qmllint doc: Add assignment-in-conditionHEADdev

Task-number: QTBUG-127037
Pick-to: 6.10
Change-Id: Ibafc358bfec707799d947634d3dda331643c4cdd
Reviewed-by: Leena Miettinen <[email protected]>
Reviewed-by: Ulf Hermann <[email protected]>
Reviewed-by: Sami Shalayel <[email protected]>

1 files changed, 63 insertions, 0 deletions

diff --git a/src/qml/doc/src/qmllint/warn-assignment-in-condition.qdoc b/src/qml/doc/src/qmllint/warn-assignment-in-condition.qdoc
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+++ b/src/qml/doc/src/qmllint/warn-assignment-in-condition.qdoc
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+// Copyright (C) 2025 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+\page qmllint-warnings-and-errors-assignment-in-condition.html
+\ingroup qmllint-warnings-and-errors
+\qmllintwarningcategory warn-assignment-in-condition
+
+\title Warn about using assignment in conditions
+\brief [assignment-in-condition] An assignment statement is used inside a condition
+
+\section1 Warn about using assignment in conditions
+
+\section2 What happened?
+You used an assignment inside an \c{if-condition}.
+
+\section2 Why is this bad?
+This is often a mistake, and a comparison should have been used. If it was intentional, it is still
+often considered confusing.
+
+\section2 Example
+\qml
+import QtQuick
+
+Item {
+    id: root
+    Component.onCompleted: {
+       // mistake: should have been a comparison
+       if (width = height)
+           console.log("A square")
+       let mypoint = Qt.point(1,2)
+       let hit = false
+       // intentional, but possibly misleading
+       if (hit = root.contains(myPoint))
+           console.log("hit")
+       root.enabled = hit
+    }
+}
+\endqml
+
+To fix this warning, change the assignment to a comparison if it was a mistake. Otherwise, wrap the
+assignment into parentheses to indicate that it was done intentionally.
+
+\qml
+import QtQuick
+
+Item {
+    id: root
+    Component.onCompleted: {
+       // fixed
+       if (width === height)
+           console.log("A square")
+       let mypoint = Qt.point(1,2)
+       let hit = false
+       // intentional
+       if ((hit = root.contains(point)))
+           console.log("hit")
+       root.enabled = hit
+    }
+}
+\endqml
+*/
+