From b2d444d782ba9eb9b2719cde66902f4b9e5da5ba Mon Sep 17 00:00:00 2001
From: Daniel Patterson <daniel@mapbox.com>
Date: Fri, 24 Jul 2015 18:45:33 -0700
Subject: [PATCH] Only replace fingerprint file when MD5 changes.  Avoids
 rebuilding several things if nothing has actually changes, as cmake is only
 looking at timestamps.

---
 cmake/FingerPrint-Config.cmake | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/cmake/FingerPrint-Config.cmake b/cmake/FingerPrint-Config.cmake
index a3325d305..857dedd89 100644
--- a/cmake/FingerPrint-Config.cmake
+++ b/cmake/FingerPrint-Config.cmake
@@ -1,10 +1,24 @@
 set(OLDFILE ${SOURCE_DIR}/util/fingerprint_impl.hpp)
-if (EXISTS ${OLDFILE})
-	file(REMOVE_RECURSE ${OLDFILE})
-endif()
+set(NEWFILE ${OLDFILE}.tmp)
+set(INFILE ${OLDFILE}.in)
 file(MD5 ${SOURCE_DIR}/prepare.cpp MD5PREPARE)
 file(MD5 ${SOURCE_DIR}/data_structures/static_rtree.hpp MD5RTREE)
 file(MD5 ${SOURCE_DIR}/util/graph_loader.hpp MD5GRAPH)
 file(MD5 ${SOURCE_DIR}/server/data_structures/internal_datafacade.hpp MD5OBJECTS)
 
-CONFIGURE_FILE(${SOURCE_DIR}/util/fingerprint_impl.hpp.in ${SOURCE_DIR}/util/fingerprint_impl.hpp)
+CONFIGURE_FILE(${INFILE} ${NEWFILE})
+
+file(MD5 ${NEWFILE} MD5NEW)
+
+if (EXISTS ${OLDFILE})
+    file(MD5 ${OLDFILE} MD5OLD)
+    if(NOT ${MD5NEW} STREQUAL ${MD5OLD})
+	    file(REMOVE_RECURSE ${OLDFILE})
+        file(RENAME ${NEWFILE} ${OLDFILE})
+    else()
+        file(REMOVE_RECURSE ${NEWFILE})
+        message(STATUS "Fingerprint unchanged, not regenerating")
+    endif()
+else()
+    file(RENAME ${NEWFILE} ${OLDFILE})
+endif()