ENH: prevent in-source build (following discussion on the ITK dev list)

CMake/PreventInSourceBuilds.cmake

+#
+# This function will prevent in-source builds
+function(AssureOutOfSourceBuilds)
+  # make sure the user doesn't play dirty with symlinks
+  get_filename_component(srcdir "${CMAKE_SOURCE_DIR}" REALPATH)
+  get_filename_component(bindir "${CMAKE_BINARY_DIR}" REALPATH)
+
+  # disallow in-source builds
+  if("${srcdir}" STREQUAL "${bindir}")
+    message("######################################################")
+    message("# OTB should not be configured & built in the OTB source directory")
+    message("# You must run cmake in a build directory.")
+    message("# For example:")
+    message("# mkdir OTB-Sandbox ; cd OTB-Sandbox")
+    message("# hg clone http://hg.orfeo-toolbox.org/OTB # or download & unpack the source tarball")
+    message("# mkdir OTB-Binary ")
+    message("# this will create the following directory structure ")
+    message("#  ")
+    message("# OTB-Sandbox")
+    message("#  +--OTB ")
+    message("#  +--OTB-Binary ")
+    message("#  ")
+    message("# Then you can proceed to configure and build ")
+    message("# by using the following commands ")
+    message("#  ")
+    message("# cd OTB-Binary")
+    message("# ccmake ../OTB")
+    message("# make ")
+    message("#  ")
+    message("# NOTE: Given that you already tried to make an in-source build")
+    message("#       CMake have already created several files & directories")
+    message("#       in your source tree. run 'hg status' to find them and")
+    message("#       remove them by doing:")
+    message("#  ")
+    message("#       cd OTB-Sandbox/OTB")
+    message("#       hg purge ")
+    message("#  ")
+    message("######################################################")
+    message(FATAL_ERROR "Quitting configuration")
+  endif()
+endfunction()
+
+AssureOutOfSourceBuilds()

CMakeLists.txt

@@ -6,6 +6,11 @@ IF(COMMAND CMAKE_POLICY)
   CMAKE_POLICY(SET CMP0003 NEW)
 ENDIF(COMMAND CMAKE_POLICY)
 
+#-----------------------------------------------------------------------------
+# Sanity check -- prevent in-source builds
+#
+INCLUDE(${CMAKE_CURRENT_SOURCE_DIR}/CMake/PreventInSourceBuilds.cmake)
+
 PROJECT(OTB)
 
 # Path to additional CMake modules