fix(markdown-renderer): preserve list margin spacing

The extra spacing can be before of after leader, so try to preserve it
on both positions.

Fixes #213

mistletoe/markdown_renderer.py

@@ -314,17 +314,22 @@ def render_list(
     def render_list_item(
         self, token: block_token.ListItem, max_line_length: int
     ) -> Iterable[str]:
-        indentation = len(token.leader) + 1 if self.normalize_whitespace else token.prepend - token.indentation
+        if self.normalize_whitespace:
+            prepend = len(token.leader) + 1
+            indentation = 0
+        else:
+            prepend = token.prepend
+            indentation = token.indentation
         max_child_line_length = (
-            max_line_length - indentation if max_line_length else None
+            max_line_length - prepend if max_line_length else None
         )
         lines = self.blocks_to_lines(
             token.children, max_line_length=max_child_line_length
         )
         return self.prefix_lines(
             list(lines) or [""],
-            token.leader + " " * (indentation - len(token.leader)),
-            " " * indentation
+            " " * indentation + token.leader + " " * (prepend - len(token.leader) - indentation),
+            " " * prepend,
         )
 
     def render_table(

test/test_markdown_renderer.py

@@ -138,11 +138,11 @@ def test_numbered_list(self):
         ]
         output = self.roundtrip(input)
         expected = [
-            "22) *emphasized list item*\n",
-            "96) \n",
-            "128) here begins a nested list.\n",
-            "     + apples\n",
-            "     + bananas\n",
+            "  22) *emphasized list item*\n",
+            "  96) \n",
+            " 128) here begins a nested list.\n",
+            "       + apples\n",
+            "       + bananas\n",
         ]
         self.assertEqual(output, "".join(expected))
 
@@ -157,8 +157,7 @@ def test_bulleted_list(self):
         output = self.roundtrip(input)
         self.assertEqual(output, "".join(input))
 
-    # we don't currently support keeping margin indentation:
-    def test_list_item_margin_indentation_not_preserved(self):
+    def test_list_item_margin_indentation_preserved(self):
         # 0 to 4 spaces of indentation from the margin
         input = [
             "- 0 space: ok.\n",
@@ -173,6 +172,36 @@ def test_list_item_margin_indentation_not_preserved(self):
             "      subsequent line.\n",
         ]
         output = self.roundtrip(input)
+        expected = [
+            "- 0 space: ok.\n",
+            "  subsequent line.\n",
+            " - 1 space: ok.\n",
+            "   subsequent line.\n",
+            "  - 2 spaces: ok.\n",
+            "    subsequent line.\n",
+            # note: we still always normalize the indentation of all list item lines:
+            "   - 3 spaces: ok.\n",
+            "     subsequent line.\n",
+            "     - 4 spaces: in the paragraph of the above list item.\n",
+            "     subsequent line.\n",
+        ]
+        self.assertEqual(output, "".join(expected))
+
+    def test_list_item_margin_indentation_normalized(self):
+        # 0 to 4 spaces of indentation from the margin
+        input = [
+            "- 0 space: ok.\n",
+            "  subsequent line.\n",
+            " - 1 space: ok.\n",
+            "   subsequent line.\n",
+            "  - 2 spaces: ok.\n",
+            "    subsequent line.\n",
+            "   - 3 spaces: ok.\n",
+            "     subsequent line.\n",
+            "    - 4 spaces: in the paragraph of the above list item.\n",
+            "      subsequent line.\n",
+        ]
+        output = self.roundtrip(input, normalize_whitespace=True)
         expected = [
             "- 0 space: ok.\n",
             "  subsequent line.\n",