Preserve type information from docstrings if no type annotation is present and parameter has default value.

Fixes #574.

Author: christianaguilera-foundry

src/sphinx_autodoc_typehints/__init__.py

@@ -830,8 +830,18 @@ def _inject_signature(
             insert_index = len(lines)
 
         if insert_index is not None:
+            update_only = False
+
             if annotation is None:
+                # If there is no type annotation, but the type happens to exist in the input
+                # docstring, use it as a base.
                 type_annotation = f":type {arg_name}: "
+                for i, line in enumerate(lines):
+                    if line.startswith(type_annotation):
+                        type_annotation = line.rstrip()
+                        insert_index = i
+                        update_only = True
+                        break
             else:
                 short_literals = app.config.python_display_short_literal_types
                 formatted_annotation = add_type_css_class(
@@ -844,7 +854,10 @@ def _inject_signature(
                 if formatted_default:
                     type_annotation = _append_default(app, lines, insert_index, type_annotation, formatted_default)
 
-            lines.insert(insert_index, type_annotation)
+            if update_only:
+                lines[insert_index] = type_annotation
+            else:
+                lines.insert(insert_index, type_annotation)
 
 
 def _append_default(
@@ -864,7 +877,10 @@ def _append_default(
         lines[append_index] += formatted_default
 
     else:  # add to last param doc line
-        type_annotation += formatted_default
+        if type_annotation.endswith(" "):
+            type_annotation += formatted_default
+        else:
+            type_annotation = f"{type_annotation}, {formatted_default}"
 
     return type_annotation
 

tests/roots/test-dummy/dummy_module_without_complete_typehints.py

@@ -35,3 +35,14 @@ def function_with_defaults_and_some_typehints(x: int = 0, y=None) -> str:  # noq
     :param x: foo
     :param y: bar
     """
+
+
+def function_with_defaults_and_type_information_in_docstring(x, y=0) -> str:  # noqa: ANN001
+    """
+    Function docstring.
+
+    :type x: int
+    :type y: int
+    :param x: foo
+    :param y: bar
+    """

tests/test_sphinx_autodoc_typehints.py

@@ -1074,6 +1074,18 @@ def test_default_annotation_without_typehints(app: SphinxTestApp, status: String
 
        Return type:
           "str"
+
+    dummy_module_without_complete_typehints.function_with_defaults_and_type_information_in_docstring(x, y=0)
+
+       Function docstring.
+
+       Parameters:
+          * **x** ("int") -- foo
+
+          * **y** ("int", default: "0") -- bar
+
+       Return type:
+          "str"
     """
     assert text_contents == dedent(expected_contents)