Fix docstring trimming for non-empty first lines

Allow trim_docstring to handle docstrings where the text starts on the first line, preventing rendering errors in admindoc. Adds tests for single-line and non-empty first-line docstrings.

django/contrib/admindocs/utils.py

@@ -34,7 +34,9 @@ def trim_docstring(docstring):
         return ''
     # Convert tabs to spaces and split into lines
     lines = docstring.expandtabs().splitlines()
-    indent = min(len(line) - len(line.lstrip()) for line in lines if line.lstrip())
+    # Determine indentation from all lines except the first (PEP 257)
+    indent_lines = [line for line in lines[1:] if line.lstrip()]
+    indent = min(len(line) - len(line.lstrip()) for line in indent_lines) if indent_lines else 0
     trimmed = [lines[0].lstrip()] + [line[indent:].rstrip() for line in lines[1:]]
     return "\n".join(trimmed).strip()
 

tests/admin_docs/test_utils.py

@@ -44,6 +44,23 @@ class TestUtils(AdminDocsSimpleTestCase):
         )
         self.assertEqual(trim_docstring_output, trimmed_docstring)
 
+    def test_trim_docstring_first_line_not_empty(self):
+        """
+        Test trim_docstring with docstrings where text starts on the first line.
+        This is a common docstring style and should not cause errors.
+        """
+        docstring = """test tests something.
+        This is the second line.
+        """
+        expected = "test tests something.\nThis is the second line."
+        self.assertEqual(trim_docstring(docstring), expected)
+
+    def test_trim_docstring_single_line(self):
+        """Test trim_docstring with a single-line docstring."""
+        docstring = """Single line docstring."""
+        expected = "Single line docstring."
+        self.assertEqual(trim_docstring(docstring), expected)
+
     def test_parse_docstring(self):
         title, description, metadata = parse_docstring(self.docstring)
         docstring_title = (