Flickable: fix minXExtent/minYExtent when content is smaller than view

At the moment, defining leftMargin (or topMargin) and contentWidth
(or contentHeight) so that "leftMargin+contentWidth < flickable.width"
(or topMargin+contentHeight < flickable.height) leads to widthRatio
(or heightRatio) having value != 1.
The value should, however, be 1, as the content is completely visible
inside the view, margins included.

As a sideeffect, under the assumptions described above, it will now
not be possible to scroll the leftMargin (or topMargin) out of screen,
something which was possible (and it shouldn't have) before this fix.

Task-number: QTBUG-53726
Change-Id: I22426c8038e90a2cfc7445914206eae0e781a3fb
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/quick/items/qquickflickable.cpp

@@ -1580,13 +1580,13 @@ qreal QQuickFlickable::minXExtent() const
 qreal QQuickFlickable::maxXExtent() const
 {
     Q_D(const QQuickFlickable);
-    return qMin<qreal>(0, width() - vWidth() - d->hData.endMargin);
+    return qMin<qreal>(minXExtent(), width() - vWidth() - d->hData.endMargin);
 }
 /* returns -ve */
 qreal QQuickFlickable::maxYExtent() const
 {
     Q_D(const QQuickFlickable);
-    return qMin<qreal>(0, height() - vHeight() - d->vData.endMargin);
+    return qMin<qreal>(minYExtent(), height() - vHeight() - d->vData.endMargin);
 }
 
 void QQuickFlickable::componentComplete()

tests/auto/quick/qquickflickable/data/ratios_smallContent.qml

@@ -0,0 +1,19 @@
+import QtQuick 2.0
+
+Flickable {
+    property double heightRatioIs: visibleArea.heightRatio
+    property double widthRatioIs: visibleArea.widthRatio
+
+    width: 200
+    height: 200
+    contentWidth: item.width
+    contentHeight: item.height
+    topMargin: 20
+    leftMargin: 40
+
+    Item {
+        id: item
+        width: 100
+        height: 100
+    }
+}

tests/auto/quick/qquickflickable/tst_qquickflickable.cpp

@@ -95,6 +95,7 @@ private slots:
     void movementFromProgrammaticFlick();
     void cleanup();
     void contentSize();
+    void ratios_smallContent();
 
 private:
     void flickWithTouch(QQuickWindow *window, QTouchDevice *touchDevice, const QPoint &from, const QPoint &to);
@@ -1817,6 +1818,33 @@ void tst_qquickflickable::contentSize()
     QCOMPARE(chspy.count(), 1);
 }
 
+// QTBUG-53726
+void tst_qquickflickable::ratios_smallContent()
+{
+    QScopedPointer<QQuickView> window(new QQuickView);
+    window->setSource(testFileUrl("ratios_smallContent.qml"));
+    QTRY_COMPARE(window->status(), QQuickView::Ready);
+    QQuickViewTestUtil::centerOnScreen(window.data());
+    QQuickViewTestUtil::moveMouseAway(window.data());
+    window->setTitle(QTest::currentTestFunction());
+    window->show();
+    QVERIFY(QTest::qWaitForWindowExposed(window.data()));
+    QQuickItem *root = window->rootObject();
+    QVERIFY(root);
+    QQuickFlickable *obj = qobject_cast<QQuickFlickable*>(root);
+    QVERIFY(obj != 0);
+
+    //doublecheck the item, as specified by contentWidth/Height, fits in the view
+    //use tryCompare to allow a bit of stabilization in component's properties
+    QTRY_COMPARE(obj->leftMargin() + obj->contentWidth() + obj->rightMargin() <= obj->width(), true);
+    QTRY_COMPARE(obj->topMargin() + obj->contentHeight() + obj->bottomMargin() <= obj->height(), true);
+
+    //the whole item fits in the flickable, heightRatio should be 1
+    QCOMPARE(obj->property("heightRatioIs").toDouble(), 1.);
+    QCOMPARE(obj->property("widthRatioIs").toDouble(), 1.);
+}
+
+
 QTEST_MAIN(tst_qquickflickable)
 
 #include "tst_qquickflickable.moc"