Cursive::ncurses & cie now return io::Result<Self>

CHANGELOG.md

@@ -8,6 +8,9 @@
   `find_id()` was added instead.
 - Breaking change: replaced `set_fps(i32)` with `set_autorefresh(bool)`
 - Breaking change: updated the Backend trait for a simpler input system
+- Breaking change: `Cursive::{ncurses, pancurses, termion}` now return
+  `io::Result<Self>` instead of panicking. `Cursive::default()` still unwraps.
+  - Also added `Cursive::try_new` for failible backends.
 - Updated to Rust 2018 (now requires rustc > 1.31)
 - Add a logging implementation (`logger::init()`) and a `DebugConsole`
   (`cursive::toggle_debug_console()`)

src/backend/blt.rs

@@ -32,6 +32,7 @@ pub struct Backend {
 impl Backend {
     /// Creates a new BearLibTerminal-based backend.
     pub fn init() -> Box<dyn backend::Backend> {
+        // TODO: Add some error handling?
         terminal::open("Cursive", 80, 24);
         terminal::set(terminal::config::Window::empty().resizeable(true));
         terminal::set(vec![

src/backend/curses/n.rs

@@ -58,13 +58,16 @@ fn write_to_tty(bytes: &[u8]) -> io::Result<()> {
 
 impl Backend {
     /// Creates a new ncurses-based backend.
-    pub fn init() -> Box<dyn backend::Backend> {
+    pub fn init() -> io::Result<Box<dyn backend::Backend>> {
         // Check the $TERM variable.
         if std::env::var("TERM")
             .map(|var| var.is_empty())
             .unwrap_or(true)
         {
-            panic!("$TERM is unset. Cannot initialize ncurses interface.");
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                "$TERM is unset. Cannot initialize ncurses interface.",
+            ));
         }
 
         // Change the locale.
@@ -111,7 +114,7 @@ impl Backend {
         // This asks the terminal to provide us with mouse drag events
         // (Mouse move when a button is pressed).
         // Replacing 1002 with 1003 would give us ANY mouse move.
-        write_to_tty(b"\x1B[?1002h").unwrap();
+        write_to_tty(b"\x1B[?1002h")?;
 
         let c = Backend {
             current_style: Cell::new(ColorPair::from_256colors(0, 0)),
@@ -121,7 +124,7 @@ impl Backend {
             input_buffer: None,
         };
 
-        Box::new(c)
+        Ok(Box::new(c))
     }
 
     /// Save a new color pair.

src/backend/curses/pan.rs

@@ -34,10 +34,12 @@ fn find_closest_pair(pair: ColorPair) -> (i16, i16) {
 
 impl Backend {
     /// Creates a new pancurses-based backend.
-    pub fn init() -> Box<dyn backend::Backend> {
+    pub fn init() -> std::io::Result<Box<dyn backend::Backend>> {
         ::std::env::set_var("ESCDELAY", "25");
 
+        // TODO: use pancurses::newterm()
         let window = pancurses::initscr();
+
         window.keypad(true);
         window.timeout(0);
         pancurses::noecho();
@@ -55,7 +57,7 @@ impl Backend {
         // (Mouse move when a button is pressed).
         // Replacing 1002 with 1003 would give us ANY mouse move.
         print!("\x1B[?1002h");
-        stdout().flush().expect("could not flush stdout");
+        stdout().flush()?;
 
         let c = Backend {
             current_style: Cell::new(ColorPair::from_256colors(0, 0)),
@@ -66,7 +68,7 @@ impl Backend {
             window,
         };
 
-        Box::new(c)
+        Ok(Box::new(c))
     }
 
     /// Save a new color pair.

src/backend/termion.rs

@@ -43,20 +43,16 @@ pub struct Backend {
 
 impl Backend {
     /// Creates a new termion-based backend.
-    pub fn init() -> Box<dyn backend::Backend> {
+    pub fn init() -> std::io::Result<Box<dyn backend::Backend>> {
         // Use a ~8MB buffer
         // Should be enough for a single screen most of the time.
         let terminal =
             RefCell::new(AlternateScreen::from(MouseTerminal::from(
-                BufWriter::with_capacity(
-                    8_000_000,
-                    File::create("/dev/tty").unwrap(),
-                )
-                .into_raw_mode()
-                .unwrap(),
+                BufWriter::with_capacity(8_000_000, File::create("/dev/tty")?)
+                    .into_raw_mode()?,
             )));
 
-        write!(terminal.borrow_mut(), "{}", termion::cursor::Hide).unwrap();
+        write!(terminal.borrow_mut(), "{}", termion::cursor::Hide)?;
 
         let (input_sender, input_receiver) = crossbeam_channel::unbounded();
         let (resize_sender, resize_receiver) = crossbeam_channel::bounded(0);
@@ -96,7 +92,7 @@ impl Backend {
             resize_receiver,
         };
 
-        Box::new(c)
+        Ok(Box::new(c))
     }
 
     fn apply_colors(&self, colors: theme::ColorPair) {

src/cursive.rs

@@ -75,14 +75,14 @@ impl<F: FnOnce(&mut Cursive) -> () + Send> CbFunc for F {
 #[cfg(feature = "termion-backend")]
 impl Default for Cursive {
     fn default() -> Self {
-        Self::termion()
+        Self::termion().unwrap()
     }
 }
 
 #[cfg(all(not(feature = "termion-backend"), feature = "pancurses-backend"))]
 impl Default for Cursive {
     fn default() -> Self {
-        Self::pancurses()
+        Self::pancurses().unwrap()
     }
 }
 
@@ -105,11 +105,23 @@ impl Default for Cursive {
 ))]
 impl Default for Cursive {
     fn default() -> Self {
-        Self::ncurses()
+        Self::ncurses().unwrap()
     }
 }
 
 impl Cursive {
+    /// Shortcut for `Cursive::try_new` with non-failible init function.
+    ///
+    /// You probably don't want to use this function directly. Instead,
+    /// `Cursive::default()` or `Cursive::ncurses()` may be what you're
+    /// looking for.
+    pub fn new<F>(backend_init: F) -> Self
+    where
+        F: FnOnce() -> Box<dyn backend::Backend>,
+    {
+        Self::try_new::<_, ()>(|| Ok(backend_init())).unwrap()
+    }
+
     /// Creates a new Cursive root, and initialize the back-end.
     ///
     /// * If you just want a cursive instance, use `Cursive::default()`.
@@ -128,17 +140,15 @@ impl Cursive {
     /// # use cursive::{Cursive, backend};
     /// let siv = Cursive::new(backend::dummy::Backend::init); // equivalent to Cursive::dummy()
     /// ```
-    pub fn new<F>(backend_init: F) -> Self
+    pub fn try_new<F, E>(backend_init: F) -> Result<Self, E>
     where
-        F: FnOnce() -> Box<dyn backend::Backend>,
+        F: FnOnce() -> Result<Box<dyn backend::Backend>, E>,
     {
         let theme = theme::load_default();
 
         let (cb_sink, cb_source) = crossbeam_channel::unbounded();
 
-        let backend = backend_init();
-
-        Cursive {
+        backend_init().map(|backend| Cursive {
             autorefresh: false,
             theme,
             screens: vec![views::StackView::new()],
@@ -151,25 +161,25 @@ impl Cursive {
             cb_sink,
             backend,
             user_data: Box::new(()),
-        }
+        })
     }
 
     /// Creates a new Cursive root using a ncurses backend.
     #[cfg(feature = "ncurses-backend")]
-    pub fn ncurses() -> Self {
-        Self::new(backend::curses::n::Backend::init)
+    pub fn ncurses() -> std::io::Result<Self> {
+        Self::try_new(backend::curses::n::Backend::init)
     }
 
     /// Creates a new Cursive root using a pancurses backend.
     #[cfg(feature = "pancurses-backend")]
-    pub fn pancurses() -> Self {
-        Self::new(backend::curses::pan::Backend::init)
+    pub fn pancurses() -> std::io::Result<Self> {
+        Self::try_new(backend::curses::pan::Backend::init)
     }
 
     /// Creates a new Cursive root using a termion backend.
     #[cfg(feature = "termion-backend")]
-    pub fn termion() -> Self {
-        Self::new(backend::termion::Backend::init)
+    pub fn termion() -> std::io::Result<Self> {
+        Self::try_new(backend::termion::Backend::init)
     }
 
     /// Creates a new Cursive root using a bear-lib-terminal backend.