document policy on supported toolchain generations

docs/policies/toolchains.md

@@ -0,0 +1,33 @@
+# Supported Toolchain Generations Policy {: #policy_toolchains }
+
+!!! note
+     This policy will be implemented as part of the release of [EasyBuild 5.0][overview]
+
+For the central EasyBuild repositories, we support a set of toolchain generations.
+
+* Accept PRs only for the 6 most recent toolchain generations.
+* Deprecate toolchains generations 7 and 8, including closing PRs and issues for these toolchains.
+* Archive easyconfigs using toolchain generation 9 (and older).
+
+## Notes
+
+* This assumes we continue with two toolchain generations per year.
+* A toolchain generation exists when we have an lettered (i.e. 2024a) toolchain in `develop`.
+
+## Background
+
+The central easyconfigs repository is intended to provide references easyconfigs. For the reference easyconfigs we
+aim to have only one version of a software being used as a dependency in each toolchain generation. (There are
+exceptions, but we aim to keep these limited.)
+
+Sites and users can then supplement these easyconfigs via there own collection of easyconfigs. This additional
+collection is added via the [robot search path][robot_search_path].
+
+## Example
+
+As of November 2023 the latest toolchain generation is `2023b`.
+
+* Supported: 2023b, 2023a, 2022b, 2022a, 2021b, 2021a
+* Deprecated: 2020b and 2020a
+* Archived (and unsupported): 2019b and older
+

mkdocs.yml

@@ -108,6 +108,8 @@ nav:
   - List of supported software: version-specific/supported-software.md
   - Getting help: getting-help.md
   - User survey: user-survey/index.md
+  - Policies:
+      Supported Toolchain Generations: policies/toolchains.md
   - Other topics:
       - Alternative installation methods: installation-alternative.md
       - Configuration (legacy): legacy/configuration.md