add CMakePackageConfigHelpers: configure_package_config_file()

The function configure_package_config_file() may be used instead of
configure_file() for generating the Config.cmake files for installation,
they help to make those files relocatable.

Alex

Modules/CMakePackageConfigHelpers.cmake

+# - CONFIGURE_PACKAGE_CONFIG_FILE(), WRITE_BASIC_PACKAGE_VERSION_FILE()
+#
+#    CONFIGURE_PACKAGE_CONFIG_FILE(<input> <output> INSTALL_DESTINATION <path>
+#                                                   [PATH_VARS <var1> <var2> ... <varN>]
+#                                                   [NO_SET_AND_CHECK_MACRO] )
+#
+# CONFIGURE_PACKAGE_CONFIG_FILE() should be used instead of the plain
+# CONFIGURE_FILE() command when creating the <Name>Config.cmake or <Name>-config.cmake
+# file for installing a project or library. It helps making the resulting package
+# relocatable by avoiding hardcoded paths in the installed Config.cmake file.
+#
+# In a FooConfig.cmake file there may be code like this to make the
+# install destinations know to the using project:
+#   set(FOO_INCLUDE_DIR   "@CMAKE_INSTALL_FULL_INCLUDEDIR@" )
+#   set(FOO_DATA_DIR   "@CMAKE_INSTALL_PREFIX@/@RELATIVE_DATA_INSTALL_DIR@" )
+#   set(FOO_ICONS_DIR   "@CMAKE_INSTALL_PREFIX@/share/icons" )
+#   ...logic to determine installedPrefix from the own location...
+#   set(FOO_CONFIG_DIR  "${installedPrefix}/@CONFIG_INSTALL_DIR@" )
+# All 4 options shown above are not sufficient, since the first 3 hardcode
+# the absolute directory locations, and the 4th case works only if the logic
+# to determine the installedPrefix is correct, and if CONFIG_INSTALL_DIR contains
+# a relative path, which in general cannot be guaranteed.
+# This has the effect that the resulting FooConfig.cmake file would work poorly
+# under Windows and OSX, where users are used to choose the install location
+# of a binary package at install time, independent from how CMAKE_INSTALL_PREFIX
+# was set at build/cmake time.
+#
+# Using CONFIGURE_PACKAGE_CONFIG_FILE() helps. If used correctly, it makes the
+# resulting FooConfig.cmake file relocatable.
+# Usage:
+#   1. write a FooConfig.cmake.in file as you are used to
+#   2. insert a line containing only the string "@PACKAGE_INIT@"
+#   3. instead of SET(FOO_DIR "@SOME_INSTALL_DIR@"), use SET(FOO_DIR "@PACKAGE_SOME_INSTALL_DIR@")
+#      (this must be after the @PACKAGE_INIT@ line)
+#   4. instead of using the normal CONFIGURE_FILE(), use CONFIGURE_PACKAGE_CONFIG_FILE()
+#
+# The <input> and <output> arguments are the input and output file, the same way
+# as in CONFIGURE_FILE().
+#
+# The <path> given to INSTALL_DESTINATION must be the destination where the FooConfig.cmake
+# file will be installed to. This can either be a relative or absolute path, both work.
+#
+# The variables <var1> to <varN> given as PATH_VARS are the variables which contain
+# install destinations. For each of them the macro will create a helper variable
+# PACKAGE_<var...>. These helper variables must be used
+# in the FooConfig.cmake.in file for setting the installed location. They are calculated
+# by CONFIGURE_PACKAGE_CONFIG_FILE() so that they are always relative to the
+# installed location of the package. This works both for relative and also for absolute locations.
+# For absolute locations it works only if the absolute location is a subdirectory
+# of CMAKE_INSTALL_PREFIX.
+#
+# By default configure_package_config_file() also generates a macro set_and_check()
+# into the FooConfig.cmake file. This should be used instead of the normal set()
+# command for setting directories and file locations. Additionally to setting the
+# variable it also checks that the referenced file or directory actually exists
+# and fails with a FATAL_ERROR otherwise. This makes sure that the created
+# FooConfig.cmake file does not contain wrong references.
+# When using the NO_SET_AND_CHECK_MACRO, this macro is not generated into the
+# FooConfig.cmake file.
+#
+# Example:
+# CMakeLists.txt:
+#   set(INCLUDE_INSTALL_DIR include/ ... CACHE )
+#   set(LIB_INSTALL_DIR lib/ ... CACHE )
+#   set(SYSCONFIG_INSTALL_DIR etc/foo/ ... CACHE )
+#   ...
+#   include(CMakePackageConfigHelpers)
+#   configure_package_config_file(FooConfig.cmake.in ${CMAKE_CURRENT_BINARY_DIR}/FooConfig.cmake
+#                                 INSTALL_DESTINATION ${LIB_INSTALL_DIR}/Foo/cmake
+#                                 PATH_VARS INCLUDE_INSTALL_DIR SYSCONFIG_INSTALL_DIR)
+#  install(FILES ${CMAKE_CURRENT_BINARY_DIR}/FooConfig.cmake DESTINATION ${LIB_INSTALL_DIR}/Foo/cmake )
+#
+# FooConfig.cmake.in:
+#   set(FOO_VERSION x.y.z)
+#   ...
+#   @PACKAGE_INIT@
+#   ...
+#   set_and_check(FOO_INCLUDE_DIR "@PACKAGE_INCLUDE_INSTALL_DIR@")
+#   set_and_check(FOO_SYSCONFIG_DIR "@PACKAGE_SYSCONFIG_INSTALL_DIR@")
+
+
+#=============================================================================
+# Copyright 2012 Alexander Neundorf <neundorf@kde.org>
+#
+# Distributed under the OSI-approved BSD License (the "License");
+# see accompanying file Copyright.txt for details.
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+# (To distribute this file outside of CMake, substitute the full
+#  License text for the above reference.)
+
+include(CMakeParseArguments)
+
+
+function(CONFIGURE_PACKAGE_CONFIG_FILE _inputFile _outputFile)
+  set(options NO_SET_AND_CHECK_MACRO)
+  set(oneValueArgs INSTALL_DESTINATION )
+  set(multiValueArgs PATH_VARS )
+
+  cmake_parse_arguments(CCF "${options}" "${oneValueArgs}" "${multiValueArgs}"  ${ARGN})
+
+  if(CCF_UNPARSED_ARGUMENTS)
+    message(FATAL_ERROR "Unknown keywords given to CONFIGURE_PACKAGE_CONFIG_FILE(): \"${CCF_UNPARSED_ARGUMENTS}\"")
+  endif()
+
+  if(NOT CCF_INSTALL_DESTINATION)
+    message(FATAL_ERROR "No INSTALL_DESTINATION given to CONFIGURE_PACKAGE_CONFIG_FILE()")
+  endif()
+
+  if(IS_ABSOLUTE "${CCF_INSTALL_DESTINATION}")
+    set(absInstallDir "${CCF_INSTALL_DESTINATION}")
+  else()
+    set(absInstallDir "${CMAKE_INSTALL_PREFIX}/${CCF_INSTALL_DESTINATION}")
+  endif()
+  file(RELATIVE_PATH PACKAGE_RELATIVE_PATH "${absInstallDir}" "${CMAKE_INSTALL_PREFIX}" )
+
+  foreach(var ${CCF_PATH_VARS})
+    if(NOT DEFINED ${var})
+      message(FATAL_ERROR "Variable ${var} does not exist")
+    else()
+      if(IS_ABSOLUTE "${${var}}")
+        string(REPLACE "${CMAKE_INSTALL_PREFIX}" "\${PACKAGE_PREFIX_DIR}"
+                        PACKAGE_${var} "${${var}}")
+      else()
+        set(PACKAGE_${var} "\${PACKAGE_PREFIX_DIR}/${${var}}")
+      endif()
+    endif()
+  endforeach()
+
+  set(PACKAGE_INIT "
+####### Expanded from @PACKAGE_INIT@ by configure_package_config_file() #######
+get_filename_component(PACKAGE_PREFIX_DIR \"\${CMAKE_CURRENT_LIST_DIR}/${PACKAGE_RELATIVE_PATH}\" ABSOLUTE)
+")
+
+  if(NOT CCF_NO_SET_AND_CHECK_MACRO)
+    set(PACKAGE_INIT "${PACKAGE_INIT}
+macro(set_and_check _var _file)
+  set(\${_var} \"\${_file}\")
+  if(NOT EXISTS \"\${_file}\")
+    message(FATAL_ERROR \"File or directory \${_file} referenced by variable \${_var} does not exist !\")
+  endif()
+endmacro()
+")
+  endif()
+
+  set(PACKAGE_INIT "${PACKAGE_INIT}
+####################################################################################")
+
+  configure_file("${_inputFile}" "${_outputFile}" @ONLY)
+
+endfunction()

Tests/FindPackageTest/CMakeLists.txt

@@ -304,6 +304,34 @@ SET(CMakeTestExportPackage_DIR "" CACHE FILEPATH
 STRING(REGEX REPLACE "-.*$" "" version ${CMAKE_VERSION})
 FIND_PACKAGE(CMakeTestExportPackage 1.${version} EXACT REQUIRED)
 
+#-----------------------------------------------------------------------------
+# Test configure_package_config_file().
+
+include(CMakePackageConfigHelpers)
+
+set(INCLUDE_INSTALL_DIR include )
+set(SHARE_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/share/" )
+set(CURRENT_BUILD_DIR "${CMAKE_CURRENT_BINARY_DIR}" )
+
+configure_package_config_file(RelocatableConfig.cmake.in "${CMAKE_CURRENT_BINARY_DIR}/RelocatableConfig.cmake"
+                              INSTALL_DESTINATION "${CMAKE_INSTALL_PREFIX}"
+                              PATH_VARS INCLUDE_INSTALL_DIR SHARE_INSTALL_DIR CURRENT_BUILD_DIR
+                             )
+
+include("${CMAKE_CURRENT_BINARY_DIR}/RelocatableConfig.cmake")
+
+if(NOT "${RELOC_INCLUDE_DIR}" STREQUAL "${CMAKE_CURRENT_BINARY_DIR}/include")
+  message(SEND_ERROR "RELOC_INCLUDE_DIR set by configure_package_config_file() is set to \"${RELOC_INCLUDE_DIR}\" (expected \"${CMAKE_CURRENT_BINARY_DIR}/include\")")
+endif()
+
+if(NOT "${RELOC_SHARE_DIR}" STREQUAL "${CMAKE_CURRENT_BINARY_DIR}/share/")
+  message(SEND_ERROR "RELOC_SHARE_DIR set by configure_package_config_file() is set to \"${RELOC_SHARE_DIR}\" (expected \"${CMAKE_CURRENT_BINARY_DIR}/share/\")")
+endif()
+
+if(NOT "${RELOC_BUILD_DIR}" STREQUAL "${CMAKE_CURRENT_BINARY_DIR}")
+  message(SEND_ERROR "RELOC_BUILD_DIR set by configure_package_config_file() is set to \"${RELOC_BUILD_DIR}\" (expected \"${CMAKE_CURRENT_BINARY_DIR}\")")
+endif()
+
 #-----------------------------------------------------------------------------
 # Test write_basic_config_version_file().
 

Tests/FindPackageTest/RelocatableConfig.cmake.in

+@PACKAGE_INIT@
+
+set(RELOC_INCLUDE_DIR "@PACKAGE_INCLUDE_INSTALL_DIR@")
+set(RELOC_SHARE_DIR "@PACKAGE_SHARE_INSTALL_DIR@")
+set_and_check(RELOC_BUILD_DIR "@PACKAGE_CURRENT_BUILD_DIR@")