feat(no_std)!: make ratatui compatible with #![no_std] (#1794)

Resolves #1781

This PR makes it possible to compile ratatui with `#![no_std]`.
Also makes me answer "We Are So Embedded" to "Are We Embedded Yet?"

BREAKING-CHANGES.md

@@ -22,6 +22,7 @@ This is a quick summary of the sections below:
   - `TestBackend` now uses `core::convert::Infallible` for error handling instead of `std::io::Error`
   - Disabling `default-features` will now disable layout cache, which can have a negative impact on performance
   - `Layout::init_cache` and `Layout::DEFAULT_CACHE_SIZE` are now only available if `layout-cache` feature is enabled
+  - Disabling `default-features` suppresses the error message if `show_cursor()` fails when dropping `Terminal`
 - [v0.29.0](#v0290)
   - `Sparkline::data` takes `IntoIterator<Item = SparklineBar>` instead of `&[u64]` and is no longer const
   - Removed public fields from `Rect` iterators
@@ -86,6 +87,13 @@ This is a quick summary of the sections below:
 
 ## Unreleased (0.30.0)
 
+### Disabling `default-features` suppresses the error message if `show_cursor()` fails when dropping `Terminal` ([#1794])
+
+[#1794]: https://github.com/ratatui/ratatui/pull/1794
+
+Since disabling `default-features` disables `std`, printing to stderr is not possible. It is
+recommended to re-enable `std` when not using Ratatui in `no_std` environment.
+
 ### `Layout::init_cache` and `Layout::DEFAULT_CACHE_SIZE` are now only available if `layout-cache` feature is enabled ([#1795])
 
 [#1795]: https://github.com/ratatui/ratatui/pull/1795

ratatui-core/src/layout/layout.rs

@@ -1,9 +1,7 @@
-use alloc::format;
 use alloc::rc::Rc;
 use alloc::vec::Vec;
 use core::iter;
 use core::num::NonZeroUsize;
-use std::dbg;
 
 use hashbrown::HashMap;
 use itertools::Itertools;
@@ -1020,8 +1018,9 @@ fn changes_to_rects(
 /// please leave this here as it's useful for debugging unit tests when we make any changes to
 /// layout code - we should replace this with tracing in the future.
 #[expect(dead_code)]
+#[cfg(feature = "std")]
 fn debug_elements(elements: &[Element], changes: &HashMap<Variable, f64>) {
-    let variables = format!(
+    let variables = alloc::format!(
         "{:?}",
         elements
             .iter()
@@ -1031,7 +1030,7 @@ fn debug_elements(elements: &[Element], changes: &HashMap<Variable, f64>) {
             ))
             .collect::<Vec<(f64, f64)>>()
     );
-    dbg!(variables);
+    std::dbg!(variables);
 }
 
 /// A container used by the solver inside split

ratatui-core/src/lib.rs

@@ -43,9 +43,9 @@
 #![warn(clippy::std_instead_of_alloc)]
 #![warn(clippy::alloc_instead_of_core)]
 
-extern crate std;
-
 extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std;
 
 pub mod backend;
 pub mod buffer;

ratatui-core/src/terminal/terminal.rs

@@ -1,5 +1,3 @@
-use std::eprintln;
-
 use crate::backend::{Backend, ClearType};
 use crate::buffer::{Buffer, Cell};
 use crate::layout::{Position, Rect, Size};
@@ -91,8 +89,10 @@ where
     fn drop(&mut self) {
         // Attempt to restore the cursor state
         if self.hidden_cursor {
+            #[allow(unused_variables)]
             if let Err(err) = self.show_cursor() {
-                eprintln!("Failed to show the cursor: {err}");
+                #[cfg(feature = "std")]
+                std::eprintln!("Failed to show the cursor: {err}");
             }
         }
     }

ratatui-widgets/src/lib.rs

@@ -1,3 +1,4 @@
+#![no_std]
 // show the feature flags in the generated documentation
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
@@ -80,7 +81,6 @@
 //!
 //! This project is licensed under the MIT License. See the [LICENSE](../LICENSE) file for details.
 
-#![no_std]
 #![warn(clippy::std_instead_of_core)]
 #![warn(clippy::std_instead_of_alloc)]
 #![warn(clippy::alloc_instead_of_core)]

ratatui/Cargo.toml

@@ -31,11 +31,14 @@ rustdoc-args = ["--cfg", "docsrs"]
 default = ["crossterm", "underline-color", "all-widgets", "macros", "layout-cache"]
 #! Generally an application will only use one backend, so you should only enable one of the following features:
 ## enables the [`CrosstermBackend`](backend::CrosstermBackend) backend and adds a dependency on [`crossterm`].
-crossterm = ["dep:ratatui-crossterm"]
+crossterm = ["std", "dep:ratatui-crossterm"]
 ## enables the [`TermionBackend`](backend::TermionBackend) backend and adds a dependency on [`termion`].
-termion = ["dep:ratatui-termion"]
+termion = ["std", "dep:ratatui-termion"]
 ## enables the [`TermwizBackend`](backend::TermwizBackend) backend and adds a dependency on [`termwiz`].
-termwiz = ["dep:ratatui-termwiz"]
+termwiz = ["std", "dep:ratatui-termwiz"]
+
+## enables std
+std = ["ratatui-core/std"]
 
 #! The following optional features are available for all backends:
 ## enables serialization and deserialization of style and color types using the [`serde`] crate.
@@ -50,7 +53,7 @@ serde = [
 ]
 
 ## enables layout cache
-layout-cache = ["ratatui-core/layout-cache"]
+layout-cache = ["std", "ratatui-core/layout-cache"]
 
 ## enables conversions from colors in the [`palette`] crate to [`Color`](crate::style::Color).
 palette = ["ratatui-core/palette", "dep:palette"]

ratatui/src/init.rs

@@ -198,7 +198,7 @@ pub fn try_init_with_options(options: TerminalOptions) -> io::Result<DefaultTerm
 pub fn restore() {
     if let Err(err) = try_restore() {
         // There's not much we can do if restoring the terminal fails, so we just print the error
-        eprintln!("Failed to restore terminal: {err}");
+        std::eprintln!("Failed to restore terminal: {err}");
     }
 }
 
@@ -236,7 +236,7 @@ pub fn try_restore() -> io::Result<()> {
 /// original panic hook. This ensures that the terminal is left in a good state when a panic occurs.
 fn set_panic_hook() {
     let hook = std::panic::take_hook();
-    std::panic::set_hook(Box::new(move |info| {
+    std::panic::set_hook(alloc::boxed::Box::new(move |info| {
         restore();
         hook(info);
     }));

ratatui/src/lib.rs

@@ -1,3 +1,4 @@
+#![no_std]
 // show the feature flags in the generated documentation
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
@@ -323,6 +324,14 @@
 //! [Forum]: https://forum.ratatui.rs
 //! [Sponsors Badge]: https://img.shields.io/github/sponsors/ratatui?logo=github&style=flat-square&color=1370D3
 
+#![warn(clippy::std_instead_of_core)]
+#![warn(clippy::std_instead_of_alloc)]
+#![warn(clippy::alloc_instead_of_core)]
+
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std;
+
 /// re-export the `palette` crate so that users don't have to add it as a dependency
 #[cfg(feature = "palette")]
 pub use palette;

ratatui/src/widgets/stateful_widget_ref.rs

@@ -81,6 +81,11 @@ where
 
 #[cfg(test)]
 mod tests {
+    use alloc::borrow::ToOwned;
+    use alloc::boxed::Box;
+    use alloc::format;
+    use alloc::string::{String, ToString};
+
     use rstest::{fixture, rstest};
 
     use super::*;
@@ -129,7 +134,7 @@ mod tests {
         impl StatefulWidgetRef for Bytes {
             type State = [u8];
             fn render_ref(&self, area: Rect, buf: &mut Buffer, state: &mut Self::State) {
-                let slice = std::str::from_utf8(state).unwrap();
+                let slice = core::str::from_utf8(state).unwrap();
                 Line::from(format!("Bytes: {slice}")).render(area, buf);
             }
         }
@@ -145,7 +150,7 @@ mod tests {
         impl StatefulWidget for &Bytes {
             type State = [u8];
             fn render(self, area: Rect, buf: &mut Buffer, state: &mut Self::State) {
-                let slice = std::str::from_utf8(state).unwrap();
+                let slice = core::str::from_utf8(state).unwrap();
                 Line::from(format!("Bytes: {slice}")).render(area, buf);
             }
         }

ratatui/src/widgets/widget_ref.rs

@@ -1,3 +1,5 @@
+use alloc::string::String;
+
 use super::Widget;
 use crate::buffer::Buffer;
 use crate::layout::Rect;
@@ -166,6 +168,10 @@ impl<W: WidgetRef> WidgetRef for Option<W> {
 
 #[cfg(test)]
 mod tests {
+    use alloc::boxed::Box;
+    use alloc::vec;
+    use alloc::vec::Vec;
+
     use rstest::{fixture, rstest};
 
     use super::*;