syntax.qdoc

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// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
\page qmllint-warnings-and-errors-syntax.html
\ingroup qmllint-warnings-and-errors
 
\title Syntax
\brief [syntax] Various syntactic errors.
 
\qmllintwarningcategory syntax
 
\section1 Nested inline components are not supported
 
\section2 What happened?
You defined an \l{qtqml-documents-definetypes.html#inline-components}{inline component}
inside another inline component.
 
\section2 Why is this bad?
The QML language does not allow nested inline components. Always define inline components
inside the root item of the QML file.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component Correct: Item {
        component Evil: Item { ... }
        ...
    }
}
 
\endqml
To fix this warning, move all components to the root item of the QML file.
\qml
import QtQuick
 
Item {
    component NotEvilAnymore: Item { ... }
    component Correct: Item {
        ...
    }
}
 
\endqml
 
\section1 Inline component declaration must be followed by a typename
 
\section2 What happened?
You defined an \l{qtqml-documents-definetypes.html#inline-components}{inline component}
with an invalid base type.
 
\section2 Why is this bad?
Inline components need a base type to inherit from.
 
\section2 Example
\qml
import QtQuick
 
Item {
    property Item someProperty
    component InlineComponent: someProperty {}
}
 
\endqml
In this case, \c someProperty is not a valid type name, as it is a property name.
To fix this warning, use a valid Type as the component's base type:
\qml
import QtQuick
 
Item {
    property Item someProperty
    component InlineComponent: Item { ... }
}
 
\endqml
 
\section1 Invalid alias expression: an initializer is needed
 
\section2 What happened?
You defined a \l{qtqml-syntax-objectattributes.html#property-aliases}{property alias}
without its aliased property.
 
\section2 Why is this bad?
Alias properties always need to have their aliased property or id in their definition.
 
\section2 Example
\qml
import QtQuick
 
Item {
    id: root
    property int someProperty
    property alias aliasProperty
}
 
\endqml
To fix this warning, replace the alias with a normal property, or add the missing
aliased property:
\qml
import QtQuick
 
Item {
    id: root
    property int someProperty
    property alias withAliasedProperty: root.someProperty
}
 
\endqml
 
\section1 Invalid alias expression: only ids and field member expressions can be aliased
 
\section2 What happened?
You defined a \l{qtqml-syntax-objectattributes.html#property-aliases}{property alias}
that aliases an expression other than an ID or a field member expression.
 
A field member expression is an expression of the form \c {someId.someProperty}.
 
\section2 Why is this bad?
Alias properties always need to have their aliased property in their definition, and can't
bind to other expressions than IDs and field member expressions.
 
\section2 Example
\qml
import QtQuick
 
Item {
    property int p
    property alias someProperty: p + 1
}
 
\endqml
To fix this warning, replace the alias with a normal property or bind it to an id or
field member expression:
\qml
import QtQuick
 
Item {
    id: root
    property int p
    property int someProperty: p + 1
    property alias alternative: root.p
}
 
\endqml
 
\section1 Id must be followed by an identifier
 
\section2 What happened?
You defined an \l{qtqml-syntax-objectattributes.html#the-id-attribute}{id} without
a value.
 
\section2 Why is this bad?
The QML language does not allow empty ids.
 
\section2 Example
\qml
import QtQuick
 
Item {
    id:;
}
 
\endqml
To fix this warning, bind the id to a valid name:
\qml
import QtQuick
 
Item {
    id: root;
}
 
\endqml
 
\section1 Failed to parse id
 
\section2 What happened?
You bound an \l{qtqml-syntax-objectattributes.html#the-id-attribute}{id} to an
expression other than a name.
 
\section2 Why is this bad?
The QML language only allows names as bindings to ids; more complex expressions
can't be used.
 
\section2 Example
\qml
import QtQuick
 
Item {
    property int a
    property int b
    function f() {
        if (true)
            return a
        return b
    }
 
    id: f()
}
\endqml
To fix this warning, bind the id to a valid name or declare a property and set up a binding:
\qml
import QtQuick
 
Item {
    property int a
    property int b
    function f() {
        if (true)
            return a
        return b
    }
 
    id: someItem // it would be confusing to call it `f` like the function
    property int alternative: f()
}
\endqml
 
\section1 Declaring an object which is not a QML object as a list member
 
\section2 What happened?
You added an expression other than an \l{qtqml-typesystem-objecttypes.html}{object} into a
list of objects.
 
\section2 Why is this bad?
The QML language only allows objects in object lists.
 
\section2 Example
\qml
import QtQuick
 
Item {
    property int hello
    property list<Item> myList: [
        Item {}, hello{}
    ]
}
 
\endqml
To fix this warning, use a valid object type, or remove the item from the list:
\qml
import QtQuick
 
Item {
    component Hello: Item {}
    property list<Item> myList: [
        Item {}, Hello{}
    ]
}
 
\endqml
 
\section1 Enums declared inside of inline components are ignored
 
\section2 What happened?
You defined an \l{qtqml-syntax-objectattributes.html#enumeration-attributes}{enum}
inside an inline component.
 
\section2 Why is this bad?
The QML language only allows enum definitions inside the root
item of the QML file. Enums declared inside an inline
component are unusable, even inside the inline component. The same applies to
enums declared inside non-root QML objects.
 
\section2 Example
\qml
import QtQuick
 
Item {
    component MyInlineComponent: Item {
        enum MyEnum { Hello, World }
    }
}
 
\endqml
To fix this warning, move the enum declaration into the root element of the
QML file:
\qml
import QtQuick
 
Item {
    enum MyEnum { Hello, World }
    component MyInlineComponent: Item {
    }
}
 
\endqml
 
\section1 Unknown argument to pragma
 
\section2 What happened?
You specified an invalid argument to a \l{qtqml-documents-structure.html#pragmas}{pragma}.
 
\section2 Why is this bad?
The pragma will have no effect.
 
\section2 Example
\qml
pragma ComponentBehavior: Buond
import QtQuick
 
Item {
}
 
\endqml
You can fix this warning by removing the pragma or fixing a potential typo:
\qml
pragma ComponentBehavior: Bound
import QtQuick
 
Item {
}
 
\endqml
*/