numpy
diff --git a/‎numpy/core/overrides.py
Lines changed: 20 additions & 2 deletions b/‎numpy/core/overrides.py
Lines changed: 20 additions & 2 deletions
diff --git a/‎numpy/tests/test_public_api.py
Lines changed: 16 additions & 0 deletions b/‎numpy/tests/test_public_api.py
Lines changed: 16 additions & 0 deletions
@@ -1,6 +1,7 @@
 """Implementation of __array_function__ overrides from NEP-18."""
 import collections
 import functools
+import ast
 import os
 import textwrap
 
@@ -86,6 +87,23 @@ def set_array_function_like_doc(public_api):
 ArgSpec = collections.namedtuple('ArgSpec', 'args varargs keywords defaults')
 
 
+def extract_text_signature(obj, docstring):
+    head = docstring.lstrip().split('\n')[0]
+    objname = obj.__name__
+    if not head.startswith(objname):
+        return None
+    return head
+
+
+def add_docstring_with_textsig(implementation, doc):
+    if doc is None:
+        return
+    textsig = extract_text_signature(implementation, doc)
+    if textsig is not None:
+        doc = '{}\n--\n\n{}'.format(textsig, doc)
+    add_docstring(implementation, doc)
+
+
 def verify_matching_signatures(implementation, dispatcher):
     """Verify that a dispatcher function has the right signature."""
     implementation_spec = ArgSpec(*getargspec(implementation))
@@ -162,7 +180,7 @@ def array_function_dispatch(dispatcher, module=None, verify=True,
     if not ARRAY_FUNCTION_ENABLED:
         def decorator(implementation):
             if docs_from_dispatcher:
-                add_docstring(implementation, dispatcher.__doc__)
+                add_docstring_with_textsig(implementation, dispatcher.__doc__)
             if module is not None:
                 implementation.__module__ = module
             return implementation
@@ -173,7 +191,7 @@ def decorator(implementation):
             verify_matching_signatures(implementation, dispatcher)
 
         if docs_from_dispatcher:
-            add_docstring(implementation, dispatcher.__doc__)
+            add_docstring_with_textsig(implementation, dispatcher.__doc__)
 
         @functools.wraps(implementation)
         def public_api(*args, **kwargs):
 
@@ -2,6 +2,7 @@
 import subprocess
 import pkgutil
 import types
+import inspect
 import importlib
 import warnings
 
@@ -459,3 +460,18 @@ def check_importable(module_name):
         raise AssertionError("Modules that are not really public but looked "
                              "public and can not be imported: "
                              "{}".format(module_names))
+
+
+@pytest.mark.skipif(sys.flags.optimize < 2, reason='docstring stripped')
+def test_all_function_have_signature():
+    allowlist = {'concatenate', 'where'}
+
+    for key, value in inspect.getmembers(numpy):
+        if not inspect.isfunction(value):
+            continue
+        if key in allowlist:
+            continue
+        try:
+            inspect.signature(value)
+        except ValueError:
+            raise AssertionError("No signature found for {}".format(key))