[coq_makefile] Enforce warn_error for plugins.

The amount of dangerous warnings in plugins is out of hand, including
some very serious ones.

As Coq developers are maintaining plugins these days it makes sense to
require the contributions to follow the same coding discipline as in
the main tree, thus we require the set of warnings fatal warnings to
be the same in Coq and in plugins.

We don't mark deprecation as fatal as to allow time for migration.

Fixes #6974

1 files changed, 20 insertions, 0 deletions

diff --git a/dev/ci/README-users.md b/dev/ci/README-users.md
index 01769aeddb..06b617d4c1 100644
--- a/dev/ci/README-users.md
+++ b/dev/ci/README-users.md
@@ -45,6 +45,26 @@ using [coqbot](https://github.com/coq/bot); meanwhile, a workaround is
 to give merge permissions to someone from the Coq team as to help with
 these kind of merges.
 
+### OCaml and plugin-specific considerations
+
+Developments that link against Coq's OCaml API [most of them are known
+as "plugins"] do have some special requirements:
+
+- Coq's OCaml API is not stable. We hope to improve this in the future
+  but as of today you should expect to have to merge a fair amount of
+  "overlays", usually in the form of Pull Requests from Coq developers
+  in order to keep your plugin compatible with Coq master.
+
+  In order to alleviate the load, you can delegate the merging of such
+  compatibility pull requests to Coq developers themselves, by
+  granting access to the plugin repository or by using `bots` such as
+  [Bors](https://github.com/apps/bors) that allow for automatic
+  management of Pull Requests.
+
+- Plugins in the CI should compile with the OCaml flags that Coq
+  uses. In particular, warnings that are considered fatal by the Coq
+  developers _must_ be also fatal for plugin CI code.
+
 ### Add your development by submitting a pull request
 
 Add a new `ci-mydev.sh` script to [`dev/ci`](.); set the corresponding