Add tests for :dedent: option of code-block directive

tests/roots/test-directive-code/dedent.rst

@@ -0,0 +1,64 @@
+dedent option
+-------------
+
+.. code-block::
+
+   First line
+   Second line
+       Third line
+   Fourth line
+
+ReST has no fixed indent and only a change in indention is significant not the amount [1]_.
+Thus, the following code inside the code block is not indent even it looks so with respect to the previous block.
+
+.. code-block::
+
+       First line
+       Second line
+           Third line
+       Fourth line
+
+Having an option "fixates" the indent to be 3 spaces, thus the code inside the code block is indented by 4 spaces.
+
+.. code-block::
+   :class: dummy
+
+       First line
+       Second line
+           Third line
+       Fourth line
+
+The code has 6 spaces indent, minus 4 spaces dedent should yield a 2 space indented code in the output.
+
+.. code-block::
+   :dedent: 4
+
+         First line
+         Second line
+             Third line
+         Fourth line
+
+Dedenting by zero, should not strip any spaces and be a no-op.
+
+.. note::
+   This can be used as an alternative to ``:class: dummy`` above, to fixate the ReST indention of the block.
+
+.. code-block::
+   :dedent: 0
+
+       First line
+       Second line
+           Third line
+       Fourth line
+
+Dedent without argument should autostrip common whitespace at the beginning.
+
+.. code-block::
+   :dedent:
+
+       First line
+       Second line
+           Third line
+       Fourth line
+
+.. [1] https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#indentation

tests/test_directive_code.py

@@ -580,3 +580,29 @@ def test_linenothreshold(app, status, warning):
     # literal include not using linenothreshold (no line numbers)
     assert ('<span></span><span class="c1"># Very small literal include '
             '(linenothreshold check)</span>' in html)
+
+@pytest.mark.sphinx('dummy', testroot='directive-code')
+def test_code_block_dedent(app, status, warning):
+    app.builder.build(['dedent'])
+    doctree = app.env.get_doctree('dedent')
+    codeblocks = list(doctree.traverse(nodes.literal_block))
+    # Note: comparison string should not have newlines at the beginning or end
+    text_0_indent = '''First line
+Second line
+    Third line
+Fourth line'''
+    text_2_indent = '''  First line
+  Second line
+      Third line
+  Fourth line'''
+    text_4_indent = '''    First line
+    Second line
+        Third line
+    Fourth line'''
+
+    assert codeblocks[0].astext() == text_0_indent
+    assert codeblocks[1].astext() == text_0_indent
+    assert codeblocks[2].astext() == text_4_indent
+    assert codeblocks[3].astext() == text_2_indent
+    assert codeblocks[4].astext() == text_4_indent
+    assert codeblocks[5].astext() == text_0_indent