Document the versioning scheme

This documents the versioning scheme proposed with #18938, refined as
part of the discussion #19003 (first drafted patch) and #19034 (second
drafted patch) and applied with commit 6d55a11.

docs/website/docs/developers/general/versioning-scheme.md

@@ -0,0 +1,72 @@
+---
+icon: octicons/versions-16
+---
+
+# Versioning scheme
+
+A shared version format is used for the packages
+
+* `iree-base-compiler` (formally named `iree-compiler`)
+* `iree-base-runtime` (formally named `iree-runtime`)
+* `iree-turbine`
+
+## Overview
+
+Type of build | Version format | Version example
+------------- | -------------- | ---------------
+Stable release (PyPI) | `X.Y.Z` | `3.0.0`
+Nightly release (GitHub `schedule`) | `X.Y.ZrcYYYYMMDD` | `3.0.0rc20241029`
+Dev release (GitHub `pull_request`) | `X.Y.Z.devNN` | `3.0.0.dev+6d55a11`
+Local build | `X.Y.Z.devNN` | `3.0.0.dev+6d55a11`
+
+### Key
+
+Identifier | Explanation
+---------- | -----------
+`X` | Major version
+`Y` | Minor version
+`Z` | Patch version
+`rc` | release candidate (`main` branch)
+`dev` | developer build (code on pull request branches)
+`YYYY` | Year, e.g. `2024`
+`MM` | Month, e.g. `10`
+`DD` | Day, e.g. `29`
+`NN` | git commit hash, e.g. `6d55a11`
+
+## Composition of version numbers
+
+A release number is in the format of `X.Y.Z` (MAJOR.MAJOR.PATCH)
+
+* `X` and `Y` are defined as shared version numbers between all packages.
+* The patch level `Z` MAY be incremented individually.
+* A PATCH release contains only bug fixes and the version `Z` (`x.y.Z`) MUST be
+  incremented. A bug fix is an internal change that fixes incorrect behavior
+  and MUST NOT introduce breaking changes.
+* A MINOR release (unlike SemVer) as well as a MAJOR release MAY contain
+  backwards-incompatible, breaking changes, like API changes and removals and
+  furthermore bug fixes and new features.
+
+### Development and nightly releases
+
+* Development builds (e.g. from a regular CI) MUST be released with a version
+  number defined as `X.Y.Z.dev+NN`, where `NN` is the git commit hash.
+* Nightly releases MUST be released with a version number defined as `X.Y.ZrcYYYYMMDD`.
+* The intent is to promote a recent, high quality release candidate to a final
+  version.
+
+Binary stamps and tools will continue to report the original release candidate version.
+
+## Semantics
+
+The following semantics apply:
+
+* If the version `X` (`X.y.z`) is increased for one package, the version number
+  change MUST be adopted by all (other) packages. The same applies for the
+  version `Y` (`x.Y.Z`).
+* If the version `X` or `Y` are changed, `Z` MUST be set `0`.
+* After a release, `Y` MUST be increased to ensure precedence of nightly builds.
+  For example:
+    * The latest stable release published on November 15th 2024 is versioned as
+      version `3.0.0`.
+    * The next nightly builds are released as `3.1.0rc20241116`.
+    * The next stable release is released as or `3.1.0`.

docs/website/mkdocs.yml

@@ -197,6 +197,7 @@ nav:
           - "developers/general/developer-tips.md"
           - "developers/general/github-actions.md"
           - "developers/general/release-management.md"
+          - "developers/general/versioning-scheme.md"
           - "developers/general/testing-guide.md"
       - "Building":
           - "developers/building/bazel.md"