Geany plugin to toggle long line marker between off and line mode using keybinding or menu item.

Makefile

#!/usr/bin/env make

llt_cflags = $(CFLAGS) -g -Wall -Werror $(shell pkg-config --cflags geany)
llt_ldflags = $(LDFLAGS) $(shell pkg-config --libs geany)

all: llt.so

llt.so: plugin.o
	$(CC) -shared $(llt_cflags) -o $@ $^ $(llt_ldflags)

plugin.o: plugin.c
	$(CC) -c -fPIC $(llt_cflags) -o $@ $<

install:
	cp llt.so ~/.config/geany/plugins/

clean:
	$(RM) *.o *.so

plugin.c

#include <geanyplugin.h>

GeanyPlugin    *geany_plugin;
GeanyFunctions *geany_functions;
GeanyData      *geany_data;

PLUGIN_VERSION_CHECK(211)

PLUGIN_SET_INFO(_("LongLineToggler"),
	_("Adds a keybinding and menu item to toggle long-line marker"), "0.01",
	"Matthew Brush <matt@geany.org>")

static const char *menu_view_name = "menu_view1_menu";
static const char *menu_previous_sibling = "menu_show_indentation_guides1";
static GtkWidget *long_line_toggler_widget = NULL;

static gboolean edge_active_toggle_kb(guint key_id)
{
	gtk_check_menu_item_set_active(GTK_CHECK_MENU_ITEM(long_line_toggler_widget),
		!gtk_check_menu_item_get_active(GTK_CHECK_MENU_ITEM(long_line_toggler_widget)));
	return FALSE; // let others handle it too
}

static void edge_mode_menu_toggled(GtkCheckMenuItem *menuitem, gpointer user_data)
{
	GeanyDocument *doc = document_get_current();
	if (!DOC_VALID(doc)) return;
	ScintillaObject *sci = doc->editor->sci;
	gint mode = scintilla_send_message(sci, SCI_GETEDGEMODE, 0, 0);
	guint i;
	foreach_document(i) {
		doc = document_index(i);
		// Note: only disabled or line edge mode supported, not background mode
		scintilla_send_message(doc->editor->sci, SCI_SETEDGEMODE,
			(mode == EDGE_NONE) ? EDGE_LINE : EDGE_NONE, 0);
	}
}

static inline gint where_to_put_item(GtkContainer *container)
{
	gint index = 0;
	GtkWidget *after_wid = ui_lookup_widget(geany_data->main_widgets->window,
		menu_previous_sibling);
	GList *iter, *children = gtk_container_get_children(GTK_CONTAINER(container));
	for (iter = children; iter != NULL; iter = g_list_next(iter)) {
		if (GTK_WIDGET(iter->data) == after_wid) {
			g_list_free(children);
			return index;
		}
		index++;
	}
	g_list_free(children);
	return -1;
}

static gboolean is_line_currently_shown()
{
	GeanyDocument *doc = document_get_current();
	if (!DOC_VALID(doc)) return FALSE;
	ScintillaObject *sci = doc->editor->sci;
	return (scintilla_send_message(sci, SCI_GETEDGEMODE, 0, 0) != EDGE_NONE);
}

// handle case of no documents open when the keybinding is toggled, to
// synchronize the new/opened document setting with the menu item's
static void when_a_document_is_opened(GObject *unused, GeanyDocument *doc,
	gpointer user_data)
{
	scintilla_send_message(doc->editor->sci, SCI_SETEDGEMODE,
		gtk_check_menu_item_get_active(GTK_CHECK_MENU_ITEM(long_line_toggler_widget)) ?
			EDGE_LINE : EDGE_NONE, 0);
}

static void add_menu_item_on_startup(GObject *unused, gpointer user_data)
{
	GtkWidget *menu = ui_lookup_widget(geany_data->main_widgets->window, menu_view_name);
	long_line_toggler_widget = gtk_check_menu_item_new_with_label(_("Show Long Line Marker"));
	gtk_menu_shell_append(GTK_MENU_SHELL(menu), long_line_toggler_widget);
	gint item_pos = where_to_put_item(GTK_CONTAINER(menu));
	if (item_pos > -1)
		gtk_menu_reorder_child(GTK_MENU(menu), long_line_toggler_widget, item_pos + 1);
	gtk_check_menu_item_set_active(GTK_CHECK_MENU_ITEM(long_line_toggler_widget),
		is_line_currently_shown());
	g_signal_connect(long_line_toggler_widget, "toggled",
		G_CALLBACK(edge_mode_menu_toggled), NULL);
	plugin_signal_connect(geany_plugin, NULL, "document-open", TRUE,
		G_CALLBACK(when_a_document_is_opened), NULL);
	plugin_signal_connect(geany_plugin, NULL, "document-new", TRUE,
		G_CALLBACK(when_a_document_is_opened), NULL);
	gtk_widget_show(long_line_toggler_widget);
}

void plugin_init(void)
{
	plugin_signal_connect(geany_plugin, NULL, "geany-startup-complete",
		TRUE, G_CALLBACK(add_menu_item_on_startup), NULL);
	keybindings_set_item(
		plugin_set_key_group(geany_plugin, "LongLineToggler", 1, NULL),
		0, (GeanyKeyCallback) edge_active_toggle_kb, 0, 0, "long-line-toggler",
		"Toggle long line marker", NULL);
}

void plugin_cleanup(void)
{
	if (GTK_IS_WIDGET(long_line_toggler_widget))
		gtk_widget_destroy(long_line_toggler_widget);
	long_line_toggler_widget = NULL;
}