From 6d261267547280380ea174c894aa07c21c31db7e Mon Sep 17 00:00:00 2001
From: Roland Kaufmann <roland.kaufmann@uni.no>
Date: Tue, 5 Mar 2013 14:45:37 +0100
Subject: [PATCH] Only regenerate config var file if actually changed

---
 CMakeLists.txt                   | 12 +++++++++++-
 cmake/Modules/ConfigVars.cmake   |  5 ++---
 cmake/Modules/OpmDistClean.cmake |  1 +
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 26a4e57..c0a2d6e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -118,7 +118,10 @@ opm_sources (${project})
 # includes the necessary defines by the dependencies
 include (ConfigVars)
 list (APPEND ${project}_CONFIG_VARS ${${project}_CONFIG_VAR})
-set (CONFIG_H "${PROJECT_BINARY_DIR}/config.h")
+
+# write configuration variables to this file. note that it is a temporary.
+message (STATUS "Writing config file \"${PROJECT_BINARY_DIR}/config.h\"...")
+set (CONFIG_H "${PROJECT_BINARY_DIR}/config.h.tmp")
 configure_vars (
 	FILE  CXX  ${CONFIG_H}
 	WRITE ${${project}_CONFIG_VARS}
@@ -130,6 +133,13 @@ define_fc_func (
 	IF HAVE_LAPACK
 	)
 
+# overwrite the config.h that is used by the code only if we have some
+# real changes. thus, we don't have to recompile if a reconfigure is run
+# due to some files being added, for instance
+execute_process (COMMAND
+	${CMAKE_COMMAND} -E copy_if_different ${CONFIG_H} ${PROJECT_BINARY_DIR}/config.h
+	)
+
 # compile main library; pull in all required includes and libraries
 include (OpmCompile)
 opm_compile (${project})
diff --git a/cmake/Modules/ConfigVars.cmake b/cmake/Modules/ConfigVars.cmake
index 072d2b7..ad81e98 100644
--- a/cmake/Modules/ConfigVars.cmake
+++ b/cmake/Modules/ConfigVars.cmake
@@ -27,7 +27,6 @@
 
 function (configure_vars obj syntax filename verb)
   # this is just to make the syntax look like the build-in commands
-  message (STATUS "Writing config file \"${filename}\"...")
   if (NOT ("${obj}" STREQUAL "FILE" AND
 		(("${verb}" STREQUAL "WRITE") OR ("${verb}" STREQUAL "APPEND"))))
 	message (FATAL_ERROR "Syntax error in argument list")
@@ -47,10 +46,10 @@ function (configure_vars obj syntax filename verb)
   # to avoid confusion from other configuration files.
   get_filename_component (_config_path "${filename}" PATH)
   get_filename_component (_config_file "${filename}" NAME)
-  if ("${_config_file}" STREQUAL "config.h")
+  if ("${_config_file}" MATCHES "config\\.h(\\..+)?")
 	add_definitions (-DHAVE_CONFIG_H=1)
 	include_directories (BEFORE "${_config_path}")
-  endif ("${_config_file}" STREQUAL "config.h")
+  endif ("${_config_file}" MATCHES "config\\.h(\\..+)?")
   
   # only write the current value of each variable once
   set (_args ${ARGN})
diff --git a/cmake/Modules/OpmDistClean.cmake b/cmake/Modules/OpmDistClean.cmake
index 03bba48..5bdea6d 100644
--- a/cmake/Modules/OpmDistClean.cmake
+++ b/cmake/Modules/OpmDistClean.cmake
@@ -17,6 +17,7 @@ macro (opm_dist_clean opm)
 	cmake_install.cmake
 	Makefile
 	config.h
+	config.h.tmp
 	${${opm}_NAME}-config.cmake
 	${${opm}_NAME}-config-version.cmake
 	${${opm}_NAME}-install.cmake