Troubleshooting sip assignHelper != NULL assertion

[Phil Thompson]

On 28/05/2020 16:30, Scott Talbert wrote:
> On Thu, 28 May 2020, Phil Thompson wrote:
> 
>>>>> Hi,
>>>>> 
>>>>> I'm running into the following assertion in wxPython that I don't
>>>>> quite understand:
>>>>> 
>>>>> python3: ../../../../sip/siplib/siplib.c:3444: parseResult: 
>>>>> Assertion
>>>>> `assign_helper != NULL' failed.
>>>>> 
>>>>> This is the relevant C++ class:
>>>>> 
>>>>> class wxPGWindowList
>>>>> {
>>>>> public:
>>>>>     wxPGWindowList(wxWindow* primary, wxWindow* secondary = NULL)
>>>>>         : m_primary(primary)
>>>>>         , m_secondary(secondary)
>>>>>     {
>>>>>     }
>>>>> 
>>>>>     void SetSecondary(wxWindow* secondary) { m_secondary = 
>>>>> secondary; }
>>>>> 
>>>>>     wxWindow* GetPrimary() const { return m_primary; }
>>>>>     wxWindow* GetSecondary() const { return m_secondary; }
>>>>> 
>>>>>     wxWindow*   m_primary;
>>>>>     wxWindow*   m_secondary;
>>>>> };
>>>> 
>>>> It doesn't matter what the C++ class looks like, it's the 
>>>> corresponding .sip that would be of interest.
>>> 
>>> My bad, here it is:
>>> class wxPGWindowList
>>> {
>>>     %Docstring
>>>         PGWindowList(primary, secondary=None)
>>> 
>>>         Contains a list of editor windows returned by CreateControls.
>>>     %End
>>>     %TypeHeaderCode
>>>         #include <wx/propgrid/editors.h>
>>>     %End
>>> 
>>> public:
>>>     wxPGWindowList(
>>>         wxWindow * primary,
>>>         wxWindow * secondary = NULL
>>>     );
>>> 
>>>     void SetSecondary(
>>>         wxWindow * secondary
>>>     );
>>>     %Docstring
>>>         SetSecondary(secondary)
>>>     %End
>>> 
>>>     wxWindow * GetPrimary() const;
>>>     %Docstring
>>>         GetPrimary() -> wx.Window
>>> 
>>>         Gets window of primary editor.
>>>     %End
>>> 
>>>     wxWindow * GetSecondary() const;
>>>     %Docstring
>>>         GetSecondary() -> wx.Window
>>> 
>>>         Gets window of secondary editor.
>>>     %End
>>> 
>>>     public:
>>> 
>>> 
>>>     %Property(name=Primary, get=GetPrimary)
>>>     %Property(name=Secondary, get=GetSecondary, set=SetSecondary)
>>> };  // end of class wxPGWindowList
>>> 
>>> 
>>>>> The assertion occurs when trying to return an instance of
>>>>> wxPGWindowList in a Python method, e.g.:
>>>>> 
>>>>> def foo():
>>>>>     return wxpg.PGWindowList(a, b)
>>>>> 
>>>>> From what I can tell, there is no assignment helper assigned by sip
>>>>> because there is no default constructor?  I may be missing 
>>>>> something,
>>>>> but I can't see why a default constructor would be needed.
>>>> 
>>>> You don't say what version of the sip module you are using but I'm 
>>>> guessing that that assertion is when it's parsing the Python object 
>>>> returned by a re-implementation of a C++ virtual. That doesn't seem 
>>>> to be happening in the above which suggests things aren't happening 
>>>> where you think they are.
>>> 
>>> sip module version is 4.19.19.  You are correct, I oversimplified 
>>> what
>>> is actually happening.  This is really what is happening:
>>> 
>>> class LargeImageEditor(wxpg.PGEditor):
>>>     def CreateControls(self, propgrid, property, pos, sz):
>>>         ...
>>>         return wxpg.PGWindowList(self.tc, btn)
>>> 
>>> Where CreateControls is a C++ virtual, relevant .sip snippet:
>>> 
>>>     virtual
>>>     wxPGWindowList CreateControls(
>>>         wxPropertyGrid * propgrid,
>>>         wxPGProperty * property,
>>>         const wxPoint & pos,
>>>         const wxSize & size
>>>     ) const = 0;
>>>     %Docstring
>>>         CreateControls(propgrid, property, pos, size) -> PGWindowList
>>> 
>>>         Instantiates editor controls.
>>>     %End
>> 
>> So SIP need to copy the wxPGWindowList from the stack to the heap. 
>> Shouldn't CreateControls return a pointer to the wxPGWindowList?
>> 
>> Of course SIP should detect this when generating the code rather than 
>> rely on a runtime assertion.
> 
> That is probably how I would have designed the API, but alas it wasn't
> done that way.  :)
> 
> Shouldn't a (default) copy constructor be sufficient to copy the
> wxPGWindowList in this case?

SIP may be being too conservative when determining if there is an 
implied copy ctor. Try adding an explicit copy ctor to the 
wxPGWindowList .sip file.

Phil