Fix generation of api code for C++ classes with object members.

Fixes Github issue #1886.

Cython/Compiler/ModuleNode.py

@@ -901,6 +901,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                     code.put("virtual ")
                     has_virtual_methods = True
                 code.putln("%s;" % attr.type.declaration_code(attr.cname))
+            is_implementing = 'init_module' in code.globalstate.parts
             if constructor or py_attrs:
                 if constructor:
                     arg_decls = []
@@ -917,6 +918,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 else:
                     arg_decls = ["void"]
                     arg_names = []
+                if is_implementing:
                   code.putln("%s(%s) {" % (type.cname, ", ".join(arg_decls)))
                   if py_attrs:
                       code.put_ensure_gil()
@@ -927,9 +929,12 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                   if py_attrs:
                       code.put_release_ensured_gil()
                   code.putln("}")
+                else:
+                  code.putln("%s(%s);" % (type.cname, ", ".join(arg_decls)))
             if destructor or py_attrs or has_virtual_methods:
                 if has_virtual_methods:
                     code.put("virtual ")
+                if is_implementing:
                   code.putln("~%s() {" % type.cname)
                   if py_attrs:
                       code.put_ensure_gil()
@@ -940,8 +945,11 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                           code.put_var_xdecref(attr, nanny=False);
                       code.put_release_ensured_gil()
                   code.putln("}")
+                else:
+                  code.putln("~%s();" % type.cname)
             if py_attrs:
                 # Also need copy constructor and assignment operators.
+                if is_implementing:
                   code.putln("%s(const %s& __Pyx_other) {" % (type.cname, type.cname))
                   code.put_ensure_gil()
                   for attr in scope.var_entries:
@@ -962,6 +970,9 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                   code.putln("}")
                   code.putln("return *this;")
                   code.putln("}")
+                else:
+                  code.putln("%s(const %s& __Pyx_other);" % (type.cname, type.cname))
+                  code.putln("%s& operator=(const %s& __Pyx_other);" % (type.cname, type.cname))
             code.putln("};")
 
     def generate_enum_definition(self, entry, code):

tests/run/cpp_classes_def.pyx

@@ -226,6 +226,18 @@ def test_CppClassWithObjectMemberCopyAssign(name):
     print "Nothing alive."
 
 
+# Github issue #1886.
+cdef public cppclass PublicCppClassWithObjectMember:
+  object o
+
+def test_PublicCppClassWithObjectMember():
+  """
+  >>> test_PublicCppClassWithObjectMember()
+  """
+  cdef PublicCppClassWithObjectMember c
+  assert c.o is None
+
+
 cdef cppclass UncopyableConstructorArgument:
     unique_ptr[vector[int]] member
     __init__(unique_ptr[vector[int]] arg):