From 63adc635971e63b6f20540dd2dd276d9cb536a08 Mon Sep 17 00:00:00 2001
From: yo-h <55373593+yo-h@users.noreply.github.com>
Date: Wed, 26 Feb 2020 18:35:16 -0500
Subject: [PATCH] `CONTRIBUTING.md`: add paragraph on maintaining backwards
 compatibility

---
 CONTRIBUTING.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0583374555b..649af08b996 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -46,6 +46,10 @@ Follow the steps below to help other users understand what your query does, and
    Query help files explain the purpose of your query to other users. Write your query help in a `.qhelp` file and save it in the same directory as your new query. 
    For more information on writing query help, see the [Query help style guide](https://github.com/Semmle/ql/blob/master/docs/query-help-style-guide.md).
 
+7. **Maintain backwards compatibility**
+
+The standard CodeQL libraries must evolve in a backwards compatible manner. If any backwards incompatible changes need to be made, the existing API must first be marked as deprecated. This is done by adding a `deprecated` annotation along with a QLDoc reference to the replacement API. Only after at least one full release cycle has elapsed may the old API be removed.
+
 In addition to contributions to our standard queries and libraries, we also welcome contributions of a more experimental nature, which do not need to fulfill all the requirements listed above. See the guidelines for [experimental queries and libraries](docs/experimental.md) for details.
 
 ## Using your personal data