Disable setting background color in QInputMethodEvent

IME managers may set background and foreground color of the composition
string. Since there is no Chromium API for setting the foreground color,
changing the background color to black may produce "black-on-black" text.
Chromium locks the background color to transparent thus we do the same
in this fix.

Task-number: QTBUG-58362
Task-number: QTBUG-60031
Change-Id: I939c8aaaa847de191890d6924ba3c7652465f8a0
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

2 files changed, 7 insertions, 5 deletions

diff --git a/src/core/render_widget_host_view_qt.cpp b/src/core/render_widget_host_view_qt.cpp
index 96cddfb4b..332be89f8 100644
--- a/src/core/render_widget_host_view_qt.cpp
+++ b/src/core/render_widget_host_view_qt.cpp
@@ -1149,11 +1149,7 @@ void RenderWidgetHostViewQt::handleInputMethodEvent(QInputMethodEvent *ev)
             if (format.underlineStyle() != QTextCharFormat::NoUnderline)
                 underlineColor = format.underlineColor();
 
-            QColor backgroundColor(0, 0, 0, 0);
-            if (format.background().style() != Qt::NoBrush)
-                backgroundColor = format.background().color();
-
-            underlines.push_back(blink::WebCompositionUnderline(start, end, toSk(underlineColor), /*thick*/ false, toSk(backgroundColor)));
+            underlines.push_back(blink::WebCompositionUnderline(start, end, toSk(underlineColor), /*thick*/ false, SK_ColorTRANSPARENT));
             break;
         }
         case QInputMethodEvent::Cursor:
diff --git a/tests/auto/widgets/qwebengineview/tst_qwebengineview.cpp b/tests/auto/widgets/qwebengineview/tst_qwebengineview.cpp
index 75795c170..78190622c 100644
--- a/tests/auto/widgets/qwebengineview/tst_qwebengineview.cpp
+++ b/tests/auto/widgets/qwebengineview/tst_qwebengineview.cpp
@@ -1012,8 +1012,14 @@ void tst_QWebEngineView::inputMethodsTextFormat()
     QTextCharFormat format;
     format.setUnderlineStyle(static_cast<QTextCharFormat::UnderlineStyle>(underlineStyle));
     format.setUnderlineColor(underlineColor);
+
+    // Setting background color is disabled for Qt WebEngine because some IME manager
+    // sets background color to black and there is no API for setting the foreground color.
+    // This may result black text on black background. However, we still test it to ensure
+    // changing background color doesn't cause any crash.
     if (backgroundColor.isValid())
         format.setBackground(QBrush(backgroundColor));
+
     attrs.append(QInputMethodEvent::Attribute(QInputMethodEvent::TextFormat, start, length, format));
 
     QInputMethodEvent im(string, attrs);