Test that *args tuple is not copied if possible (GH-3086)

tests/run/extstarargs.pyx

-__doc__ = u"""
+cdef sorteditems(d):
+    return tuple(sorted(d.items()))
+
+
+cdef class Silly:
+
+    def __init__(self, *a):
+        """
         >>> s = Silly(1,2,3, 'test')
-    >>> (spam,grail,swallow,creosote,onlyt,onlyk,tk) = (
-    ...     s.spam,s.grail,s.swallow,s.creosote,s.onlyt,s.onlyk,s.tk)
+        """
 
-    >>> spam(1,2,3)
+    def spam(self, x, y, z):
+        """
+        >>> s = Silly()
+        >>> s.spam(1,2,3)
         (1, 2, 3)
-    >>> spam(1,2)
+        >>> s.spam(1,2)
         Traceback (most recent call last):
         TypeError: spam() takes exactly 3 positional arguments (2 given)
-    >>> spam(1,2,3,4)
+        >>> s.spam(1,2,3,4)
         Traceback (most recent call last):
         TypeError: spam() takes exactly 3 positional arguments (4 given)
-    >>> spam(1,2,3, a=1) #doctest: +ELLIPSIS
+        >>> s.spam(1,2,3, a=1)
         Traceback (most recent call last):
         TypeError: spam() got an unexpected keyword argument 'a'
+        """
+        return (x, y, z)
 
-    >>> grail(1,2,3)
+    def grail(self, x, y, z, *a):
+        """
+        >>> s = Silly()
+        >>> s.grail(1,2,3)
         (1, 2, 3, ())
-    >>> grail(1,2,3,4)
+        >>> s.grail(1,2,3,4)
         (1, 2, 3, (4,))
-    >>> grail(1,2,3,4,5,6,7,8,9)
+        >>> s.grail(1,2,3,4,5,6,7,8,9)
         (1, 2, 3, (4, 5, 6, 7, 8, 9))
-    >>> grail(1,2)
+        >>> s.grail(1,2)
         Traceback (most recent call last):
         TypeError: grail() takes at least 3 positional arguments (2 given)
-    >>> grail(1,2,3, a=1) #doctest: +ELLIPSIS
+        >>> s.grail(1,2,3, a=1)
         Traceback (most recent call last):
         TypeError: grail() got an unexpected keyword argument 'a'
+        """
+        return (x, y, z, a)
 
-    >>> swallow(1,2,3)
+    def swallow(self, x, y, z, **k):
+        """
+        >>> s = Silly()
+        >>> s.swallow(1,2,3)
         (1, 2, 3, ())
-    >>> swallow(1,2,3,4)
+        >>> s.swallow(1,2,3,4)
         Traceback (most recent call last):
         TypeError: swallow() takes exactly 3 positional arguments (4 given)
-    >>> swallow(1,2,3, a=1, b=2)
+        >>> s.swallow(1,2,3, a=1, b=2)
         (1, 2, 3, (('a', 1), ('b', 2)))
-    >>> swallow(1,2,3, x=1)
+        >>> s.swallow(1,2,3, x=1)
         Traceback (most recent call last):
         TypeError: swallow() got multiple values for keyword argument 'x'
+        """
+        return (x, y, z, sorteditems(k))
 
-    >>> creosote(1,2,3)
+    def creosote(self, x, y, z, *a, **k):
+        """
+        >>> s = Silly()
+        >>> s.creosote(1,2,3)
         (1, 2, 3, (), ())
-    >>> creosote(1,2,3,4)
+        >>> s.creosote(1,2,3,4)
         (1, 2, 3, (4,), ())
-    >>> creosote(1,2,3, a=1)
+        >>> s.creosote(1,2,3, a=1)
         (1, 2, 3, (), (('a', 1),))
-    >>> creosote(1,2,3,4, a=1, b=2)
+        >>> s.creosote(1,2,3,4, a=1, b=2)
         (1, 2, 3, (4,), (('a', 1), ('b', 2)))
-    >>> creosote(1,2,3,4, x=1)
+        >>> s.creosote(1,2,3,4, x=1)
         Traceback (most recent call last):
         TypeError: creosote() got multiple values for keyword argument 'x'
+        """
+        return (x, y, z, a, sorteditems(k))
 
-    >>> onlyt(1)
+    def onlyt(self, *a):
+        """
+        >>> s = Silly()
+        >>> s.onlyt(1)
         (1,)
-    >>> onlyt(1,2)
+        >>> s.onlyt(1,2)
         (1, 2)
-    >>> onlyt(a=1)
+        >>> s.onlyt(a=1)
         Traceback (most recent call last):
         TypeError: onlyt() got an unexpected keyword argument 'a'
-    >>> onlyt(1, a=2)
+        >>> s.onlyt(1, a=2)
         Traceback (most recent call last):
         TypeError: onlyt() got an unexpected keyword argument 'a'
+        >>> test_no_copy_args(s.onlyt)
+        True
+        """
+        return a
 
-    >>> onlyk(a=1)
+    def onlyk(self, **k):
+        """
+        >>> s = Silly()
+        >>> s.onlyk(a=1)
         (('a', 1),)
-    >>> onlyk(a=1, b=2)
+        >>> s.onlyk(a=1, b=2)
         (('a', 1), ('b', 2))
-    >>> onlyk(1)
+        >>> s.onlyk(1)
         Traceback (most recent call last):
         TypeError: onlyk() takes exactly 0 positional arguments (1 given)
-    >>> onlyk(1, 2)
+        >>> s.onlyk(1, 2)
         Traceback (most recent call last):
         TypeError: onlyk() takes exactly 0 positional arguments (2 given)
-    >>> onlyk(1, a=1, b=2)
+        >>> s.onlyk(1, a=1, b=2)
         Traceback (most recent call last):
         TypeError: onlyk() takes exactly 0 positional arguments (1 given)
+        """
+        return sorteditems(k)
 
-    >>> tk(a=1)
+    def tk(self, *a, **k):
+        """
+        >>> s = Silly()
+        >>> s.tk(a=1)
         (('a', 1),)
-    >>> tk(a=1, b=2)
+        >>> s.tk(a=1, b=2)
         (('a', 1), ('b', 2))
-    >>> tk(1)
+        >>> s.tk(1)
         (1,)
-    >>> tk(1, 2)
+        >>> s.tk(1, 2)
         (1, 2)
-    >>> tk(1, a=1, b=2)
+        >>> s.tk(1, a=1, b=2)
         (1, ('a', 1), ('b', 2))
-"""
-
-
-cdef sorteditems(d):
-    l = list(d.items())
-    l.sort()
-    return tuple(l)
-
-
-cdef class Silly:
-
-    def __init__(self, *a):
-        pass
-
-    def spam(self, x, y, z):
-        return (x, y, z)
-
-    def grail(self, x, y, z, *a):
-        return (x, y, z, a)
-
-    def swallow(self, x, y, z, **k):
-        return (x, y, z, sorteditems(k))
-
-    def creosote(self, x, y, z, *a, **k):
-        return (x, y, z, a, sorteditems(k))
+        """
+        return a + sorteditems(k)
 
-    def onlyt(self, *a):
+    def t_kwonly(self, *a, k):
+        """
+        >>> s = Silly()
+        >>> test_no_copy_args(s.t_kwonly, k=None)
+        True
+        """
         return a
 
-    def onlyk(self, **k):
-        return sorteditems(k)
 
-    def tk(self, *a, **k):
-        return a + sorteditems(k)
+def test_no_copy_args(func, **kw):
+    """
+    func is a function such that func(*args, **kw) returns args.
+    We test that no copy is made of the args tuple.
+    This tests both the caller side and the callee side.
+    """
+    args = (1, 2, 3)
+    return func(*args, **kw) is args

tests/run/starargs.pyx

 cdef sorteditems(d):
-    l = list(d.items())
-    l.sort()
-    return tuple(l)
+    return tuple(sorted(d.items()))
+
 
 def spam(x, y, z):
     """
@@ -79,6 +78,8 @@ def onlyt(*a):
     >>> onlyt(1, a=2)
     Traceback (most recent call last):
     TypeError: onlyt() got an unexpected keyword argument 'a'
+    >>> test_no_copy_args(onlyt)
+    True
     """
     return a
 
@@ -114,3 +115,20 @@ def tk(*a, **k):
     (1, ('a', 1), ('b', 2))
     """
     return a + sorteditems(k)
+
+def t_kwonly(*a, k):
+    """
+    >>> test_no_copy_args(t_kwonly, k=None)
+    True
+    """
+    return a
+
+
+def test_no_copy_args(func, **kw):
+    """
+    func is a function such that func(*args, **kw) returns args.
+    We test that no copy is made of the args tuple.
+    This tests both the caller side and the callee side.
+    """
+    args = (1, 2, 3)
+    return func(*args, **kw) is args