[docs] add version warning to documentation for non-latest versions

Author: david-lev

docs/source/_templates/version-warning.html

@@ -0,0 +1,16 @@
+{% if not is_latest %}
+<div style="
+      background-color: #fff8dc;
+      border: 1px solid #f0e68c;
+      color: #555;
+      padding: 10px 15px;
+      text-align: center;
+      font-size: 0.95rem;
+      margin-bottom: 1rem;
+      border-radius: 4px;
+      box-shadow: inset 0 1px 0 rgba(255,255,255,0.3);
+  ">
+  ⚠ You are viewing documentation for version <b>{{ current_version }}</b>.
+  The latest version is <a href="/en/latest/">here</a>.
+</div>
+{% endif %}

docs/source/conf.py

@@ -33,6 +33,21 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
+
+html_context = {
+    "is_latest": os.environ.get("READTHEDOCS_VERSION_TYPE") == "latest",
+    "current_version": os.environ.get("READTHEDOCS_VERSION", "unknown"),
+}
+html_sidebars = {
+    "**": [
+        "navbar-logo.html",
+        "icon-links.html",
+        "version-warning.html",
+        "search-button-field.html",
+        "sbt-sidebar-nav.html",
+    ]
+}
+
 extensions = [
     "sphinx.ext.autodoc",
     "sphinx_copybutton",