bpo-37860: re-add netlify.toml to set up deploy previews for docs (#92852)

* Revert "bpo-46184: remove `netlify.toml` (#30272)"

This reverts commit fbaf2e6.

* Delete runtime.txt

* Create runtime.txt

* Delete runtime.txt

* Update netlify.toml

* Update netlify.toml

* Add netlify badge

* Update Doc/tools/templates/layout.html

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

* Update layout.html

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Author: epicfaace

Doc/conf.py

@@ -105,6 +105,14 @@
 # Short title used e.g. for <title> HTML tags.
 html_short_title = '%s Documentation' % release
 
+# Deployment preview information, from Netlify
+# (See netlify.toml and https://docs.netlify.com/configure-builds/environment-variables/#git-metadata)
+html_context = {
+    "is_deployment_preview": os.getenv("IS_DEPLOYMENT_PREVIEW"),
+    "repository_url": os.getenv("REPOSITORY_URL"),
+    "pr_id": os.getenv("REVIEW_ID")
+}
+
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
 html_last_updated_fmt = '%b %d, %Y'

Doc/tools/templates/layout.html

@@ -8,6 +8,19 @@
     <a href="/3/{{ pagename }}{{ file_suffix }}">{% trans %} Python documentation for the current stable release{% endtrans %}</a>.
 </div>
 {%- endif %}
+
+{%- if is_deployment_preview %}
+<div id="deployment-preview-warning" style="padding: .5em; text-align: center; background-color: #fff2ba; color: #6a580e;">
+  <div style="float: right; margin-top: -10px; margin-left: 10px;">
+    <a href="https://www.netlify.com">
+      <img src="https://www.netlify.com/img/global/badges/netlify-color-accent.svg" alt="Deploys by Netlify" />
+    </a>
+  </div>
+  {% trans %}This is a deploy preview created from a <a href="{{ repository_url }}/pull/{{ pr_id }}">pull request</a>.
+  For authoritative documentation, see the {% endtrans %}
+  <a href="https://docs.python.org/3/{{ pagename }}{{ file_suffix }}">{% trans %} the current stable release{% endtrans %}</a>.
+</div>
+{%- endif %}
 {% endblock %}
 
 {% block rootrellink %}

netlify.toml

@@ -0,0 +1,8 @@
+[build]
+    base = "Doc/"
+    command = "make html"
+    publish = "build/html"
+
+[build.environment]
+  PYTHON_VERSION = "3.8"
+  IS_DEPLOYMENT_PREVIEW = "true"