include optional sphinx dependency in cmake build

CMakeLists.txt

@@ -636,6 +636,13 @@ IF(NOT ENABLE_META_EXAMPLES)
     SET(ENABLE_COOKBOOK 0)
 ENDIF()
 
+find_package(Sphinx)
+IF(NOT SPHINX_FOUND)
+    message("-- Sphinx is required for building cookbook. Disabling.")
+    SET(ENABLE_COOKBOOK 0)
+ENDIF()
+
+
 FIND_PACKAGE(LpSolve)
 IF (LPSOLVE_FOUND)
 	SET(USE_LPSOLVE 1)

cmake/FindSphinx.cmake

@@ -0,0 +1,24 @@
+# Talen from https://llvm.org/svn/llvm-project/llvm/trunk/cmake/modules/FindSphinx.cmake
+# under "UIUC" BSD-Style license.
+# CMake find_package() Module for Sphinx documentation generator
+# http://sphinx-doc.org/
+#
+# Example usage:
+#
+# find_package(Sphinx)
+#
+# If successful the following variables will be defined
+# SPHINX_FOUND
+# SPHINX_EXECUTABLE
+
+find_program(SPHINX_EXECUTABLE
+             NAMES sphinx-build sphinx-build2
+             DOC "Path to sphinx-build executable")
+
+# Handle REQUIRED and QUIET arguments
+# this will also set SPHINX_FOUND to true if SPHINX_EXECUTABLE exists
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(Sphinx
+                                  "Failed to locate sphinx-build executable"
+                                  SPHINX_EXECUTABLE)
+

doc/cookbook/CMakeLists.txt

@@ -1,8 +1,6 @@
 #PROJECT(sphinxdoc)
 #cmake_minimum_required(VERSION 2.8.8)
 
-set(SPHINX_EXECUTABLE "sphinx-build")
-
 # configured documentation tools and intermediate build results
 set(BINARY_BUILD_DIR "${CMAKE_CURRENT_BINARY_DIR}/_build")