+# Next, turn it off if any of the preconditions are unsatisified
+if (NOT PYTHON_EXECUTABLE)
+ set(HTML_BUILD_IS_POSSIBLE OFF)
+ set(HTML_BUILD_NOT_POSSIBLE_REASON "Python is required")
+elseif (NOT SPHINX_FOUND)
+ # Hardly anything gets built if Sphinx is not available, so don't bother.
+ set(HTML_BUILD_IS_POSSIBLE OFF)
+ set(HTML_BUILD_NOT_POSSIBLE_REASON "Sphinx is required")
+endif()
+if (NOT MANUAL_BUILD_IS_POSSIBLE)
+ list(APPEND HTML_BUILD_WARNINGS
+ "Reference PDF manual was not built, so links to it do not work")
+endif()
+if (NOT DOXYGEN_EXECUTABLE)
+ list(APPEND HTML_BUILD_WARNINGS
+ "Doxygen was not available, so links to Doxygen do not work")
+endif()
+if (NOT DOXYGEN_DOT_EXECUTABLE)
+ list(APPEND HTML_BUILD_WARNINGS
+ "dot/graphviz was not found, so some graphs are missing")
+endif()