[Interest] Qt 6.5.2 and qmllint questions/issues

[Ulf Hermann]

Hi Matthew,

> -- QtLocation --
> The linter is unable to resolve types in QtLocation. Adding the 
> following dependencies to qml/QtLocation/qmldir resolved the problem:
> 
>     depends QtQuick
>     depends QtPositioning

Thanks for catching this. See 
https://codereview.qt-project.org/c/qt/qtlocation/+/500504 for a fix.

> -- Enums in gadgets --
> The linter is unable to resolve enums defined in gadgets (Type not found 
> in namespace [unresolved-type]). The class definition looks like this:
> 
>     struct MyType
>     {
>          Q_GADGET
>          QML_ELEMENT

This doesn't work. MyType is a value type and value types must have 
lower case names. QML_ELEMENT exposes it under an upper case name here 
("MyType"). Even if you were to give it a lower case name using 
QML_NAMED_ELEMENT you could still not access its enums, though, because 
types with lower case names are (by default) not addressable in QML.

So, what you want to do is expose MyType as a namespace instead:

namespace MyTypeNamespace {
     Q_NAMESPACE
     QML_FOREIGN_NAMESPACE(MyType)
     QML_NAMED_ELEMENT(MyType)
}

> The runtime reference works. Following the instructions here 
> https://doc.qt.io/qt-6/qtqml-cppintegration-overview.html, even with the 
> QML_UNCREATABLE macro, the type could still not be resolved. Looking at 
> the qmltypes file, if the 'accessSemantics' for the type is changed to 
> 'reference' from 'value' the linter works. Is this a problem with 
> linter, or possibly with the macro annotations of the type?

You cannot have reference semantics on a value type. A type with 
reference semantics (aka an "object type") needs to be derived from 
QObject and have a Q_OBJECT macro. The engine plays somewhat loose with 
that and allows you to still access enums from such broken types. We 
should amend the documentation to warn about this problem and also 
generate a run time warning from the engine.

> -- 'as' operator --
> The 'as' operator has been used to deal with the 'missing-property' 
> warning in this type of pattern in QML
> 
>     Loader {
>        id: loader
>        sourceComponent: Dialog { ... }
>     }
> 
>     ... {
>        (loader.item as Dialog).open()
>     }
> 
> This silences the linter, but at runtime there is an error, in this case 
> when the 'open()' function is called: 'TypeError: true is not a function'.
> What is the status of the 'as' operator? It doesn't appear to be 
> documented. Can it be used, or does it have known short-comings?

This should work. Type assertions (aka "as cast") are documented in 
https://doc.qt.io/qt-6/qtqml-javascript-hostenvironment.html . What kind 
of object does the loader produce here? Can you please open a bug report 
with a minimal example?

> Please also note the type registration is done manually, not with the 
> code generated by qmltyperegistrar. Any pointers would be appreciated.

My pointer about that is rather simple: Do use qmltyperegistrar and have 
it generate consistent type registrations. That will probably fix some 
of your problems.

best regards,
Ulf Hermann