[fractal/version] gtk: Implement version command line

[Daniel Garcia Moreno <danigm src gnome org>]

commit e37bb4a354a3563f2586ac1ab42b7c0b1d35bfa4
Author: Daniel García Moreno <dani danigm net>
Date:   Fri Jun 12 09:54:02 2020 +0200

    gtk: Implement version command line
    
    Fix https://gitlab.gnome.org/GNOME/fractal/-/issues/639

 fractal-gtk/src/main.rs | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)
---
diff --git a/fractal-gtk/src/main.rs b/fractal-gtk/src/main.rs
index fe7dea09..a8b9a2b7 100644
--- a/fractal-gtk/src/main.rs
+++ b/fractal-gtk/src/main.rs
@@ -58,7 +58,10 @@ fn main() -> Result<(), Box<dyn Error>> {
     gst::init()?;
 
     // Create a Application with default flags
-    let application = gtk::Application::new(Some(config::APP_ID), gio::ApplicationFlags::empty())?;
+    let application = gtk::Application::new(
+        Some(config::APP_ID),
+        gio::ApplicationFlags::HANDLES_COMMAND_LINE,
+    )?;
 
     application.set_resource_base_path(Some("/org/gnome/Fractal"));
 
@@ -66,6 +69,20 @@ fn main() -> Result<(), Box<dyn Error>> {
         App::on_startup(application);
     });
 
+    application.connect_command_line(|app, command| {
+        for arg in command.get_arguments() {
+            match arg.to_str() {
+                Some("-V") | Some("--version") => {
+                    println!("{}", config::VERSION);
+                    app.quit();
+                }
+                _ => {}
+            };
+        }
+
+        0
+    });
+
     application.run(&args().collect::<Vec<_>>());
 
     Ok(())