Date:   Sat, 28 Oct 2023 18:29:31 +0200
From:   Vegard Nossum <vegard.nossum@...cle.com>
To:     Jonathan Corbet <corbet@....net>
Cc:     linux-doc@...r.kernel.org,
        Federico Vaga <federico.vaga@...a.pv.it>,
        Akira Yokosawa <akiyks@...il.com>,
        Carlos Bilbao <carlos.bilbao@....com>,
        Alex Shi <alexs@...nel.org>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Hu Haowen <src.res.211@...il.com>,
        linux-kernel@...r.kernel.org,
        Vegard Nossum <vegard.nossum@...cle.com>
Subject: [PATCH] docs: translations: add translations links when they exist

Add a new Sphinx extension that knows about the translations of kernel
documentation and can insert links to the translations at the top of
the document.

It basically works like this:

1. Register a new node type, LanguagesNode.

2. Register a new transform, TranslationsTransform, that inserts a new
   LanguageNode at the top of every document. The LanguageNode contains
   "pending references" to translations of the document. The key here
   is that these are pending (i.e. unresolved) references that may or
   may not actually exist.

3. Register a 'doctree-resolved' event that iterates over all the
   LanguageNode nodes. Any unresolved references are filtered out; the
   list of resolved references is passed to the 'translations.html'
   template and rendered as an HTML node (if HTML output is selected).

Testing: make htmldocs with v7.3.0.

Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
---
 Documentation/conf.py                         |  2 +-
 Documentation/sphinx-static/custom.css        |  8 ++
 .../sphinx/templates/translations.html        | 12 +++
 Documentation/sphinx/translations.py          | 96 +++++++++++++++++++
 4 files changed, 117 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/sphinx/templates/translations.html
 create mode 100644 Documentation/sphinx/translations.py

diff --git a/Documentation/conf.py b/Documentation/conf.py
index d4fdf6a3875a..64eab500b2cd 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -55,7 +55,7 @@ needs_sphinx = '1.7'
 extensions = ['kerneldoc', 'rstFlatTable', 'kernel_include',
               'kfigure', 'sphinx.ext.ifconfig', 'automarkup',
               'maintainers_include', 'sphinx.ext.autosectionlabel',
-              'kernel_abi', 'kernel_feat']
+              'kernel_abi', 'kernel_feat', 'translations']
 
 if major >= 3:
     if (major > 3) or (minor > 0 or patch >= 2):
diff --git a/Documentation/sphinx-static/custom.css b/Documentation/sphinx-static/custom.css
index 084a884f6fb7..33adee4a35d9 100644
--- a/Documentation/sphinx-static/custom.css
+++ b/Documentation/sphinx-static/custom.css
@@ -73,3 +73,11 @@ input.kernel-toc-toggle { display: none; }
     h3.kernel-toc-contents { display: inline; }
     div.kerneltoc a { color: black; }
 }
+
+/* Language selection bar */
+div.language-selection {
+    background: #eeeeee;
+    border: 1px solid #cccccc;
+    margin-bottom: 1em;
+    padding: .5em;
+}
diff --git a/Documentation/sphinx/templates/translations.html b/Documentation/sphinx/templates/translations.html
new file mode 100644
index 000000000000..08afb595c203
--- /dev/null
+++ b/Documentation/sphinx/templates/translations.html
@@ -0,0 +1,12 @@
+<!-- SPDX-License-Identifier: GPL-2.0 -->
+<!-- Copyright © 2023, Oracle and/or its affiliates. -->
+
+{# Create a language bar for translations #}
+{% if languages|length > 0: %}
+<div class="language-selection">
+Languages:
+{% for ref in languages: %}
+<a href="{{ ref.refuri }}">{{ ref.astext() }}</a>{% if not loop.last %}, {% endif %}
+{% endfor %}
+</div>
+{% endif %}
diff --git a/Documentation/sphinx/translations.py b/Documentation/sphinx/translations.py
new file mode 100644
index 000000000000..e1da811bdaf0
--- /dev/null
+++ b/Documentation/sphinx/translations.py
@@ -0,0 +1,96 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright © 2023, Oracle and/or its affiliates.
+# Author: Vegard Nossum <vegard.nossum@...cle.com>
+#
+# Add translation links to the top of the document.
+#
+
+import os
+
+from docutils import nodes
+from docutils.transforms import Transform
+
+import sphinx
+from sphinx import addnodes
+from sphinx.errors import NoUri
+
+all_languages = {
+    # English is always first
+    None: 'English',
+
+    # Keep the rest sorted alphabetically
+    'zh_CN': 'Chinese',
+    'it_IT': 'Italian',
+    'ja_JP': 'Japanese',
+    'ko_KR': 'Korean',
+    'sp_SP': 'Spanish',
+    'zh_TW': 'Taiwanese',
+}
+
+class LanguagesNode(nodes.Element):
+    pass
+
+class TranslationsTransform(Transform):
+    default_priority = 900
+
+    def apply(self):
+        app = self.document.settings.env.app
+        if app.builder.format not in ['html']:
+            return
+
+        docname = self.document.settings.env.docname
+
+        this_lang_code = None
+        components = docname.split(os.sep)
+        if components[0] == 'translations' and len(components) > 2:
+            this_lang_code = components[1]
+
+            # normalize docname to be the untranslated one
+            docname = os.path.join(*components[2:])
+
+        new_nodes = LanguagesNode()
+
+        for lang_code, lang_name in all_languages.items():
+            if lang_code == this_lang_code:
+                continue
+
+            if lang_code is None:
+                target_name = docname
+            else:
+                target_name = os.path.join('translations', lang_code, docname)
+
+            pxref = addnodes.pending_xref('', refdomain='std',
+                reftype='doc', reftarget='/' + target_name, modname=None,
+                classname=None, refexplicit=True)
+            pxref += nodes.Text(lang_name)
+            new_nodes += pxref
+
+        self.document.insert(0, new_nodes)
+
+def process_languages(app, doctree, docname):
+    for node in doctree.traverse(LanguagesNode):
+        languages = []
+
+        # Iterate over the child nodes; any resolved links will have
+        # the type 'nodes.reference', while unresolved links will be
+        # type 'nodes.Text'.
+        languages = list(filter(lambda xref:
+            isinstance(xref, nodes.reference), node.children))
+
+        html_content = app.builder.templates.render('translations.html',
+            context={
+                'languages': languages,
+            })
+
+        node.replace_self(nodes.raw('', html_content, format='html'))
+
+def setup(app):
+    app.add_node(LanguagesNode)
+    app.add_transform(TranslationsTransform)
+    app.connect('doctree-resolved', process_languages)
+
+    return {
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
+    }
-- 
2.34.1

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