makeover_immediate/

table.rs

//! Columns, narrowing, cell parts and the sort caret, over `egui_extras`.
//!
//! `makeover-webview`'s `list` module and `makeover-tui`'s `table` in the shape
//! immediate mode allows. It owns the same four things: which columns exist, how
//! wide they are, which ones survive a narrow viewport, and what each part of a
//! cell is. It does not own what goes in a cell, which here is not a policy but
//! a fact of the mode: a cell's contents are drawn by the app's own closure, the
//! way [`group`](crate::group) already takes one per field.
//!
//! # Why `egui_extras` and not egui
//!
//! egui itself has no table. [`egui::Grid`] gives no per-column sizing, no
//! sticky header and no scroll sync, which is why audiofiles reached for
//! `egui_extras::TableBuilder` rather than building on `Grid`. Writing a third
//! answer here would be reimplementing that crate worse, so this is a mapping
//! layer over it.
//!
//! It is the first dependency this crate has taken beyond egui itself, and it
//! moves in lockstep with egui's own version, which is the cost worth naming.
//!
//! # What immediate mode costs the narrowing
//!
//! The terminal renderer measures a [`Width::Content`] column from its cells,
//! because it holds every cell before it draws any. Here the cells do not exist
//! until the app's closure runs, so nothing can be measured before the layout is
//! decided.
//!
//! That splits the answer in two, and both halves are honest:
//!
//! - **Sizing** hands a content column to
//!   [`egui_extras::Column::auto`], which measures it and holds the result
//!   between frames. This is better than the terminal gets, not worse.
//! - **Narrowing** cannot wait for that, so it budgets every column at its
//!   declared [`floor`](Column::floor), in `ch` of the body face. A column that
//!   turns out wider than its floor is still drawn; it is the *decision to drop*
//!   that uses the declared number, and it is the number the terminal counts in
//!   cells and the webview hides a column under, so the three drop together.
//!
//! # The table model
//!
//! Wiki `table-model`, drawn the way `makeover-webview` draws it, since egui
//! paints the same pixels a browser does: a raised ground inside a hairline
//! frame, the header a sunken strip over a `bevel-dark` edge in secondary
//! capitals, rows 45 points tall with a hairline between them, a stripe on
//! every second row and a tone under the pointer. A table holding a
//! [`ColumnKind::Code`] column keeps the frame and the header and drops the
//! stripe, the hairlines and the tall row.
//!
//! The row fills are painted here rather than by egui_extras, for two reasons
//! the crate cannot be configured past. Its stripe falls on the first row where
//! the model's falls on the second, and its selection repaints the row's text
//! in the selection stroke, which loses a failed row's red on exactly the row
//! the user picked. A selected row takes `row-selected` behind its text and
//! nothing else.
//!
//! # Why positions are the bug
//!
//! Carried from the other two renderers, because the mistake is not a CSS
//! mistake and not a terminal one. goingson hides its mobile columns with
//! `nth-child(n+5)` against a seven-column table; insert a column left of the
//! cut and the wrong one disappears, silently. A renderer narrows by raising a
//! cutoff and never by counting.

use crate::Palette;
use egui::{Response, RichText, Sense, Ui};
use egui_extras::{Column as Track, TableBuilder};
use makeover_layout::{CellPart, Column, ColumnKind, Priority, Sort, Width};

/// The cutoffs, weakest first.
///
/// [`Priority`] is `#[non_exhaustive]` and a tier added upstream has to be added
/// here in its place in the sequence, or a table will never narrow to it. Grep
/// this when adopting a new `makeover-layout`; `makeover-tui` carries the same
/// list for the same reason, and the two have to agree or a description narrows
/// differently in a window than in a terminal.
const CUTOFFS: [Priority; 3] = [Priority::Optional, Priority::Secondary, Priority::Essential];

/// The lengths the description deferred, in points.
///
/// [`Width`] says `Content`, `Fixed` or `Fill` and carries no magnitude, because
/// a magnitude is an answer for one renderer and the description is read by
/// three. The other two renderers hold this same type over CSS lengths and over
/// terminal cells.
#[derive(Debug, Clone, Copy, Default)]
pub struct Sizing<'a> {
    /// `(column name, points)`. The track for a [`Width::Fixed`] column, the
    /// floor for a [`Width::Fill`] one, and the narrowing budget for a
    /// [`Width::Content`] one.
    pub lengths: &'a [(&'a str, f32)],
    /// Used for a column with no entry above.
    pub fallback: f32,
}

impl Sizing<'_> {
    /// The length for a named column.
    fn length_for(&self, name: &str) -> f32 {
        self.lengths
            .iter()
            .find(|(column, _)| *column == name)
            .map_or(self.fallback, |(_, length)| *length)
    }
}

/// The tones and metrics a table draws with.
///
/// Metrics only, and the tones come from [`Palette`]. That is the division this
/// crate already draws: [`FieldStyle`](crate::FieldStyle) carries gaps and a
/// marker while the colours stay in the palette, and a table's colours are the
/// palette's `content`, `content_muted` and `action` rather than six new ones.
/// `makeover-tui` splits it the other way round because its palette carries no
/// text tones at all.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct TableStyle {
    /// The height of the heading row.
    pub header_height: f32,
    /// The height of a body row: the model's 45, `--row-block` at
    /// `makeover-geometry`'s base.
    pub row_height: f32,
    /// The height of a row in a table holding code, which is one line of
    /// source rather than a record.
    pub code_row_height: f32,
    /// The ground between the table's frame and the cells at either end of a
    /// row: the webview's `gap-group`, which pads both ends of a row.
    pub edge_padding: f32,
    /// The caret drawn after the heading of an ascending column.
    ///
    /// Defaults to [`Sort::glyph`], which is where the spelling lives now:
    /// three renderers holding the same literal agreed by coincidence. Bare,
    /// with no leading space -- the gap is [`heading`]'s, written once for all
    /// three states rather than baked into two strings and forgotten in the
    /// third.
    pub ascending: &'static str,
    /// Drawn after the heading of a descending column.
    pub descending: &'static str,
    /// Whether the user can drag the divider between two columns.
    ///
    /// The one knob that is not a metric. Not every setting egui_extras has
    /// becomes a field here: a sticky heading is what `TableBuilder::header`
    /// does and there is no version that does not, and the stripe is the table
    /// model's at every host, so a knob for either would offer a choice this
    /// renderer cannot make. Off by default: the description has no word for
    /// resizing, so a default that turned it on would be this renderer adding a
    /// claim the other two cannot make.
    ///
    /// It does not fight the narrowing. A drag moves a track for the frames it
    /// is held; [`cutoff_for`] still decides which columns exist, off each
    /// column's declared [`floor`](Column::floor), so a resize can never drop a
    /// column.
    pub resizable: bool,
}

impl Default for TableStyle {
    fn default() -> Self {
        Self {
            header_height: 32.0,
            row_height: 45.0,
            code_row_height: 20.0,
            edge_padding: 12.0,
            ascending: Sort::Ascending.glyph(),
            descending: Sort::Descending.glyph(),
            resizable: false,
        }
    }
}

/// The body's own facts for this frame: how many rows, which are selected, and
/// which one to bring into view.
///
/// Held apart from [`TableStyle`] because none of it is style and none of it
/// survives the frame: a row count changes when a folder does, a selection when
/// the user clicks, and a scroll request exists for exactly one frame. Held
/// apart from the [`Column`] slice because none of it is description either.
/// The description says what a table *is*, and this says what it holds right
/// now.
///
/// Both of the optional fields are here rather than left to the app because
/// egui_extras answers them on a handle the app never sees: `set_selected` is a
/// method on the row, and `scroll_to_row` a method on the builder, and this
/// crate owns both. That is the same reason [`cell`] exists.
#[derive(Default)]
pub struct Body<'a> {
    /// How many rows to draw.
    pub rows: usize,
    /// Whether a row is selected, by index.
    ///
    /// A predicate rather than a set, so an app whose selection is a range, a
    /// bitmap or a single index does not have to build a collection to be asked.
    /// `None` is a table no row of which is selected, which is not the same
    /// claim as a predicate that always answers false and costs nothing to make.
    pub selected: Option<&'a dyn Fn(usize) -> bool>,
    /// A row to bring into view this frame.
    ///
    /// Set it from a request the app then clears, the way a keyboard cursor
    /// moving off-screen raises one: held rather than taken, it would fight
    /// every scroll the user makes with the mouse.
    pub scroll_to: Option<usize>,
}

impl std::fmt::Debug for Body<'_> {
    // Hand-written because `selected` is a closure and `#[derive(Debug)]` will
    // not have it. What is worth printing is whether one was supplied.
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Body")
            .field("rows", &self.rows)
            .field("selected", &self.selected.is_some())
            .field("scroll_to", &self.scroll_to)
            .finish()
    }
}

/// The colour a cell of this part takes.
///
/// [`CellPart`] is `#[non_exhaustive]`, and a member added upstream lands on
/// `content`: a part this renderer has not learned draws as text, which is a
/// cell rendering plainly rather than a build that stops. Grep this when
/// adopting a new `makeover-layout`.
#[must_use]
pub const fn part_color(part: Option<CellPart>, palette: &Palette) -> egui::Color32 {
    match part {
        // A token paints its own background and carries its own tone. What is
        // set here is what shows between them, not what paints them.
        Some(CellPart::Tokens) => palette.content_muted,
        // The drift `CellPart` exists to end: a control in a cell inheriting the
        // cell's text colour. Both of these take the action intent instead.
        Some(CellPart::Actions | CellPart::Link) => palette.action,
        _ => palette.content,
    }
}

/// Draw a cell's contents with the tone its part takes.
///
/// The app calls this inside its own cell closure, wrapping whatever it draws.
/// A scoping function rather than a parameter on [`table`], for the reason
/// [`frame`](crate::frame) is one: the part is a property of the cell, the cell
/// does not exist until the closure runs, and immediate mode has no cascade to
/// carry the answer down on its own. This is the cascade, for one scope.
///
/// ```no_run
/// # use makeover_layout::CellPart;
/// # let palette: makeover_immediate::Palette = unimplemented!();
/// # let ui: &mut egui::Ui = unimplemented!();
/// makeover_immediate::table::cell(ui, Some(CellPart::Link), &palette, |ui| {
///     ui.label("opens the item");
/// });
/// ```
pub fn cell<R>(
    ui: &mut Ui,
    part: Option<CellPart>,
    palette: &Palette,
    add_contents: impl FnOnce(&mut Ui) -> R,
) -> R {
    let restore = ui.visuals().override_text_color;
    ui.visuals_mut().override_text_color = Some(part_color(part, palette));
    let out = add_contents(ui);
    ui.visuals_mut().override_text_color = restore;
    out
}

/// The heading, in capitals, with the caret if the table is ordered by this
/// column.
///
/// Capitals because the header strip's label is set that way at every host.
/// A column [`sorted`](Column::sorted) but not [`sortable`](Column::sortable)
/// still gets its caret. Both combinations mean something, which is why the
/// description holds the two fields apart: a list ordered by a key the user
/// cannot change is a real thing, and the caret is how it says so.
#[must_use]
pub fn heading(column: &Column<'_>, style: &TableStyle) -> String {
    let caret = match column.sorted {
        Some(Sort::Ascending) => style.ascending,
        Some(Sort::Descending) => style.descending,
        // Sortable and not sorted draws the idle mark, in the ascending
        // spelling because that is the direction a first press takes. What
        // separates it from the column in force is the tone, which is
        // [`press`]'s to pick.
        None if column.sortable => style.ascending,
        None => return column.name.to_uppercase(),
    };
    format!("{} {caret}", column.name.to_uppercase())
}

/// Whether the columns kept at `cutoff` fit in `width`.
///
/// Budgeted at each column's declared [`floor`](Column::floor) in `ch`, turned
/// into points by `ch`, the width of one figure in the face the table draws
/// in. Nothing can be measured before the app's closure has drawn a cell, and
/// nothing needs to be: the floor is the number the terminal counts in cells
/// and the webview hides a column under, so all three drop at one declared
/// width.
fn fits(columns: &[Column<'_>], ch: f32, edge: f32, cutoff: Priority, width: f32) -> bool {
    columns
        .iter()
        .filter(|c| c.kept_at(cutoff))
        .map(|c| f32::from(c.floor()) * ch + 2.0 * edge)
        .sum::<f32>()
        <= width
}

/// The weakest cutoff whose columns fit in `width`.
///
/// Raised until the layout fits, and never past [`Priority::Essential`]: the
/// essential columns are what makes a row identify itself, so a window too
/// narrow for them gets them squeezed rather than dropped. Nothing here counts
/// positions, so which column drops is a property of the column.
#[must_use]
pub fn cutoff_for(columns: &[Column<'_>], ch: f32, edge: f32, width: f32) -> Priority {
    for cutoff in CUTOFFS {
        if fits(columns, ch, edge, cutoff, width) {
            return cutoff;
        }
    }
    Priority::Essential
}

/// The track for one column.
fn track(column: &Column<'_>, sizing: &Sizing<'_>) -> Track {
    match column.width {
        // The one place immediate mode beats the terminal: egui_extras measures
        // this and remembers it between frames, where `makeover-tui` has to walk
        // the cells itself.
        Width::Content => Track::auto(),
        Width::Fixed => Track::exact(sizing.length_for(column.name)),
        // Includes a width added to the description since this renderer was
        // built. Taking the slack above a floor is the behaviour that makes no
        // claim, which is the same fallback the webview renderer's `auto` track
        // is chosen to be.
        _ => Track::remainder().at_least(sizing.length_for(column.name)),
    }
}

/// A described table, narrowed for the width available.
///
/// `draw` is called once per cell of each kept column, in column order, for each
/// of [`Body::rows`] rows. Taking a closure rather than a slice of contents is
/// what keeps the app's own data borrowed one cell at a time, which is
/// [`group`](crate::group)'s reasoning and immediate mode's habit.
///
/// `body` is borrowed immutably and `draw` is `FnMut`, which is the split a
/// caller has to plan for: a selection read by [`Body::selected`] cannot be the
/// same value `draw` mutates. Snapshot it before the call. That is not this
/// crate imposing anything. It is the borrow the app already takes when it
/// clones its row list to hand egui a closure.
///
/// Returns the sortable column whose heading was pressed this frame, if any. The
/// app owns the ordering, so this reports the press and changes nothing: what a
/// press *calls* is an address, and the description names none. That is
/// [`Column::sortable`]'s own documented split.
///
/// A heading is only pressable when its column says
/// [`sortable`](Column::sortable). A column sorted by a key the user cannot
/// change still draws its caret and does not answer.
pub fn table<'a>(
    ui: &mut Ui,
    columns: &'a [Column<'a>],
    body: &Body<'_>,
    sizing: &Sizing<'_>,
    palette: &Palette,
    style: &TableStyle,
    mut draw: impl FnMut(&mut Ui, &'a Column<'a>, usize),
) -> Option<&'a Column<'a>> {
    // One `ch` in the face the cells are drawn in, which is what a declared
    // floor counts.
    let ch = {
        let font = egui::TextStyle::Body.resolve(ui.style());
        ui.fonts_mut(|fonts| fonts.glyph_width(&font, '0'))
    };
    let cutoff = cutoff_for(columns, ch, style.edge_padding, ui.available_width());
    let kept: Vec<&'a Column<'a>> = columns.iter().filter(|c| c.kept_at(cutoff)).collect();

    // egui_extras panics on a table with no tracks, and a description whose
    // every column dropped is reachable: `kept_at` keeps the essential ones, and
    // a table described with none at all has nothing to keep.
    if kept.is_empty() {
        return None;
    }

    let code = kept.iter().any(|column| column.kind == ColumnKind::Code);
    let row_height = if code {
        style.code_row_height
    } else {
        style.row_height
    };
    // The whole width the table takes, which is the frame's: a cell only knows
    // its own track. The fills stop a stroke's width inside it, so no row
    // paints over the frame.
    let outer = ui.available_rect_before_wrap();
    let across = outer.x_range();
    let fills = egui::Rangef::new(across.min + 1.0, across.max - 1.0);
    let top = ui.cursor().top();
    // Reserved before the table draws, so the ground lands under it once the
    // table's height is known.
    let ground = ui.painter().add(egui::Shape::Noop);
    // How far down the header and the drawn rows reach, which is the frame's
    // bottom. Not the scroll area's rect, which is the room the table was
    // offered rather than the room it took.
    let reach = std::cell::Cell::new(top);
    let inner = outer.shrink2(egui::vec2(style.edge_padding, 0.0));
    // Written through a Cell rather than returned, because egui_extras hands the
    // header and the body their own closures and neither can return a value past
    // the other.
    let pressed = std::cell::Cell::new(None::<&'a Column<'a>>);

    let viewport = ui
        .scope_builder(egui::UiBuilder::new().max_rect(inner), |ui| {
            let mut builder = TableBuilder::new(ui)
                .striped(false)
                .resizable(style.resizable)
                // Not a knob, because there is no second honest answer: a cell's
                // contents sit on the row's centre line. CSS says `vertical-align:
                // middle` and a terminal row is one line tall, so a field offering the
                // choice would be offering one only this renderer could take. egui's own
                // default is top-aligned, which is why it has to be said at all.
                .cell_layout(egui::Layout::left_to_right(egui::Align::Center));
            for column in &kept {
                builder = builder.column(track(column, sizing));
            }
            if let Some(row) = body.scroll_to {
                builder = builder.scroll_to_row(row, None);
            }

            builder
                .header(style.header_height, |mut header| {
                    for (at, column) in kept.iter().enumerate() {
                        header.col(|ui| {
                            if at == 0 {
                                strip(ui, fills, &reach, palette);
                            }
                            placed(ui, column, |ui| {
                                if press(ui, column, palette, style) {
                                    pressed.set(Some(column));
                                }
                            });
                        });
                    }
                })
                .body(|table_body| {
                    table_body.rows(row_height, body.rows, |mut row| {
                        let index = row.index();
                        let selected = body.selected.is_some_and(|selected| selected(index));
                        for (at, column) in kept.iter().enumerate() {
                            row.col(|ui| {
                                // In the first cell and across the whole row, before
                                // any cell's contents: a selection marks the row, and
                                // a fill per cell would leave the gaps unpainted.
                                if at == 0 {
                                    let row = Row {
                                        index,
                                        selected,
                                        code,
                                    };
                                    ground_row(ui, fills, row, &reach, palette);
                                }
                                placed(ui, column, |ui| draw(ui, column, index));
                            });
                        }
                    });
                })
                .inner_rect
        })
        .inner;

    let bottom = reach.get().min(viewport.bottom());
    let frame = egui::Rect::from_x_y_ranges(across, top..=bottom);
    ui.painter().set(
        ground,
        egui::epaint::RectShape::filled(frame, 0, palette.raised),
    );
    ui.painter().rect_stroke(
        frame,
        0,
        egui::Stroke::new(1.0, palette.row_rule),
        egui::StrokeKind::Inside,
    );

    pressed.get()
}

/// What decides one body row's fill.
#[derive(Clone, Copy)]
struct Row {
    index: usize,
    selected: bool,
    code: bool,
}

/// The rect a row's fill covers: the whole table's width, and the cell's
/// height with the half of the spacing either side that egui_extras leaves
/// between rows.
fn row_rect(ui: &Ui, across: egui::Rangef) -> egui::Rect {
    let half = 0.5 * ui.spacing().item_spacing.y;
    let cell = ui.max_rect();
    egui::Rect::from_x_y_ranges(across, (cell.top() - half)..=(cell.bottom() + half))
}

/// The header strip: sunken, with the `bevel-dark` edge under it.
fn strip(ui: &Ui, across: egui::Rangef, reach: &std::cell::Cell<f32>, palette: &Palette) {
    let rect = row_rect(ui, across);
    reach.set(reach.get().max(rect.bottom()));
    ui.painter().rect_filled(rect, 0, palette.sunken);
    ui.painter().hline(
        across,
        rect.bottom(),
        egui::Stroke::new(1.0, palette.bevel_dark),
    );
}

/// One body row's fill and the hairline above it.
///
/// Selected, then hovered, then the stripe on every second row, and the first
/// of those that holds is the fill. A table holding code takes the selection
/// and the hover and neither the stripe nor the hairline, which break the
/// reading of source one line to a row.
fn ground_row(
    ui: &Ui,
    across: egui::Rangef,
    Row {
        index,
        selected,
        code,
    }: Row,
    reach: &std::cell::Cell<f32>,
    palette: &Palette,
) {
    let rect = row_rect(ui, across);
    reach.set(reach.get().max(rect.bottom()));
    let fill = if selected {
        Some(palette.row_selected)
    } else if ui.rect_contains_pointer(rect) {
        Some(palette.row_hover)
    } else if !code && index % 2 == 1 {
        Some(palette.row_stripe)
    } else {
        None
    };
    if let Some(fill) = fill {
        ui.painter().rect_filled(rect, 0, fill);
    }
    if !code && index > 0 {
        ui.painter()
            .hline(across, rect.top(), egui::Stroke::new(1.0, palette.row_rule));
    }
}

/// A cell laid out the way its column's kind says, wiki `table-model`.
///
/// Alignment is the kind fact this renderer acts on. A number or actions
/// column runs right to left, on the row's centre line like every cell, and
/// its heading does the same so the label sits over its figures. The face and
/// the figures a kind names are the caller's, who draws the cell's contents.
fn placed(ui: &mut Ui, column: &Column<'_>, add: impl FnOnce(&mut Ui)) {
    if column.kind.aligns_end() {
        ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), add);
    } else {
        add(ui);
    }
}

/// What a heading's caret is drawn in.
///
/// Three states (wiki `three-tone-convention`), carried by the caret as the
/// webview carries them: the column in force takes content, a column offering
/// to reorder takes secondary, and a column that is not a control draws no
/// caret. The label is the strip's own secondary ink in every state.
///
/// The offering state may not take `content_muted`, which is what
/// [`State::Disabled`](makeover_layout::State::Disabled) resolves to: a heading
/// the user can press would be claiming it will not answer.
fn caret_color(column: &Column<'_>, palette: &Palette) -> egui::Color32 {
    match column.sorted {
        Some(_) => palette.content,
        None => palette.content_secondary,
    }
}

/// One heading, and whether it was pressed.
fn press(ui: &mut Ui, column: &Column<'_>, palette: &Palette, style: &TableStyle) -> bool {
    // The strip's type: small, strong and tracked, as the webview sets it, with
    // the caret in its own run so it can take its own tone.
    let size = egui::TextStyle::Small.resolve(ui.style()).size;
    let heading = heading(column, style);
    let label_len = column.name.to_uppercase().len();
    let mut job = egui::text::LayoutJob::default();
    RichText::new(&heading[..label_len])
        .color(palette.content_secondary)
        .small()
        .strong()
        .extra_letter_spacing(0.06 * size)
        .append_to(
            &mut job,
            ui.style(),
            egui::FontSelection::Default,
            egui::Align::Center,
        );
    if heading.len() > label_len {
        RichText::new(&heading[label_len..])
            .color(caret_color(column, palette))
            .small()
            .append_to(
                &mut job,
                ui.style(),
                egui::FontSelection::Default,
                egui::Align::Center,
            );
    }
    let text = job;
    if !column.sortable {
        // Not sensed. A heading a user cannot press must not look like one they
        // can, which is the affordance `Column::sortable` exists to carry, and
        // the missing caret is half of saying so.
        ui.label(text);
        return false;
    }
    let response: Response = ui
        .add(egui::Label::new(text).sense(Sense::click()))
        .on_hover_cursor(egui::CursorIcon::PointingHand);
    // Announced as the control it is, rather than as the `Label` it is drawn
    // with. egui maps a `Label` to `Role::Label` whatever it senses, so until
    // 2026-08-22 a screen reader was told this was static text and a user who
    // could not see the pointer change had no way to know the table sorts.
    // The same argument the comment above makes about affordance, made about
    // the half of the interface that is not pixels.
    //
    // The name is the column's own, not `heading`'s: the caret is a rendering of
    // `Column::sorted`, and reading a triangle aloud after every heading is
    // noise. Which column is in force is a fact a client should get from the
    // sort state, and egui has nowhere to put that yet -- worth revisiting if it
    // grows a sort field on `WidgetInfo`.
    response.widget_info(|| {
        egui::WidgetInfo::labeled(egui::WidgetType::Button, ui.is_enabled(), column.name)
    });
    response.clicked()
}

#[cfg(test)]
mod tests {
    use super::*;
    use makeover_layout::ColumnKind;

    /// What the accessibility tree says a heading row drew.
    ///
    /// egui builds it from the `WidgetInfo` each widget reports, so this is
    /// what a screen reader would be handed rather than a second opinion.
    fn announced(draw: impl FnMut(&mut Ui)) -> Vec<(egui::accesskit::Role, String)> {
        let ctx = egui::Context::default();
        ctx.enable_accesskit();
        let mut draw = draw;
        let input = || egui::RawInput {
            screen_rect: Some(egui::Rect::from_min_size(
                egui::Pos2::ZERO,
                egui::vec2(800.0, 600.0),
            )),
            ..Default::default()
        };
        let _ = ctx.run_ui(input(), &mut draw);
        let out = ctx.run_ui(input(), &mut draw);
        out.platform_output
            .accesskit_update
            .expect("accesskit is on")
            .nodes
            .iter()
            .map(|(_, node)| {
                (
                    node.role(),
                    node.label()
                        .or_else(|| node.value())
                        .unwrap_or_default()
                        .to_owned(),
                )
            })
            .collect()
    }

    #[test]
    fn a_sortable_heading_is_announced_as_something_you_press() {
        let column = Column {
            name: "Name",
            width: Width::Fill,
            priority: Priority::Essential,
            kind: ColumnKind::Text,
            min: None,
            sortable: true,
            sorted: Some(Sort::Ascending),
        };
        let p = palette();
        let drawn = announced(|ui| {
            press(ui, &column, &p, &TableStyle::default());
        });

        // The name is the column's, with no caret in it: the glyph renders
        // `Column::sorted` and is not part of what the control is called.
        assert!(
            drawn
                .iter()
                .any(|(role, name)| *role == egui::accesskit::Role::Button && name == "Name"),
            "{drawn:?}"
        );
    }

    #[test]
    fn a_heading_that_is_not_a_control_is_not_announced_as_one() {
        let column = Column {
            name: "Tags",
            width: Width::Fixed,
            priority: Priority::Optional,
            kind: ColumnKind::Text,
            min: None,
            sortable: false,
            sorted: None,
        };
        let p = palette();
        let drawn = announced(|ui| {
            press(ui, &column, &p, &TableStyle::default());
        });

        assert!(
            !drawn
                .iter()
                .any(|(role, _)| *role == egui::accesskit::Role::Button),
            "a heading with no sort answers nothing and must not claim to: {drawn:?}"
        );
    }
    use egui::Color32;

    fn palette() -> Palette {
        Palette {
            page: Color32::from_rgb(1, 1, 1),
            raised: Color32::from_rgb(2, 2, 2),
            overlay: Color32::from_rgb(3, 3, 3),
            well: Color32::from_rgb(4, 4, 4),
            sunken: Color32::from_rgb(5, 5, 5),
            bevel_light: Color32::WHITE,
            bevel_dark: Color32::BLACK,
            elevation: Color32::from_black_alpha(46),
            content: Color32::from_rgb(6, 6, 6),
            content_secondary: Color32::from_rgb(56, 56, 56),
            content_muted: Color32::from_rgb(7, 7, 7),
            action: Color32::from_rgb(8, 8, 8),
            danger: Color32::from_rgb(9, 9, 9),
            success: Color32::from_rgb(10, 10, 10),
            warning: Color32::from_rgb(11, 11, 11),
            info: Color32::from_rgb(12, 12, 12),
            border: Color32::from_rgb(200, 200, 200),
            info_surface: Color32::from_rgb(201, 201, 201),
            success_surface: Color32::from_rgb(202, 202, 202),
            warning_surface: Color32::from_rgb(203, 203, 203),
            danger_surface: Color32::from_rgb(204, 204, 204),
            row_stripe: Color32::from_rgb(205, 205, 205),
            row_hover: Color32::from_rgb(206, 206, 206),
            row_rule: Color32::from_rgb(207, 207, 207),
            row_selected: Color32::from_rgb(208, 208, 208),
        }
    }

    fn columns() -> Vec<Column<'static>> {
        vec![
            Column {
                name: "name",
                width: Width::Fill,
                priority: Priority::Essential,
                kind: ColumnKind::Text,
                min: None,
                sortable: true,
                sorted: Some(Sort::Ascending),
            },
            Column {
                name: "size",
                width: Width::Fixed,
                priority: Priority::Secondary,
                kind: ColumnKind::Text,
                min: None,
                sortable: true,
                sorted: None,
            },
            Column {
                name: "note",
                width: Width::Content,
                priority: Priority::Optional,
                kind: ColumnKind::Text,
                min: None,
                sortable: false,
                sorted: None,
            },
        ]
    }

    fn sizing() -> Sizing<'static> {
        Sizing {
            lengths: &[("name", 120.0), ("size", 60.0), ("note", 80.0)],
            fallback: 40.0,
        }
    }

    #[test]
    fn narrowing_drops_the_optional_column_first_and_the_essential_one_never() {
        // Floors of 16ch (the name fills), 8 and 8, at 10 points a ch, and 12
        // points of edge either side of each: 184, 104 and 104.
        let cols = columns();
        assert_eq!(cutoff_for(&cols, 10.0, 12.0, 392.0), Priority::Optional);
        assert_eq!(cutoff_for(&cols, 10.0, 12.0, 391.0), Priority::Secondary);
        assert_eq!(cutoff_for(&cols, 10.0, 12.0, 288.0), Priority::Secondary);
        assert_eq!(cutoff_for(&cols, 10.0, 12.0, 287.0), Priority::Essential);
        // Narrower than the essential column, which stays anyway.
        assert_eq!(cutoff_for(&cols, 10.0, 12.0, 10.0), Priority::Essential);
    }

    #[test]
    fn the_same_floors_drop_at_the_same_ch_count_as_a_terminal() {
        // A terminal counts one cell a ch. At one point a ch and no edge, the
        // cut falls on the floors alone, which is the number both other hosts
        // read, so a description narrows at one declared width everywhere.
        let cols = columns();
        assert_eq!(cutoff_for(&cols, 1.0, 0.0, 32.0), Priority::Optional);
        assert_eq!(cutoff_for(&cols, 1.0, 0.0, 31.0), Priority::Secondary);
        assert_eq!(cutoff_for(&cols, 1.0, 0.0, 24.0), Priority::Secondary);
        assert_eq!(cutoff_for(&cols, 1.0, 0.0, 23.0), Priority::Essential);
    }

    #[test]
    fn a_column_inserted_left_of_the_cut_does_not_change_what_drops() {
        // The goingson bug, as a test. `nth-child(n+5)` against a seven-column
        // table hides whatever lands at position five, so inserting a column
        // moves the cut onto a different column with nothing edited.
        //
        // Asserted at a fixed cutoff, because that is where the two ways of
        // addressing a column disagree. A narrower budget SHOULD drop more; what
        // must not change is which ones, for a given cutoff.
        let dropped = |cols: &[Column<'_>], cutoff| -> Vec<String> {
            cols.iter()
                .filter(|c| !c.kept_at(cutoff))
                .map(|c| c.name.to_owned())
                .collect()
        };
        let before = columns();
        let mut after = vec![Column {
            name: "mark",
            width: Width::Fixed,
            priority: Priority::Essential,
            kind: ColumnKind::Text,
            min: None,
            sortable: false,
            sorted: None,
        }];
        after.extend(columns());

        for cutoff in CUTOFFS {
            assert_eq!(dropped(&before, cutoff), dropped(&after, cutoff));
        }
        assert_eq!(dropped(&before, Priority::Secondary), vec!["note"]);
    }

    #[test]
    fn the_two_renderers_narrow_a_description_the_same_way() {
        // The cutoff ladder is duplicated in `makeover-tui` because neither
        // crate depends on the other, and duplication is what drifts. This is
        // the assertion that would catch it: the ladder is the description's
        // order, weakest first, and a tier added upstream belongs in both.
        assert_eq!(CUTOFFS.len(), 3);
        assert!(CUTOFFS.windows(2).all(|pair| pair[0] < pair[1]));
        assert_eq!(CUTOFFS[0], Priority::Optional);
        assert_eq!(CUTOFFS[2], Priority::Essential);
    }

    #[test]
    fn a_content_column_is_measured_by_egui_and_budgeted_by_its_floor() {
        // The split the module header names. The track defers to egui_extras,
        // which can measure; the narrowing cannot wait for that and uses the
        // declared floor. Both readings of the same column, and both honest.
        let cols = columns();
        let note = &cols[2];
        assert!(matches!(note.width, Width::Content));
        assert_eq!(note.floor(), 8, "undeclared, so the kind's floor");
        // Floors of 16, 8 and 8ch at 10 points, each with 12 points of edge
        // either side: 392 fits and 391 does not, whatever the cells turn out to
        // hold.
        assert!(fits(&cols, 10.0, 12.0, Priority::Optional, 392.0));
        assert!(!fits(&cols, 10.0, 12.0, Priority::Optional, 391.0));
    }

    #[test]
    fn a_column_with_no_length_of_its_own_takes_the_fallback() {
        let column = Column {
            name: "unlisted",
            width: Width::Fixed,
            priority: Priority::Essential,
            kind: ColumnKind::Text,
            min: None,
            sortable: false,
            sorted: None,
        };
        // The fallback sizes a track and nothing else: which columns exist is
        // the floor's to decide.
        assert!((sizing().length_for(column.name) - 40.0).abs() < f32::EPSILON);
    }

    #[test]
    fn the_parts_a_cell_can_be_are_coloured_apart() {
        // The drift `CellPart` exists to end: one colour for a whole cell paints
        // a control as though it were text.
        let p = palette();
        assert_eq!(part_color(Some(CellPart::Value), &p), p.content);
        assert_eq!(part_color(Some(CellPart::Tokens), &p), p.content_muted);
        assert_eq!(part_color(Some(CellPart::Actions), &p), p.action);
        assert_eq!(part_color(Some(CellPart::Link), &p), p.action);
        assert_ne!(part_color(Some(CellPart::Link), &p), p.content);
        // A cell mixing parts says nothing, and takes the text colour.
        assert_eq!(part_color(None, &p), p.content);
    }

    #[test]
    fn a_heading_carries_a_caret_when_it_is_ordered_by_or_offers_to_be() {
        let style = TableStyle::default();
        let cols = columns();
        assert_eq!(heading(&cols[0], &style), "NAME \u{25B2}");
        // Sortable and idle. It draws the mark a first press would give, which
        // is what stops the press from widening the column and shifting the
        // ones after it.
        assert_eq!(heading(&cols[1], &style), "SIZE \u{25B2}");
        // Not a control. Nothing to mark.
        assert_eq!(heading(&cols[2], &style), "NOTE");
    }

    #[test]
    fn the_three_states_of_a_heading_are_carried_by_its_caret() {
        // wiki `three-tone-convention`, as the webview draws it: the caret in
        // force takes content, the idle caret secondary, and a heading that is
        // not a control has no caret. The offering state may not take
        // content_muted, which is what `State::Disabled` resolves to.
        let p = palette();
        let cols = columns();
        let style = TableStyle::default();
        assert_eq!(caret_color(&cols[0], &p), p.content);
        assert_eq!(caret_color(&cols[1], &p), p.content_secondary);
        assert_ne!(caret_color(&cols[1], &p), p.content_muted);
        assert!(
            !heading(&cols[2], &style).contains(' '),
            "an inert heading has no caret"
        );
    }

    #[test]
    fn a_column_sorted_without_being_sortable_still_draws_its_caret() {
        // A list ordered by a key the user cannot change is a real thing to
        // describe, which is why the description holds the two fields apart.
        let column = Column {
            name: "rank",
            width: Width::Content,
            priority: Priority::Essential,
            kind: ColumnKind::Text,
            min: None,
            sortable: false,
            sorted: Some(Sort::Descending),
        };
        assert_eq!(heading(&column, &TableStyle::default()), "RANK \u{25BC}");
    }

    #[test]
    fn the_carets_match_the_terminal_renderers() {
        // Two crates, one glyph pair, and no dependency between them to enforce
        // it. A description sorted ascending must not point up in a window and
        // down in a terminal.
        // Composition rather than agreement since makeover-layout 0.27.5: both
        // read `Sort::glyph`, so a fourth spelling cannot appear in one crate.
        let style = TableStyle::default();
        assert_eq!(style.ascending, Sort::Ascending.glyph());
        assert_eq!(style.descending, Sort::Descending.glyph());
        // Bare. The gap is `heading`'s, so a consumer swapping the glyph for an
        // ASCII one does not have to remember to bring a space with it.
        assert_eq!(style.ascending.trim(), style.ascending);
    }

    #[test]
    fn resizing_is_off_because_the_description_has_no_word_for_it() {
        // egui_extras offers it and the other two renderers cannot say it. A
        // default that turned it on would be this renderer adding a claim.
        assert!(!TableStyle::default().resizable);
    }

    #[test]
    fn a_record_row_is_the_models_45_and_a_code_row_is_one_line() {
        let style = TableStyle::default();
        assert!((style.row_height - 45.0).abs() < f32::EPSILON);
        assert!(style.code_row_height < style.row_height);
    }

    #[test]
    fn a_body_claims_nothing_until_it_is_asked_to() {
        // The default is a table of no rows, no selection and no scroll
        // request. All three absences are the honest reading of an app that has
        // not said otherwise, which is why they are `Option` and not a
        // predicate that always answers false.
        let body = Body::default();
        assert_eq!(body.rows, 0);
        assert!(body.selected.is_none());
        assert!(body.scroll_to.is_none());
    }

    #[test]
    fn a_selection_is_asked_per_row_and_not_collected() {
        // A predicate, so an app whose selection is a range or a single index
        // does not build a set to be asked. Exercised the way `table` asks it:
        // once per row index, in order.
        let selected = |index: usize| index.is_multiple_of(2);
        let body = Body {
            rows: 4,
            selected: Some(&selected),
            scroll_to: None,
        };
        let f = body.selected.expect("a predicate was supplied");
        assert_eq!(
            (0..body.rows).map(f).collect::<Vec<_>>(),
            vec![true, false, true, false]
        );
    }

    #[test]
    fn narrowing_reads_the_declared_widths_and_not_a_dragged_track() {
        // `resizable` lets the user move a divider, and `cutoff_for` must not
        // hear about it: a drag that could drop a column would make the
        // narrowing a thing the user does by accident rather than a property of
        // the description. That `cutoff_for` takes the columns and two numbers,
        // and no `TableStyle` or track state, is the structural half of the
        // guarantee; this is the behavioural half, and it is what would fail if a
        // measured width were ever threaded in beside the declared floor.
        let cols = columns();
        assert_eq!(cutoff_for(&cols, 10.0, 12.0, 392.0), Priority::Optional);
        assert_eq!(cutoff_for(&cols, 10.0, 12.0, 288.0), Priority::Secondary);
    }
}