Significant digits were lost in QDoubleSpinBox range when changing precision

When setting the range, the actual value precision was lost because the min
and max were saved after being formatted to the current precison (decimals
property), thus losing information. We now keep the user original values, and
use these whenever the decimals property is changed. Auto-test included.

Reviewed-by: leo
Task-number: QTBUG-6496

2 files changed, 26 insertions, 3 deletions

diff --git a/src/gui/widgets/qspinbox.cpp b/src/gui/widgets/qspinbox.cpp
index 50b225c..f382f96 100644
--- a/src/gui/widgets/qspinbox.cpp
+++ b/src/gui/widgets/qspinbox.cpp
@@ -99,6 +99,10 @@ public:
         Q_Q(QDoubleSpinBox);
         q->setInputMethodHints(Qt::ImhFormattedNumbersOnly);
     }
+
+    // When fiddling with the decimals property, we may lose precision in these properties.
+    double actualMin;
+    double actualMax;
 };
 
 
@@ -762,6 +766,7 @@ double QDoubleSpinBox::minimum() const
 void QDoubleSpinBox::setMinimum(double minimum)
 {
     Q_D(QDoubleSpinBox);
+    d->actualMin = minimum;
     const QVariant m(d->round(minimum));
     d->setRange(m, (d->variantCompare(d->maximum, m) > 0 ? d->maximum : m));
 }
@@ -792,6 +797,7 @@ double QDoubleSpinBox::maximum() const
 void QDoubleSpinBox::setMaximum(double maximum)
 {
     Q_D(QDoubleSpinBox);
+    d->actualMax = maximum;
     const QVariant m(d->round(maximum));
     d->setRange((d->variantCompare(d->minimum, m) < 0 ? d->minimum : m), m);
 }
@@ -813,6 +819,8 @@ void QDoubleSpinBox::setMaximum(double maximum)
 void QDoubleSpinBox::setRange(double minimum, double maximum)
 {
     Q_D(QDoubleSpinBox);
+    d->actualMin = minimum;
+    d->actualMax = maximum;
     d->setRange(QVariant(d->round(minimum)), QVariant(d->round(maximum)));
 }
 
@@ -843,7 +851,7 @@ void QDoubleSpinBox::setDecimals(int decimals)
     Q_D(QDoubleSpinBox);
     d->decimals = qBound(0, decimals, DBL_MAX_10_EXP + DBL_DIG);
 
-    setRange(minimum(), maximum()); // make sure values are rounded
+    setRange(d->actualMin, d->actualMax); // make sure values are rounded
     setValue(value());
 }
 
@@ -1051,8 +1059,10 @@ QVariant QSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
 
 QDoubleSpinBoxPrivate::QDoubleSpinBoxPrivate()
 {
-    minimum = QVariant(0.0);
-    maximum = QVariant(99.99);
+    actualMin = 0.0;
+    actualMax = 99.99;
+    minimum = QVariant(actualMin);
+    maximum = QVariant(actualMax);
     value = minimum;
     singleStep = QVariant(1.0);
     decimals = 2;
diff --git a/tests/auto/qdoublespinbox/tst_qdoublespinbox.cpp b/tests/auto/qdoublespinbox/tst_qdoublespinbox.cpp
index a3f0915..35cffd6 100644
--- a/tests/auto/qdoublespinbox/tst_qdoublespinbox.cpp
+++ b/tests/auto/qdoublespinbox/tst_qdoublespinbox.cpp
@@ -149,6 +149,7 @@ private slots:
 
     void taskQTBUG_5008_textFromValueAndValidate();
     void taskQTBUG_6670_selectAllWithPrefix();
+    void taskQTBUG_6496_fiddlingWithPrecision();
 
 public slots:
     void valueChangedHelper(const QString &);
@@ -1096,5 +1097,17 @@ void tst_QDoubleSpinBox::taskQTBUG_6670_selectAllWithPrefix()
     QCOMPARE(spin.value(), 12.);
 }
 
+void tst_QDoubleSpinBox::taskQTBUG_6496_fiddlingWithPrecision()
+{
+    QDoubleSpinBox dsb;
+    dsb.setRange(0, 0.991);
+    dsb.setDecimals(1);
+    QCOMPARE(dsb.maximum(), 1.0);
+    dsb.setDecimals(2);
+    QCOMPARE(dsb.maximum(), 0.99);
+    dsb.setDecimals(3);
+    QCOMPARE(dsb.maximum(), 0.991);
+}
+
 QTEST_MAIN(tst_QDoubleSpinBox)
 #include "tst_qdoublespinbox.moc"