login: prefill dialog after a failed login attempt

After a failed login the dialog was recreated empty, so a single
mistyped password meant retyping the server URL and username too, and
on a first-time login everything the user had just typed was lost.
Fill the form with the credentials of the last attempt so that a wrong
password only needs retyping. Nothing is written to the keyring on
failure: credentials are stored on success and cleared only on
explicit logout.

src/login_dialog.rs

@@ -1,4 +1,6 @@
 use gtk4::glib;
+use gtk4::prelude::*;
+use gtk4::subclass::prelude::*;
 
 glib::wrapper! {
     pub struct LoginDialog(ObjectSubclass<imp::LoginDialog>)
@@ -10,12 +12,19 @@ impl LoginDialog {
     pub fn new() -> Self {
         glib::Object::new()
     }
+
+    /// Pre-fill the form, e.g. after a failed login attempt so that the
+    /// server URL, username and password don't have to be retyped.
+    pub fn set_prefill(&self, server_url: &str, username: &str, password: &str) {
+        let imp = self.imp();
+        imp.server_url_row.set_text(server_url);
+        imp.username_row.set_text(username);
+        imp.password_row.set_text(password);
+    }
 }
 
 mod imp {
     use super::*;
-    use gtk4::prelude::*;
-    use gtk4::subclass::prelude::*;
     use gtk4::CompositeTemplate;
     use libadwaita::prelude::*;
     use libadwaita::subclass::prelude::*;

src/window.rs

@@ -557,12 +557,15 @@ pub mod imp {
             if let Some((server_url, username, password)) = credentials::load_credentials() {
                 self.do_login(server_url, username, password, false);
             } else {
-                self.show_login_dialog();
+                self.show_login_dialog(None);
             }
         }
 
-        fn show_login_dialog(&self) {
+        fn show_login_dialog(&self, prefill: Option<(String, String, String)>) {
             let dialog = LoginDialog::new();
+            if let Some((server_url, username, password)) = prefill {
+                dialog.set_prefill(&server_url, &username, &password);
+            }
             let win = self.obj();
             let win_weak = win.downgrade();
             dialog.connect_local("logged-in", false, move |args| {
@@ -580,6 +583,7 @@ pub mod imp {
         fn do_login(&self, server_url: String, username: String, password: String, store: bool) {
             let is_auto = !store;
             let win_weak = self.obj().downgrade();
+            let prefill = (server_url.clone(), username.clone(), password.clone());
             crate::runtime::spawn(
                 async move { Api::login(&server_url, &username, &password).await
                     .map(|api| (api, server_url, username, password)) },
@@ -615,7 +619,7 @@ pub mod imp {
                                 let toast = libadwaita::Toast::new("Offline — showing cached articles");
                                 win.imp().toast_overlay.add_toast(toast);
                             } else {
-                                win.imp().show_login_dialog();
+                                win.imp().show_login_dialog(Some(prefill));
                                 win.imp().show_error_dialog("Login Failed", &e);
                             }
                         }
@@ -652,7 +656,7 @@ pub mod imp {
                         }
                         win.imp().sidebar_content.set_visible_child_name("placeholder");
                         win.imp().article_menu_button.set_visible(false);
-                        win.imp().show_login_dialog();
+                        win.imp().show_login_dialog(None);
                     }
                 }
             });