Infra: Add new directives to point to PEP's canonical content (#2702)

As originally discussed in #2692 , this adds a three new custom directives intended to be used at the top of PEPs:

* `pep-banner`, a generic admonition banner that can be subclassed with an arbitrary message,
* `canonical-docs`, which renders a banner linking to a `Final` PEP's canonical documentation/specification.
* `canonical-pypa-spec`, a banner for packaging interoperability PEPs linking to the canonical PyPA specs.

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

conf.py

@@ -10,7 +10,7 @@ sys.path.append(str(Path("pep_sphinx_extensions").absolute()))
 
 # Add 'include_patterns' as a config variable
 from sphinx.config import Config
-Config.config_values['include_patterns'] = [], 'env', []
+Config.config_values["include_patterns"] = [], "env", []
 del Config
 
 # -- Project information -----------------------------------------------------
@@ -21,7 +21,11 @@ master_doc = "contents"
 # -- General configuration ---------------------------------------------------
 
 # Add any Sphinx extension module names here, as strings.
-extensions = ["pep_sphinx_extensions", "sphinx.ext.githubpages"]
+extensions = [
+"pep_sphinx_extensions",
+"sphinx.ext.intersphinx",
+"sphinx.ext.githubpages",
+]
 
 # The file extensions of source files. Sphinx uses these suffixes as sources.
 source_suffix = {
@@ -46,6 +50,13 @@ exclude_patterns = [
     "pep-0012/pep-NNNN.rst",
 ]
 
+# Intersphinx configuration
+intersphinx_mapping = {
+    'python': ('https://docs.python.org/3/', None),
+    'packaging': ('https://packaging.python.org/en/latest/', None),
+}
+intersphinx_disabled_reftypes = []
+
 # -- Options for HTML output -------------------------------------------------
 
 # HTML output settings
@@ -60,4 +71,4 @@ html_permalinks = False  # handled in the PEPContents transform
 html_baseurl = "https://peps.python.org"  # to create the CNAME file
 gettext_auto_build = False  # speed-ups
 
-templates_path = ['pep_sphinx_extensions/pep_theme/templates']  # Theme template relative paths from `confdir`
+templates_path = ["pep_sphinx_extensions/pep_theme/templates"]  # Theme template relative paths from `confdir`

pep-0012.rst

@@ -649,6 +649,66 @@ If you find that you need to use a backslash in your text, consider
 using inline literals or a literal block instead.
 
 
+Canonical Documentation and Intersphinx
+---------------------------------------
+
+As :pep:`PEP 1 describes <1#pep-maintenance>`,
+PEPs are considered historical documents once marked Final,
+and their canonical documentation/specification should be moved elsewhere.
+To indicate this, use the ``canonical-docs`` directive
+or an appropriate subclass
+(currently ``canonical-pypa-spec`` for packaging standards).
+
+Furthermore, you can use
+`Intersphinx references
+<https://www.sphinx-doc.org/en/master/usage/extensions/intersphinx.html>`_
+to other Sphinx sites,
+currently the `Python documentation <https://docs.python.org/>`_
+and `packaging.python.org <https://packaging.python.org/>`_,
+to easily cross-reference pages, sections and Python/C objects.
+This works with both the "canonical" directives and anywhere in your PEP.
+
+Add the directive between the headers and the first section of the PEP
+(typically the Abstract)
+and pass as an argument an Intersphinx reference of the canonical doc/spec
+(or if the target is not on a Sphinx site, a `reST hyperlink <Hyperlinks_>`__).
+
+For example,
+to create a banner pointing to the :mod:`python:sqlite3` docs,
+you would write the following::
+
+    .. canonical-doc:: :mod:`python:sqlite3`
+
+which would generate the banner:
+
+    .. canonical-doc:: :mod:`python:sqlite3`
+
+Or for a PyPA spec,
+such as the :ref:`packaging:core-metadata`,
+you would use::
+
+    .. canonical-pypa-spec:: :ref:`packaging:core-metadata`
+
+which renders as:
+
+    .. canonical-pypa-spec:: :ref:`packaging:core-metadata`
+
+The argument accepts arbitrary reST,
+so you can include multiple linked docs/specs and name them whatever you like,
+and you can also include directive content that will be inserted into the text.
+The following advanced example::
+
+    .. canonical-doc:: the :ref:`python:sqlite3-connection-objects` and :exc:`python:~sqlite3.DataError` docs
+
+        Also, see the :ref:`Data Persistence docs <persistence>` for other examples.
+
+would render as:
+
+    .. canonical-doc:: the :ref:`python:sqlite3-connection-objects` and :exc:`python:sqlite3.DataError` docs
+
+        Also, see the :ref:`Data Persistence docs <persistence>` for other examples.
+
+
 Habits to Avoid
 ===============
 

pep_sphinx_extensions/__init__.py

@@ -10,6 +10,7 @@ from sphinx import project
 
 from pep_sphinx_extensions.pep_processor.html import pep_html_builder
 from pep_sphinx_extensions.pep_processor.html import pep_html_translator
+from pep_sphinx_extensions.pep_processor.parsing import pep_banner_directive
 from pep_sphinx_extensions.pep_processor.parsing import pep_parser
 from pep_sphinx_extensions.pep_processor.parsing import pep_role
 from pep_sphinx_extensions.pep_processor.transforms import pep_references
@@ -93,6 +94,14 @@ def setup(app: Sphinx) -> dict[str, bool]:
 
     app.add_post_transform(pep_references.PEPReferenceRoleTitleText)
 
+    # Register custom directives
+    app.add_directive(
+        "pep-banner", pep_banner_directive.PEPBanner)
+    app.add_directive(
+        "canonical-doc", pep_banner_directive.CanonicalDocBanner)
+    app.add_directive(
+        "canonical-pypa-spec", pep_banner_directive.CanonicalPyPASpecBanner)
+
     # Register event callbacks
     app.connect("builder-inited", _update_config_for_builder)  # Update configuration values for builder used
     app.connect("env-before-read-docs", create_pep_zero)  # PEP 0 hook

pep_sphinx_extensions/pep_processor/parsing/pep_banner_directive.py

@@ -0,0 +1,101 @@
+"""Roles to insert custom admonitions pointing readers to canonical content."""
+
+from __future__ import annotations
+
+from docutils import nodes
+from docutils.parsers import rst
+
+
+PYPA_SPEC_BASE_URL = "https://packaging.python.org/en/latest/specifications/"
+
+
+class PEPBanner(rst.Directive):
+    """Insert a special banner admonition in a PEP document."""
+
+    has_content = True
+    required_arguments = 0
+    optional_arguments = 1
+    final_argument_whitespace = True
+    option_spec = {}
+
+    admonition_pre_template = ""
+    admonition_pre_text = ""
+    admonition_post_text = ""
+
+    admonition_class = nodes.important
+    css_classes = ["pep-banner"]
+
+
+    def run(self) -> list[nodes.admonition]:
+
+        if self.arguments:
+            link_content = self.arguments[0]
+            pre_text = self.admonition_pre_template.format(
+                link_content=link_content)
+        else:
+            pre_text = self.admonition_pre_text
+
+        pre_text_node = nodes.paragraph(pre_text)
+        pre_text_node.line = self.lineno
+        pre_node, pre_msg = self.state.inline_text(pre_text, self.lineno)
+        pre_text_node.extend(pre_node + pre_msg)
+
+        post_text = self.admonition_post_text
+        post_text_node = nodes.paragraph(post_text)
+        post_text_node.line = self.lineno
+        post_node, post_msg = self.state.inline_text(post_text, self.lineno)
+        post_text_node.extend(post_node + post_msg)
+
+        source_lines = [pre_text] + list(self.content or []) + [post_text]
+        admonition_node = self.admonition_class(
+            "\n".join(source_lines), classes=self.css_classes)
+
+        admonition_node.append(pre_text_node)
+        if self.content:
+            self.state.nested_parse(
+                self.content, self.content_offset, admonition_node)
+        admonition_node.append(post_text_node)
+
+        return [admonition_node]
+
+
+class CanonicalDocBanner(PEPBanner):
+    """Insert an admonition pointing readers to a PEP's canonical docs."""
+
+    admonition_pre_template = (
+        "This PEP is a historical document. "
+        "The up-to-date, canonical documentation can now be found "
+        "at {link_content}."
+    )
+    admonition_pre_text = (
+        "This PEP is a historical document. "
+        "The up-to-date, canonical documentation can now be found elsewhere."
+    )
+    admonition_post_text = (
+        "See :pep:`1` for how to propose changes."
+    )
+
+    css_classes = [*PEPBanner.css_classes, "canonical-doc"]
+
+
+
+class CanonicalPyPASpecBanner(PEPBanner):
+    """Insert a specialized admonition for PyPA packaging specifications."""
+
+    admonition_pre_template = (
+        "This PEP is a historical document. "
+        "the up-to-date, canonical spec, {link_content}, is maintained on "
+        f"the `PyPA specs page <{PYPA_SPEC_BASE_URL}>`__."
+    )
+    admonition_pre_text = (
+        "This PEP is a historical document. "
+        "The up-to-date, canonical specification is maintained on "
+        f"the `PyPA specs page <{PYPA_SPEC_BASE_URL}>`__."
+    )
+    admonition_post_text = (
+        "See the `PyPA specification update process "
+        "<https://www.pypa.io/en/latest/specifications/#handling-fixes-and-other-minor-updates>`__ "
+        "for how to propose changes."
+    )
+
+    css_classes = [*PEPBanner.css_classes, "canonical-pypa-spec"]