Fixed over-zealous optimization of append attribute usage to "__Pyx_PyObject_Append" (GH-4834)

Fixes https://github.com/cython/cython/issues/4828

3 files changed, 36 insertions, 2 deletions

diff --git a/Cython/Compiler/ExprNodes.py b/Cython/Compiler/ExprNodes.py
index 69632a4fe..2c5d70936 100644
--- a/Cython/Compiler/ExprNodes.py
+++ b/Cython/Compiler/ExprNodes.py
@@ -306,8 +306,8 @@ class ExprNode(Node):
     #                            Cached result of subexpr_nodes()
     #  use_managed_ref boolean   use ref-counted temps/assignments/etc.
     #  result_is_used  boolean   indicates that the result will be dropped and the
-    #  is_numpy_attribute   boolean   Is a Numpy module attribute
     #                            result_code/temp_result can safely be set to None
+    #  is_numpy_attribute   boolean   Is a Numpy module attribute
     #  annotation   ExprNode or None    PEP526 annotation for names or expressions
 
     result_ctype = None
diff --git a/Cython/Compiler/Optimize.py b/Cython/Compiler/Optimize.py
index 3cb77efe2..7e9435ba0 100644
--- a/Cython/Compiler/Optimize.py
+++ b/Cython/Compiler/Optimize.py
@@ -2860,7 +2860,7 @@ class OptimizeBuiltinCalls(Visitor.NodeRefCleanupMixin,
         """Optimistic optimisation as X.append() is almost always
         referring to a list.
         """
-        if len(args) != 2 or node.result_is_used:
+        if len(args) != 2 or node.result_is_used or node.function.entry:
             return node
 
         return ExprNodes.PythonCapiCallNode(
diff --git a/tests/run/append.pyx b/tests/run/append.pyx
index 1976780d5..dcc3fe7c9 100644
--- a/tests/run/append.pyx
+++ b/tests/run/append.pyx
@@ -1,3 +1,5 @@
+cimport cython
+
 class A:
     def append(self, x):
         print u"appending", x
@@ -94,3 +96,35 @@ def method_name():
     'append'
     """
     return [].append.__name__
+
+@cython.test_assert_path_exists(
+    '//PythonCapiCallNode')
+def append_optimized(probably_list):
+    """
+    >>> l = []
+    >>> append_optimized(l)
+    >>> l
+    [1]
+    """
+    probably_list.append(1)
+
+cdef class AppendBug:
+    # https://github.com/cython/cython/issues/4828
+    # if the attribute "append" is found it shouldn't be replaced with
+    # __Pyx_PyObject_Append
+    cdef object append
+    def __init__(self, append):
+        self.append = append
+
+@cython.test_fail_if_path_exists(
+    '//PythonCapiCallNode')
+def specific_attribute(AppendBug a):
+    """
+    >>> def append_to_default_arg(a, arg=[]):
+    ...    arg.append(a)
+    ...    return arg
+    >>> specific_attribute(AppendBug(append_to_default_arg))
+    >>> append_to_default_arg(None)
+    [1, None]
+    """
+    a.append(1)