Infra: Add nicer 404 page (#4184)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Makefile

@@ -40,6 +40,7 @@ htmllive: _ensure-sphinx-autobuild html
 .PHONY: dirhtml
 dirhtml: BUILDER = dirhtml
 dirhtml: html
+	mv $(BUILDDIR)/404/index.html $(BUILDDIR)/404.html
 
 ## linkcheck      to check validity of links within PEP sources
 .PHONY: linkcheck

peps/conf.py

@@ -19,6 +19,7 @@ master_doc = "contents"
 
 # Add any Sphinx extension module names here, as strings.
 extensions = [
+    "notfound.extension",
     "pep_sphinx_extensions",
     "sphinx.ext.extlinks",
     "sphinx.ext.intersphinx",
@@ -85,6 +86,10 @@ extlinks = {
     "pypi": ("https://pypi.org/project/%s/", "%s"),
 }
 
+# sphinx-notfound-page
+# https://sphinx-notfound-page.readthedocs.io/en/latest/faq.html#does-this-extension-work-with-github-pages
+notfound_urls_prefix = None
+
 # -- Options for HTML output -------------------------------------------------
 
 _PSE_PATH = _ROOT / "pep_sphinx_extensions"

requirements.txt

@@ -4,6 +4,7 @@ Pygments >= 2.9.0
 # See https://github.com/sphinx-doc/sphinx/pull/11100
 Sphinx >= 5.1.1, != 6.1.0, != 6.1.1, < 8.1.0
 docutils >= 0.19.0
+sphinx-notfound-page >= 1.0.2
 
 # For tests
 pytest