Support and prefer ``.jinja`` to ``_t`` for static templates (#11165)

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

66 files changed, 299 insertions, 60 deletions

diff --git a/CHANGES b/CHANGES
index a66c2c460..8a77524fe 100644
--- a/CHANGES
+++ b/CHANGES
@@ -23,6 +23,11 @@ Deprecated
 ----------
 
 * #11247: Deprecate the legacy ``intersphinx_mapping`` format
+* #11165: Warn when the ``_t`` suffix is used for template files. The formal
+  deprecation process will begin no earlier than 31 December 2024.
+  Templates should change to use the ``.jinja`` filename suffix instead.
+  For more information, see :ref:`theming-static-templates`.
+  Patch by James Addison and Adam Turner
 
 Features added
 --------------
@@ -60,6 +65,10 @@ Features added
   ``= 'xelatex'``.  Patch by Dimitar Dimitrov
 * #11109, #9643: Add :confval:`python_display_short_literal_types` option for
   condensed rendering of ``Literal`` types.
+* #11165: Support the `officially recommended`_ ``.jinja`` suffix for template
+  files. Patch by James Addison
+
+  .. _officially recommended: https://jinja.palletsprojects.com/en/latest/templates/#template-file-extension
 
 Bugs fixed
 ----------
diff --git a/doc/development/theming.rst b/doc/development/theming.rst
index 3a156fa4f..65216787f 100644
--- a/doc/development/theming.rst
+++ b/doc/development/theming.rst
@@ -156,13 +156,51 @@ template static files as well as HTML files.  Therefore, Sphinx supports
 so-called "static templates", like this:
 
 If the name of a file in the ``static/`` directory of a theme (or in the user's
-static path, for that matter) ends with ``_t``, it will be processed by the
-template engine.  The ``_t`` will be left from the final file name.  For
-example, the *classic* theme has a file ``static/classic.css_t`` which uses
-templating to put the color options into the stylesheet.  When a documentation
+static path, for that matter) ends with ``.jinja``, it will be processed by the
+template engine.  The ``.jinja`` will be removed from the final file name.  For
+example, the *classic* theme has a file ``static/classic.css.jinja`` which uses
+templating to put the colour options into the stylesheet.  When a documentation
 is built with the classic theme, the output directory will contain a
 ``_static/classic.css`` file where all template tags have been processed.
 
+.. versionchanged:: 6.2
+
+   The preferred suffix for static templates is now ``.jinja``, in line with
+   the Jinja project's `recommended file extension`_.
+
+   The ``_t`` file suffix for static templates is now considered 'legacy', and
+   support will eventually be removed. The standard deprecation process will
+   begin no earlier than 31 December 2024, at which point using ``_t`` suffixes
+   will emit ``RemovedInSphinx__Warning`` warnings.
+
+   If a static template with a ``_t`` suffix is detected, it will be processed
+   by the template engine, with the ``_t`` suffix removed from the final file
+   name.
+
+   To silence the warning for ``_t`` suffixes, the new
+   ``sphinx.deprecation.OldJinjaSuffixWarning`` class has been added for use
+   with Python's standard `warning control`_ mechanisms. This class will be
+   removed no earlier than 31 December 2024, so guard any imports with a
+   try/except block.
+   For example, in a ``setup()`` function:
+
+   .. code:: python
+
+       import warnings
+
+       def setup(app):
+           try:
+               from sphinx.deprecation import OldJinjaSuffixWarning
+           except ImportError:
+               pass  # Only silence the warning if it exists!
+           else:
+               warnings.filterwarnings('ignore', category=OldJinjaSuffixWarning)
+
+           ...
+
+  .. _recommended file extension: https://jinja.palletsprojects.com/en/latest/templates/#template-file-extension
+  .. _warning control: https://docs.python.org/3/library/warnings.html#the-warnings-filter
+
 
 Use custom page metadata in HTML templates
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/doc/latex.rst b/doc/latex.rst
index 1a9f6a2ec..e82ff1060 100644
--- a/doc/latex.rst
+++ b/doc/latex.rst
@@ -1811,12 +1811,12 @@ Miscellany
 .. hint::
 
    As an experimental feature, Sphinx can use user-defined template file for
-   LaTeX source if you have a file named ``_templates/latex.tex_t`` in your
+   LaTeX source if you have a file named ``_templates/latex.tex.jinja`` in your
    project.
 
-   Additional files ``longtable.tex_t``, ``tabulary.tex_t`` and
-   ``tabular.tex_t`` can be added to ``_templates/`` to configure some aspects
-   of table rendering (such as the caption position).
+   Additional files ``longtable.tex.jinja``, ``tabulary.tex.jinja`` and
+   ``tabular.tex.jinja`` can be added to ``_templates/`` to configure some
+   aspects of table rendering (such as the caption position).
 
    .. versionadded:: 1.6
       currently all template variables are unstable and undocumented.
diff --git a/sphinx/builders/_epub_base.py b/sphinx/builders/_epub_base.py
index dfe4877ec..f06ff520b 100644
--- a/sphinx/builders/_epub_base.py
+++ b/sphinx/builders/_epub_base.py
@@ -603,7 +603,8 @@ class EpubBuilder(StandaloneHTMLBuilder):
                                             html.escape(self.refnodes[0]['refuri'])))
 
         # write the project file
-        copy_asset_file(path.join(self.template_dir, 'content.opf_t'), self.outdir, metadata)
+        content_t = path.join(self.template_dir, 'content.opf.jinja')
+        copy_asset_file(content_t, self.outdir, metadata)
 
     def new_navpoint(self, node: dict[str, Any], level: int, incr: bool = True) -> NavPoint:
         """Create a new entry in the toc from the node at given level."""
@@ -686,7 +687,7 @@ class EpubBuilder(StandaloneHTMLBuilder):
         navpoints = self.build_navpoints(refnodes)
         level = max(item['level'] for item in self.refnodes)
         level = min(level, self.config.epub_tocdepth)
-        copy_asset_file(path.join(self.template_dir, 'toc.ncx_t'), self.outdir,
+        copy_asset_file(path.join(self.template_dir, 'toc.ncx.jinja'), self.outdir,
                         self.toc_metadata(level, navpoints))
 
     def build_epub(self) -> None:
diff --git a/sphinx/builders/changes.py b/sphinx/builders/changes.py
index 5c118bef9..f6b9152f9 100644
--- a/sphinx/builders/changes.py
+++ b/sphinx/builders/changes.py
@@ -133,10 +133,10 @@ class ChangesBuilder(Builder):
                 f.write(self.templates.render('changes/rstsource.html', ctx))
         themectx = {'theme_' + key: val for (key, val) in
                     self.theme.get_options({}).items()}
-        copy_asset_file(path.join(package_dir, 'themes', 'default', 'static', 'default.css_t'),
-                        self.outdir, context=themectx, renderer=self.templates)
-        copy_asset_file(path.join(package_dir, 'themes', 'basic', 'static', 'basic.css'),
-                        self.outdir)
+        default_t = path.join(package_dir, 'themes', 'default', 'static', 'default.css.jinja')
+        copy_asset_file(default_t, self.outdir, context=themectx, renderer=self.templates)
+        basic = path.join(package_dir, 'themes', 'basic', 'static', 'basic.css')
+        copy_asset_file(basic, self.outdir)
 
     def hl(self, text: str, version: str) -> str:
         text = html.escape(text)
diff --git a/sphinx/builders/epub3.py b/sphinx/builders/epub3.py
index 03f4684d1..aaae0bcee 100644
--- a/sphinx/builders/epub3.py
+++ b/sphinx/builders/epub3.py
@@ -184,7 +184,7 @@ class Epub3Builder(_epub_base.EpubBuilder):
             # 'includehidden'
             refnodes = self.refnodes
         navlist = self.build_navlist(refnodes)
-        copy_asset_file(path.join(self.template_dir, 'nav.xhtml_t'), self.outdir,
+        copy_asset_file(path.join(self.template_dir, 'nav.xhtml.jinja'), self.outdir,
                         self.navigation_doc_metadata(navlist))
 
         # Add nav.xhtml to epub file
diff --git a/sphinx/builders/gettext.py b/sphinx/builders/gettext.py
index 4d460109b..414ed50bd 100644
--- a/sphinx/builders/gettext.py
+++ b/sphinx/builders/gettext.py
@@ -283,7 +283,7 @@ class MessageCatalogBuilder(I18nBuilder):
             ensuredir(path.join(self.outdir, path.dirname(textdomain)))
 
             context['messages'] = list(catalog)
-            content = GettextRenderer(outdir=self.outdir).render('message.pot_t', context)
+            content = GettextRenderer(outdir=self.outdir).render('message.pot.jinja', context)
 
             pofn = path.join(self.outdir, textdomain + '.pot')
             if should_write(pofn, content):
diff --git a/sphinx/builders/latex/__init__.py b/sphinx/builders/latex/__init__.py
index f1f0cff2b..b8472a3c0 100644
--- a/sphinx/builders/latex/__init__.py
+++ b/sphinx/builders/latex/__init__.py
@@ -402,7 +402,7 @@ class LaTeXBuilder(Builder):
         # use pre-1.6.x Makefile for make latexpdf on Windows
         if os.name == 'nt':
             staticdirname = path.join(package_dir, 'texinputs_win')
-            copy_asset_file(path.join(staticdirname, 'Makefile_t'),
+            copy_asset_file(path.join(staticdirname, 'Makefile.jinja'),
                             self.outdir, context=context)
 
     @progress_message(__('copying additional files'))
@@ -441,7 +441,7 @@ class LaTeXBuilder(Builder):
         if self.context['babel'] or self.context['polyglossia']:
             context['addtocaptions'] = r'\addto\captions%s' % self.babel.get_language()
 
-        filename = path.join(package_dir, 'templates', 'latex', 'sphinxmessages.sty_t')
+        filename = path.join(package_dir, 'templates', 'latex', 'sphinxmessages.sty.jinja')
         copy_asset_file(filename, self.outdir, context=context, renderer=LaTeXRenderer())
 
 
diff --git a/sphinx/cmd/quickstart.py b/sphinx/cmd/quickstart.py
index 6122ddd98..580fa7d6d 100644
--- a/sphinx/cmd/quickstart.py
+++ b/sphinx/cmd/quickstart.py
@@ -370,29 +370,29 @@ def generate(
             if 'quiet' not in d:
                 print(__('File %s already exists, skipping.') % fpath)
 
-    conf_path = os.path.join(templatedir, 'conf.py_t') if templatedir else None
+    conf_path = os.path.join(templatedir, 'conf.py.jinja') if templatedir else None
     if not conf_path or not path.isfile(conf_path):
-        conf_path = os.path.join(package_dir, 'templates', 'quickstart', 'conf.py_t')
+        conf_path = os.path.join(package_dir, 'templates', 'quickstart', 'conf.py.jinja')
     with open(conf_path, encoding="utf-8") as f:
         conf_text = f.read()
 
     write_file(path.join(srcdir, 'conf.py'), template.render_string(conf_text, d))
 
     masterfile = path.join(srcdir, d['master'] + d['suffix'])
-    if template._has_custom_template('quickstart/master_doc.rst_t'):
+    if template._has_custom_template('quickstart/master_doc.rst.jinja'):
         msg = ('A custom template `master_doc.rst_t` found. It has been renamed to '
                '`root_doc.rst_t`.  Please rename it on your project too.')
         print(colorize('red', msg))
-        write_file(masterfile, template.render('quickstart/master_doc.rst_t', d))
+        write_file(masterfile, template.render('quickstart/master_doc.rst.jinja', d))
     else:
-        write_file(masterfile, template.render('quickstart/root_doc.rst_t', d))
+        write_file(masterfile, template.render('quickstart/root_doc.rst.jinja', d))
 
     if d.get('make_mode') is True:
-        makefile_template = 'quickstart/Makefile.new_t'
-        batchfile_template = 'quickstart/make.bat.new_t'
+        makefile_template = 'quickstart/Makefile.new.jinja'
+        batchfile_template = 'quickstart/make.bat.new.jinja'
     else:
-        makefile_template = 'quickstart/Makefile_t'
-        batchfile_template = 'quickstart/make.bat_t'
+        makefile_template = 'quickstart/Makefile.jinja'
+        batchfile_template = 'quickstart/make.bat.jinja'
 
     if d['makefile'] is True:
         d['rsrcdir'] = 'source' if d['sep'] else '.'
diff --git a/sphinx/deprecation.py b/sphinx/deprecation.py
index fbd5463cc..7d5a2d2ab 100644
--- a/sphinx/deprecation.py
+++ b/sphinx/deprecation.py
@@ -62,3 +62,31 @@ def _deprecation_warning(
 
     warnings.warn(message + " Check CHANGES for Sphinx API modifications.",
                   warning_class, stacklevel=3)
+
+
+class OldJinjaSuffixWarning(PendingDeprecationWarning):
+    """Warning class for ``_old_jinja_template_suffix_warning``.
+
+    This class exists only so that extensions and themes can silence the legacy
+    filename warning via Python's `warning control`_ mechanisms. See
+    :ref:`theming-static-templates` for an example.
+
+    This warning class will be removed, and the warning class changed to the
+    appropriate RemovedInSphinx_0Warning no earlier than 31 December 2024, at
+    which point the standard deprecation process for ``_t`` template suffixes
+    will start.
+
+    .. _warning control: https://docs.python.org/3/library/warnings.html#the-warnings-filter
+    """
+
+
+def _old_jinja_template_suffix_warning(filename: str) -> None:
+    if filename.endswith('_t'):
+        warnings.warn(
+            f"{filename!r}: the '_t' suffix for Jinja templates is deprecated. "
+            "If the file is a template, use the suffix '.jinja' instead. "
+            'For more information, see '
+            'https://www.sphinx-doc.org/en/master/development/theming.html#static-templates',
+            OldJinjaSuffixWarning,
+            stacklevel=3,
+        )
diff --git a/sphinx/ext/apidoc.py b/sphinx/ext/apidoc.py
index 108515d73..9c9336075 100644
--- a/sphinx/ext/apidoc.py
+++ b/sphinx/ext/apidoc.py
@@ -102,7 +102,7 @@ def create_module_file(package: str, basename: str, opts: Any,
         'qualname': qualname,
         'automodule_options': options,
     }
-    text = ReSTRenderer([user_template_dir, template_dir]).render('module.rst_t', context)
+    text = ReSTRenderer([user_template_dir, template_dir]).render('module.rst.jinja', context)
     write_file(qualname, text, opts)
 
 
@@ -138,7 +138,8 @@ def create_package_file(root: str, master_package: str, subroot: str, py_files:
         'show_headings': not opts.noheadings,
         'maxdepth': opts.maxdepth,
     }
-    text = ReSTRenderer([user_template_dir, template_dir]).render('package.rst_t', context)
+    engine = ReSTRenderer([user_template_dir, template_dir])
+    text = engine.render('package.rst.jinja', context)
     write_file(pkgname, text, opts)
 
     if submodules and opts.separatemodules:
@@ -163,7 +164,7 @@ def create_modules_toc_file(modules: list[str], opts: Any, name: str = 'modules'
         'maxdepth': opts.maxdepth,
         'docnames': modules,
     }
-    text = ReSTRenderer([user_template_dir, template_dir]).render('toc.rst_t', context)
+    text = ReSTRenderer([user_template_dir, template_dir]).render('toc.rst.jinja', context)
     write_file(name, text, opts)
 
 
diff --git a/sphinx/ext/imgmath.py b/sphinx/ext/imgmath.py
index 34d716686..975cbcca5 100644
--- a/sphinx/ext/imgmath.py
+++ b/sphinx/ext/imgmath.py
@@ -19,6 +19,7 @@ from sphinx import package_dir
 from sphinx.application import Sphinx
 from sphinx.builders import Builder
 from sphinx.config import Config
+from sphinx.deprecation import _old_jinja_template_suffix_warning
 from sphinx.errors import SphinxError
 from sphinx.locale import _, __
 from sphinx.util import logging, sha1
@@ -95,16 +96,20 @@ def generate_latex_macro(image_format: str,
     }
 
     if config.imgmath_use_preview:
-        template_name = 'preview.tex_t'
+        template_name = 'preview.tex'
     else:
-        template_name = 'template.tex_t'
+        template_name = 'template.tex'
 
     for template_dir in config.templates_path:
-        template = path.join(confdir, template_dir, template_name)
-        if path.exists(template):
-            return LaTeXRenderer().render(template, variables)
-
-    return LaTeXRenderer(templates_path).render(template_name, variables)
+        # TODO: deprecate '_t' template suffix support after 2024-12-31
+        for template_suffix in ('_t', '.jinja'):
+            template = path.join(confdir, template_dir, template_name + template_suffix)
+            if path.exists(template):
+                _old_jinja_template_suffix_warning(template)
+                return LaTeXRenderer().render(template, variables)
+
+    # Default: fallback to a pathless in-library jinja template
+    return LaTeXRenderer(templates_path).render(f"{template_name}.jinja", variables)
 
 
 def ensure_tempdir(builder: Builder) -> str:
diff --git a/sphinx/templates/apidoc/module.rst_t b/sphinx/templates/apidoc/module.rst.jinja
index 249027855..249027855 100644
--- a/sphinx/templates/apidoc/module.rst_t
+++ b/sphinx/templates/apidoc/module.rst.jinja
diff --git a/sphinx/templates/apidoc/package.rst_t b/sphinx/templates/apidoc/package.rst.jinja
index 2229c311b..2229c311b 100644
--- a/sphinx/templates/apidoc/package.rst_t
+++ b/sphinx/templates/apidoc/package.rst.jinja
diff --git a/sphinx/templates/apidoc/toc.rst_t b/sphinx/templates/apidoc/toc.rst.jinja
index f0877eeb2..f0877eeb2 100644
--- a/sphinx/templates/apidoc/toc.rst_t
+++ b/sphinx/templates/apidoc/toc.rst.jinja
diff --git a/sphinx/templates/epub3/content.opf_t b/sphinx/templates/epub3/content.opf.jinja
index 417888c7e..417888c7e 100644
--- a/sphinx/templates/epub3/content.opf_t
+++ b/sphinx/templates/epub3/content.opf.jinja
diff --git a/sphinx/templates/epub3/nav.xhtml_t b/sphinx/templates/epub3/nav.xhtml.jinja
index 2a32c2039..2a32c2039 100644
--- a/sphinx/templates/epub3/nav.xhtml_t
+++ b/sphinx/templates/epub3/nav.xhtml.jinja
diff --git a/sphinx/templates/epub3/toc.ncx_t b/sphinx/templates/epub3/toc.ncx.jinja
index 0ea7ca366..0ea7ca366 100644
--- a/sphinx/templates/epub3/toc.ncx_t
+++ b/sphinx/templates/epub3/toc.ncx.jinja
diff --git a/sphinx/templates/gettext/message.pot_t b/sphinx/templates/gettext/message.pot.jinja
index 6138f54c9..6138f54c9 100644
--- a/sphinx/templates/gettext/message.pot_t
+++ b/sphinx/templates/gettext/message.pot.jinja
diff --git a/sphinx/templates/imgmath/preview.tex_t b/sphinx/templates/imgmath/preview.tex.jinja
index f3fdcda07..f3fdcda07 100644
--- a/sphinx/templates/imgmath/preview.tex_t
+++ b/sphinx/templates/imgmath/preview.tex.jinja
diff --git a/sphinx/templates/imgmath/template.tex_t b/sphinx/templates/imgmath/template.tex.jinja
index 92fa8b021..92fa8b021 100644
--- a/sphinx/templates/imgmath/template.tex_t
+++ b/sphinx/templates/imgmath/template.tex.jinja
diff --git a/sphinx/templates/latex/latex.tex_t b/sphinx/templates/latex/latex.tex.jinja
index deb030504..deb030504 100644
--- a/sphinx/templates/latex/latex.tex_t
+++ b/sphinx/templates/latex/latex.tex.jinja
diff --git a/sphinx/templates/latex/longtable.tex_t b/sphinx/templates/latex/longtable.tex.jinja
index f5cb522ce..f5cb522ce 100644
--- a/sphinx/templates/latex/longtable.tex_t
+++ b/sphinx/templates/latex/longtable.tex.jinja
diff --git a/sphinx/templates/latex/sphinxmessages.sty_t b/sphinx/templates/latex/sphinxmessages.sty.jinja
index ef2750f6a..ef2750f6a 100644
--- a/sphinx/templates/latex/sphinxmessages.sty_t
+++ b/sphinx/templates/latex/sphinxmessages.sty.jinja
diff --git a/sphinx/templates/latex/tabular.tex_t b/sphinx/templates/latex/tabular.tex.jinja
index 0a9310a5e..0a9310a5e 100644
--- a/sphinx/templates/latex/tabular.tex_t
+++ b/sphinx/templates/latex/tabular.tex.jinja
diff --git a/sphinx/templates/latex/tabulary.tex_t b/sphinx/templates/latex/tabulary.tex.jinja
index 6ebcec6d2..6ebcec6d2 100644
--- a/sphinx/templates/latex/tabulary.tex_t
+++ b/sphinx/templates/latex/tabulary.tex.jinja
diff --git a/sphinx/templates/quickstart/Makefile_t b/sphinx/templates/quickstart/Makefile.jinja
index 14b2dc594..14b2dc594 100644
--- a/sphinx/templates/quickstart/Makefile_t
+++ b/sphinx/templates/quickstart/Makefile.jinja
diff --git a/sphinx/templates/quickstart/Makefile.new_t b/sphinx/templates/quickstart/Makefile.new.jinja
index 1a527578b..1a527578b 100644
--- a/sphinx/templates/quickstart/Makefile.new_t
+++ b/sphinx/templates/quickstart/Makefile.new.jinja
diff --git a/sphinx/templates/quickstart/conf.py_t b/sphinx/templates/quickstart/conf.py.jinja
index 383648675..383648675 100644
--- a/sphinx/templates/quickstart/conf.py_t
+++ b/sphinx/templates/quickstart/conf.py.jinja
diff --git a/sphinx/templates/quickstart/make.bat_t b/sphinx/templates/quickstart/make.bat.jinja
index dfc619ae3..dfc619ae3 100644
--- a/sphinx/templates/quickstart/make.bat_t
+++ b/sphinx/templates/quickstart/make.bat.jinja
diff --git a/sphinx/templates/quickstart/make.bat.new_t b/sphinx/templates/quickstart/make.bat.new.jinja
index c89237ba2..c89237ba2 100644
--- a/sphinx/templates/quickstart/make.bat.new_t
+++ b/sphinx/templates/quickstart/make.bat.new.jinja
diff --git a/sphinx/templates/quickstart/root_doc.rst_t b/sphinx/templates/quickstart/root_doc.rst.jinja
index 3aa98af08..3aa98af08 100644
--- a/sphinx/templates/quickstart/root_doc.rst_t
+++ b/sphinx/templates/quickstart/root_doc.rst.jinja
diff --git a/sphinx/texinputs/Makefile_t b/sphinx/texinputs/Makefile.jinja
index 96bb0fed1..96bb0fed1 100644
--- a/sphinx/texinputs/Makefile_t
+++ b/sphinx/texinputs/Makefile.jinja
diff --git a/sphinx/texinputs/latexmkjarc_t b/sphinx/texinputs/latexmkjarc.jinja
index c7403a90b..c7403a90b 100644
--- a/sphinx/texinputs/latexmkjarc_t
+++ b/sphinx/texinputs/latexmkjarc.jinja
diff --git a/sphinx/texinputs/latexmkrc_t b/sphinx/texinputs/latexmkrc.jinja
index a33b54148..a33b54148 100644
--- a/sphinx/texinputs/latexmkrc_t
+++ b/sphinx/texinputs/latexmkrc.jinja
diff --git a/sphinx/texinputs/make.bat_t b/sphinx/texinputs/make.bat.jinja
index da2805afd..da2805afd 100644
--- a/sphinx/texinputs/make.bat_t
+++ b/sphinx/texinputs/make.bat.jinja
diff --git a/sphinx/texinputs_win/Makefile_t b/sphinx/texinputs_win/Makefile.jinja
index 4131762a8..4131762a8 100644
--- a/sphinx/texinputs_win/Makefile_t
+++ b/sphinx/texinputs_win/Makefile.jinja
diff --git a/sphinx/themes/agogo/static/agogo.css_t b/sphinx/themes/agogo/static/agogo.css.jinja
index a23869425..a23869425 100644
--- a/sphinx/themes/agogo/static/agogo.css_t
+++ b/sphinx/themes/agogo/static/agogo.css.jinja
diff --git a/sphinx/themes/basic/static/basic.css_t b/sphinx/themes/basic/static/basic.css.jinja
index 9d5e4419d..9d5e4419d 100644
--- a/sphinx/themes/basic/static/basic.css_t
+++ b/sphinx/themes/basic/static/basic.css.jinja
diff --git a/sphinx/themes/basic/static/documentation_options.js_t b/sphinx/themes/basic/static/documentation_options.js.jinja
index fd6943fb3..fd6943fb3 100644
--- a/sphinx/themes/basic/static/documentation_options.js_t
+++ b/sphinx/themes/basic/static/documentation_options.js.jinja
diff --git a/sphinx/themes/basic/static/language_data.js_t b/sphinx/themes/basic/static/language_data.js.jinja
index 80f2a4f53..80f2a4f53 100644
--- a/sphinx/themes/basic/static/language_data.js_t
+++ b/sphinx/themes/basic/static/language_data.js.jinja
diff --git a/sphinx/themes/bizstyle/static/bizstyle.css_t b/sphinx/themes/bizstyle/static/bizstyle.css.jinja
index 1f012c4c2..1f012c4c2 100644
--- a/sphinx/themes/bizstyle/static/bizstyle.css_t
+++ b/sphinx/themes/bizstyle/static/bizstyle.css.jinja
diff --git a/sphinx/themes/bizstyle/static/bizstyle.js_t b/sphinx/themes/bizstyle/static/bizstyle.js.jinja
index fd0865e5d..fd0865e5d 100644
--- a/sphinx/themes/bizstyle/static/bizstyle.js_t
+++ b/sphinx/themes/bizstyle/static/bizstyle.js.jinja
diff --git a/sphinx/themes/classic/static/classic.css_t b/sphinx/themes/classic/static/classic.css.jinja
index 8a903e822..8a903e822 100644
--- a/sphinx/themes/classic/static/classic.css_t
+++ b/sphinx/themes/classic/static/classic.css.jinja
diff --git a/sphinx/themes/classic/static/sidebar.js_t b/sphinx/themes/classic/static/sidebar.js.jinja
index 32ae506aa..32ae506aa 100644
--- a/sphinx/themes/classic/static/sidebar.js_t
+++ b/sphinx/themes/classic/static/sidebar.js.jinja
diff --git a/sphinx/themes/epub/static/epub.css_t b/sphinx/themes/epub/static/epub.css.jinja
index 767d558be..767d558be 100644
--- a/sphinx/themes/epub/static/epub.css_t
+++ b/sphinx/themes/epub/static/epub.css.jinja
diff --git a/sphinx/themes/haiku/static/haiku.css_t b/sphinx/themes/haiku/static/haiku.css.jinja
index bccc3ea06..bccc3ea06 100644
--- a/sphinx/themes/haiku/static/haiku.css_t
+++ b/sphinx/themes/haiku/static/haiku.css.jinja
diff --git a/sphinx/themes/nature/static/nature.css_t b/sphinx/themes/nature/static/nature.css.jinja
index a2f3710e1..a2f3710e1 100644
--- a/sphinx/themes/nature/static/nature.css_t
+++ b/sphinx/themes/nature/static/nature.css.jinja
diff --git a/sphinx/themes/nonav/static/nonav.css_t b/sphinx/themes/nonav/static/nonav.css.jinja
index 71e3ffc08..71e3ffc08 100644
--- a/sphinx/themes/nonav/static/nonav.css_t
+++ b/sphinx/themes/nonav/static/nonav.css.jinja
diff --git a/sphinx/themes/pyramid/static/epub.css_t b/sphinx/themes/pyramid/static/epub.css.jinja
index 798054bdf..798054bdf 100644
--- a/sphinx/themes/pyramid/static/epub.css_t
+++ b/sphinx/themes/pyramid/static/epub.css.jinja
diff --git a/sphinx/themes/pyramid/static/pyramid.css_t b/sphinx/themes/pyramid/static/pyramid.css.jinja
index 4de532798..4de532798 100644
--- a/sphinx/themes/pyramid/static/pyramid.css_t
+++ b/sphinx/themes/pyramid/static/pyramid.css.jinja
diff --git a/sphinx/themes/scrolls/static/scrolls.css_t b/sphinx/themes/scrolls/static/scrolls.css.jinja
index c8b947d40..c8b947d40 100644
--- a/sphinx/themes/scrolls/static/scrolls.css_t
+++ b/sphinx/themes/scrolls/static/scrolls.css.jinja
diff --git a/sphinx/themes/sphinxdoc/static/sphinxdoc.css_t b/sphinx/themes/sphinxdoc/static/sphinxdoc.css.jinja
index 36d05907e..36d05907e 100644
--- a/sphinx/themes/sphinxdoc/static/sphinxdoc.css_t
+++ b/sphinx/themes/sphinxdoc/static/sphinxdoc.css.jinja
diff --git a/sphinx/themes/traditional/static/traditional.css_t b/sphinx/themes/traditional/static/traditional.css.jinja
index 085c98a8c..085c98a8c 100644
--- a/sphinx/themes/traditional/static/traditional.css_t
+++ b/sphinx/themes/traditional/static/traditional.css.jinja
diff --git a/sphinx/util/fileutil.py b/sphinx/util/fileutil.py
index 03928710e..4185fb246 100644
--- a/sphinx/util/fileutil.py
+++ b/sphinx/util/fileutil.py
@@ -8,6 +8,7 @@ from typing import TYPE_CHECKING, Callable
 
 from docutils.utils import relative_path
 
+from sphinx.deprecation import _old_jinja_template_suffix_warning
 from sphinx.util.osutil import copyfile, ensuredir
 from sphinx.util.typing import PathMatcher
 
@@ -15,6 +16,19 @@ if TYPE_CHECKING:
     from sphinx.util.template import BaseRenderer
 
 
+def _template_basename(filename: str) -> str | None:
+    """Given an input filename:
+    If the input looks like a template, then return the filename output should
+    be written to.  Otherwise, return no result (None)."""
+    # TODO: deprecate '_t' template suffix support after 2024-12-31
+    if filename.lower().endswith('_t'):
+        _old_jinja_template_suffix_warning(filename)
+        return filename[:-2]
+    elif filename.lower().endswith(".jinja"):
+        return filename[:-6]
+    return None
+
+
 def copy_asset_file(source: str, destination: str,
                     context: dict | None = None,
                     renderer: BaseRenderer | None = None) -> None:
@@ -35,14 +49,13 @@ def copy_asset_file(source: str, destination: str,
         # Use source filename if destination points a directory
         destination = os.path.join(destination, os.path.basename(source))
 
-    if source.lower().endswith('_t') and context is not None:
+    if _template_basename(source) and context is not None:
         if renderer is None:
             from sphinx.util.template import SphinxRenderer
             renderer = SphinxRenderer()
 
         with open(source, encoding='utf-8') as fsrc:
-            if destination.lower().endswith('_t'):
-                destination = destination[:-2]
+            destination = _template_basename(destination) or destination
             with open(destination, 'w', encoding='utf-8') as fdst:
                 fdst.write(renderer.render_string(fsrc.read(), context))
     else:
diff --git a/sphinx/writers/latex.py b/sphinx/writers/latex.py
index e50b11b4f..215fd4c76 100644
--- a/sphinx/writers/latex.py
+++ b/sphinx/writers/latex.py
@@ -16,7 +16,7 @@ from docutils import nodes, writers
 from docutils.nodes import Element, Node, Text
 
 from sphinx import addnodes, highlighting
-from sphinx.deprecation import RemovedInSphinx70Warning
+from sphinx.deprecation import RemovedInSphinx70Warning, _old_jinja_template_suffix_warning
 from sphinx.domains import IndexEntry
 from sphinx.domains.std import StandardDomain
 from sphinx.errors import SphinxError
@@ -435,7 +435,8 @@ class LaTeXTranslator(SphinxTranslator):
             'body': ''.join(self.body),
             'indices': self.generate_indices(),
         })
-        return self.render('latex.tex_t', self.elements)
+        template = self._find_template('latex.tex')
+        return self.render(template, self.elements)
 
     def hypertarget(self, id: str, withdoc: bool = True, anchor: bool = True) -> str:
         if withdoc:
@@ -512,14 +513,21 @@ class LaTeXTranslator(SphinxTranslator):
 
         return ''.join(ret)
 
-    def render(self, template_name: str, variables: dict[str, Any]) -> str:
-        renderer = LaTeXRenderer(latex_engine=self.config.latex_engine)
+    def _find_template(self, template_name: str) -> str:
         for template_dir in self.config.templates_path:
-            template = path.join(self.builder.confdir, template_dir,
-                                 template_name)
-            if path.exists(template):
-                return renderer.render(template, variables)
+            # TODO: deprecate '_t' template suffix support after 2024-12-31
+            for template_suffix in ('_t', '.jinja'):
+                template = path.join(self.builder.confdir, template_dir,
+                                     template_name + template_suffix)
+                if path.exists(template):
+                    _old_jinja_template_suffix_warning(template)
+                    return template
+
+        # Default: fallback to a pathless in-library jinja template
+        return f"{template_name}.jinja"
 
+    def render(self, template_name: str, variables: dict[str, Any]) -> str:
+        renderer = LaTeXRenderer(latex_engine=self.config.latex_engine)
         return renderer.render(template_name, variables)
 
     @property
@@ -902,8 +910,8 @@ class LaTeXTranslator(SphinxTranslator):
     def depart_table(self, node: Element) -> None:
         labels = self.hypertarget_to(node)
         table_type = self.table.get_table_type()
-        table = self.render(table_type + '.tex_t',
-                            {'table': self.table, 'labels': labels})
+        template = self._find_template(f"{table_type}.tex")
+        table = self.render(template, {'table': self.table, 'labels': labels})
         self.body.append(BLANKLINE)
         self.body.append(table)
         self.body.append(CR)
diff --git a/tests/roots/test-html_assets/extra/API.html_t b/tests/roots/test-html_assets/extra/API.html.jinja
index 34ecd9df1..34ecd9df1 100644
--- a/tests/roots/test-html_assets/extra/API.html_t
+++ b/tests/roots/test-html_assets/extra/API.html.jinja
diff --git a/tests/roots/test-html_assets/static/API.html_t b/tests/roots/test-html_assets/static/API.html.jinja
index 34ecd9df1..34ecd9df1 100644
--- a/tests/roots/test-html_assets/static/API.html_t
+++ b/tests/roots/test-html_assets/static/API.html.jinja
diff --git a/tests/roots/test-latex-table/_mytemplates/latex/longtable.tex_t b/tests/roots/test-latex-table/_mytemplates/latex/longtable.tex.jinja
index e2cb1db0a..e2cb1db0a 100644
--- a/tests/roots/test-latex-table/_mytemplates/latex/longtable.tex_t
+++ b/tests/roots/test-latex-table/_mytemplates/latex/longtable.tex.jinja
diff --git a/tests/roots/test-latex-table/_mytemplates/latex/tabulary.tex_t b/tests/roots/test-latex-table/_mytemplates/latex/tabulary.tex_t
new file mode 100644
index 000000000..c7afd28c5
--- /dev/null
+++ b/tests/roots/test-latex-table/_mytemplates/latex/tabulary.tex_t
@@ -0,0 +1,2 @@
+<# TODO: deprecate '_t' template suffix support after 2024-12-31 #>
+AU REVOIR, KANIGGETS
diff --git a/tests/roots/test-theming/test_theme/staticfiles/static/statictmpl.html_t b/tests/roots/test-theming/test_theme/staticfiles/static/statictmpl.html.jinja
index 4ab292b42..4ab292b42 100644
--- a/tests/roots/test-theming/test_theme/staticfiles/static/statictmpl.html_t
+++ b/tests/roots/test-theming/test_theme/staticfiles/static/statictmpl.html.jinja
diff --git a/tests/test_build_html.py b/tests/test_build_html.py
index 013c09bdb..c5c84f8b1 100644
--- a/tests/test_build_html.py
+++ b/tests/test_build_html.py
@@ -1153,7 +1153,7 @@ def test_html_assets(app):
     # html_extra_path
     assert (app.outdir / '.htaccess').exists()
     assert not (app.outdir / '.htpasswd').exists()
-    assert (app.outdir / 'API.html_t').exists()
+    assert (app.outdir / 'API.html.jinja').exists()
     assert (app.outdir / 'css/style.css').exists()
     assert (app.outdir / 'rimg.png').exists()
     assert not (app.outdir / '_build' / 'index.html').exists()
diff --git a/tests/test_build_latex.py b/tests/test_build_latex.py
index e39ac303c..5dce900e2 100644
--- a/tests/test_build_latex.py
+++ b/tests/test_build_latex.py
@@ -1379,6 +1379,10 @@ def test_latex_table_custom_template_caseA(app, status, warning):
     result = (app.outdir / 'python.tex').read_text(encoding='utf8')
     assert 'SALUT LES COPAINS' in result
 
+    # # TODO: deprecate '_t' template suffix support after 2024-12-31
+    assert 'TODO' not in result
+    assert 'AU REVOIR, KANIGGETS' in result
+
 
 @pytest.mark.sphinx('latex', testroot='latex-table',
                     confoverrides={'templates_path': ['_mytemplates']})
diff --git a/tests/test_deprecation.py b/tests/test_deprecation.py
new file mode 100644
index 000000000..77a4af731
--- /dev/null
+++ b/tests/test_deprecation.py
@@ -0,0 +1,114 @@
+import warnings
+from pathlib import Path
+
+import pytest
+
+from sphinx import deprecation
+
+
+def test_old_jinja_suffix_warning_is_warning():
+    assert isinstance(deprecation.OldJinjaSuffixWarning, type)
+    assert issubclass(deprecation.OldJinjaSuffixWarning, Warning)
+    assert issubclass(deprecation.OldJinjaSuffixWarning, PendingDeprecationWarning)
+
+    with pytest.warns(deprecation.OldJinjaSuffixWarning):
+        warnings.warn('test_1', category=deprecation.OldJinjaSuffixWarning)
+
+    with pytest.warns(PendingDeprecationWarning):
+        warnings.warn('test_2', category=deprecation.OldJinjaSuffixWarning)
+
+    with pytest.warns(Warning):
+        warnings.warn('test_3', category=deprecation.OldJinjaSuffixWarning)
+
+
+def test_old_jinja_suffix_warning_simplefilter_always(recwarn):
+    assert len(recwarn) == 0
+    warnings.resetwarnings()
+
+    warnings.simplefilter('always', category=deprecation.OldJinjaSuffixWarning)
+    warnings.warn('test_simplefilter_always', category=deprecation.OldJinjaSuffixWarning)
+
+    assert len(recwarn) == 1
+    caught_warning = recwarn[0]
+    assert caught_warning.category is deprecation.OldJinjaSuffixWarning
+    assert str(caught_warning.message) == 'test_simplefilter_always'
+
+
+def test_old_jinja_suffix_warning_filterwarnings_always(recwarn):
+    assert len(recwarn) == 0
+    warnings.resetwarnings()
+
+    warnings.filterwarnings('always', category=deprecation.OldJinjaSuffixWarning)
+    warnings.warn('test_filterwarnings_always', category=deprecation.OldJinjaSuffixWarning)
+
+    assert len(recwarn) == 1
+    caught_warning = recwarn[0]
+    assert caught_warning.category is deprecation.OldJinjaSuffixWarning
+    assert str(caught_warning.message) == 'test_filterwarnings_always'
+
+
+def test_old_jinja_suffix_warning_simplefilter_ignore(recwarn):
+    assert len(recwarn) == 0
+    warnings.resetwarnings()
+
+    warnings.simplefilter('ignore', deprecation.OldJinjaSuffixWarning)
+    warnings.warn('test_simplefilter_ignore', category=deprecation.OldJinjaSuffixWarning)
+
+    assert len(recwarn) == 0
+
+
+def test_old_jinja_suffix_warning_filterwarnings_ignore(recwarn):
+    assert len(recwarn) == 0
+    warnings.resetwarnings()
+
+    warnings.filterwarnings('ignore', category=deprecation.OldJinjaSuffixWarning)
+    warnings.warn('test_filterwarnings_ignore', category=deprecation.OldJinjaSuffixWarning)
+
+    assert len(recwarn) == 0
+
+
+def test__old_jinja_template_suffix_no_warning_css(recwarn):
+    assert len(recwarn) == 0
+    warnings.resetwarnings()
+    warnings.simplefilter('always', category=deprecation.OldJinjaSuffixWarning)
+
+    deprecation._old_jinja_template_suffix_warning('template.css')
+
+    assert len(recwarn) == 0
+
+
+def test__old_jinja_template_suffix_no_warning_jinja(recwarn):
+    assert len(recwarn) == 0
+    warnings.resetwarnings()
+    warnings.simplefilter('always', category=deprecation.OldJinjaSuffixWarning)
+
+    deprecation._old_jinja_template_suffix_warning('template.css.jinja')
+
+    assert len(recwarn) == 0
+
+
+def test__old_jinja_template_suffix_warning__t():
+    with pytest.warns(deprecation.OldJinjaSuffixWarning,
+                      match=r"the '_t' suffix for Jinja templates is deprecated"):
+        deprecation._old_jinja_template_suffix_warning('template.css_t')
+
+
+def test__old_jinja_template_suffix_warning_stacklevel():
+    # _old_jinja_template_suffix_warning is only called within functions that
+    # use template files.
+    def do_something_with_templates(filename):
+        deprecation._old_jinja_template_suffix_warning(filename)
+
+    # TOJTSWS line number marker
+    with pytest.warns(deprecation.OldJinjaSuffixWarning) as caught:
+        do_something_with_templates('template.css_t')
+
+    lines = [b''] + Path(__file__).read_bytes().splitlines()
+    line_number = lines.index(b'    # TOJTSWS line number marker') + 2
+
+    assert len(caught) == 1
+    caught_warning = caught[0]
+    assert caught_warning.category is deprecation.OldJinjaSuffixWarning
+    assert "the '_t' suffix for Jinja templates is deprecated" in str(caught_warning.message)
+    assert caught_warning.filename == __file__
+    assert caught_warning.lineno == line_number
diff --git a/tests/test_util_fileutil.py b/tests/test_util_fileutil.py
index 7ea12508c..86f2c96b4 100644
--- a/tests/test_util_fileutil.py
+++ b/tests/test_util_fileutil.py
@@ -3,7 +3,7 @@
 from unittest import mock
 
 from sphinx.jinja2glue import BuiltinTemplateLoader
-from sphinx.util.fileutil import copy_asset, copy_asset_file
+from sphinx.util.fileutil import _template_basename, copy_asset, copy_asset_file
 
 
 class DummyTemplateLoader(BuiltinTemplateLoader):
@@ -28,9 +28,9 @@ def test_copy_asset_file(tempdir):
     assert src.read_text(encoding='utf8') == dest.read_text(encoding='utf8')
 
     # copy template file
-    src = (tempdir / 'asset.txt_t')
+    src = (tempdir / 'asset.txt.jinja')
     src.write_text('# {{var1}} data')
-    dest = (tempdir / 'output.txt_t')
+    dest = (tempdir / 'output.txt.jinja')
 
     copy_asset_file(src, dest, {'var1': 'template'}, renderer)
     assert not dest.exists()
@@ -38,7 +38,7 @@ def test_copy_asset_file(tempdir):
     assert (tempdir / 'output.txt').read_text(encoding='utf8') == '# template data'
 
     # copy template file to subdir
-    src = (tempdir / 'asset.txt_t')
+    src = (tempdir / 'asset.txt.jinja')
     src.write_text('# {{var1}} data')
     subdir1 = (tempdir / 'subdir')
     subdir1.makedirs()
@@ -48,14 +48,14 @@ def test_copy_asset_file(tempdir):
     assert (subdir1 / 'asset.txt').read_text(encoding='utf8') == '# template data'
 
     # copy template file without context
-    src = (tempdir / 'asset.txt_t')
+    src = (tempdir / 'asset.txt.jinja')
     subdir2 = (tempdir / 'subdir2')
     subdir2.makedirs()
 
     copy_asset_file(src, subdir2)
     assert not (subdir2 / 'asset.txt').exists()
-    assert (subdir2 / 'asset.txt_t').exists()
-    assert (subdir2 / 'asset.txt_t').read_text(encoding='utf8') == '# {{var1}} data'
+    assert (subdir2 / 'asset.txt.jinja').exists()
+    assert (subdir2 / 'asset.txt.jinja').read_text(encoding='utf8') == '# {{var1}} data'
 
 
 def test_copy_asset(tempdir):
@@ -65,12 +65,12 @@ def test_copy_asset(tempdir):
     source = (tempdir / 'source')
     source.makedirs()
     (source / 'index.rst').write_text('index.rst', encoding='utf8')
-    (source / 'foo.rst_t').write_text('{{var1}}.rst', encoding='utf8')
+    (source / 'foo.rst.jinja').write_text('{{var1}}.rst', encoding='utf8')
     (source / '_static').makedirs()
     (source / '_static' / 'basic.css').write_text('basic.css', encoding='utf8')
     (source / '_templates').makedirs()
     (source / '_templates' / 'layout.html').write_text('layout.html', encoding='utf8')
-    (source / '_templates' / 'sidebar.html_t').write_text('sidebar: {{var2}}', encoding='utf8')
+    (source / '_templates' / 'sidebar.html.jinja').write_text('sidebar: {{var2}}', encoding='utf8')
 
     # copy a single file
     assert not (tempdir / 'test1').exists()
@@ -101,3 +101,14 @@ def test_copy_asset(tempdir):
     assert not (destdir / '_static' / 'basic.css').exists()
     assert (destdir / '_templates' / 'layout.html').exists()
     assert not (destdir / '_templates' / 'sidebar.html').exists()
+
+
+def test_template_basename():
+    assert not _template_basename("asset.txt")
+    assert _template_basename("asset.txt.jinja") == "asset.txt"
+    assert _template_basename("sidebar.html.jinja") == "sidebar.html"
+
+
+def test_legacy_template_basename():
+    # TODO: deprecate '_t' template suffix support after 2024-12-31
+    assert _template_basename("asset.txt_t") == "asset.txt"
diff --git a/utils/babel_runner.py b/utils/babel_runner.py
index 5e62efe86..3f963c918 100644
--- a/utils/babel_runner.py
+++ b/utils/babel_runner.py
@@ -42,7 +42,9 @@ METHOD_MAP = [
     # Extraction from Python source files
     ('**.py', extract_python),
     # Extraction from Jinja2 template files
+    ('**/templates/latex/**.tex.jinja', extract_jinja2),
     ('**/templates/latex/**.tex_t', extract_jinja2),
+    ('**/templates/latex/**.sty.jinja', extract_jinja2),
     ('**/templates/latex/**.sty_t', extract_jinja2),
     # Extraction from Jinja2 HTML templates
     ('**/themes/**.html', extract_jinja2),
@@ -50,6 +52,7 @@ METHOD_MAP = [
     ('**/themes/**.xml', extract_jinja2),
     # Extraction from JavaScript files
     ('**.js', extract_javascript),
+    ('**.js.jinja', extract_javascript),
     ('**.js_t', extract_javascript),
 ]
 OPTIONS_MAP = {
@@ -58,7 +61,9 @@ OPTIONS_MAP = {
         'encoding': 'utf-8',
     },
     # Extraction from Jinja2 template files
+    '**/templates/latex/**.tex.jinja': TEX_DELIMITERS.copy(),
     '**/templates/latex/**.tex_t': TEX_DELIMITERS.copy(),
+    '**/templates/latex/**.sty.jinja': TEX_DELIMITERS.copy(),
     '**/templates/latex/**.sty_t': TEX_DELIMITERS.copy(),
     # Extraction from Jinja2 HTML templates
     '**/themes/**.html': {