Filtering out Caps Lock key events in an input method can prevent GUI applications from detecting changes in the Caps Lock state. For example, in the following example, the Caps Lock warning in a GTK3 Entry widget no longer functions as expected.

/*
 * gcc -o gtk3-entry gtk3-entry.c `pkg-config --cflags --libs gtk+-3.0`
 */

#include <gtk/gtk.h>

int
main (int argc, char *argv[])
{
    GtkWidget *window;
    GtkWidget *entry;

    gtk_init (&argc, &argv);

    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    entry = gtk_entry_new ();
    gtk_entry_set_visibility (GTK_ENTRY (entry), FALSE);
    gtk_container_add (GTK_CONTAINER (window), entry);
    gtk_widget_show_all (window);

    gtk_main ();

    return 0;
}

Works well (Caps lock warning is shown) without ibus-rime:

Doesn't work properly (Caps lock warning is not shown) with ibus-rime:

RFR @lotem Thanks

Maybe we should always return kRejected for Caps Lock to pass through the IME.
The same applies to other modifier keys for mode switching, like Shift.

I cannot remember the specific reason why these events are reported as such, maybe because they conceptually are "processed by the IME" as hotkeys.

@fxliang @LEOYoon-Tsaw

This change can affect other platforms in unexpected ways. Please help verify.

The code comments in ascii_composer specifically mentioned Windows; and macOS defined system level features of the Caps Lock key. Personally I almost never use Caps Lock so I'm not experienced.

I don't know how good old caps lock works, and how to test this.

I don't know how good old caps lock works, and how to test this.

IIRC, the good_old_caps_lock behavior is:

good_old_caps_lock: true

• Caps Lock works as usual, it toggles uppercase letters.
• Rime does not intercept it for switching input modes.

good_old_caps_lock: false

• Caps Lock is repurposed by Rime to toggle input method states (switch between English/Chinese).
• It no longer changes letter case.

Maybe we should always return kRejected for Caps Lock to pass through the IME.

When good_old_caps_lock is set to false, pressing Caps Lock no longer toggles letter case. If the Caps Lock event is passed through to the application. For above GTK entry case, it may show the "Caps Lock is on" indicator, but still fails to produce uppercase letters when typing. That doesn't seem quite right either.

I don't know how good old caps lock works, and how to test this.

IIRC, the good_old_caps_lock behavior is:

good_old_caps_lock: true

• Caps Lock works as usual, it toggles uppercase letters.
• Rime does not intercept it for switching input modes.

good_old_caps_lock: false

• Caps Lock is repurposed by Rime to toggle input method states (switch between English/Chinese).
• It no longer changes letter case.

with ci output

good_old_caps_lock: true
capslock switch ascii_mode and capslock state( in rime and capslock led )

good_old_caps_lock: false
capslock switch ascii_mode but not capslock state( when capslock led on/off normally ). caps state work normally with other ime

保守修改，應該能行，發現問題再說吧。