feat(no_std): remove redundant std usages in ratatui-core (#1753)

Resolves https://github.com/ratatui/ratatui/issues/1751

Cargo.lock

@@ -2551,6 +2551,7 @@ dependencies = [
  "cassowary",
  "compact_str",
  "document-features",
+ "hashbrown",
  "indoc",
  "itertools 0.13.0",
  "lru",

ratatui-core/Cargo.toml

@@ -48,6 +48,7 @@ bitflags = "2.3"
 cassowary = "0.3"
 compact_str = "0.8.0"
 document-features = { workspace = true, optional = true }
+hashbrown = "0.15.2"
 indoc.workspace = true
 itertools.workspace = true
 lru = "0.12.0"

ratatui-core/src/backend.rs

@@ -100,6 +100,7 @@
 //! [Examples]: https://github.com/ratatui/ratatui/tree/main/ratatui/examples/README.md
 //! [Backend Comparison]: https://ratatui.rs/concepts/backends/comparison/
 //! [Ratatui Website]: https://ratatui.rs
+use core::ops;
 use std::io;
 
 use strum::{Display, EnumString};
@@ -341,8 +342,7 @@ pub trait Backend {
     /// For examples of how this function is expected to work, refer to the tests for
     /// [`TestBackend::scroll_region_up`].
     #[cfg(feature = "scrolling-regions")]
-    fn scroll_region_up(&mut self, region: std::ops::Range<u16>, line_count: u16)
-        -> io::Result<()>;
+    fn scroll_region_up(&mut self, region: ops::Range<u16>, line_count: u16) -> io::Result<()>;
 
     /// Scroll a region of the screen downwards, where a region is specified by a (half-open) range
     /// of rows.
@@ -363,11 +363,7 @@ pub trait Backend {
     /// For examples of how this function is expected to work, refer to the tests for
     /// [`TestBackend::scroll_region_down`].
     #[cfg(feature = "scrolling-regions")]
-    fn scroll_region_down(
-        &mut self,
-        region: std::ops::Range<u16>,
-        line_count: u16,
-    ) -> io::Result<()>;
+    fn scroll_region_down(&mut self, region: ops::Range<u16>, line_count: u16) -> io::Result<()>;
 }
 
 #[cfg(test)]

ratatui-core/src/backend/test.rs

@@ -1,8 +1,9 @@
 //! This module provides the `TestBackend` implementation for the [`Backend`] trait.
 //! It is used in the integration tests to verify the correctness of the library.
 
-use std::fmt::{self, Write};
-use std::{io, iter};
+use core::fmt::{self, Write};
+use core::{iter, ops};
+use std::io;
 
 use unicode_width::UnicodeWidthStr;
 
@@ -54,7 +55,7 @@ fn buffer_view(buffer: &Buffer) -> String {
             } else {
                 overwritten.push((x, c.symbol()));
             }
-            skip = std::cmp::max(skip, c.symbol().width()).saturating_sub(1);
+            skip = core::cmp::max(skip, c.symbol().width()).saturating_sub(1);
         }
         view.push('"');
         if !overwritten.is_empty() {
@@ -363,7 +364,7 @@ impl Backend for TestBackend {
     }
 
     #[cfg(feature = "scrolling-regions")]
-    fn scroll_region_up(&mut self, region: std::ops::Range<u16>, scroll_by: u16) -> io::Result<()> {
+    fn scroll_region_up(&mut self, region: ops::Range<u16>, scroll_by: u16) -> io::Result<()> {
         let width: usize = self.buffer.area.width.into();
         let cell_region_start = width * region.start.min(self.buffer.area.height) as usize;
         let cell_region_end = width * region.end.min(self.buffer.area.height) as usize;
@@ -409,11 +410,7 @@ impl Backend for TestBackend {
     }
 
     #[cfg(feature = "scrolling-regions")]
-    fn scroll_region_down(
-        &mut self,
-        region: std::ops::Range<u16>,
-        scroll_by: u16,
-    ) -> io::Result<()> {
+    fn scroll_region_down(&mut self, region: ops::Range<u16>, scroll_by: u16) -> io::Result<()> {
         let width: usize = self.buffer.area.width.into();
         let cell_region_start = width * region.start.min(self.buffer.area.height) as usize;
         let cell_region_end = width * region.end.min(self.buffer.area.height) as usize;
@@ -1026,7 +1023,7 @@ mod tests {
         #[case([A, B, C, D, E], 2..2, 2, [],                    [A, B, C, D, E])]
         fn scroll_region_up<const L: usize, const M: usize, const N: usize>(
             #[case] initial_screen: [&'static str; L],
-            #[case] range: std::ops::Range<u16>,
+            #[case] range: ops::Range<u16>,
             #[case] scroll_by: u16,
             #[case] expected_scrollback: [&'static str; M],
             #[case] expected_buffer: [&'static str; N],
@@ -1060,7 +1057,7 @@ mod tests {
         #[case([A, B, C, D, E], 2..2, 2, [A, B, C, D, E])]
         fn scroll_region_down<const M: usize, const N: usize>(
             #[case] initial_screen: [&'static str; M],
-            #[case] range: std::ops::Range<u16>,
+            #[case] range: ops::Range<u16>,
             #[case] scroll_by: u16,
             #[case] expected_buffer: [&'static str; N],
         ) {

ratatui-core/src/buffer/buffer.rs

@@ -1,5 +1,5 @@
-use std::fmt;
-use std::ops::{Index, IndexMut};
+use core::ops::{Index, IndexMut};
+use core::{cmp, fmt};
 
 use unicode_segmentation::UnicodeSegmentation;
 use unicode_width::UnicodeWidthStr;
@@ -499,8 +499,8 @@ impl Buffer {
 
             to_skip = current.symbol().width().saturating_sub(1);
 
-            let affected_width = std::cmp::max(current.symbol().width(), previous.symbol().width());
-            invalidated = std::cmp::max(affected_width, invalidated).saturating_sub(1);
+            let affected_width = cmp::max(current.symbol().width(), previous.symbol().width());
+            invalidated = cmp::max(affected_width, invalidated).saturating_sub(1);
         }
         updates
     }
@@ -592,7 +592,7 @@ impl fmt::Debug for Buffer {
                 } else {
                     overwritten.push((x, c.symbol()));
                 }
-                skip = std::cmp::max(skip, c.symbol().width()).saturating_sub(1);
+                skip = cmp::max(skip, c.symbol().width()).saturating_sub(1);
                 #[cfg(feature = "underline-color")]
                 {
                     let style = (c.fg, c.bg, c.underline_color, c.modifier);
@@ -638,7 +638,7 @@ impl fmt::Debug for Buffer {
 
 #[cfg(test)]
 mod tests {
-    use std::iter;
+    use core::iter;
 
     use itertools::Itertools;
     use rstest::{fixture, rstest};

ratatui-core/src/layout/constraint.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use core::fmt;
 
 use strum::EnumIs;
 

ratatui-core/src/layout/layout.rs

@@ -1,12 +1,12 @@
-use std::cell::RefCell;
-use std::collections::HashMap;
-use std::iter;
-use std::num::NonZeroUsize;
-use std::rc::Rc;
+use alloc::rc::Rc;
+use core::cell::RefCell;
+use core::iter;
+use core::num::NonZeroUsize;
 
 use cassowary::strength::REQUIRED;
 use cassowary::WeightedRelation::{EQ, GE, LE};
 use cassowary::{AddConstraintError, Expression, Solver, Variable};
+use hashbrown::HashMap;
 use itertools::Itertools;
 use lru::LruCache;
 
@@ -1404,7 +1404,7 @@ mod tests {
     /// - underflow: constraint is for less than the full space
     /// - overflow: constraint is for more than the full space
     mod split {
-        use std::ops::Range;
+        use core::ops::Range;
 
         use itertools::Itertools;
         use pretty_assertions::assert_eq;

ratatui-core/src/layout/margin.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use core::fmt;
 
 #[derive(Debug, Default, Clone, Copy, Eq, PartialEq, Hash)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]

ratatui-core/src/layout/position.rs

@@ -1,5 +1,5 @@
 #![warn(missing_docs)]
-use std::fmt;
+use core::fmt;
 
 use crate::layout::Rect;
 

ratatui-core/src/layout/rect.rs

@@ -1,6 +1,6 @@
 #![warn(missing_docs)]
-use std::cmp::{max, min};
-use std::fmt;
+use core::cmp::{max, min};
+use core::fmt;
 
 use crate::layout::{Margin, Position, Size};
 

ratatui-core/src/layout/size.rs

@@ -1,5 +1,5 @@
 #![warn(missing_docs)]
-use std::fmt;
+use core::fmt;
 
 use crate::layout::Rect;
 

ratatui-core/src/lib.rs

@@ -38,6 +38,8 @@
 //!
 //! This project is licensed under the MIT License. See the [LICENSE](../LICENSE) file for details.
 
+extern crate alloc;
+
 pub mod backend;
 pub mod buffer;
 pub mod layout;

ratatui-core/src/style.rs

@@ -68,7 +68,7 @@
 //!
 //! [`Span`]: crate::text::Span
 
-use std::fmt;
+use core::fmt;
 
 use bitflags::bitflags;
 pub use color::{Color, ParseColorError};

ratatui-core/src/style/color.rs

@@ -1,7 +1,7 @@
 #![allow(clippy::unreadable_literal)]
 
-use std::fmt;
-use std::str::FromStr;
+use core::fmt;
+use core::str::FromStr;
 
 use crate::style::stylize::{ColorDebug, ColorDebugKind};
 
@@ -249,7 +249,7 @@ impl fmt::Display for ParseColorError {
     }
 }
 
-impl std::error::Error for ParseColorError {}
+impl core::error::Error for ParseColorError {}
 
 /// Converts a string representation to a `Color` instance.
 ///
@@ -505,7 +505,7 @@ impl From<(u8, u8, u8, u8)> for Color {
 
 #[cfg(test)]
 mod tests {
-    use std::error::Error;
+    use core::error::Error;
 
     #[cfg(feature = "palette")]
     use palette::{Hsl, Hsluv};

ratatui-core/src/style/stylize.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use core::fmt;
 
 use crate::style::{Color, Modifier, Style};
 use crate::text::Span;

ratatui-core/src/terminal/viewport.rs

@@ -1,4 +1,4 @@
-use std::fmt;
+use core::fmt;
 
 use crate::layout::Rect;
 

ratatui-core/src/text/line.rs

@@ -1,7 +1,7 @@
 #![deny(missing_docs)]
 #![warn(clippy::pedantic, clippy::nursery, clippy::arithmetic_side_effects)]
-use std::borrow::Cow;
-use std::fmt;
+use alloc::borrow::Cow;
+use core::fmt;
 
 use unicode_truncate::UnicodeTruncateStr;
 
@@ -531,12 +531,12 @@ impl<'a> Line<'a> {
     }
 
     /// Returns an iterator over the spans of this line.
-    pub fn iter(&self) -> std::slice::Iter<Span<'a>> {
+    pub fn iter(&self) -> core::slice::Iter<Span<'a>> {
         self.spans.iter()
     }
 
     /// Returns a mutable iterator over the spans of this line.
-    pub fn iter_mut(&mut self) -> std::slice::IterMut<Span<'a>> {
+    pub fn iter_mut(&mut self) -> core::slice::IterMut<Span<'a>> {
         self.spans.iter_mut()
     }
 
@@ -561,7 +561,7 @@ impl<'a> Line<'a> {
 
 impl<'a> IntoIterator for Line<'a> {
     type Item = Span<'a>;
-    type IntoIter = std::vec::IntoIter<Span<'a>>;
+    type IntoIter = alloc::vec::IntoIter<Span<'a>>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.spans.into_iter()
@@ -570,7 +570,7 @@ impl<'a> IntoIterator for Line<'a> {
 
 impl<'a> IntoIterator for &'a Line<'a> {
     type Item = &'a Span<'a>;
-    type IntoIter = std::slice::Iter<'a, Span<'a>>;
+    type IntoIter = core::slice::Iter<'a, Span<'a>>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.iter()
@@ -579,7 +579,7 @@ impl<'a> IntoIterator for &'a Line<'a> {
 
 impl<'a> IntoIterator for &'a mut Line<'a> {
     type Item = &'a mut Span<'a>;
-    type IntoIter = std::slice::IterMut<'a, Span<'a>>;
+    type IntoIter = core::slice::IterMut<'a, Span<'a>>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.iter_mut()
@@ -638,7 +638,7 @@ where
 }
 
 /// Adds a `Span` to a `Line`, returning a new `Line` with the `Span` added.
-impl<'a> std::ops::Add<Span<'a>> for Line<'a> {
+impl<'a> core::ops::Add<Span<'a>> for Line<'a> {
     type Output = Self;
 
     fn add(mut self, rhs: Span<'a>) -> Self::Output {
@@ -648,7 +648,7 @@ impl<'a> std::ops::Add<Span<'a>> for Line<'a> {
 }
 
 /// Adds two `Line`s together, returning a new `Text` with the contents of the two `Line`s.
-impl<'a> std::ops::Add<Self> for Line<'a> {
+impl<'a> core::ops::Add<Self> for Line<'a> {
     type Output = Text<'a>;
 
     fn add(self, rhs: Self) -> Self::Output {
@@ -656,7 +656,7 @@ impl<'a> std::ops::Add<Self> for Line<'a> {
     }
 }
 
-impl<'a> std::ops::AddAssign<Span<'a>> for Line<'a> {
+impl<'a> core::ops::AddAssign<Span<'a>> for Line<'a> {
     fn add_assign(&mut self, rhs: Span<'a>) {
         self.spans.push(rhs);
     }
@@ -831,7 +831,7 @@ impl Styled for Line<'_> {
 
 #[cfg(test)]
 mod tests {
-    use std::iter;
+    use core::iter;
 
     use rstest::{fixture, rstest};
 

ratatui-core/src/text/masked.rs

@@ -1,5 +1,5 @@
-use std::borrow::Cow;
-use std::fmt;
+use alloc::borrow::Cow;
+use core::fmt;
 
 use crate::text::Text;
 

ratatui-core/src/text/span.rs

@@ -1,5 +1,5 @@
-use std::borrow::Cow;
-use std::fmt;
+use alloc::borrow::Cow;
+use core::fmt;
 
 use unicode_segmentation::UnicodeSegmentation;
 use unicode_width::UnicodeWidthStr;
@@ -384,7 +384,7 @@ where
     }
 }
 
-impl<'a> std::ops::Add<Self> for Span<'a> {
+impl<'a> core::ops::Add<Self> for Span<'a> {
     type Output = Line<'a>;
 
     fn add(self, rhs: Self) -> Self::Output {

ratatui-core/src/text/text.rs

@@ -1,6 +1,6 @@
 #![warn(missing_docs)]
-use std::borrow::Cow;
-use std::fmt;
+use alloc::borrow::Cow;
+use core::fmt;
 
 use crate::buffer::Buffer;
 use crate::layout::{Alignment, Rect};
@@ -504,12 +504,12 @@ impl<'a> Text<'a> {
     }
 
     /// Returns an iterator over the lines of the text.
-    pub fn iter(&self) -> std::slice::Iter<Line<'a>> {
+    pub fn iter(&self) -> core::slice::Iter<Line<'a>> {
         self.lines.iter()
     }
 
     /// Returns an iterator that allows modifying each line.
-    pub fn iter_mut(&mut self) -> std::slice::IterMut<Line<'a>> {
+    pub fn iter_mut(&mut self) -> core::slice::IterMut<Line<'a>> {
         self.lines.iter_mut()
     }
 
@@ -558,7 +558,7 @@ impl<'a> Text<'a> {
 
 impl<'a> IntoIterator for Text<'a> {
     type Item = Line<'a>;
-    type IntoIter = std::vec::IntoIter<Self::Item>;
+    type IntoIter = alloc::vec::IntoIter<Self::Item>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.lines.into_iter()
@@ -567,7 +567,7 @@ impl<'a> IntoIterator for Text<'a> {
 
 impl<'a> IntoIterator for &'a Text<'a> {
     type Item = &'a Line<'a>;
-    type IntoIter = std::slice::Iter<'a, Line<'a>>;
+    type IntoIter = core::slice::Iter<'a, Line<'a>>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.iter()
@@ -576,7 +576,7 @@ impl<'a> IntoIterator for &'a Text<'a> {
 
 impl<'a> IntoIterator for &'a mut Text<'a> {
     type Item = &'a mut Line<'a>;
-    type IntoIter = std::slice::IterMut<'a, Line<'a>>;
+    type IntoIter = core::slice::IterMut<'a, Line<'a>>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.iter_mut()
@@ -641,7 +641,7 @@ where
     }
 }
 
-impl<'a> std::ops::Add<Line<'a>> for Text<'a> {
+impl<'a> core::ops::Add<Line<'a>> for Text<'a> {
     type Output = Self;
 
     fn add(mut self, line: Line<'a>) -> Self::Output {
@@ -653,7 +653,7 @@ impl<'a> std::ops::Add<Line<'a>> for Text<'a> {
 /// Adds two `Text` together.
 ///
 /// This ignores the style and alignment of the second `Text`.
-impl std::ops::Add<Self> for Text<'_> {
+impl core::ops::Add<Self> for Text<'_> {
     type Output = Self;
 
     fn add(mut self, text: Self) -> Self::Output {
@@ -662,7 +662,7 @@ impl std::ops::Add<Self> for Text<'_> {
     }
 }
 
-impl<'a> std::ops::AddAssign<Line<'a>> for Text<'a> {
+impl<'a> core::ops::AddAssign<Line<'a>> for Text<'a> {
     fn add_assign(&mut self, line: Line<'a>) {
         self.push_line(line);
     }
@@ -743,7 +743,7 @@ impl Styled for Text<'_> {
 
 #[cfg(test)]
 mod tests {
-    use std::iter;
+    use core::iter;
 
     use rstest::{fixture, rstest};
 

ratatui-core/src/widgets/stateful_widget.rs

@@ -170,7 +170,7 @@ 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);
         }
     }