feat: add "edit desktop entry" to the desktop file context menu

Opening a .desktop file launches the application it describes, so the
file manager offered no way to look at or change the file itself: the
only way out was a terminal. Reported upstream on 2025-05-11 and still
open.

Add an "Edit desktop entry" action to the context menu, next to the
entry own desktop actions. It opens the file with the default
text/plain handler instead of its application/x-desktop one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

i18n/en/cosmic_files.ftl

@@ -342,6 +342,7 @@ extract-here = Extract
 new-file = New file...
 new-folder = New folder...
 open-in-terminal = Open in terminal
+edit-desktop-entry = Edit desktop entry
 move-to = Move to...
 move-to-trash = Move to trash
 restore-from-trash = Restore from trash

i18n/fr/cosmic_files.ftl

@@ -349,6 +349,7 @@ extract-here = Extraire
 new-file = Nouveau fichier...
 new-folder = Nouveau dossier...
 open-in-terminal = Ouvrir dans le terminal
+edit-desktop-entry = Modifier le fichier .desktop
 move-to-trash = Déplacer vers la corbeille
 restore-from-trash = Restaurer depuis la corbeille
 remove-from-sidebar = Supprimer de la barre latérale

src/app.rs

@@ -247,6 +247,7 @@ pub enum Action {
     CosmicSettingsWallpaper,
     DesktopViewOptions,
     Delete,
+    EditDesktopEntry,
     EditHistory,
     EditLocation,
     Eject,
@@ -320,6 +321,7 @@ impl Action {
             Self::CosmicSettingsWallpaper => Message::CosmicSettings("wallpaper"),
             Self::Delete => Message::Delete(entity_opt),
             Self::DesktopViewOptions => Message::DesktopViewOptions,
+            Self::EditDesktopEntry => Message::EditDesktopEntry(entity_opt),
             Self::EditHistory => Message::ToggleContextPage(ContextPage::EditHistory),
             Self::EditLocation => Message::TabMessage(entity_opt, tab::Message::EditLocationEnable),
             Self::Eject => Message::Eject,
@@ -455,6 +457,7 @@ pub enum Message {
     DesktopDialogs(bool),
     DialogCancel,
     DialogComplete,
+    EditDesktopEntry(Option<Entity>),
     Eject,
     FileDialogMessage(DialogMessage),
     DialogPush(DialogPage, Option<widget::Id>),
@@ -1060,6 +1063,21 @@ impl App {
         }
     }
 
+    /// Open paths with the default text editor, ignoring their own MIME type.
+    ///
+    /// Desktop entries launch the application they describe when opened, so
+    /// `open_file` never shows the file itself. This gives the file manager a
+    /// way to edit one without falling back to a terminal.
+    fn edit_file(&self, paths: &[PathBuf]) -> Task<Message> {
+        let Ok(text_plain) = "text/plain".parse::<Mime>() else {
+            return Task::none();
+        };
+        if !self.launch_from_mime_cache(&text_plain, paths) {
+            log::warn!("no application registered for text/plain, cannot edit {paths:?}");
+        }
+        Task::none()
+    }
+
     fn launch_from_mime_cache<P>(&self, mime: &Mime, paths: &[P]) -> bool
     where
         P: std::fmt::Debug + AsRef<Path> + AsRef<std::ffi::OsStr>,
@@ -4114,6 +4132,21 @@ impl Application for App {
                 }
                 None => {}
             },
+            Message::EditDesktopEntry(entity_opt) => {
+                let entity = entity_opt.unwrap_or_else(|| self.tab_model.active());
+                if let Some(tab) = self.tab_model.data::<Tab>(entity)
+                    && let Some(items) = tab.items_opt()
+                {
+                    let paths: Vec<PathBuf> = items
+                        .iter()
+                        .filter(|item| item.selected)
+                        .filter_map(|item| item.path_opt().cloned())
+                        .collect();
+                    if !paths.is_empty() {
+                        return self.edit_file(&paths);
+                    }
+                }
+            }
             Message::OpenWithDialog(entity_opt) => {
                 let entity = entity_opt.unwrap_or_else(|| self.tab_model.active());
                 if let Some(tab) = self.tab_model.data::<Tab>(entity)

src/menu.rs

@@ -214,6 +214,8 @@ pub fn context_menu<'a>(
                         |(i, action)| menu_item(action.name, Action::ExecEntryAction(i)).into(),
                     ));
                 }
+                children
+                    .push(menu_item(fl!("edit-desktop-entry"), Action::EditDesktopEntry).into());
                 children.push(divider::horizontal::light().into());
                 children.push(menu_item(fl!("rename"), Action::Rename).into());
                 children.push(menu_item(fl!("cut"), Action::Cut).into());