Take care to preserve cpdef method docstrings when prepending signatures.

Cython/Compiler/AutoDocTransforms.py

@@ -135,7 +135,14 @@ class EmbedSignature(CythonTransform):
                 doc_holder = self.class_node.entry.type.scope
             else:
                 doc_holder = node.entry
-            new_doc  = self._embed_signature(signature, doc_holder.doc)
+
+            if doc_holder.doc is not None:
+                old_doc = doc_holder.doc
+            elif not is_constructor and getattr(node, 'py_func', None) is not None:
+                old_doc = node.py_func.entry.doc
+            else:
+                old_doc = None
+            new_doc  = self._embed_signature(signature, old_doc)
             doc_holder.doc = EncodedString(new_doc)
             if not is_constructor and getattr(node, 'py_func', None) is not None:
                 node.py_func.entry.doc = EncodedString(new_doc)
@@ -152,7 +159,13 @@ class EmbedSignature(CythonTransform):
             node.declarator.args,
             return_type=node.return_type)
         if signature:
-            new_doc  = self._embed_signature(signature, node.entry.doc)
+            if node.entry.doc is not None:
+                old_doc = node.entry.doc
+            elif hasattr(node, 'py_func') and node.py_func is not None:
+                old_doc = node.py_func.entry.doc
+            else:
+                old_doc = None
+            new_doc  = self._embed_signature(signature, old_doc)
             node.entry.doc = EncodedString(new_doc)
             if hasattr(node, 'py_func') and node.py_func is not None:
                 node.py_func.entry.doc = EncodedString(new_doc)

tests/run/embedsignatures.pyx

@@ -32,12 +32,20 @@ __doc__ = ur"""
     >>> print (Ext.k.__doc__)
     Ext.k(self, a, b, c=1, *args, d=42, e=17, f, **kwds)
 
+    >>> print (Ext.l.__doc__)
+    Ext.l(self, a, b, c=1, *args, d=42, e=17, f, **kwds)
+    Existing string
+
     >>> print (Ext.get_int.__doc__)
     Ext.get_int(self) -> int
 
     >>> print (Ext.get_float.__doc__)
     Ext.get_float(self) -> float
 
+    >>> print (Ext.get_str.__doc__)
+    Ext.get_str(self) -> str
+    Existing string
+
     >>> print (Ext.clone.__doc__)
     Ext.clone(self) -> Ext
 
@@ -50,6 +58,12 @@ __doc__ = ur"""
     >>> with_doc_2.__doc__
     'with_doc_2(a, b, c)\n\n    Existing string\n    '
 
+    >>> with_doc_3.__doc__
+    'with_doc_3(a, b, c)\nExisting string'
+
+    >>> with_doc_4.__doc__
+    'with_doc_4(int a, str b, list c) -> str\n\n    Existing string\n    '
+
     >>> types.__doc__
     'types(Ext a, int b, unsigned short c, float d, e)'
 
@@ -146,12 +160,20 @@ cdef class Ext:
     def k(self, a, b, c=1, *args, d = 42, e = 17, f, **kwds):
         pass
 
+    def l(self, a, b, c=1, *args, d = 42, e = 17, f, **kwds):
+        """Existing string"""
+        pass
+
     cpdef int get_int(self):
         return 0
 
     cpdef float get_float(self):
         return 0.0
 
+    cpdef str get_str(self):
+        """Existing string"""
+        return "string"
+
     cpdef Ext clone(self):
         return Ext(1,2)
 
@@ -171,6 +193,16 @@ def with_doc_2(a, b, c):
     """
     pass
 
+cpdef with_doc_3(a, b, c):
+    """Existing string"""
+    pass
+
+cpdef str with_doc_4(int a, str b, list c):
+    """
+    Existing string
+    """
+    return b
+
 cpdef char f_c(char c):
     return c