refactor(ui): extract the busy indicator into a widget, item 134

The status bar's sync bar was a bare QProgressBar configured inline in
MainWindow, and item 123's send popup needs the same thing again. It also
needs the half MainWindow does not use: the popup drains a determinate bar
through its cancellable countdown and switches THE SAME widget to
indeterminate when send_command starts and the duration stops being
knowable. Building that inline a second time is what this removes.

BusyIndicator carries both modes. setBusy() resets the range as well as the
visibility, so the switch out of the countdown cannot leave the bar drawing
its last fraction, and setProgress() treats a total of zero as busy rather
than passing it through: setRange(0, 0) IS the indeterminate range, so a
zero total would otherwise hand the caller an animating bar while it
believed it had drawn an empty one.

Only the bar is extracted, not the status label the backlog row mentions
beside it. m_statusLabel has 34 uses across MainWindow for transient
messages, selection counts and sync phases; it belongs to the window rather
than to the indicator, and the send popup owns its own phase text.

The hidden-on-construction test needs a shown parent, which cost a mutation
to find. Measured against a standalone Qt program: a parentless widget
reports isVisible() false and isHidden() true whether or not hide() was ever
called, so both obvious assertions passed against a constructor with the
hide() deleted. What differs is WA_WState_ExplicitShowHide, and the
behaviour it produces appears only once a parent is shown, which is how the
status bar holds this widget.

All five mutations checked and killed: the zero-total guard, the range reset
in setBusy(), the value clamp, the show() in setProgress() and the hide() in
the constructor.

1 files changed, 136 insertions, 0 deletions

diff --git a/tests/test_busyindicator.cpp b/tests/test_busyindicator.cpp
new file mode 100644
index 0000000..3f267c7
--- /dev/null
+++ b/tests/test_busyindicator.cpp
@@ -0,0 +1,136 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <QtTest>
+
+#include "busyindicator.h"
+
+class TestBusyIndicator : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void itStartsIndeterminateAndHidden();
+    void itStaysHiddenInsideAShownParent();
+    void setProgressShowsARealFraction();
+    void aTotalOfZeroFallsBackToBusyRatherThanAnEmptyBar();
+    void itSwitchesBackFromDeterminateToIndeterminate();
+    void aValueOutsideTheRangeIsClamped();
+};
+
+void TestBusyIndicator::itStartsIndeterminateAndHidden()
+{
+    BusyIndicator indicator;
+
+    // setRange(0, 0) is what Qt reads as indeterminate, and it is the state
+    // the status bar's sync indicator lives in.
+    QCOMPARE(indicator.minimum(), 0);
+    QCOMPARE(indicator.maximum(), 0);
+    QVERIFY(!indicator.isDeterminate());
+}
+
+void TestBusyIndicator::itStaysHiddenInsideAShownParent()
+{
+    // The hidden-on-construction property needs a SHOWN PARENT to be
+    // observable at all, and both obvious probes measure nothing without one.
+    // Measured against a standalone Qt program: a parentless widget reports
+    // isVisible() false and isHidden() true whether or not hide() was ever
+    // called, so a mutation deleting the constructor's hide() survives both
+    // assertions. What differs is WA_WState_ExplicitShowHide, and the
+    // behaviour it produces appears only once a parent is shown, which is how
+    // MainWindow's status bar holds this widget.
+    QWidget parent;
+    BusyIndicator *indicator = new BusyIndicator(&parent);
+    parent.show();
+
+    QVERIFY2(!indicator->isBusy(),
+             "the indicator showed itself as soon as its parent appeared");
+
+    indicator->setBusy(true);
+    QVERIFY(indicator->isBusy());
+}
+
+void TestBusyIndicator::setProgressShowsARealFraction()
+{
+    BusyIndicator indicator;
+    indicator.setProgress(3, 10);
+
+    QVERIFY2(indicator.isDeterminate(),
+             "a bar given a total stayed in the indeterminate range");
+    QCOMPARE(indicator.maximum(), 10);
+    QCOMPARE(indicator.value(), 3);
+
+    // Showing a fraction means being visible. A caller that set progress and
+    // got a hidden widget would have to remember a second call.
+    QVERIFY(indicator.isBusy());
+}
+
+void TestBusyIndicator::aTotalOfZeroFallsBackToBusyRatherThanAnEmptyBar()
+{
+    // The trap this guards: setRange(0, 0) IS the indeterminate range, so a
+    // total of zero passed straight through would hand the caller an
+    // animating bar while it believed it had drawn an empty fraction. Making
+    // it explicitly busy is the honest reading of "no total known".
+    BusyIndicator indicator;
+    indicator.setProgress(0, 0);
+
+    QVERIFY(!indicator.isDeterminate());
+    QVERIFY2(indicator.isBusy(),
+             "a total of zero left the indicator hidden and silent");
+
+    indicator.setProgress(5, -1);
+    QVERIFY(!indicator.isDeterminate());
+    QVERIFY(indicator.isBusy());
+}
+
+void TestBusyIndicator::itSwitchesBackFromDeterminateToIndeterminate()
+{
+    // The send popup's whole reason for one widget rather than two: it drains
+    // a determinate bar through the undo countdown, then switches THE SAME
+    // widget to indeterminate when send_command starts and the duration stops
+    // being knowable. A setBusy() that left a stale range would keep drawing
+    // the countdown's last fraction.
+    BusyIndicator indicator;
+    indicator.setProgress(9, 10);
+    QVERIFY(indicator.isDeterminate());
+
+    indicator.setBusy(true);
+    QVERIFY2(!indicator.isDeterminate(),
+             "the bar kept the countdown's range after switching to busy");
+    QCOMPARE(indicator.maximum(), 0);
+    QVERIFY(indicator.isBusy());
+
+    indicator.setBusy(false);
+    QVERIFY(!indicator.isBusy());
+}
+
+void TestBusyIndicator::aValueOutsideTheRangeIsClamped()
+{
+    // A countdown driven by a timer can overshoot its own total by a tick.
+    // Qt leaves an out-of-range value unset rather than clamping, which shows
+    // the PREVIOUS fraction, so the bar would appear to stall near the end.
+    BusyIndicator indicator;
+    indicator.setProgress(50, 10);
+    QCOMPARE(indicator.value(), 10);
+
+    indicator.setProgress(-5, 10);
+    QCOMPARE(indicator.value(), 0);
+}
+
+QTEST_MAIN(TestBusyIndicator)
+#include "test_busyindicator.moc"