Close #7784: i18n: The alt text for image is translated by default

Make alt text for image translatable by default without settings of
gettext_additional_targets.

CHANGES

@@ -7,6 +7,8 @@ Dependencies
 Incompatible changes
 --------------------
 
+* #7784: i18n: The msgid for alt text of image is changed
+
 Deprecated
 ----------
 
@@ -26,6 +28,8 @@ Features added
 * #7745: html: inventory is broken if the docname contains a space
 * #7902: html theme: Add a new option :confval:`globaltoc_maxdepth` to control
   the behavior of globaltoc in sidebar
+* #7784: i18n: The alt text for image is translated by default (without
+  :confval:`gettext_additional_targets` setting)
 * #7052: add ``:noindexentry:`` to the Python, C, C++, and Javascript domains.
   Update the documentation to better reflect the relationship between this option
   and the ``:noindex:`` option.

doc/usage/configuration.rst

@@ -802,13 +802,16 @@ documentation on :ref:`intl` for details.
    :literal-block: literal blocks (``::`` annotation and ``code-block`` directive)
    :doctest-block: doctest block
    :raw: raw content
-   :image: image/figure uri and alt
+   :image: image/figure uri
 
    For example: ``gettext_additional_targets = ['literal-block', 'image']``.
 
    The default is ``[]``.
 
    .. versionadded:: 1.3
+   .. versionchanged:: 3.2
+
+      The alt text for image is translated by default.
 
 .. confval:: figure_language_filename
 

sphinx/transforms/i18n.py

@@ -238,6 +238,10 @@ def apply(self, **kwargs: Any) -> None:
                 node.details['nodes'][0]['content'] = msgstr
                 continue
 
+            if isinstance(node, nodes.image) and node.get('alt') == msg:
+                node['alt'] = msgstr
+                continue
+
             # Avoid "Literal block expected; none found." warnings.
             # If msgstr ends with '::' then it cause warning message at
             # parser.parse() processing.
@@ -441,8 +445,9 @@ def get_ref_key(node: addnodes.pending_xref) -> Tuple[str, str, str]:
             if isinstance(node, LITERAL_TYPE_NODES):
                 node.rawsource = node.astext()
 
-            if isinstance(node, IMAGE_TYPE_NODES):
-                node.update_all_atts(patch)
+            if isinstance(node, nodes.image) and node.get('alt') != msg:
+                node['uri'] = patch['uri']
+                continue  # do not mark translated
 
             node['translated'] = True  # to avoid double translation
 

sphinx/util/nodes.py

@@ -201,6 +201,10 @@ def is_translatable(node: Node) -> bool:
     if isinstance(node, addnodes.translatable):
         return True
 
+    # image node marked as translatable or having alt text
+    if isinstance(node, nodes.image) and (node.get('translatable') or node.get('alt')):
+        return True
+
     if isinstance(node, nodes.Inline) and 'translatable' not in node:  # type: ignore
         # inline node must not be translated if 'translatable' is not set
         return False
@@ -228,9 +232,6 @@ def is_translatable(node: Node) -> bool:
             return False
         return True
 
-    if isinstance(node, nodes.image) and node.get('translatable'):
-        return True
-
     if isinstance(node, addnodes.meta):
         return True
     if is_pending_meta(node):
@@ -264,10 +265,13 @@ def extract_messages(doctree: Element) -> Iterable[Tuple[Element, str]]:
             msg = node.rawsource
             if not msg:
                 msg = node.astext()
-        elif isinstance(node, IMAGE_TYPE_NODES):
-            msg = '.. image:: %s' % node['uri']
+        elif isinstance(node, nodes.image):
             if node.get('alt'):
-                msg += '\n   :alt: %s' % node['alt']
+                yield node, node['alt']
+            if node.get('translatable'):
+                msg = '.. image:: %s' % node['uri']
+            else:
+                msg = None
         elif isinstance(node, META_TYPE_NODES):
             msg = node.rawcontent
         elif isinstance(node, nodes.pending) and is_pending_meta(node):

tests/roots/test-intl/xx/LC_MESSAGES/figure.po

@@ -37,19 +37,17 @@ msgstr "BLOCK"
 msgid "image url and alt"
 msgstr "IMAGE URL AND ALT"
 
-msgid ""
-".. image:: img.png\n"
-"   :alt: img"
-msgstr ""
-".. image:: i18n.png\n"
-"   :alt: IMG -> I18N"
+msgid "img"
+msgstr "IMG -> I18N"
 
-msgid ""
-".. image:: i18n.png\n"
-"   :alt: i18n"
-msgstr ""
-".. image:: img.png\n"
-"   :alt: I18N -> IMG"
+msgid ".. image:: img.png"
+msgstr ".. image:: i18n.png"
+
+msgid "i18n"
+msgstr "I18N -> IMG"
+
+msgid ".. image:: i18n.png"
+msgstr ".. image:: img.png"
 
 msgid "image on substitution"
 msgstr "IMAGE ON SUBSTITUTION"

tests/test_intl.py

@@ -345,9 +345,9 @@ def test_text_figure_captions(app):
               "14.2. IMAGE URL AND ALT\n"
               "=======================\n"
               "\n"
-              "[image: i18n][image]\n"
+              "[image: I18N -> IMG][image]\n"
               "\n"
-              "   [image: img][image]\n"
+              "   [image: IMG -> I18N][image]\n"
               "\n"
               "\n"
               "14.3. IMAGE ON SUBSTITUTION\n"
@@ -1102,12 +1102,12 @@ def test_additional_targets_should_not_be_translated(app):
 
     result = (app.outdir / 'figure.html').read_text()
 
-    # alt and src for image block should not be translated
-    expected_expr = """<img alt="i18n" src="_images/i18n.png" />"""
+    # src for image block should not be translated (alt is translated)
+    expected_expr = """<img alt="I18N -&gt; IMG" src="_images/i18n.png" />"""
     assert_count(expected_expr, result, 1)
 
-    # alt and src for figure block should not be translated
-    expected_expr = """<img alt="img" src="_images/img.png" />"""
+    # src for figure block should not be translated (alt is translated)
+    expected_expr = """<img alt="IMG -&gt; I18N" src="_images/img.png" />"""
     assert_count(expected_expr, result, 1)