Provide effective size policy of Layout in its attached properties

The QML Layout, by default, has an effective size policy for shrinking
and expanding. But its attached properties
(Layout.fillHeight/Layout.fillWidth) don't reflect the same.

This patch provides an effective size policy of the Layout in its
corresponding attached properties (Layout.fillWidth/Layout.fillHeight),
and the same has been updated in the documentation.

Fixes: QTBUG-139699
Pick-to: 6.10 6.8 6.5
Change-Id: I133fc8161a321678aaeb160aabf3065112dea32a
Reviewed-by: Jan Arve Sæther <[email protected]>

3 files changed, 24 insertions, 6 deletions

diff --git a/src/quicklayouts/qquicklayout.cpp b/src/quicklayouts/qquicklayout.cpp
index 97219a1daa..4185f43aa0 100644
--- a/src/quicklayouts/qquicklayout.cpp
+++ b/src/quicklayouts/qquicklayout.cpp
@@ -308,6 +308,8 @@ void QQuickLayoutAttached::setMaximumImplicitSize(const QSizeF &sz)
     set to the preferred width.
     The default depends on implicit (built-in) size policy of item.
 
+    \note By default, this property is \c true for layouts.
+
     \sa fillHeight
 */
 void QQuickLayoutAttached::setFillWidth(bool fill)
@@ -329,6 +331,8 @@ void QQuickLayoutAttached::setFillWidth(bool fill)
     set to the preferred height.
     The default depends on implicit (built-in) size policy of the item.
 
+    \note By default, this property is \c true for layouts.
+
     \sa fillWidth
 */
 void QQuickLayoutAttached::setFillHeight(bool fill)
diff --git a/src/quicklayouts/qquicklayout_p.h b/src/quicklayouts/qquicklayout_p.h
index 971862a145..c75e4e6103 100644
--- a/src/quicklayouts/qquicklayout_p.h
+++ b/src/quicklayouts/qquicklayout_p.h
@@ -221,21 +221,27 @@ public:
     void setMaximumImplicitSize(const QSizeF &sz);
 
     bool fillWidth() const {
-        if (auto *itemPriv = itemForSizePolicy(m_isFillWidthSet)) {
+        bool effectiveFillWidth = m_fillWidth;
+        if (!m_isFillWidthSet && qobject_cast<QQuickLayout *>(item())) {
+            effectiveFillWidth = true;
+        } else if (auto *itemPriv = itemForSizePolicy(m_isFillWidthSet)) {
             QLayoutPolicy::Policy hPolicy = itemPriv->sizePolicy().horizontalPolicy();
-            return hPolicy & QLayoutPolicy::GrowFlag;
+            effectiveFillWidth = (hPolicy & QLayoutPolicy::GrowFlag);
         }
-        return m_fillWidth;
+        return effectiveFillWidth;
     }
     void setFillWidth(bool fill);
     bool isFillWidthSet() const { return m_isFillWidthSet; }
 
     bool fillHeight() const {
-        if (auto *itemPriv = itemForSizePolicy(m_isFillHeightSet)) {
+        bool effectiveFillHeight = m_fillHeight;
+        if (!m_isFillHeightSet && qobject_cast<QQuickLayout *>(item())) {
+            effectiveFillHeight = true;
+        } else if (auto *itemPriv = itemForSizePolicy(m_isFillHeightSet)) {
             QLayoutPolicy::Policy vPolicy = itemPriv->sizePolicy().verticalPolicy();
-            return vPolicy & QLayoutPolicy::GrowFlag;
+            effectiveFillHeight = (vPolicy & QLayoutPolicy::GrowFlag);
         }
-        return m_fillHeight;
+        return effectiveFillHeight;
     }
     void setFillHeight(bool fill);
     bool isFillHeightSet() const { return m_isFillHeightSet; }
diff --git a/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml b/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml
index 56198f0d2e..cb61c6c31a 100644
--- a/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml
+++ b/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml
@@ -100,6 +100,14 @@ Item {
             }
         }
 
+        function test_defaultSizePolicyForLayout() {
+            var layout = layout_columnLayout_Component.createObject(container)
+            waitForRendering(layout)
+            compare(layout.Layout.fillWidth, true)
+            compare(layout.Layout.fillHeight, true)
+            layout.destroy()
+        }
+
         function test_warnAboutLayoutItemsWithAnchors()
         {
             var regex = new RegExp(".*: Detected anchors on an item that is managed by a layout. "