Replace Option<Action> with ActionOption

This allows us to mark ActionOption as
`#[must_use]`, which helps prevent ignoring
actions accidentally (e.g. by forgetting to handle
a return value).  See
rust-lang/rust#71368 for
more context.

tui/src/state_store/action.rs

@@ -1,5 +1,19 @@
-#[derive(Debug, Clone)]
+/// The set of actions that can be performed in the application's state store.
+///
+/// This enum represents the different types of actions that can be dispatched to the
+/// state store, which will then update the application's state accordingly.
+#[must_use]
+#[derive(Debug, Clone, PartialEq)]
 pub enum Action {
+    /// No action.
+    /// 
+    /// This is used when no action is needed. While we could model this as an
+    /// `Option<Action>`, this would preclude marking the type as #[must_use],
+    /// and thus invite code that accidentally ignores actions returned from functions.
+    /// 
+    /// See https://github.com/rust-lang/rust/issues/71368 for a more detailed
+    /// discussion of this issue.
+    None,
     ConnectToServerRequest { addr: String },
     SendMessage { content: String },
     SelectRoom { room: String },

tui/src/ui_management/components/component.rs

@@ -9,8 +9,7 @@ pub trait Component {
     // Returns a name used to describe the component in the UI.
     fn name(&self) -> &str;
 
-    #[must_use]
-    fn handle_key_event(&mut self, key: KeyEvent) -> Option<Action>;
+    fn handle_key_event(&mut self, key: KeyEvent) -> Action;
 }
 
 pub trait ComponentRender<Props> {

tui/src/ui_management/components/input_box.rs

@@ -95,7 +95,7 @@ impl Component for InputBox {
         "Input Box"
     }
 
-    fn handle_key_event(&mut self, key: KeyEvent) -> Option<Action> {
+    fn handle_key_event(&mut self, key: KeyEvent) -> Action {
         if key.kind == KeyEventKind::Press {
             match key.code {
                 KeyCode::Char(to_insert) => {
@@ -113,7 +113,7 @@ impl Component for InputBox {
                 _ => {}
             }
         }
-        None
+        Action::None
     }
 }
 

tui/src/ui_management/pages/chat_page/chat_page.rs

@@ -171,9 +171,9 @@ impl Component for ChatPage {
         "Chat Page"
     }
 
-    fn handle_key_event(&mut self, key: KeyEvent) -> Option<Action> {
+    fn handle_key_event(&mut self, key: KeyEvent) -> Action {
         if key.kind != KeyEventKind::Press {
-            return None;
+            return Action::None;
         }
 
         let active_section = self.active_section.clone();
@@ -186,25 +186,23 @@ impl Component for ChatPage {
                     self.active_section = Some(last_hovered_section.clone());
                     self.get_section_activation_for_section(&last_hovered_section)
                         .activate();
-                    None
+                    Action::None
                 }
                 KeyCode::Left => {
                     self.hover_previous();
-                    None
+                    Action::None
                 }
                 KeyCode::Right => {
                     self.hover_next();
-                    None
+                    Action::None
                 }
-                KeyCode::Char('q') => Some(Action::Exit),
-                KeyCode::Char('c') if key.modifiers.contains(KeyModifiers::CONTROL) => {
-                    Some(Action::Exit)
-                }
-                _ => None,
+                KeyCode::Char('q') => Action::Exit,
+                KeyCode::Char('c') if key.modifiers.contains(KeyModifiers::CONTROL) => Action::Exit,
+                _ => Action::None,
             },
             Some(section) => {
-                // FIXME: return the result of this function call!!!!
-                let action = self.get_component_for_section_mut(&section)
+                let action = self
+                    .get_component_for_section_mut(&section)
                     .handle_key_event(key);
 
                 // disable the section according to the action taken

tui/src/ui_management/pages/chat_page/components/message_input_box.rs

@@ -43,13 +43,12 @@ impl MessageInputBox {
         }
     }
 
-    #[must_use]
-    fn submit_message(&mut self) -> Option<Action> {
-        let mut ret = None;
+    fn submit_message(&mut self) -> Action {
+        let mut ret = Action::None;
         if !self.input_box.is_empty() {
-            ret = Some(Action::SendMessage {
+            ret = Action::SendMessage {
                 content: String::from(self.input_box.text()),
-            });
+            };
             self.input_box.reset();
         }
         ret
@@ -65,16 +64,16 @@ impl Component for MessageInputBox {
         "Message Input"
     }
 
-    fn handle_key_event(&mut self, key: KeyEvent) -> Option<Action> {
+    fn handle_key_event(&mut self, key: KeyEvent) -> Action {
         if key.kind == KeyEventKind::Press && self.props.active_room.is_some() {
             let action = self.input_box.handle_key_event(key);
-            assert!(action.is_none());
+            assert_eq!(action, Action::None);
 
             if key.code == KeyCode::Enter {
                 return self.submit_message();
             }
         }
-        None
+        Action::None
     }
 }
 

tui/src/ui_management/pages/chat_page/components/room_list.rs

@@ -124,30 +124,30 @@ impl Component for RoomList {
         "Room List"
     }
 
-    fn handle_key_event(&mut self, key: KeyEvent) -> Option<Action>{
+    fn handle_key_event(&mut self, key: KeyEvent) -> Action {
         if key.kind != KeyEventKind::Press {
-            None
+            Action::None
         } else {
             match key.code {
                 KeyCode::Up => {
                     self.previous();
-                    None
+                    Action::None
                 }
                 KeyCode::Down => {
                     self.next();
-                    None
+                    Action::None
                 }
                 KeyCode::Enter if self.list_state.selected().is_some() => {
                     let selected_idx = self.list_state.selected().unwrap();
 
                     let rooms = self.rooms();
                     let room_state = rooms.get(selected_idx).unwrap();
 
-                    Some(Action::SelectRoom {
+                    Action::SelectRoom {
                         room: room_state.name.clone(),
-                    })
+                    }
                 }
-                _ => None,
+                _ => Action::None,
             }
         }
     }

tui/src/ui_management/pages/connect_page/connect_page.rs

@@ -1,11 +1,13 @@
 use crossterm::event::{KeyCode, KeyEvent, KeyEventKind, KeyModifiers};
 use ratatui::{prelude::*, widgets::*, Frame};
 
-use crate::state_store::ServerConnectionStatus;
-use crate::state_store::{action::Action, State};
-
-use crate::ui_management::components::input_box;
-use crate::ui_management::components::{input_box::InputBox, Component, ComponentRender};
+use crate::{
+    state_store::{action::Action, ServerConnectionStatus, State},
+    ui_management::components::{
+        input_box::{self, InputBox},
+        Component, ComponentRender,
+    },
+};
 
 struct Props {
     error_message: Option<String>,
@@ -47,14 +49,14 @@ impl ConnectPage {
         }
     }
 
-    fn connect_to_server(&mut self) -> Option<Action> {
+    fn connect_to_server(&mut self) -> Action {
         if self.input_box.is_empty() {
-            return None;
+            return Action::None;
         }
 
-        Some(Action::ConnectToServerRequest {
+        Action::ConnectToServerRequest {
             addr: self.input_box.text().to_string(),
-        })
+        }
     }
 }
 
@@ -69,21 +71,19 @@ impl Component for ConnectPage {
         "Connect Page"
     }
 
-    fn handle_key_event(&mut self, key: KeyEvent) -> Option<Action> {
+    fn handle_key_event(&mut self, key: KeyEvent) -> Action {
         let action = self.input_box.handle_key_event(key);
-        assert!(action.is_none());
+        assert_eq!(action, Action::None);
 
         if key.kind != KeyEventKind::Press {
-            return None;
+            return Action::None;
         }
 
         match key.code {
             KeyCode::Enter => self.connect_to_server(),
-            KeyCode::Char('q') => Some(Action::Exit),
-            KeyCode::Char('c') if key.modifiers.contains(KeyModifiers::CONTROL) => {
-                Some(Action::Exit)
-            }
-            _ => None
+            KeyCode::Char('q') => Action::Exit,
+            KeyCode::Char('c') if key.modifiers.contains(KeyModifiers::CONTROL) => Action::Exit,
+            _ => Action::None,
         }
     }
 }

tui/src/ui_management/pages/mod.rs

@@ -76,7 +76,7 @@ impl Component for AppRouter {
         self.get_active_page_component().name()
     }
 
-    fn handle_key_event(&mut self, key: KeyEvent) -> Option<Action> {
+    fn handle_key_event(&mut self, key: KeyEvent) -> Action {
         self.get_active_page_component_mut().handle_key_event(key)
     }
 }

tui/src/ui_management/ui_manager.rs

@@ -60,7 +60,8 @@ impl UiManager {
                 // Catch and handle crossterm events
                maybe_event = crossterm_events.next() => match maybe_event {
                     Some(Ok(Event::Key(key)))  => {
-                        if let Some(action) = app_router.handle_key_event(key) {
+                        let action = app_router.handle_key_event(key);
+                        if action != Action::None {
                             self.action_tx.send(action)?;
                         }
                     },