When passing keyword arguments from unpacked dict literals, prevent duplicate...

When passing keyword arguments from unpacked dict literals, prevent duplicate dict keys from raising an error and instead overwrite the previous one.
Closes GH-2963.

CHANGES.rst

@@ -66,6 +66,11 @@ Bugs fixed
   the first character if multiple characters should have been returned.
   They now use the original Python methods again.
 
+* Nested dict literals in function call kwargs could incorrectly raise an
+  error about duplicate keyword arguments, which are allowed when passing
+  them from dict literals.
+  (Github issue #2963)
+
 * Item access (subscripting) with integer indices/keys always tried the
   Sequence protocol before the Mapping protocol, which diverged from Python
   semantics.  It now passes through the Mapping protocol first when supported.

Cython/Compiler/Optimize.py

@@ -4422,25 +4422,25 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
         args = []
         items = []
 
-        def add(arg):
+        def add(parent, arg):
             if arg.is_dict_literal:
-                if items:
-                    items[0].key_value_pairs.extend(arg.key_value_pairs)
+                if items and items[-1].reject_duplicates == arg.reject_duplicates:
+                    items[-1].key_value_pairs.extend(arg.key_value_pairs)
                 else:
                     items.append(arg)
-            elif isinstance(arg, ExprNodes.MergedDictNode):
+            elif isinstance(arg, ExprNodes.MergedDictNode) and parent.reject_duplicates == arg.reject_duplicates:
                 for child_arg in arg.keyword_args:
-                    add(child_arg)
+                    add(arg, child_arg)
             else:
                 if items:
-                    args.append(items[0])
+                    args.extend(items)
                     del items[:]
                 args.append(arg)
 
         for arg in node.keyword_args:
-            add(arg)
+            add(node, arg)
         if items:
-            args.append(items[0])
+            args.extend(items)
 
         if len(args) == 1:
             arg = args[0]

tests/run/pep448_extended_unpacking.pyx

@@ -464,6 +464,10 @@ def unpack_dict_simple(it):
     return {**it}
 
 
+@cython.test_assert_path_exists('//MergedDictNode')
+@cython.test_fail_if_path_exists(
+    '//MergedDictNode//MergedDictNode',
+)
 def unpack_dict_from_iterable(it):
     """
     >>> d = unpack_dict_from_iterable(dict(a=1, b=2, c=3))
@@ -536,3 +540,28 @@ def unpack_dict_keep_originals(a, b, c):
     True
     """
     return {**a, **b, 2: 4, **c}
+
+
+@cython.test_assert_path_exists(
+    '//MergedDictNode',
+    '//MergedDictNode//MergedDictNode',
+    '//MergedDictNode//MergedDictNode//DictNode',
+)
+def unpack_in_call(f):
+    """
+    >>> def f(a=1, test=2, **kwargs):
+    ...     return a, test, sorted(kwargs.items())
+    >>> wrapped = unpack_in_call(f)
+    >>> wrapped(1)
+    (1, 1, [('more', 2)])
+    >>> wrapped(test='overwritten')
+    (1, 1, [('more', 2)])
+    >>> wrapped(b=3)
+    (1, 1, [('b', 3), ('more', 2)])
+    >>> wrapped(more=4)
+    Traceback (most recent call last):
+    TypeError: function() got multiple values for keyword argument 'more'
+    """
+    def wrapper(*args, **kwargs):
+        return f(*args, more=2, **{**kwargs, 'test': 1})
+    return wrapper