docs: Show development version warning using theme

.readthedocs.yaml

@@ -14,6 +14,15 @@ build:
     - curl
     - jq
   jobs:
+    post_checkout:
+      # Read the Docs clones with --depth 50 and without tags, so hatch-vcs cannot find
+      # the release tag and falls back to a "0.1.dev50" version. That is what reaches
+      # the docs as Sphinx's ``version`` and ``release``, so without this the published
+      # documentation for a release reports itself as 0.1.dev50.
+      #
+      # --unshallow errors on an already complete clone, so fall back to fetching the
+      # tags alone rather than ignoring every failure.
+      - git fetch --tags --unshallow || git fetch --tags
     post_create_environment:
       - pip install uv
     post_install:

docs/citations.rst

@@ -1,9 +1,12 @@
 Use and Citations
 =================
 
-.. raw:: html
+.. ifconfig:: is_development_build
 
-   <p id="dev-version"><strong>Warning:</strong> This is a development version and should not be cited. To find the specific version to cite, please go to <a href="https://pyhf.readthedocs.io/">ReadTheDocs</a>.</p>
+   .. warning::
+
+      This is a development version and should not be cited. To find the specific
+      version to cite, please go to `ReadTheDocs <https://pyhf.readthedocs.io/>`__.
 
 Citation
 --------

docs/conf.py

@@ -16,6 +16,7 @@
 # documentation root, use Path('../relative_path_to_dir').resolve() to make it absolute, like shown here.
 
 import importlib.metadata
+import os
 import sys
 from pathlib import Path
 
@@ -36,6 +37,7 @@ def setup(app):
     app.add_css_file(
         "https://cdnjs.cloudflare.com/ajax/libs/github-fork-ribbon-css/0.2.2/gh-fork-ribbon.min.css"
     )
+    app.add_config_value("is_development_build", default=False, rebuild="env")
 
 
 # -- General configuration ------------------------------------------------
@@ -240,11 +242,38 @@ def setup(app):
 #
 html_theme = "pydata_sphinx_theme"
 
+# Read the Docs provides its own version switcher, so these docs do not need one, but
+# its notification addon renders nothing, so the development version still has to say
+# so for itself. That covers the GitHub Pages deployment and local builds, neither of
+# which is on Read the Docs, along with Read the Docs' own "latest" and its pull
+# request previews, which set READTHEDOCS_VERSION to the pull request number. Builds of
+# "stable" and of a release tag say nothing.
+#
+# The theme's own 'show_version_warning_banner' cannot be used for this, as it is only
+# rendered when a version switcher 'json_url' is configured.
+is_development_build = (
+    os.environ.get("READTHEDOCS") != "True"
+    or os.environ.get("READTHEDOCS_VERSION") == "latest"
+    or os.environ.get("READTHEDOCS_VERSION_TYPE") == "external"
+)
+
+_announcement = (
+    "This is a development version. The latest stable version is at "
+    '<a href="https://pyhf.readthedocs.io/">pyhf.readthedocs.io</a>.'
+    if is_development_build
+    else ""
+)
+
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
 #
-html_theme_options = {"header_links_before_dropdown": 6}
+html_theme_options = {
+    "header_links_before_dropdown": 6,
+    # c.f. https://pydata-sphinx-theme.readthedocs.io/en/stable/user_guide/announcements.html
+    "announcement": _announcement,
+    "sticky_banners": True,
+}
 
 # Add any paths that contain custom themes here, relative to this directory.
 html_theme_path = []
@@ -274,12 +303,7 @@ def setup(app):
 # so a file named "default.css" will overwrite the builtin "default.css".
 html_static_path = ["_static"]
 
-html_css_files = [
-    "css/custom.css",
-]
-
 html_js_files = [
-    "js/custom.js",
     (
         "https://views.scientific-python.org/js/plausible.js",
         {"data-domain": "pyhf.readthedocs.io", "defer": "defer"},

docs/index.rst

@@ -22,10 +22,6 @@
    release-notes
    contributors
 
-.. raw:: html
-
-   <p id="dev-version"><strong>Warning:</strong> This is a development version. The latest stable version is at <a href="https://pyhf.readthedocs.io/">ReadTheDocs</a>.</p>
-
 ..
   Comment: Splice the JupyterLite example into the README by looking for a particular comment