Merge bitcoin-core/gui#343: Improve the GUI responsiveness when progress dialogs are used

4935ac5 qt: Improve GUI responsiveness (Hennadii Stepanov)
7585010 qt, macos: Fix GUIUtil::PolishProgressDialog bug (Hennadii Stepanov)

Pull request description:

  [`QProgressDialog`](https://doc.qt.io/qt-5/qprogressdialog.html) estimates the time the operation will take (based on time for steps), and only shows itself if that estimate is beyond [`minimumDuration`](https://doc.qt.io/qt-5/qprogressdialog.html#minimumDuration-prop).

  The default `minimumDuration` value is [4 seconds](https://doc.qt.io/qt-5/qprogressdialog.html#details), and it could make users think that the GUI is frozen.

  This PR sets `minimumDuration` to zero for all progress dialogs, that affects ones in the `WalletControllerActivity` class.

ACKs for top commit:
  ryanofsky:
    Code review ACK 4935ac5. I'm not very familiar with this API but all the changes and explanations make sense and are very clear, and this seems like it should be an improvement.
  promag:
    Code review ACK 4935ac5.
  jarolrod:
    ACK 4935ac5

Tree-SHA512: 2ddd74e7fd87894d341d2439dbaa544d031a350f7f57d4c7e9fbba977dc24080fe60fd7a80a542b1647f1de9091d7fd04a36eab695088d4d75fb836548e99b5f

Author: hebasto

src/qt/bitcoingui.cpp

@@ -1926,7 +1926,6 @@ void BitcoinGUI::showProgress(const QString &title, int nProgress)
         progressDialog = new QProgressDialog(title, QString(), 0, 100, this);
         GUIUtil::PolishProgressDialog(progressDialog);
         progressDialog->setWindowModality(Qt::ApplicationModal);
-        progressDialog->setMinimumDuration(0);
         progressDialog->setAutoClose(false);
         progressDialog->setValue(0);
     } else if (nProgress == 100) {

src/qt/guiutil.cpp

@@ -1874,10 +1874,12 @@ void PolishProgressDialog(QProgressDialog* dialog)
     // Workaround for macOS-only Qt bug; see: QTBUG-65750, QTBUG-70357.
     const int margin = TextWidth(dialog->fontMetrics(), ("X"));
     dialog->resize(dialog->width() + 2 * margin, dialog->height());
-    dialog->show();
-#else
-    Q_UNUSED(dialog);
 #endif
+    // QProgressDialog estimates the time the operation will take (based on time
+    // for steps), and only shows itself if that estimate is beyond minimumDuration.
+    // The default minimumDuration value is 4 seconds, and it could make users
+    // think that the GUI is frozen.
+    dialog->setMinimumDuration(0);
 }
 
 int TextWidth(const QFontMetrics& fm, const QString& text)

src/qt/walletcontroller.cpp

@@ -178,6 +178,9 @@ void WalletControllerActivity::showProgressDialog(const QString& label_text)
     m_progress_dialog->setCancelButton(nullptr);
     m_progress_dialog->setWindowModality(Qt::ApplicationModal);
     GUIUtil::PolishProgressDialog(m_progress_dialog);
+    // The setValue call forces QProgressDialog to start the internal duration estimation.
+    // See details in https://bugreports.qt.io/browse/QTBUG-47042.
+    m_progress_dialog->setValue(0);
 }
 
 void WalletControllerActivity::destroyProgressDialog()

src/qt/walletview.cpp

@@ -462,7 +462,6 @@ void WalletView::showProgress(const QString &title, int nProgress)
         progressDialog = new QProgressDialog(title, tr("Cancel"), 0, 100, this);
         GUIUtil::PolishProgressDialog(progressDialog);
         progressDialog->setWindowModality(Qt::ApplicationModal);
-        progressDialog->setMinimumDuration(0);
         progressDialog->setAutoClose(false);
         progressDialog->setValue(0);
     } else if (nProgress == 100) {