Preserve leading whitespace lines in rST (#271)

CHANGELOG.rst

@@ -8,6 +8,10 @@ Changelog
 
 * Expand Markdown detection to all Python language names from Pygments: ``py``, ``sage``, ``python3``, ``py3``, and ``numpy``.
 
+* Preserve leading blank lines with whitespace in reStructuredText code blocks.
+
+  Thanks to Julianus Pfeuffer for the report in `Issue #217 <https://github.com/adamchainz/blacken-docs/issues/217>`__.
+
 * Remove ``language_version`` from ``.pre-commit-hooks.yaml``.
   This change allows ``default_language_version`` in ``.pre-commit-config.yaml` to take precedence.
 

src/blacken_docs/__init__.py

@@ -37,7 +37,7 @@
     rf"{DOCTEST_TYPES}::.*"
     rf")\n"
     rf"((?P=indent) +:.*\n)*"
-    rf"\n*"
+    rf"( *\n)*"
     rf")"
     rf"(?P<code>(^((?P=indent) +.*)?\n)+)",
     re.MULTILINE,

tests/test_blacken_docs.py

@@ -381,6 +381,24 @@ def test_format_src_rst_indented():
     )
 
 
+def test_format_src_rst_code_block_indent():
+    before = "\n".join(
+        [
+            ".. code-block:: python",
+            "   ",
+            "   f(1,2,3)\n",
+        ]
+    )
+    after, _ = blacken_docs.format_str(before, BLACK_MODE)
+    assert after == "\n".join(
+        [
+            ".. code-block:: python",
+            "   ",
+            "   f(1, 2, 3)\n",
+        ]
+    )
+
+
 def test_format_src_rst_with_highlight_directives():
     before = (
         ".. code-block:: python\n"