Fix #5770: doctest: Follow highlight_language on highlighting doctest block

CHANGES

@@ -31,6 +31,8 @@ Incompatible changes
   will use the text font not the math font. The ``LGR`` font encoding must be
   added to the ``'fontenc'`` key of :confval:`latex_elements` for this to work
   (only if it is needed by the document, of course).
+* #5770: doctest: Follow :confval:`highlight_language` on highlighting doctest
+  block.  As a result, they are highlighted as python3 by default.
 
 Deprecated
 ----------

sphinx/ext/doctest.py

@@ -122,9 +122,15 @@ class TestDirective(SphinxDirective):
             # only save if it differs from code
             node['test'] = test
         if self.name == 'doctest':
-            node['language'] = 'pycon'
+            if self.config.highlight_language in ('py', 'python'):
+                node['language'] = 'pycon'
+            else:
+                node['language'] = 'pycon3'  # default
         elif self.name == 'testcode':
-            node['language'] = 'python'
+            if self.config.highlight_language in ('py', 'python'):
+                node['language'] = 'python'
+            else:
+                node['language'] = 'python3'  # default
         elif self.name == 'testoutput':
             # don't try to highlight output
             node['language'] = 'none'

tests/test_ext_doctest.py

@@ -11,6 +11,7 @@
 import os
 from collections import Counter
 
+from docutils import nodes
 import pytest
 from packaging.specifiers import InvalidSpecifier
 from packaging.version import InvalidVersion
@@ -32,6 +33,23 @@ def test_build(app, status, warning):
     assert cleanup_called == 3, 'testcleanup did not get executed enough times'
 
 
+@pytest.mark.sphinx('dummy', testroot='ext-doctest')
+def test_highlight_language_default(app, status, warning):
+    app.build()
+    doctree = app.env.get_doctree('doctest')
+    for node in doctree.traverse(nodes.literal_block):
+        assert node['language'] in ('python3', 'pycon3', 'none')
+
+
+@pytest.mark.sphinx('dummy', testroot='ext-doctest',
+                    confoverrides={'highlight_language': 'python'})
+def test_highlight_language_python2(app, status, warning):
+    app.build()
+    doctree = app.env.get_doctree('doctest')
+    for node in doctree.traverse(nodes.literal_block):
+        assert node['language'] in ('python', 'pycon', 'none')
+
+
 def test_is_allowed_version():
     assert is_allowed_version('<3.4', '3.3') is True
     assert is_allowed_version('<3.4', '3.3') is True