From b9c24f8a929a7c6dd84f5e8f9e82e05be1d1b94e Mon Sep 17 00:00:00 2001
From: wmayer <wmayer@users.sourceforge.net>
Date: Tue, 21 Aug 2018 13:20:58 +0200
Subject: [PATCH] reduce compile time after each time cmake configure is
 executed (swig)

---
 src/Base/CMakeLists.txt | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/Base/CMakeLists.txt b/src/Base/CMakeLists.txt
index 467d1df2bf..73edf0738d 100644
--- a/src/Base/CMakeLists.txt
+++ b/src/Base/CMakeLists.txt
@@ -90,7 +90,27 @@ generate_from_xml(UnitPy)
 generate_from_xml(QuantityPy)
 
 if(SWIG_FOUND)
-    execute_process(COMMAND ${SWIG_EXECUTABLE} -python -external-runtime ${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.h)
+    # Create the file swigpyrun.hh and then compare with the file swigpyrun.h.
+    # If the files are different or if swigpyrun.h doesn't exist then copy swigpyrun.hh.
+    # This is to avoid to having to build the target each time cmake configure is executed.
+    execute_process(COMMAND ${SWIG_EXECUTABLE} -python -external-runtime ${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.hh)
+    if (EXISTS "${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.h")
+        execute_process(
+            COMMAND ${CMAKE_COMMAND} -E compare_files ${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.hh
+                                                      ${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.h
+            RESULT_VARIABLE DIFFERENT_FILES
+            OUTPUT_QUIET
+            ERROR_QUIET
+        )
+
+        if (DIFFERENT_FILES)
+            execute_process(COMMAND "${CMAKE_COMMAND}" -E copy "${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.hh"
+                                                               "${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.h")
+        endif()
+    else()
+        execute_process(COMMAND "${CMAKE_COMMAND}" -E copy "${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.hh"
+                                                           "${CMAKE_CURRENT_BINARY_DIR}/swigpyrun.h")
+    endif()
     add_definitions(-DHAVE_SWIG=1)
 endif(SWIG_FOUND)