PKG_NAME@_PROTO_LIBRARIES
 
-list(APPEND @PKG_NAME@_INCLUDE_DIRS @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@)
-list(APPEND @PKG_NAME@_INCLUDE_DIRS @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@/gazebo-@GAZEBO_MAJOR_VERSION@)
+list(APPEND @PKG_NAME@_INCLUDE_DIRS ${GAZEBO_INSTALL_INCLUDE_DIR})
+list(APPEND @PKG_NAME@_INCLUDE_DIRS ${GAZEBO_INSTALL_INCLUDE_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@)
 
-list(APPEND @PKG_NAME@_LIBRARY_DIRS @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@)
-list(APPEND @PKG_NAME@_LIBRARY_DIRS @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@/gazebo-@GAZEBO_MAJOR_VERSION@/plugins)
+list(APPEND @PKG_NAME@_LIBRARY_DIRS ${GAZEBO_INSTALL_LIB_DIR})
+list(APPEND @PKG_NAME@_LIBRARY_DIRS ${GAZEBO_INSTALL_LIB_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/plugins)
 
-list(APPEND @PKG_NAME@_CFLAGS -I@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@)
-list(APPEND @PKG_NAME@_CFLAGS -I@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@/gazebo-@GAZEBO_MAJOR_VERSION@)
+list(APPEND @PKG_NAME@_CFLAGS -I${GAZEBO_INSTALL_INCLUDE_DIR})
+list(APPEND @PKG_NAME@_CFLAGS -I${GAZEBO_INSTALL_INCLUDE_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@)
 
 if (GAZEBO_HAS_BULLET)
   if (PKG_CONFIG_FOUND)
@@ -139,7 +146,7 @@ endif ()
 foreach(lib @PKG_LIBRARIES@)
   set(onelib "${lib}-NOTFOUND")
   find_library(onelib ${lib}
-    PATHS "@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@"
+    PATHS "${GAZEBO_INSTALL_LIB_DIR}"
     NO_DEFAULT_PATH
     )
   if(NOT onelib)
@@ -216,6 +223,6 @@ list(APPEND @PKG_NAME@_INCLUDE_DIRS ${IGNITION-FUEL_TOOLS_INCLUDE_DIRS})
 list(APPEND @PKG_NAME@_LIBRARY_DIRS ${IGNITION-FUEL_TOOLS_LIBRARY_DIRS})
 list(APPEND @PKG_NAME@_LIBRARIES ${IGNITION-FUEL_TOOLS_LIBRARIES})
 
-list(APPEND @PKG_NAME@_LDFLAGS -Wl,-rpath,@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@/gazebo-@GAZEBO_MAJOR_VERSION@/plugins)
-list(APPEND @PKG_NAME@_LDFLAGS -L@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@)
-list(APPEND @PKG_NAME@_LDFLAGS -L@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@/gazebo-@GAZEBO_MAJOR_VERSION@/plugins)
+list(APPEND @PKG_NAME@_LDFLAGS -Wl,-rpath,${GAZEBO_INSTALL_LIB_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/plugins)
+list(APPEND @PKG_NAME@_LDFLAGS -L${GAZEBO_INSTALL_LIB_DIR})
+list(APPEND @PKG_NAME@_LDFLAGS -L${GAZEBO_INSTALL_LIB_DIR}/gazebo-@GAZEBO_MAJOR_VERSION@/plugins)