gpui/text_system/

line_wrapper.rs

use crate::{FontId, Pixels, SharedString, TextRun, TextSystem, px};
use collections::HashMap;
use std::{borrow::Cow, iter, sync::Arc};

/// Determines whether to truncate text from the start or end.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum TruncateFrom {
    /// Truncate text from the start.
    Start,
    /// Truncate text from the end.
    End,
    /// Truncate text from the middle, preserving the start and end.
    Middle,
}

/// The GPUI line wrapper, used to wrap lines of text to a given width.
pub struct LineWrapper {
    text_system: Arc<TextSystem>,
    pub(crate) font_id: FontId,
    pub(crate) font_size: Pixels,
    letter_spacing: Option<Pixels>,
    cached_ascii_char_widths: [Option<Pixels>; 128],
    cached_other_char_widths: HashMap<char, Pixels>,
}

impl LineWrapper {
    /// The maximum indent that can be applied to a line.
    pub const MAX_INDENT: u32 = 256;

    pub(crate) fn new(font_id: FontId, font_size: Pixels, text_system: Arc<TextSystem>) -> Self {
        Self {
            text_system,
            font_id,
            font_size,
            letter_spacing: None,
            cached_ascii_char_widths: [None; 128],
            cached_other_char_widths: HashMap::default(),
        }
    }

    pub(crate) fn set_letter_spacing(&mut self, letter_spacing: Option<Pixels>) {
        self.letter_spacing = letter_spacing;
    }

    /// Wrap a line of text to the given width with this wrapper's font and font size.
    pub fn wrap_line<'a>(
        &'a mut self,
        fragments: &'a [LineFragment],
        wrap_width: Pixels,
    ) -> impl Iterator<Item = Boundary> + 'a {
        let mut width = px(0.);
        let mut first_non_whitespace_ix = None;
        let mut indent = None;
        let mut last_candidate_ix = 0;
        let mut last_candidate_width = px(0.);
        let mut last_wrap_ix = 0;
        let mut prev_c = '\0';
        let mut index = 0;
        let mut previous_text_character = false;
        let mut candidates = fragments
            .iter()
            .flat_map(move |fragment| fragment.wrap_boundary_candidates())
            .peekable();
        iter::from_fn(move || {
            for candidate in candidates.by_ref() {
                let ix = index;
                index += candidate.len_utf8();
                let mut new_prev_c = prev_c;
                let mut item_had_spacing = false;
                let item_width = match candidate {
                    WrapBoundaryCandidate::Char { character: c } => {
                        if c == '\n' {
                            previous_text_character = false;
                            continue;
                        }

                        if Self::is_word_char(c) {
                            if prev_c == ' ' && c != ' ' && first_non_whitespace_ix.is_some() {
                                last_candidate_ix = ix;
                                last_candidate_width = width;
                            }
                        } else {
                            // CJK may not be space separated, e.g.: `Hello world你好世界`
                            if c != ' ' && first_non_whitespace_ix.is_some() {
                                last_candidate_ix = ix;
                                last_candidate_width = width;
                            }
                        }

                        if c != ' ' && first_non_whitespace_ix.is_none() {
                            first_non_whitespace_ix = Some(ix);
                        }

                        new_prev_c = c;

                        let width = self.width_for_char(c);
                        let spacing = if previous_text_character {
                            self.letter_spacing.unwrap_or_default()
                        } else {
                            px(0.)
                        };
                        item_had_spacing = previous_text_character;
                        previous_text_character = true;
                        width + spacing
                    }
                    WrapBoundaryCandidate::Element {
                        width: element_width,
                        ..
                    } => {
                        if prev_c == ' ' && first_non_whitespace_ix.is_some() {
                            last_candidate_ix = ix;
                            last_candidate_width = width;
                        }

                        if first_non_whitespace_ix.is_none() {
                            first_non_whitespace_ix = Some(ix);
                        }

                        element_width
                    }
                };

                width += item_width;
                if width > wrap_width && ix > last_wrap_ix {
                    if let (None, Some(first_non_whitespace_ix)) = (indent, first_non_whitespace_ix)
                    {
                        indent = Some(
                            Self::MAX_INDENT.min((first_non_whitespace_ix - last_wrap_ix) as u32),
                        );
                    }

                    if last_candidate_ix > 0 {
                        last_wrap_ix = last_candidate_ix;
                        width -= last_candidate_width;
                        width -= self.letter_spacing.unwrap_or_default();
                        last_candidate_ix = 0;
                    } else {
                        last_wrap_ix = ix;
                        width = if item_had_spacing {
                            item_width - self.letter_spacing.unwrap_or_default()
                        } else {
                            item_width
                        };
                    }

                    if let Some(indent) = indent {
                        width += self.width_for_char(' ') * indent as f32;
                    }

                    return Some(Boundary::new(last_wrap_ix, indent.unwrap_or(0)));
                }

                prev_c = new_prev_c;
            }

            None
        })
    }

    /// Determines if a line should be truncated based on its width.
    ///
    /// Returns the truncation index in `line`.
    pub fn should_truncate_line(
        &mut self,
        line: &str,
        truncate_width: Pixels,
        truncation_affix: &str,
        truncate_from: TruncateFrom,
    ) -> Option<usize> {
        let mut width = px(0.);
        let suffix_width = self.width_for_text(truncation_affix)
            + if truncation_affix.is_empty() {
                px(0.)
            } else {
                self.letter_spacing.unwrap_or_default()
            };
        let mut truncate_ix = 0;

        match truncate_from {
            TruncateFrom::Start => {
                let mut previous_text_character = false;
                for (ix, c) in line.char_indices().rev() {
                    if width + suffix_width < truncate_width {
                        truncate_ix = ix;
                    }

                    let char_width =
                        self.width_for_char_with_spacing(c, &mut previous_text_character);
                    width += char_width;

                    if width.floor() > truncate_width {
                        return Some(truncate_ix);
                    }
                }
            }
            TruncateFrom::End => {
                let mut previous_text_character = false;
                for (ix, c) in line.char_indices() {
                    if width + suffix_width < truncate_width {
                        truncate_ix = ix;
                    }

                    let char_width =
                        self.width_for_char_with_spacing(c, &mut previous_text_character);
                    width += char_width;

                    if width.floor() > truncate_width {
                        return Some(truncate_ix);
                    }
                }
            }
            TruncateFrom::Middle => {}
        }

        None
    }

    fn should_truncate_line_middle(
        &mut self,
        line: &str,
        truncate_width: Pixels,
        truncation_affix: &str,
    ) -> Option<(usize, usize)> {
        let suffix_width = truncation_affix
            .chars()
            .map(|c| self.width_for_char(c))
            .fold(px(0.0), |a, x| a + x);

        let total_width: Pixels = line
            .chars()
            .map(|c| self.width_for_char(c))
            .fold(px(0.0), |a, x| a + x);

        if total_width <= truncate_width {
            return None;
        }

        let content_budget = truncate_width - suffix_width;
        if content_budget <= px(0.) {
            return Some((0, line.len()));
        }

        let front_budget = content_budget * (2.0 / 3.0);
        let back_budget = content_budget - front_budget;

        let mut front_width = px(0.);
        let mut front_end_ix = 0usize;
        for (ix, c) in line.char_indices() {
            let char_width = self.width_for_char(c);
            if front_width + char_width > front_budget {
                break;
            }
            front_width += char_width;
            front_end_ix = ix + c.len_utf8();
        }

        let mut back_width = px(0.);
        let mut back_start_ix = line.len();
        for (ix, c) in line.char_indices().rev() {
            let char_width = self.width_for_char(c);
            if back_width + char_width > back_budget {
                break;
            }
            back_width += char_width;
            back_start_ix = ix;
        }

        if front_end_ix >= back_start_ix {
            return Some((0, line.len()));
        }

        Some((front_end_ix, back_start_ix))
    }

    /// Truncate a line of text to the given width with this wrapper's font and font size.
    pub fn truncate_line<'a>(
        &mut self,
        line: SharedString,
        truncate_width: Pixels,
        truncation_affix: &str,
        runs: &'a [TextRun],
        truncate_from: TruncateFrom,
    ) -> (SharedString, Cow<'a, [TextRun]>) {
        if truncate_from == TruncateFrom::Middle {
            if let Some((front_end_ix, back_start_ix)) =
                self.should_truncate_line_middle(&line, truncate_width, truncation_affix)
            {
                let result = SharedString::from(format!(
                    "{}{truncation_affix}{}",
                    &line[..front_end_ix],
                    &line[back_start_ix..]
                ));
                let mut runs = runs.to_vec();
                update_runs_after_middle_truncation(
                    truncation_affix,
                    &mut runs,
                    front_end_ix,
                    back_start_ix,
                );
                return (result, Cow::Owned(runs));
            } else {
                return (line, Cow::Borrowed(runs));
            }
        }

        if let Some(truncate_ix) =
            self.should_truncate_line(&line, truncate_width, truncation_affix, truncate_from)
        {
            let result = match truncate_from {
                TruncateFrom::Start => SharedString::from(format!(
                    "{truncation_affix}{}",
                    &line[line.ceil_char_boundary(truncate_ix + 1)..]
                )),
                TruncateFrom::End => SharedString::from(format!(
                    "{}{truncation_affix}",
                    line[..truncate_ix]
                        .trim_end_matches(|c: char| c.is_whitespace() || c.is_ascii_punctuation())
                )),
                TruncateFrom::Middle => unreachable!("Middle truncation is handled above"),
            };
            let mut runs = runs.to_vec();
            update_runs_after_truncation(&result, truncation_affix, &mut runs, truncate_from);
            (result, Cow::Owned(runs))
        } else {
            (line, Cow::Borrowed(runs))
        }
    }

    /// Truncate text to fit within a given number of wrapped lines.
    ///
    /// Unlike `truncate_line` which treats the text as a flat width budget
    /// (`width * max_lines`), this method accounts for word-boundary wrapping:
    /// it walks through characters once, tracking wrap boundaries and the
    /// truncation point simultaneously. When text overflows on the last
    /// allowed line, it truncates there and appends the affix.
    ///
    /// For `max_lines == 1`, this delegates to `truncate_line`.
    pub fn truncate_wrapped_line<'a>(
        &mut self,
        text: SharedString,
        wrap_width: Pixels,
        max_lines: usize,
        truncation_affix: &str,
        runs: &'a [TextRun],
        truncate_from: TruncateFrom,
    ) -> (SharedString, Cow<'a, [TextRun]>) {
        if max_lines <= 1 || truncate_from == TruncateFrom::Start {
            return self.truncate_line(
                text,
                wrap_width * max_lines,
                truncation_affix,
                runs,
                truncate_from,
            );
        }
        if truncate_from == TruncateFrom::Middle {
            return self.truncate_line(text, wrap_width, truncation_affix, runs, truncate_from);
        }

        let affix_width = self.width_for_text(truncation_affix)
            + if truncation_affix.is_empty() {
                px(0.)
            } else {
                self.letter_spacing.unwrap_or_default()
            };

        let mut width = px(0.);
        let mut line = 0usize;
        let mut first_non_whitespace_ix = None;
        let mut last_candidate_ix = 0usize;
        let mut last_candidate_width = px(0.);
        let mut last_wrap_ix = 0usize;
        let mut prev_c = '\0';
        let mut indent: Option<u32> = None;
        let mut truncate_ix = 0usize;
        let mut previous_text_character = false;

        for (ix, c) in text.char_indices() {
            if c == '\n' {
                if line >= max_lines - 1 && !text[ix + 1..].trim().is_empty() {
                    // Newline on the last allowed line with real content
                    // below. Truncate here.
                    let truncated = text[..truncate_ix]
                        .trim_end_matches(|c: char| c.is_whitespace() || c.is_ascii_punctuation());
                    let result = SharedString::from(format!("{truncated}{truncation_affix}"));
                    let mut runs = runs.to_vec();
                    update_runs_after_truncation(
                        &result,
                        truncation_affix,
                        &mut runs,
                        TruncateFrom::End,
                    );
                    return (result, Cow::Owned(runs));
                }

                // Newline before the last line: it consumes a line.
                line += 1;
                width = px(0.);
                first_non_whitespace_ix = None;
                last_candidate_ix = 0;
                last_candidate_width = px(0.);
                last_wrap_ix = ix + 1;
                prev_c = '\0';
                indent = None;
                truncate_ix = ix + 1;
                previous_text_character = false;
                continue;
            }

            let char_width = self.width_for_char_with_spacing(c, &mut previous_text_character);

            if Self::is_word_char(c) {
                if prev_c == ' ' && first_non_whitespace_ix.is_some() {
                    last_candidate_ix = ix;
                    last_candidate_width = width;
                }
            } else if c != ' ' && first_non_whitespace_ix.is_some() {
                last_candidate_ix = ix;
                last_candidate_width = width;
            }

            if c != ' ' && first_non_whitespace_ix.is_none() {
                first_non_whitespace_ix = Some(ix);
            }

            width += char_width;

            if line < max_lines - 1 {
                // Before the last line: replicate wrap_line's boundary logic.
                if width > wrap_width && ix > last_wrap_ix {
                    if let (None, Some(first_nw)) = (indent, first_non_whitespace_ix) {
                        indent = Some(Self::MAX_INDENT.min((first_nw - last_wrap_ix) as u32));
                    }

                    if last_candidate_ix > last_wrap_ix {
                        last_wrap_ix = last_candidate_ix;
                        width -= last_candidate_width;
                        width -= self.letter_spacing.unwrap_or_default();
                        last_candidate_ix = 0;
                    } else {
                        last_wrap_ix = ix;
                        width = self.width_for_char(c);
                    }

                    if let Some(ind) = indent {
                        width += self.width_for_char(' ') * ind as f32;
                    }

                    line += 1;
                    truncate_ix = last_wrap_ix;
                }
            } else {
                // On the last line: track the furthest point where the affix
                // still fits, and stop as soon as the line overflows.
                if width + affix_width <= wrap_width {
                    truncate_ix = ix + c.len_utf8();
                }

                if width > wrap_width {
                    let truncated = text[..truncate_ix]
                        .trim_end_matches(|c: char| c.is_whitespace() || c.is_ascii_punctuation());
                    let result = SharedString::from(format!("{truncated}{truncation_affix}"));
                    let mut runs = runs.to_vec();
                    update_runs_after_truncation(
                        &result,
                        truncation_affix,
                        &mut runs,
                        TruncateFrom::End,
                    );
                    return (result, Cow::Owned(runs));
                }
            }

            prev_c = c;
        }

        // Text fits within max_lines without truncation.
        (text, Cow::Borrowed(runs))
    }

    /// Any character in this list should be treated as a word character,
    /// meaning it can be part of a word that should not be wrapped.
    pub(crate) fn is_word_char(c: char) -> bool {
        // ASCII alphanumeric characters, for English, numbers: `Hello123`, etc.
        c.is_ascii_alphanumeric() ||
        // Latin script in Unicode for French, German, Spanish, etc.
        // Latin-1 Supplement
        // https://en.wikipedia.org/wiki/Latin-1_Supplement
        matches!(c, '\u{00C0}'..='\u{00FF}') ||
        // Latin Extended-A
        // https://en.wikipedia.org/wiki/Latin_Extended-A
        matches!(c, '\u{0100}'..='\u{017F}') ||
        // Latin Extended-B
        // https://en.wikipedia.org/wiki/Latin_Extended-B
        matches!(c, '\u{0180}'..='\u{024F}') ||
        // Cyrillic for Russian, Ukrainian, etc.
        // https://en.wikipedia.org/wiki/Cyrillic_script_in_Unicode
        matches!(c, '\u{0400}'..='\u{04FF}') ||

        // Vietnamese (https://vietunicode.sourceforge.net/charset/)
        matches!(c, '\u{1E00}'..='\u{1EFF}') || // Latin Extended Additional
        matches!(c, '\u{0300}'..='\u{036F}') || // Combining Diacritical Marks

        // Bengali (https://en.wikipedia.org/wiki/Bengali_(Unicode_block))
        matches!(c, '\u{0980}'..='\u{09FF}') ||

        // Some other known special characters that should be treated as word characters,
        // e.g. `a-b`, `var_name`, `I'm`/`won’t`, '@mention`, `#hashtag`, `100%`, `3.1415`,
        // `2^3`, `a~b`, `a=1`, `Self::new`, etc. Trailing punctuation like `,`, `.`, `:`, `;`
        // is included so it stays attached to the preceding word when wrapping.
        matches!(c, '-' | '_' | '.' | '\'' | '’' | '‘' | '$' | '%' | '@' | '#' | '^' | '~' | ',' | '=' | ':' | ';') ||
        // `⋯` character is special used in Zed, to keep this at the end of the line.
        matches!(c, '⋯') ||

        // Non-breaking glue characters
        matches!(c, '\u{202F}' | '\u{00A0}' | '\u{2011}')
    }

    #[inline(always)]
    fn width_for_char(&mut self, c: char) -> Pixels {
        if (c as u32) < 128 {
            if let Some(cached_width) = self.cached_ascii_char_widths[c as usize] {
                cached_width
            } else {
                let width = self
                    .text_system
                    .layout_width(self.font_id, self.font_size, c);
                self.cached_ascii_char_widths[c as usize] = Some(width);
                width
            }
        } else if let Some(cached_width) = self.cached_other_char_widths.get(&c) {
            *cached_width
        } else {
            let width = self
                .text_system
                .layout_width(self.font_id, self.font_size, c);
            self.cached_other_char_widths.insert(c, width);
            width
        }
    }

    fn width_for_char_with_spacing(
        &mut self,
        c: char,
        previous_text_character: &mut bool,
    ) -> Pixels {
        let width = self.width_for_char(c);
        let spacing = if *previous_text_character {
            self.letter_spacing.unwrap_or_default()
        } else {
            px(0.)
        };
        *previous_text_character = true;
        width + spacing
    }

    fn width_for_text(&mut self, text: &str) -> Pixels {
        let mut previous_text_character = false;
        text.chars()
            .map(|character| {
                self.width_for_char_with_spacing(character, &mut previous_text_character)
            })
            .sum()
    }
}

fn update_runs_after_truncation(
    result: &str,
    ellipsis: &str,
    runs: &mut Vec<TextRun>,
    truncate_from: TruncateFrom,
) {
    let mut truncate_at = result.len() - ellipsis.len();
    match truncate_from {
        TruncateFrom::Start => {
            for (run_index, run) in runs.iter_mut().enumerate().rev() {
                if run.len <= truncate_at {
                    truncate_at -= run.len;
                } else {
                    run.len = truncate_at + ellipsis.len();
                    runs.splice(..run_index, std::iter::empty());
                    break;
                }
            }
        }
        TruncateFrom::End => {
            for (run_index, run) in runs.iter_mut().enumerate() {
                if run.len <= truncate_at {
                    truncate_at -= run.len;
                } else {
                    run.len = truncate_at + ellipsis.len();
                    runs.truncate(run_index + 1);
                    break;
                }
            }
        }
        TruncateFrom::Middle => {
            unreachable!("Middle truncation calls this function with TruncateFrom::End directly")
        }
    }
}

fn update_runs_after_middle_truncation(
    ellipsis: &str,
    runs: &mut Vec<TextRun>,
    front_end_ix: usize,
    back_start_ix: usize,
) {
    let original_runs = std::mem::take(runs);
    let mut result_runs: Vec<TextRun> = Vec::with_capacity(original_runs.len());

    // Front segment [0, front_end_ix) + ellipsis: walk forward until the run
    // that straddles or ends at front_end_ix, then extend that run's length
    // to include the ellipsis.
    let mut front_remaining = front_end_ix;
    let mut front_done = false;
    for run in &original_runs {
        if front_done {
            break;
        }
        if run.len <= front_remaining {
            result_runs.push(run.clone());
            front_remaining -= run.len;
        } else {
            let mut partial = run.clone();
            partial.len = front_remaining + ellipsis.len();
            result_runs.push(partial);
            front_done = true;
        }
    }
    if !front_done {
        // front_end_ix landed exactly on a run boundary; append ellipsis to
        // the last front run (or, if the front is empty, to the first back run).
        if let Some(last) = result_runs.last_mut() {
            last.len += ellipsis.len();
        } else if let Some(first) = original_runs.first() {
            let mut affix_run = first.clone();
            affix_run.len = ellipsis.len();
            result_runs.push(affix_run);
        }
    }

    // Back segment [back_start_ix, original.len()): skip runs entirely in the
    // removed middle, keep the rest.
    let mut byte_pos = 0usize;
    for run in &original_runs {
        let run_end = byte_pos + run.len;
        if run_end > back_start_ix {
            if byte_pos < back_start_ix {
                // Run straddles back_start_ix; keep only the tail.
                let mut partial = run.clone();
                partial.len = run_end - back_start_ix;
                result_runs.push(partial);
            } else {
                result_runs.push(run.clone());
            }
        }
        byte_pos = run_end;
    }

    *runs = result_runs;
}

/// A fragment of a line that can be wrapped.
pub enum LineFragment<'a> {
    /// A text fragment consisting of characters.
    Text {
        /// The text content of the fragment.
        text: &'a str,
    },
    /// A non-text element with a fixed width.
    Element {
        /// The width of the element in pixels.
        width: Pixels,
        /// The UTF-8 encoded length of the element.
        len_utf8: usize,
    },
}

impl<'a> LineFragment<'a> {
    /// Creates a new text fragment from the given text.
    pub fn text(text: &'a str) -> Self {
        LineFragment::Text { text }
    }

    /// Creates a new non-text element with the given width and UTF-8 encoded length.
    pub fn element(width: Pixels, len_utf8: usize) -> Self {
        LineFragment::Element { width, len_utf8 }
    }

    fn wrap_boundary_candidates(&self) -> impl Iterator<Item = WrapBoundaryCandidate> {
        let text = match self {
            LineFragment::Text { text } => text,
            LineFragment::Element { .. } => "\0",
        };
        text.chars().map(move |character| {
            if let LineFragment::Element { width, len_utf8 } = self {
                WrapBoundaryCandidate::Element {
                    width: *width,
                    len_utf8: *len_utf8,
                }
            } else {
                WrapBoundaryCandidate::Char { character }
            }
        })
    }
}

enum WrapBoundaryCandidate {
    Char { character: char },
    Element { width: Pixels, len_utf8: usize },
}

impl WrapBoundaryCandidate {
    pub fn len_utf8(&self) -> usize {
        match self {
            WrapBoundaryCandidate::Char { character } => character.len_utf8(),
            WrapBoundaryCandidate::Element { len_utf8: len, .. } => *len,
        }
    }
}

/// A boundary between two lines of text.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct Boundary {
    /// The index of the last character in a line
    pub ix: usize,
    /// The indent of the next line.
    pub next_indent: u32,
}

impl Boundary {
    fn new(ix: usize, next_indent: u32) -> Self {
        Self { ix, next_indent }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{
        Font, FontFeatures, FontRun, FontStyle, FontWeight, Hsla, TestAppContext, TestDispatcher,
        TextRun, font,
    };
    #[cfg(target_os = "macos")]
    use crate::{WindowTextSystem, WrapBoundary};

    fn build_wrapper() -> LineWrapper {
        let dispatcher = TestDispatcher::new(0);
        let cx = TestAppContext::build(dispatcher, None);
        let id = cx.text_system().resolve_font(&font(".ZedMono"));
        LineWrapper::new(id, px(16.), cx.text_system().clone())
    }

    fn generate_test_runs(input_run_len: &[usize]) -> Vec<TextRun> {
        input_run_len
            .iter()
            .map(|run_len| TextRun {
                len: *run_len,
                font: Font {
                    family: "Dummy".into(),
                    features: FontFeatures::default(),
                    fallbacks: None,
                    weight: FontWeight::default(),
                    style: FontStyle::Normal,
                },
                ..Default::default()
            })
            .collect()
    }

    #[test]
    fn test_tracking_changes_measured_width() {
        let dispatcher = TestDispatcher::new(1);
        let cx = TestAppContext::build(dispatcher, None);
        let base = TextRun {
            len: 4,
            font: font(".ZedMono"),
            color: Hsla::default(),
            background_color: None,
            underline: None,
            strikethrough: None,
            ..Default::default()
        };
        let font_id = cx.text_system().resolve_font(&base.font);
        let platform = cx.text_system().platform_text_system_for_tests();
        let no_tracking = platform.layout_line(
            "TEST",
            px(16.),
            &[FontRun {
                len: 4,
                font_id,
                letter_spacing: None,
            }],
        );
        let wide = platform.layout_line(
            "TEST",
            px(16.),
            &[FontRun {
                len: 4,
                font_id,
                letter_spacing: Some(px(2.0)),
            }],
        );
        let tight = platform.layout_line(
            "TEST",
            px(16.),
            &[FontRun {
                len: 4,
                font_id,
                letter_spacing: Some(px(-0.5)),
            }],
        );

        assert!(wide.width > no_tracking.width);
        assert!(tight.width <= no_tracking.width);
    }

    #[test]
    fn test_tracking_changes_truncation_width() {
        let mut wrapper = build_wrapper();
        let no_tracking = wrapper.width_for_text("TEST…");
        wrapper.set_letter_spacing(Some(px(2.0)));
        let wide = wrapper.width_for_text("TEST…");

        assert!(wide > no_tracking);
    }

    #[test]
    fn test_wrap_line() {
        let mut wrapper = build_wrapper();

        assert_eq!(
            wrapper
                .wrap_line(&[LineFragment::text("aa bbb cccc ddddd eeee")], px(72.))
                .collect::<Vec<_>>(),
            &[
                Boundary::new(7, 0),
                Boundary::new(12, 0),
                Boundary::new(18, 0)
            ],
        );
        assert_eq!(
            wrapper
                .wrap_line(&[LineFragment::text("aaa aaaaaaaaaaaaaaaaaa")], px(72.0))
                .collect::<Vec<_>>(),
            &[
                Boundary::new(4, 0),
                Boundary::new(11, 0),
                Boundary::new(18, 0)
            ],
        );
        assert_eq!(
            wrapper
                .wrap_line(&[LineFragment::text("     aaaaaaa")], px(72.))
                .collect::<Vec<_>>(),
            &[
                Boundary::new(7, 5),
                Boundary::new(9, 5),
                Boundary::new(11, 5),
            ]
        );
        assert_eq!(
            wrapper
                .wrap_line(
                    &[LineFragment::text("                            ")],
                    px(72.)
                )
                .collect::<Vec<_>>(),
            &[
                Boundary::new(7, 0),
                Boundary::new(14, 0),
                Boundary::new(21, 0)
            ]
        );
        assert_eq!(
            wrapper
                .wrap_line(&[LineFragment::text("          aaaaaaaaaaaaaa")], px(72.))
                .collect::<Vec<_>>(),
            &[
                Boundary::new(7, 0),
                Boundary::new(14, 3),
                Boundary::new(18, 3),
                Boundary::new(22, 3),
            ]
        );

        // Test wrapping multiple text fragments
        assert_eq!(
            wrapper
                .wrap_line(
                    &[
                        LineFragment::text("aa bbb "),
                        LineFragment::text("cccc ddddd eeee")
                    ],
                    px(72.)
                )
                .collect::<Vec<_>>(),
            &[
                Boundary::new(7, 0),
                Boundary::new(12, 0),
                Boundary::new(18, 0)
            ],
        );

        // Test wrapping with a mix of text and element fragments
        assert_eq!(
            wrapper
                .wrap_line(
                    &[
                        LineFragment::text("aa "),
                        LineFragment::element(px(20.), 1),
                        LineFragment::text(" bbb "),
                        LineFragment::element(px(30.), 1),
                        LineFragment::text(" cccc")
                    ],
                    px(72.)
                )
                .collect::<Vec<_>>(),
            &[
                Boundary::new(5, 0),
                Boundary::new(9, 0),
                Boundary::new(11, 0)
            ],
        );

        // Test with element at the beginning and text afterward
        assert_eq!(
            wrapper
                .wrap_line(
                    &[
                        LineFragment::element(px(50.), 1),
                        LineFragment::text(" aaaa bbbb cccc dddd")
                    ],
                    px(72.)
                )
                .collect::<Vec<_>>(),
            &[
                Boundary::new(2, 0),
                Boundary::new(7, 0),
                Boundary::new(12, 0),
                Boundary::new(17, 0)
            ],
        );

        // Test with a large element that forces wrapping by itself
        assert_eq!(
            wrapper
                .wrap_line(
                    &[
                        LineFragment::text("short text "),
                        LineFragment::element(px(100.), 1),
                        LineFragment::text(" more text")
                    ],
                    px(72.)
                )
                .collect::<Vec<_>>(),
            &[
                Boundary::new(6, 0),
                Boundary::new(11, 0),
                Boundary::new(12, 0),
                Boundary::new(18, 0)
            ],
        );

        // Test with non-breaking glue characters
        assert_eq!(
            wrapper
                .wrap_line(
                    &[LineFragment::text("a\u{202F}b\u{00A0}c\u{2011}d e")],
                    px(72.0)
                )
                .collect::<Vec<_>>(),
            &[Boundary::new(12, 0),], // special chars above take up 3, 2 and 3 bytes, so boundary ends up at 12
        );
    }

    #[test]
    fn test_truncate_line_end() {
        let mut wrapper = build_wrapper();

        fn perform_test(
            wrapper: &mut LineWrapper,
            text: &'static str,
            expected: &'static str,
            ellipsis: &str,
        ) {
            let dummy_run_lens = vec![text.len()];
            let dummy_runs = generate_test_runs(&dummy_run_lens);
            let (result, dummy_runs) = wrapper.truncate_line(
                text.into(),
                px(220.),
                ellipsis,
                &dummy_runs,
                TruncateFrom::End,
            );
            assert_eq!(result, expected);
            assert_eq!(dummy_runs.first().unwrap().len, result.len());
        }

        perform_test(
            &mut wrapper,
            "aa bbb cccc ddddd eeee ffff gggg",
            "aa bbb cccc ddddd eeee",
            "",
        );
        perform_test(
            &mut wrapper,
            "aa bbb cccc ddddd eeee ffff gggg",
            "aa bbb cccc ddddd eee…",
            "…",
        );
        perform_test(
            &mut wrapper,
            "aa bbb cccc ddddd eeee ffff gggg",
            "aa bbb cccc dddd......",
            "......",
        );
        perform_test(
            &mut wrapper,
            "aa bbb cccc 🦀🦀🦀🦀🦀 eeee ffff gggg",
            "aa bbb cccc 🦀🦀🦀🦀…",
            "…",
        );
    }

    #[test]
    fn test_truncate_line_start() {
        let mut wrapper = build_wrapper();

        #[track_caller]
        fn perform_test(
            wrapper: &mut LineWrapper,
            text: &'static str,
            expected: &'static str,
            ellipsis: &str,
        ) {
            let dummy_run_lens = vec![text.len()];
            let dummy_runs = generate_test_runs(&dummy_run_lens);
            let (result, dummy_runs) = wrapper.truncate_line(
                text.into(),
                px(220.),
                ellipsis,
                &dummy_runs,
                TruncateFrom::Start,
            );
            assert_eq!(result, expected);
            assert_eq!(dummy_runs.first().unwrap().len, result.len());
        }

        perform_test(
            &mut wrapper,
            "aaaa bbbb cccc ddddd eeee fff gg",
            "cccc ddddd eeee fff gg",
            "",
        );
        perform_test(
            &mut wrapper,
            "aaaa bbbb cccc ddddd eeee fff gg",
            "…ccc ddddd eeee fff gg",
            "…",
        );
        perform_test(
            &mut wrapper,
            "aaaa bbbb cccc ddddd eeee fff gg",
            "......dddd eeee fff gg",
            "......",
        );
        perform_test(
            &mut wrapper,
            "aaaa bbbb cccc 🦀🦀🦀🦀🦀 eeee fff gg",
            "…🦀🦀🦀🦀 eeee fff gg",
            "…",
        );
    }

    #[test]
    fn test_truncate_multiple_runs_end() {
        let mut wrapper = build_wrapper();

        fn perform_test(
            wrapper: &mut LineWrapper,
            text: &'static str,
            expected: &str,
            run_lens: &[usize],
            result_run_len: &[usize],
            line_width: Pixels,
        ) {
            let dummy_runs = generate_test_runs(run_lens);
            let (result, dummy_runs) =
                wrapper.truncate_line(text.into(), line_width, "…", &dummy_runs, TruncateFrom::End);
            assert_eq!(result, expected);
            for (run, result_len) in dummy_runs.iter().zip(result_run_len) {
                assert_eq!(run.len, *result_len);
            }
        }
        // Case 0: Normal
        // Text: abcdefghijkl
        // Runs: Run0 { len: 12, ... }
        //
        // Truncate res: abcd… (truncate_at = 4)
        // Run res: Run0 { string: abcd…, len: 7, ... }
        perform_test(&mut wrapper, "abcdefghijkl", "abcd…", &[12], &[7], px(50.));
        // Case 1: Drop some runs
        // Text: abcdefghijkl
        // Runs: Run0 { len: 4, ... }, Run1 { len: 4, ... }, Run2 { len: 4, ... }
        //
        // Truncate res: abcdef… (truncate_at = 6)
        // Runs res: Run0 { string: abcd, len: 4, ... }, Run1 { string: ef…, len:
        // 5, ... }
        perform_test(
            &mut wrapper,
            "abcdefghijkl",
            "abcdef…",
            &[4, 4, 4],
            &[4, 5],
            px(70.),
        );
        // Case 2: Truncate at start of some run
        // Text: abcdefghijkl
        // Runs: Run0 { len: 4, ... }, Run1 { len: 4, ... }, Run2 { len: 4, ... }
        //
        // Truncate res: abcdefgh… (truncate_at = 8)
        // Runs res: Run0 { string: abcd, len: 4, ... }, Run1 { string: efgh, len:
        // 4, ... }, Run2 { string: …, len: 3, ... }
        perform_test(
            &mut wrapper,
            "abcdefghijkl",
            "abcdefgh…",
            &[4, 4, 4],
            &[4, 4, 3],
            px(90.),
        );
    }

    #[test]
    fn test_truncate_multiple_runs_start() {
        let mut wrapper = build_wrapper();

        #[track_caller]
        fn perform_test(
            wrapper: &mut LineWrapper,
            text: &'static str,
            expected: &str,
            run_lens: &[usize],
            result_run_len: &[usize],
            line_width: Pixels,
        ) {
            let dummy_runs = generate_test_runs(run_lens);
            let (result, dummy_runs) = wrapper.truncate_line(
                text.into(),
                line_width,
                "…",
                &dummy_runs,
                TruncateFrom::Start,
            );
            assert_eq!(result, expected);
            for (run, result_len) in dummy_runs.iter().zip(result_run_len) {
                assert_eq!(run.len, *result_len);
            }
        }
        // Case 0: Normal
        // Text: abcdefghijkl
        // Runs: Run0 { len: 12, ... }
        //
        // Truncate res: …ijkl (truncate_at = 9)
        // Run res: Run0 { string: …ijkl, len: 7, ... }
        perform_test(&mut wrapper, "abcdefghijkl", "…ijkl", &[12], &[7], px(50.));
        // Case 1: Drop some runs
        // Text: abcdefghijkl
        // Runs: Run0 { len: 4, ... }, Run1 { len: 4, ... }, Run2 { len: 4, ... }
        //
        // Truncate res: …ghijkl (truncate_at = 7)
        // Runs res: Run0 { string: …gh, len: 5, ... }, Run1 { string: ijkl, len:
        // 4, ... }
        perform_test(
            &mut wrapper,
            "abcdefghijkl",
            "…ghijkl",
            &[4, 4, 4],
            &[5, 4],
            px(70.),
        );
        // Case 2: Truncate at start of some run
        // Text: abcdefghijkl
        // Runs: Run0 { len: 4, ... }, Run1 { len: 4, ... }, Run2 { len: 4, ... }
        //
        // Truncate res: abcdefgh… (truncate_at = 3)
        // Runs res: Run0 { string: …, len: 3, ... }, Run1 { string: efgh, len:
        // 4, ... }, Run2 { string: ijkl, len: 4, ... }
        perform_test(
            &mut wrapper,
            "abcdefghijkl",
            "…efghijkl",
            &[4, 4, 4],
            &[3, 4, 4],
            px(90.),
        );
    }

    #[test]
    fn test_update_run_after_truncation_end() {
        fn perform_test(result: &str, run_lens: &[usize], result_run_lens: &[usize]) {
            let mut dummy_runs = generate_test_runs(run_lens);
            update_runs_after_truncation(result, "…", &mut dummy_runs, TruncateFrom::End);
            for (run, result_len) in dummy_runs.iter().zip(result_run_lens) {
                assert_eq!(run.len, *result_len);
            }
        }
        // Case 0: Normal
        // Text: abcdefghijkl
        // Runs: Run0 { len: 12, ... }
        //
        // Truncate res: abcd… (truncate_at = 4)
        // Run res: Run0 { string: abcd…, len: 7, ... }
        perform_test("abcd…", &[12], &[7]);
        // Case 1: Drop some runs
        // Text: abcdefghijkl
        // Runs: Run0 { len: 4, ... }, Run1 { len: 4, ... }, Run2 { len: 4, ... }
        //
        // Truncate res: abcdef… (truncate_at = 6)
        // Runs res: Run0 { string: abcd, len: 4, ... }, Run1 { string: ef…, len:
        // 5, ... }
        perform_test("abcdef…", &[4, 4, 4], &[4, 5]);
        // Case 2: Truncate at start of some run
        // Text: abcdefghijkl
        // Runs: Run0 { len: 4, ... }, Run1 { len: 4, ... }, Run2 { len: 4, ... }
        //
        // Truncate res: abcdefgh… (truncate_at = 8)
        // Runs res: Run0 { string: abcd, len: 4, ... }, Run1 { string: efgh, len:
        // 4, ... }, Run2 { string: …, len: 3, ... }
        perform_test("abcdefgh…", &[4, 4, 4], &[4, 4, 3]);
    }

    #[test]
    fn test_is_word_char() {
        #[track_caller]
        fn assert_word(word: &str) {
            for c in word.chars() {
                assert!(
                    LineWrapper::is_word_char(c),
                    "assertion failed for '{}' (unicode 0x{:x})",
                    c,
                    c as u32
                );
            }
        }

        #[track_caller]
        fn assert_not_word(word: &str) {
            let found = word.chars().any(|c| !LineWrapper::is_word_char(c));
            assert!(found, "assertion failed for '{}'", word);
        }

        assert_word("Hello123");
        assert_word("non-English");
        assert_word("var_name");
        assert_word("123456");
        assert_word("3.1415");
        assert_word("10^2");
        assert_word("1~2");
        assert_word("100%");
        assert_word("@mention");
        assert_word("#hashtag");
        assert_word("$variable");
        assert_word("a=1");
        assert_word("Self::is_word_char");
        assert_word("on;");
        assert_word("more⋯");
        assert_word("won’t");
        assert_word("‘twas");

        // Space
        assert_not_word("foo bar");

        // URL case
        assert_word("github.com");
        assert_not_word("zed-industries/zed");
        assert_not_word("zed-industries\\zed");
        assert_not_word("a=1&b=2");
        assert_not_word("foo?b=2");

        // Latin-1 Supplement
        assert_word("ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏ");
        // Latin Extended-A
        assert_word("ĀāĂ㥹ĆćĈĉĊċČčĎď");
        // Latin Extended-B
        assert_word("ƀƁƂƃƄƅƆƇƈƉƊƋƌƍƎƏ");
        // Cyrillic
        assert_word("АБВГДЕЖЗИЙКЛМНОП");
        // Vietnamese (https://github.com/zed-industries/zed/issues/23245)
        assert_word("ThậmchíđếnkhithuachạychúngcònnhẫntâmgiếtnốtsốđôngtùchínhtrịởYênBáivàCaoBằng");
        // Bengali
        assert_word("গিয়েছিলেন");
        assert_word("ছেলে");
        assert_word("হচ্ছিল");

        // non-word characters
        assert_not_word("你好");
        assert_not_word("안녕하세요");
        assert_not_word("こんにちは");
        assert_not_word("😀😁😂");
        assert_not_word("()[]{}<>");

        // Non-breaking ("Glue") characters, see https://www.unicode.org/reports/tr14/
        // (https://github.com/zed-industries/zed/issues/59664)
        assert_word("\u{202F}"); // NNBSP " "
        assert_word("\u{00A0}"); // NBSP " "
        assert_word("\u{2011}"); // NBH "‑"
    }

    // For compatibility with the test macro
    #[cfg(target_os = "macos")]
    use crate as gpui;

    // These seem to vary wildly based on the text system.
    #[cfg(target_os = "macos")]
    #[crate::test]
    fn test_wrap_shaped_line(cx: &mut TestAppContext) {
        cx.update(|cx| {
            let text_system = WindowTextSystem::new(cx.text_system().clone());

            let normal = TextRun {
                len: 0,
                font: font("Helvetica"),
                color: Default::default(),
                underline: Default::default(),
                ..Default::default()
            };
            let bold = TextRun {
                len: 0,
                font: font("Helvetica").bold(),
                ..Default::default()
            };

            let text = SharedString::from("aa bbb cccc ddddd eeee");
            let lines = text_system
                .shape_text(
                    text,
                    px(16.),
                    &[
                        normal.with_len(4),
                        bold.with_len(5),
                        normal.with_len(6),
                        bold.with_len(1),
                        normal.with_len(7),
                    ],
                    Some(px(72.)),
                    None,
                )
                .unwrap();

            assert_eq!(
                lines[0].layout.wrap_boundaries(),
                &[
                    WrapBoundary {
                        run_ix: 0,
                        glyph_ix: 7
                    },
                    WrapBoundary {
                        run_ix: 0,
                        glyph_ix: 12
                    },
                    WrapBoundary {
                        run_ix: 0,
                        glyph_ix: 18
                    }
                ],
            );
        });
    }

    #[test]
    fn test_multiline_truncation_fits_within_wrapped_lines() {
        let mut wrapper = build_wrapper();

        // With .ZedMono at 16px, each char is 9.6px wide.
        // wrap_width = 72px fits ~7 chars per line.
        //
        // "aa bbbbbb cccccc dddddd eeee ffff" with wrap_width=72px wraps as:
        //   Line 1: "aa "       (28.8px, wraps because "bbbbbb" won't fit)
        //   Line 2: "bbbbbb "   (67.2px)
        //   Line 3: "cccccc "   (67.2px)
        //   ...
        //
        // truncate_wrapped_line should wrap first to find line 2 starts at
        // "bbbbbb...", then truncate only that line to fit with ellipsis.
        let text: &str = "aa bbbbbb cccccc dddddd eeee ffff";
        let wrap_width = px(72.);
        let max_lines: usize = 2;

        let runs = generate_test_runs(&[text.len()]);
        let (truncated, _) = wrapper.truncate_wrapped_line(
            text.into(),
            wrap_width,
            max_lines,
            "\u{2026}",
            &runs,
            TruncateFrom::End,
        );

        // The truncated text, when wrapped, must fit within max_lines lines.
        let wrap_count = wrapper
            .wrap_line(&[LineFragment::text(&truncated)], wrap_width)
            .count();

        assert!(
            wrap_count < max_lines,
            "Truncated text '{}' wraps into {} visual lines, expected at most {}",
            truncated,
            wrap_count + 1,
            max_lines
        );

        // The truncated text should end with the ellipsis.
        assert!(
            truncated.ends_with('\u{2026}'),
            "Truncated text '{}' should end with ellipsis",
            truncated
        );
    }

    #[test]
    fn test_multiline_truncation_no_truncation_needed() {
        let mut wrapper = build_wrapper();

        // Text that fits in 2 lines shouldn't be truncated.
        // Line 1: "aa bbb " (67.2px), Line 2: "cccccc" (57.6px)
        let text: &str = "aa bbb cccccc";
        let wrap_width = px(72.);
        let max_lines: usize = 2;

        let runs = generate_test_runs(&[text.len()]);
        let (result, _) = wrapper.truncate_wrapped_line(
            text.into(),
            wrap_width,
            max_lines,
            "\u{2026}",
            &runs,
            TruncateFrom::End,
        );

        assert_eq!(
            result.as_ref(),
            text,
            "Text that fits should not be modified"
        );
    }

    #[test]
    fn test_multiline_truncation_three_lines() {
        let mut wrapper = build_wrapper();

        let text: &str = "aa bbb cccc ddddd eeee ffff gggg hhhh iiii jjjj";
        let wrap_width = px(72.);
        let max_lines: usize = 3;

        let runs = generate_test_runs(&[text.len()]);
        let (truncated, _) = wrapper.truncate_wrapped_line(
            text.into(),
            wrap_width,
            max_lines,
            "\u{2026}",
            &runs,
            TruncateFrom::End,
        );

        let wrap_count = wrapper
            .wrap_line(&[LineFragment::text(&truncated)], wrap_width)
            .count();

        assert!(
            wrap_count < max_lines,
            "Truncated text '{}' wraps into {} visual lines, expected at most {}",
            truncated,
            wrap_count + 1,
            max_lines
        );

        assert!(
            truncated.ends_with('\u{2026}'),
            "Truncated text '{}' should end with ellipsis",
            truncated
        );
    }

    #[test]
    fn test_multiline_truncation_with_newlines() {
        let mut wrapper = build_wrapper();

        // "hello\nworld foo bar baz" with line_clamp(2):
        // shape_text splits on \n, giving physical lines "hello" and
        // "world foo bar baz". The newline consumes line 1, so the
        // second physical line should be truncated on line 2.
        let text: &str = "hello\nworld foo bar baz";
        let wrap_width = px(72.);
        let max_lines: usize = 2;

        let runs = generate_test_runs(&[text.len()]);
        let (truncated, _) = wrapper.truncate_wrapped_line(
            text.into(),
            wrap_width,
            max_lines,
            "\u{2026}",
            &runs,
            TruncateFrom::End,
        );

        // The newline should be preserved.
        let parts: Vec<&str> = truncated.splitn(2, '\n').collect();
        assert_eq!(
            parts.len(),
            2,
            "Newline should be preserved: '{}'",
            truncated
        );
        assert_eq!(parts[0], "hello");

        // The second line should fit within wrap_width and end with ellipsis.
        let second_line_width: Pixels = parts[1].chars().map(|c| wrapper.width_for_char(c)).sum();
        assert!(
            second_line_width <= wrap_width,
            "Second line '{}' ({}px) exceeds wrap_width ({}px)",
            parts[1],
            second_line_width,
            wrap_width
        );
        assert!(
            truncated.ends_with('\u{2026}'),
            "Should end with ellipsis: '{}'",
            truncated
        );
    }

    #[test]
    fn test_multiline_truncation_newline_on_last_line() {
        let mut wrapper = build_wrapper();

        // "hello\nworld\nmore" with line_clamp(2):
        // Line 1: "hello", Line 2: "world" — but there's a third line,
        // so line 2 should be truncated with ellipsis.
        let text: &str = "hello\nworld\nmore";
        let wrap_width = px(72.);
        let max_lines: usize = 2;

        let runs = generate_test_runs(&[text.len()]);
        let (truncated, _) = wrapper.truncate_wrapped_line(
            text.into(),
            wrap_width,
            max_lines,
            "\u{2026}",
            &runs,
            TruncateFrom::End,
        );

        let parts: Vec<&str> = truncated.splitn(2, '\n').collect();
        assert_eq!(parts[0], "hello");
        assert!(
            truncated.ends_with('\u{2026}'),
            "Should end with ellipsis since there's more content: '{}'",
            truncated
        );
    }

    #[test]
    fn test_truncate_line_middle() {
        let mut wrapper = build_wrapper();

        // No truncation when text fits within a very wide budget.
        let short_text = "hello world";
        let runs = generate_test_runs(&[short_text.len()]);
        let (result, result_runs) = wrapper.truncate_line(
            short_text.into(),
            px(10000.),
            "…",
            &runs,
            TruncateFrom::Middle,
        );
        assert_eq!(result.as_ref(), short_text);
        assert_eq!(result_runs.len(), 1);
        assert_eq!(result_runs[0].len, short_text.len());

        // Basic middle truncation: long string with px(100.) budget.
        let long_text = "abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz";
        let runs = generate_test_runs(&[long_text.len()]);
        let (result, _result_runs) =
            wrapper.truncate_line(long_text.into(), px(100.), "…", &runs, TruncateFrom::Middle);
        assert!(
            result.contains('…'),
            "Middle-truncated result should contain '…', got: '{}'",
            result
        );
        assert!(
            result.chars().count() < long_text.chars().count(),
            "Middle-truncated result should be shorter than original"
        );
        assert_eq!(
            result.chars().next(),
            long_text.chars().next(),
            "Result should start with the same first character as original"
        );
        assert_eq!(
            result.chars().last(),
            long_text.chars().last(),
            "Result should end with the same last character as original"
        );

        // Degenerate case: budget so narrow that middle truncation cannot find a valid split.
        // Still show the truncation affix instead of returning the original overflowing text.
        let text = "abcdef";
        let runs = generate_test_runs(&[text.len()]);
        let (result, result_runs) =
            wrapper.truncate_line(text.into(), px(1.), "…", &runs, TruncateFrom::Middle);
        assert_eq!(result.as_ref(), "…");
        assert_eq!(result_runs.len(), 1);
        assert_eq!(result_runs[0].len, "…".len());

        // Run adjustment correctness: multiple runs across the string.
        // Verify that the returned runs' lengths sum to result.len().
        let multi_run_text = "abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz";
        let run_lens = [20, 20, multi_run_text.len() - 40];
        let runs = generate_test_runs(&run_lens);
        let (result, result_runs) = wrapper.truncate_line(
            multi_run_text.into(),
            px(100.),
            "…",
            &runs,
            TruncateFrom::Middle,
        );
        let total_run_len: usize = result_runs.iter().map(|r| r.len).sum();
        assert_eq!(
            total_run_len,
            result.len(),
            "Sum of run lengths ({}) should equal result byte length ({})",
            total_run_len,
            result.len()
        );
    }

    #[test]
    fn test_multiline_truncation_trailing_newline() {
        let mut wrapper = build_wrapper();

        // "hello\nworld\n" with line_clamp(2):
        // The trailing newline has no content after it, so no ellipsis.
        let text: &str = "hello\nworld\n";
        let wrap_width = px(72.);
        let max_lines: usize = 2;

        let runs = generate_test_runs(&[text.len()]);
        let (result, _) = wrapper.truncate_wrapped_line(
            text.into(),
            wrap_width,
            max_lines,
            "\u{2026}",
            &runs,
            TruncateFrom::End,
        );

        assert!(
            !result.ends_with('\u{2026}'),
            "Trailing newline with no content should not add ellipsis: '{}'",
            result
        );
    }

    #[test]
    fn test_multiline_truncation_newline_fits_exactly() {
        let mut wrapper = build_wrapper();

        // "hello\nworld" with line_clamp(2):
        // Exactly 2 lines, no truncation needed.
        let text: &str = "hello\nworld";
        let wrap_width = px(72.);
        let max_lines: usize = 2;

        let runs = generate_test_runs(&[text.len()]);
        let (result, _) = wrapper.truncate_wrapped_line(
            text.into(),
            wrap_width,
            max_lines,
            "\u{2026}",
            &runs,
            TruncateFrom::End,
        );

        assert_eq!(
            result.as_ref(),
            text,
            "Text that fits exactly should not be modified: '{}'",
            result
        );
    }
}