Troubleshooting sip assignHelper != NULL assertion

[Phil Thompson]

On 28/05/2020 16:52, Scott Talbert wrote:
> On Thu, 28 May 2020, Phil Thompson wrote:
> 
>> 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.
> 
> I don't think that will be enough, though.  SIP seems to only set the
> assignment helper if there are *both* a public default constructor and
> a public copy constructor, see:
> 
> https://www.riverbankcomputing.com/hg/sip/file/d85e9957e726/sipgen/transform.c#l596
> 
> Scott

Should be fixed in the current repo. SIP v4.19.23 will be released next 
week.

Be aware that the fix may expose missing private ctors in other .sip 
files - PyQt had two cases.

Thanks,
Phil