GTK: Fix reporting deletion length in the accessible

We cannot compute the length in characters after the text has been
deleted, so we need to compute it in BEFOREDELETE.  However, we need to
emit the signal once the buffer has actually changed, so we need to
cache the value in-between those events.

scintilla/gtk/ScintillaGTKAccessible.cxx

@@ -156,6 +156,7 @@ ScintillaGTKAccessible *ScintillaGTKAccessible::FromAccessible(GtkAccessible *ac
 ScintillaGTKAccessible::ScintillaGTKAccessible(GtkAccessible *accessible_, GtkWidget *widget_) :
 		accessible(accessible_),
 		sci(ScintillaGTK::FromWidget(widget_)),
+		deletionLengthChar(0),
 		old_pos(-1) {
 	g_signal_connect(widget_, "sci-notify", G_CALLBACK(SciNotify), this);
 }
@@ -857,10 +858,15 @@ void ScintillaGTKAccessible::Notify(GtkWidget *, gint, SCNotification *nt) {
 				g_signal_emit_by_name(accessible, "text-changed::insert", startChar, lengthChar);
 				UpdateCursor();
 			}
+			if (nt->modificationType & SC_MOD_BEFOREDELETE) {
+				// We cannot compute the deletion length in DELETETEXT as it requires accessing the
+				// buffer, so that the character are still present.  So, we cache the value here,
+				// and use it in DELETETEXT that fires quickly after.
+				deletionLengthChar = sci->pdoc->CountCharacters(nt->position, nt->position + nt->length);
+			}
 			if (nt->modificationType & SC_MOD_DELETETEXT) {
 				int startChar = CharacterOffsetFromByteOffset(nt->position);
-				int lengthChar = sci->pdoc->CountCharacters(nt->position, nt->position + nt->length);
-				g_signal_emit_by_name(accessible, "text-changed::delete", startChar, lengthChar);
+				g_signal_emit_by_name(accessible, "text-changed::delete", startChar, deletionLengthChar);
 				UpdateCursor();
 			}
 			if (nt->modificationType & SC_MOD_CHANGESTYLE) {

scintilla/gtk/ScintillaGTKAccessible.h

@@ -20,6 +20,8 @@ private:
 	GtkAccessible *accessible;
 	ScintillaGTK *sci;
 
+	// cached length of the deletion, in characters (see Notify())
+	int deletionLengthChar;
 	// local state for comparing
 	Position old_pos;
 	std::vector<SelectionRange> old_sels;