[Development] QML import versions

[Attila Csipa]

On 9/24/2015 5:49 PM, Alan Alpert wrote:
> The point of versioning isn't to prevent different runtime outcomes, 
> that's not possible as you have showed. But there's an implicit 
> compile step when you run a QML file at program startup, and the 
> versioning system prevents that from failing. Getting different values 
> is a problem, yes. But those lines still ran, and you could 
> theoretically use runtime error handling code. If there suddenly 
> appears a type conflict in a QML file, the compilation stage *fails* 
> and the QML code never reaches its own "runtime" to experience the 
> different outcomes (we are in the runtime of the C++ application, but 
> bailed on compilation of the QML files). 

This feels somewhat self-imposed, though. Loader {} and 
Qt.createComponent shows that, at least in theory, you can handle 
compile-stage fails from within QML. There is no fine-grained-enough 
mechanism to make real use of it (at best, you can use it as a crude way 
of detecting Qt versions/modules), but that is exactly what prevents us 
from feature-based QML code-path selection. I do wish we had a bit more 
graceful way of (handling) failing in QML.

Best regards,
Attila