QsciScintilla crash on mouse click when Qt Virtual Keyboard (QT_IM_MODULE=qtvirtualkeyboard) is enabled (Windows, text present)

[JueryWang]

On Windows, QScintilla (QsciScintilla) crashes reproducibly when Qt Virtual Keyboard is enabled as the input method module. The crash happens when the editor contains any text (non-empty) and the user clicks inside the text area with the mouse (focus/caret positioning).

• Windows

• QScintilla (QsciScintilla)

• Qt Virtual Keyboard enabled via environment variables:

  • QT_IM_MODULE=qtvirtualkeyboard
  • When QT_VIRTUALKEYBOARD_DESKTOP_DISABLE=0 (or unset), the virtual keyboard tries to participate on desktop and the crash is reproducible.
  • When QT_VIRTUALKEYBOARD_DESKTOP_DISABLE=1 , the virtual keyboard does not participate and the crash does not occur.
    What we tried We attempted to prevent the virtual keyboard from appearing only for QsciScintilla by disabling input methods on the editor widget:

• setAttribute(Qt::WA_InputMethodEnabled, false)

• Consuming IME-related events in event() (e.g. QEvent::InputMethod , QEvent::InputMethodQuery , QEvent::RequestSoftwareInputPanel , etc.)

• Calling QGuiApplication::inputMethod()->hide() in focusInEvent() / mousePressEvent()
  However, the crash still occurs when clicking the editor text area.

Expected behavior When Qt Virtual Keyboard is enabled, QsciScintilla should not crash on mouse click / caret movement. If the widget does not support the virtual keyboard, it should safely ignore/refuse IME interaction instead of crashing.

Minimal reproduction steps

1. On Windows, set:
   • QT_IM_MODULE=qtvirtualkeyboard
   • QT_VIRTUALKEYBOARD_DESKTOP_DISABLE=0
2. Create a simple app with a single QsciScintilla widget.
3. Put any text into the editor (type or setText() to non-empty).
4. Click inside the editor text area with the mouse.
5. Application crashes.
   Additional note Standard Qt widgets like QLineEdit can work with the virtual keyboard in the same application; the issue only triggers on the QsciScintilla click/focus/caret path.

[brCreate]

First of some apologies for late reply,
second some disclaimers, that I'm not the developer for QScintilla but Riverbank Computing. If you find the following method helpful please also report to Riverbank Computing's own issue reporter (somewhere https://riverbankcomputing.com/support/lists)
Ah, and one more little disclaimer -- I haven't used Qt Virtual Keyboard but I'm just synthesising the solutions from the Internet, so there (might?) be some mistakes

So basically according to your problem description it looks like the error occurs whenever you demand QScintilla to handle multibyte text like the CJKV characters. When a user clicks inside the editor already with text, the virtual keyboard queries the focused widget for its surrounding context via Qt::InputMethodQuery::ImSurroundingText and Qt::InputMethodQuery::ImCursorPosition, etc. Due to existing bugs (not by me btw, blame the Riverbank guys) it handles internal coordinate mappings during a mouse-click focus change in a peculiar manner that Qt doesn't recognise (to be more pedantic: "returning an invalid internal memory pointer") causing Segmentation Fault

So you just need to prevent the keyboard from even accessing the whole thing:

// somewhere in the 'simple app'
QsciScintilla *editor

/*create the event filter here*/ class NameThisEventFilterYourself : public QObject
{
protected:
    bool eventFilter(QObject *obj, QEvent *event) override
    {
        if (event->type() == QEvent::Type::InputMethod || event->type() == QEvent::Type::InputMethodQuery)
        {
            event->accept();
            return true;  // surpass
        }

        return QObject::eventFilter(obj, event);
    }
} *filter = new ...(editor);

// and then add this
editor->installEventFilter(filter);

Hope it helps... (legit its even not tested)

[JueryWang]

Thank you for your kindly effort and reply! This helps me fix the bug.

…

On Tue, 16 Jun 2026 at 14:37, brCreate ***@***.***> wrote: *brCreate* left a comment (brCreate/QScintilla#3) <#3 (comment)> First of some apologies for late reply, second some disclaimers, that I'm not the developer for QScintilla but Riverbank Computing. If you find the following method helpful please also report to Riverbank Computing's own issue reporter (somewhere https://riverbankcomputing.com/support/lists) Ah, and one more little disclaimer -- I haven't used Qt Virtual Keyboard but I'm just synthesising the solutions from the Internet, so there (might?) be some mistakes So basically according to your problem description it looks like the error occurs whenever you demand QScintilla to handle multibyte text like the CJKV characters. When a user clicks inside the editor already with text, the virtual keyboard queries the focused widget for its surrounding context via Qt::InputMethodQuery::ImSurroundingText and Qt::InputMethodQuery::ImCursorPosition, etc. Due to existing bugs (not by me btw, blame the Riverbank guys) it handles internal coordinate mappings during a mouse-click focus change in a peculiar manner that Qt doesn't recognise (to be more pedantic: "returning an invalid internal memory pointer") causing Segmentation Fault So you just need to prevent the keyboard from even accessing the whole thing: // somewhere in the 'simple app' QsciScintilla *editor /*create the event filter here*/ class NameThisEventFilterYourself : public QObject {protected: bool eventFilter(QObject *obj, QEvent *event) override { if (event->type() == QEvent::Type::InputMethod || event->type() == QEvent::Type::InputMethodQuery) { event->accept(); return true; // surpass } return QObject::eventFilter(obj, event); } } *filter = new ...(editor); // and then add this editor->installEventFilter(filter); Hope it helps... (legit its even not tested) — Reply to this email directly, view it on GitHub <#3?email_source=notifications&email_token=AQMKCAPEQJ4E752I6LMATYT5ADTJPA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTINZRGU3DOOJYHAZKM4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2KYZTPN52GK4S7MNWGSY3L#issuecomment-4715679882>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AQMKCAJQULLG3JXGQQBHLF35ADTJPAVCNFSNUABFKJSXA33TNF2G64TZHM3DKNZVGI2DOMZQHNEXG43VMU5TINJQG42DKNRVHA32C5QC> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/AQMKCAPHV7SAO7GLCRCKBYL5ADTJPA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTINZRGU3DOOJYHAZKM4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2KUZTPN52GK4S7NFXXG> and Android <https://github.com/notifications/mobile/android/AQMKCALJMKPFDOSEILA26X35ADTJPA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTINZRGU3DOOJYHAZKM4TFMFZW63VGMF2XI2DPOKSWK5TFNZ2K4ZTPN52GK4S7MFXGI4TPNFSA>. Download it today! You are receiving this because you authored the thread.Message ID: ***@***.***>