@@ -257,6 +257,20 @@ Tips and Guidelines for Writing Recipes
and ``-nativesdk`` ones, whenever possible. This avoids having to maintain multiple
recipe files at the same time.
+- Recipes should have tasks which are idempotent, i.e. that executing a given task
+ multiple times shouldn't change the end result. The build environment is built upon
+ this assumption and breaking it can cause obscure build failures.
+
+- For idempotence when modifying files in tasks, it is usually best to:
+
+ - copy a file ``X`` to ``X.orig`` (only if it doesn't exist already)
+ - then, copy ``X.orig`` back to ``X``,
+ - and, finally, modify ``X``.
+
+ This ensures if rerun the task always has the same end result and the
+ original file can be preserved to reuse. It also guards against an
+ interrupted build corrupting the file.
+
Patch Upstream Status
=====================