TextArea: prevent changing size of background recursively

When the x/y position of background depends on the height/width of
background and these values are not constant, the if statement in
the method resizeBackground() will always pass. And since
`resizingBackground` guard wasn't checked, any geometry change
will always call resizeBackground() and then call
themself recursively (via the change listener),
that means the height/width of background will
always be reset, no matter what value you set.
Another part of the issue was in determining the extra bits too late:
in case the background gets parented by the flickable, the new child
caused the flickable to re-calculate its metrics and thus resize
the background *prior* to remembering if it has w/h set.

As a side effect, this fix also brings the possibility to reset
previously set w/h to get the default background sizing behavior.

Inspired by da06da57002b64cf4bcde0ca708b3275a5f919ae

[ChangeLog][QtQuick][QQuickTextArea] prevent changing size
of background recursively in construction

Fixes: QTBUG-76369
Change-Id: Ide51ec1ebab63605ae3bfcc10a76a28be960ef36
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

2 files changed, 82 insertions, 7 deletions

diff --git a/src/quicktemplates2/qquicktextarea.cpp b/src/quicktemplates2/qquicktextarea.cpp
index 7fdc8f0a..f7b8969c 100644
--- a/src/quicktemplates2/qquicktextarea.cpp
+++ b/src/quicktemplates2/qquicktextarea.cpp
@@ -435,9 +435,16 @@ void QQuickTextAreaPrivate::resizeFlickableContent()
 
 void QQuickTextAreaPrivate::itemGeometryChanged(QQuickItem *item, QQuickGeometryChange change, const QRectF &diff)
 {
-    Q_UNUSED(item);
-    Q_UNUSED(change);
     Q_UNUSED(diff);
+    if (!resizingBackground && item == background) {
+        QQuickItemPrivate *p = QQuickItemPrivate::get(item);
+        // Only set hasBackgroundWidth/Height if it was a width/height change,
+        // otherwise we're prevented from setting a width/height in the future.
+        if (change.widthChange())
+            extra.value().hasBackgroundWidth = p->widthValid;
+        if (change.heightChange())
+            extra.value().hasBackgroundHeight = p->heightValid;
+    }
 
     if (flickable)
         resizeFlickableControl();
@@ -627,17 +634,17 @@ void QQuickTextArea::setBackground(QQuickItem *background)
     d->background = background;
 
     if (background) {
+        QQuickItemPrivate *p = QQuickItemPrivate::get(background);
+        if (p->widthValid || p->heightValid) {
+            d->extra.value().hasBackgroundWidth = p->widthValid;
+            d->extra.value().hasBackgroundHeight = p->heightValid;
+        }
         if (d->flickable)
             background->setParentItem(d->flickable);
         else
             background->setParentItem(this);
         if (qFuzzyIsNull(background->z()))
             background->setZ(-1);
-        QQuickItemPrivate *p = QQuickItemPrivate::get(background);
-        if (p->widthValid || p->heightValid) {
-            d->extra.value().hasBackgroundWidth = p->widthValid;
-            d->extra.value().hasBackgroundHeight = p->heightValid;
-        }
         if (isComponentComplete())
             d->resizeBackground();
         QQuickControlPrivate::addImplicitSizeListener(background, d, QQuickControlPrivate::ImplicitSizeChanges | QQuickItemPrivate::Geometry);
diff --git a/tests/auto/controls/data/tst_textarea.qml b/tests/auto/controls/data/tst_textarea.qml
index ee40c9b7..1e455ffc 100644
--- a/tests/auto/controls/data/tst_textarea.qml
+++ b/tests/auto/controls/data/tst_textarea.qml
@@ -688,4 +688,72 @@ TestCase {
         compare(control.background.width, 100)
         compare(control.background.height, 100)
     }
+
+    // QTBUG-76369
+    Component {
+        id: testResizeBackground
+        Item {
+            width: 200
+            height: 200
+            property alias textArea: textArea
+            ScrollView {
+                anchors.fill: parent
+                ScrollBar.horizontal.policy: ScrollBar.AlwaysOff
+                TextArea {
+                    id: textArea
+                    // workaround test failing due to default insets on Imagine
+                    topInset: undefined
+                    leftInset: undefined
+                    rightInset: undefined
+                    bottomInset: undefined
+                    wrapMode : TextEdit.WordWrap
+                    readOnly: false
+                    selectByMouse: true
+                    focus: true
+                    text: "test message"
+
+                    background: Rectangle {
+                        y: parent.height - height - textArea.bottomPadding / 2
+                        implicitWidth: 120
+                        height: textArea.activeFocus ? 2 : 1
+                    }
+                }
+            }
+        }
+    }
+
+    function test_resize_background() {
+        var control = createTemporaryObject(testResizeBackground, testCase)
+
+        compare(control.textArea.background.width, control.width)
+        compare(control.textArea.background.height, 1)
+        control.width = 400
+        control.height = 400
+        compare(control.textArea.background.width, control.width)
+        compare(control.textArea.background.height, 1)
+        control.width = 200
+        control.height = 200
+        compare(control.textArea.background.width, control.width)
+        compare(control.textArea.background.height, 1)
+
+        // hasBackgroundWidth=true
+        control.textArea.background.width = 1
+        compare(control.textArea.background.width, 1)
+        compare(control.textArea.background.height, 1)
+        control.width = 400
+        control.height = 400
+        compare(control.textArea.background.width, 1)
+        compare(control.textArea.background.height, 1)
+        // hasBackgroundHeight=false
+        control.textArea.background.height = undefined
+        compare(control.textArea.background.width, 1)
+        compare(control.textArea.background.height, 0)
+        control.textArea.background.y = 0
+        compare(control.textArea.background.width, 1)
+        compare(control.textArea.background.height, control.height)
+        control.width = 200
+        control.height = 200
+        compare(control.textArea.background.width, 1)
+        compare(control.textArea.background.height, control.height)
+    }
 }