editor/

editor.rs

//! The editing surface.
//!
//! The document is the single source of truth. There is no `TextField` per
//! block: a selection is a pair of `Cursor`s into one `Doc`, which is what
//! makes Enter split, Backspace merge and Tab indent into list operations
//! rather than negotiations between separate widgets each owning a string.
//!
//! Everything about *what* an edit does lives in `markdown` — `edit` and
//! `select` — and is tested there without a window. This crate owns only what
//! needs one: a focus handle, key bindings, the platform input handler, and
//! turning a click into a position.

use crate::{
    anchor::{Anchor, AnchorId, Delta},
    document::{Change, Document, DocumentEvent, Tracked},
    history::{EditKind, Run},
    link::{self, Choice},
    slash::{Slash, SlashAction, SlashAt},
    text_size,
};
use gpui::{
    App, Context, CursorStyle, ElementInputHandler, Entity, EventEmitter, FocusHandle, Focusable,
    Hsla, KeyContext, MouseButton, Render, Styled as _, Task, Window, canvas, div, prelude::*,
};
use markdown::{
    Affinity, Annotation, AppExt as _, Block, BlockKind, BlockLayouts, Cursor, Doc, Form, Mark,
    Part, Selection, Splice, Synced, Text, Typography, edit, edit::shortcut,
};
use std::{cell::RefCell, ops::Range, rc::Rc, time::Duration};
use theme::Theme;

mod anchors;
mod blocks;
mod caret;
mod clipboard;
pub(crate) mod image;
mod input;
pub mod keys;
pub(crate) mod menu;
pub(crate) mod mode;
mod pointer;
mod render;
mod sizing;
mod sync;
mod table;
mod typing;

pub use keys::init;
use keys::{
    Backspace, Copy, Cut, DecreaseTextSize, Delete, DeleteToHome, DeleteWordLeft, DeleteWordRight,
    Dismiss, DocumentEnd, DocumentStart, Down, DuplicateBlock, End, Home, IncreaseTextSize, Indent,
    InsertParagraph, KillLine, Left, MoveBlockDown, MoveBlockUp, Outdent, Paste, Redo, RemoveBlock,
    ResetTextSize, Right, SelectAll, SelectDocumentEnd, SelectDocumentStart, SelectDown, SelectEnd,
    SelectHome, SelectLeft, SelectRight, SelectUp, SelectWordLeft, SelectWordRight, SoftBreak,
    SplitBlock, ToggleBold, ToggleCode, ToggleHighlight, ToggleItalic, ToggleStrike, Undo, Up,
    WordLeft, WordRight,
};

pub const CONTEXT: &str = "BezelEditor";

/// The custom mark [`ToggleHighlight`] toggles. It does nothing until the app
/// registers a mark under this name with [`markdown::AppExt::set_marks`].
pub const HIGHLIGHT_MARK: &str = "highlight";

/// [`CONTEXT`], which every binding in [`keys`] is scoped to, plus the mark
/// that keeps `tab` for [`Editor::indent`].
fn key_context() -> KeyContext {
    let mut context = KeyContext::default();
    context.add(CONTEXT);
    context.add(ui::focus::CLAIMS_TAB);
    context
}

/// What the editor tells its host about.
///
/// An app holding comment threads has to hear that the document moved, or its
/// side of the pairing goes stale against anchors that did not. Split the way
/// [`ui::input::FieldEvent`] is, so a listener takes only the half it needs.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum EditorEvent {
    /// The document is different, and the anchors have been mapped through it.
    Changed,
    /// A click landed on an anchor's range.
    AnchorActivated(AnchorId),
    /// The pointer came over an anchor's painted text, or left it: `None`
    /// over none, and when the pointer leaves the editor.
    AnchorHovered(Option<AnchorId>),
    /// The editor switched between the document and its source, which a host
    /// lighting its own toggle has no other way to hear about — the switch can
    /// come from an undo as well as from the button.
    ModeChanged(Mode),
}

/// Which form the document is being edited in.
///
/// The trigger is the app's: a button, a menu row, a chord of its own. What is
/// here is the switch it calls, because the caret, the undo history and the
/// focus have to survive it, and only the editor owns all three.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub enum Mode {
    /// The document as it reads.
    #[default]
    Blocks,
    /// The markdown a save would write, in one editable text.
    Source,
}

/// Which of the editor's own affordances are on.
///
/// All of them unless an app says otherwise: a document with nothing
/// discoverable on it is the wrong default for a library. Turning one off is
/// for an app that puts its own in the same place — a bar with its own block
/// menu does not want the gutter handle's as well — rather than for trimming.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Chrome {
    /// The gutter handle, the menu it opens, and dragging a block by it.
    pub handle: bool,
    /// The `/` menu at an empty block.
    pub slash: bool,
    /// A fence's language label, and the picker it opens.
    pub language: bool,
    /// The menu a pasted URL drops — leave it, or make a card, a chip or the
    /// picture it points at.
    pub paste: bool,
    /// The mention menus over the app's [`crate::MentionSource`]s. Off by
    /// default.
    pub mention: bool,
}

impl Default for Chrome {
    fn default() -> Self {
        Self {
            handle: true,
            slash: true,
            language: true,
            paste: true,
            mention: false,
        }
    }
}

/// What a toolbar reads to light itself, in one call.
///
/// Every field is a question a bar asks on every frame, and each was a separate
/// reach into the document before: which marks are lit, what the block is
/// called, whether cmd-E would fence, and whether any of it applies at all.
/// Taken together so a bar cannot answer half of them from one frame and half
/// from the next.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Formatting {
    /// Which form the document is in. In [`Mode::Source`] the markup is already
    /// spelled out, so [`Self::marks`] is empty and a bar has nothing to light.
    pub mode: Mode,
    /// The marks the selection carries throughout — and at a collapsed caret,
    /// the ones the next character typed would carry, cmd-B before typing
    /// included.
    pub marks: Vec<Mark>,
    /// What the caret's block is called in [`turns`], or `None` for a block the
    /// menu does not offer. Matched on the kind and a heading's level alone: a
    /// list numbered from 7 and a fence tagged `rs` report their row.
    pub block: Option<gpui::SharedString>,
    /// The quote the caret's block sits in — see [`quotes`].
    pub quote: Option<markdown::Quoted>,
    /// Whether [`Mark::Code`] here makes a fence out of the selection rather
    /// than an inline span — the one chord whose meaning changes with what is
    /// selected, and the one a bar cannot work out for itself.
    pub fenceable: bool,
}

/// Every block a block can be turned into, and what each is called — the
/// vocabulary the slash menu and the block menu both offer, for an app building
/// a menu of its own. Pair with [`Editor::set_block`], which is what both of
/// bezel's own menus call.
pub fn turns() -> Vec<(gpui::SharedString, BlockKind)> {
    crate::slash::items()
}

/// Every quote a block can be put in, and what each is called. Pair with
/// [`Editor::toggle_quote`].
pub fn quotes() -> Vec<(gpui::SharedString, Option<markdown::QuoteKind>)> {
    crate::slash::quotes()
}

/// Shown on the focused block while it is empty — the only discoverable place
/// to say that `/` does anything.
const PLACEHOLDER: &str = "Type / for commands";

/// What tab inserts in the source, where there are no blocks to indent. Two
/// spaces, which is what markdown's own nesting is written in.
const INDENT: &str = "  ";

/// Half the caret's blink period — `ui::TextField`'s, which is the 500ms on,
/// 500ms off macOS itself uses.
const BLINK: Duration = Duration::from_millis(500);

/// The handle's box. Wide enough to be hit without crowding the margin; how
/// far left of the text it sits is [`Layout::text_inset`](crate::Layout).
const HANDLE_SIZE: f32 = 18.0;

/// How far a drag on an image's edge handle can shrink it — matches
/// `markdown::render`'s `TABLE_MIN_COLUMN_WIDTH`, the same floor for the
/// other block content a drag can resize.
const MIN_IMAGE_WIDTH: f32 = 96.0;

/// Whether a selection is prose covering more than one line — two blocks, or
/// one line break inside a single block.
///
/// What a chord means about a selection is the editor's to decide; a [`Doc`]
/// has no opinion about it. A selection reaching into a table or a fence is not
/// prose and keeps the inline behaviour, because half a table has no lines to
/// make a fence out of.
fn fenceable(doc: &Doc, selection: Selection) -> bool {
    let spans = doc.spans(selection);
    let covered = |at: &Cursor, range: &Range<usize>| {
        doc.blocks[at.block]
            .text_at(at.part)
            .and_then(|text| text.text.get(range.clone()))
    };
    spans.iter().all(|(at, _)| at.part == Part::Body)
        && (spans.len() > 1
            || spans
                .iter()
                .any(|(at, range)| covered(at, range).is_some_and(|text| text.contains('\n'))))
}

fn line_home(at: Cursor, doc: &Doc) -> Cursor {
    let Some(text) = doc
        .blocks
        .get(at.block)
        .and_then(|block| block.text_at(at.part))
    else {
        return at.home();
    };
    Cursor {
        offset: ui::input::line_start(&text.text, at.offset.min(text.text.len())),
        ..at
    }
}

fn line_end(at: Cursor, doc: &Doc) -> Cursor {
    let Some(text) = doc
        .blocks
        .get(at.block)
        .and_then(|block| block.text_at(at.part))
    else {
        return at.end(doc);
    };
    Cursor {
        offset: ui::input::line_end(&text.text, at.offset.min(text.text.len())),
        ..at
    }
}

/// The document a source view is edited as: one fence holding the markdown.
///
/// A fence rather than a paragraph because a fence is the block whose caret
/// already behaves like a plain text editor's — Enter is a newline, nothing
/// typed into it is markup, and its lines are laid out one per source line.
fn source_doc(source: &str) -> Doc {
    Doc {
        blocks: vec![Block::new(BlockKind::Code {
            language: Some(markdown::source::LANGUAGES[0].to_string()),
            code: Text::plain(source),
            height: None,
        })],
    }
}

/// A floating menu a block drops. A `Popup` rather than an `Option` for the
/// exit phase, and for the press note: the card's `on_mouse_down_out` fires on
/// the *press*, so without one a trigger's click on the *release* reopens what
/// it just shut.
pub(crate) type MenuPopup<T> = ui::popover::Popup<Dropped<T>>;

/// What a dropped menu belongs to, where it hangs, and its live row.
pub(crate) struct Dropped<T> {
    pub of: T,
    pub at: gpui::Point<gpui::Pixels>,
    pub cursor: ui::menu::Cursor,
}

impl<T> Dropped<T> {
    pub fn new(of: T, at: gpui::Point<gpui::Pixels>) -> Self {
        Self {
            of,
            at,
            cursor: ui::menu::Cursor::default(),
        }
    }
}

/// The row, column, or cell whose table menu is open.
#[derive(Clone, Copy, PartialEq, Eq)]
pub(crate) enum TableTarget {
    Row(usize),
    Column(usize),
    Cell { row: usize, column: usize },
}

/// A table's row or column, as [`markdown::Part::Cell`] numbers them.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub(crate) enum Line {
    Row(usize),
    Column(usize),
}

/// Where a reveal leaves the caret's row in the scroll box.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub(crate) enum Reveal {
    /// The least scroll that brings the row inside the box.
    Nearest,
    /// The row at the box's top edge, or as near it as the document's end
    /// allows.
    Top,
}

/// One view of a [`Document`].
///
/// Every edit notifies the entity and emits [`EditorEvent::Changed`].
///
/// The slash menu, the gutter handle and its block drag, a fence's language
/// picker, the pasted-URL menu, undo and the clipboard need no wiring;
/// [`Chrome`] turns the menus off. Hovering a table cell shows handles for its
/// row and column: a click opens insert, delete and move, a drag reorders, and
/// `escape` or a drop outside the table cancels. A right press on a cell opens
/// both sets. The strips along a table's bottom and right edges append a row
/// and a column.
pub struct Editor {
    document: Entity<Document>,
    /// This editor's snapshot of the document, its form, its marks and its
    /// anchors: what it edits, handed back to [`Self::document`] after each
    /// change, and replaced whenever another editor changes the document.
    doc: Tracked,
    /// The source view's text and the [`Tracked::revision`] it was built at.
    /// Read only in [`Mode::Source`].
    source_view: Option<(u64, markdown::SourceText)>,
    /// Highlighting the source view's text after an edit. Dropping it cancels.
    source_spans: Option<Task<()>>,
    marks: markdown::Marks,
    /// The document's markdown and blocks, shared with it — see
    /// [`Document`]'s field of the name.
    synced: Rc<RefCell<Synced>>,
    /// Which of the editor's own affordances paint. The app's, so one document
    /// can carry the lot and another none of it.
    chrome: Chrome,
    /// In [`Mode::Source`] `doc` is one fenced block holding the markdown, so
    /// every operation below that is about *blocks* asks [`Editor::blocks`]
    /// first.
    mode: Mode,
    /// Collapsed for an ordinary caret, so there is one position here rather
    /// than a caret and a range that can disagree.
    selection: Selection,
    focus_handle: FocusHandle,
    /// The IME composition range within the caret's text, underlined while it
    /// is being composed.
    marked: Option<Range<usize>>,
    /// Where each text landed last frame, so a click can be turned into a
    /// caret. Only paint knows this, so the renderer fills it.
    layouts: BlockLayouts,
    run: Run,
    /// Which half of the blink the caret is in. Flipped by [`Self::start_blink`].
    caret_on: bool,
    /// The blink, alive only while the document holds focus.
    blink: Option<Task<()>>,
    anchors: Vec<Anchor>,
    /// Ranges washed for one frame's worth of the app's say — find hits. Not
    /// mapped through edits and not in the history: the app sets them again.
    washes: Vec<(Selection, Annotation)>,
    /// Marks the next typed character will carry — cmd-B at a collapsed caret,
    /// which otherwise has no range to apply to and so would do nothing.
    /// Cleared by any motion, because they belong to a spot and not to a mood.
    stored: Vec<Mark>,
    /// The open slash menu, if `/` started one.
    slash: Option<Slash>,
    mention: Option<crate::mention::MentionMenu>,
    /// The open paste menu, if a URL landed in a block of its own.
    pasted: Option<link::Paste>,
    /// The open prompt, if an image is waiting to be told where to look.
    url_prompt: Option<image::Prompt>,
    /// The block a file being dragged over the document would land after.
    dropping: Option<usize>,
    /// The block the pointer is over, which is the only one showing a handle.
    hovered: Option<usize>,
    /// The table cell the pointer is over, whose row and column show handles.
    hovered_cell: Option<(usize, Part)>,
    /// A table row's or column's menu: the table, the line and where it hangs.
    table_drag: Option<table::TableDrag>,
    table_dragged: bool,
    table_menu: MenuPopup<(usize, TableTarget)>,
    /// The right-click menu on text, with its rows as they stood when it
    /// opened.
    text_menu: MenuPopup<Vec<ui::menu::Item>>,
    /// The right-click menu on a picture.
    image_menu: MenuPopup<markdown::PictureMenu>,
    /// A block being dragged by its handle, and where it would land.
    lifted: Option<(usize, usize)>,
    /// An image being dragged wider or narrower by its edge handle, and the
    /// width it holds now — `None` being the natural one, exactly as the
    /// document spells it. The document only learns the final width on
    /// release, the same reason `lifted` waits for the drop; carrying the
    /// document's own value here is what makes a press that never moved
    /// read back as no change at all.
    resizing: Option<(usize, Option<u32>)>,
    /// A painted block being dragged taller or shorter by its bottom handle.
    sizing: Option<sizing::Sizing>,
    /// The block menu the handle opened, over the block and its rows.
    block_menu: MenuPopup<(usize, crate::slash::Rows)>,
    /// The language menu a fence's header opened, over its block.
    language_menu: MenuPopup<usize>,
    /// Set by a floating layer's press — the gutter handle, the URL prompt —
    /// so the editor's own press does not undo what that press just did.
    press_claimed: bool,
    /// Where the editor's own box starts, so a position recorded in window
    /// coordinates can be placed inside it, and how far it reaches — which is
    /// how wide a resized image is allowed to be. Its own box rather than the
    /// picture's: a picture already narrowed would otherwise be its own
    /// ceiling, and no drag could ever widen it again.
    origin: gpui::Point<gpui::Pixels>,
    width: gpui::Pixels,
    /// The press being dragged out: what it selects by, and what it selected.
    dragging: Option<(ui::input::Granularity, Range<Cursor>)>,
    /// Whether the pointer is over painted text, which is the only place the
    /// editor claims an I-beam.
    over_text: bool,
    /// The anchor whose text the pointer is over — see
    /// [`EditorEvent::AnchorHovered`].
    over_anchor: Option<AnchorId>,
    /// The host's scroll box, when it gave one, and the reveal the caret still
    /// owes it.
    scroll: Option<gpui::ScrollHandle>,
    reveal: Option<Reveal>,
    /// Where a held drag last was, in window coordinates.
    drag_at: Option<gpui::Point<gpui::Pixels>>,
    /// Scrolls [`Self::scroll`] while a drag is held past its top or bottom.
    edge_scroll: Option<Task<()>>,
    /// Where the gutter handle was placed this frame, so the frame after can
    /// tell whether the block moved out from under it.
    handle_at: Option<gpui::Point<gpui::Pixels>>,
    /// The column held across consecutive vertical moves.
    goal: Option<gpui::Pixels>,
    /// The size the app set this document in, in points, or `None` to follow
    /// the app's own text size. Absolute rather than a factor over the ladder,
    /// so moving the interface size leaves a document set to 16pt at 16pt.
    ///
    /// What the chords move is the shared adjustment on top of this; the base
    /// itself is the app's alone.
    text_size: Option<f32>,
    /// Overrides document text-size settings for an embedded editing surface.
    pub typography: Option<Typography>,
    pub text_color: Option<Hsla>,
    /// The directory relative image paths resolve against.
    base: Option<std::path::PathBuf>,
    image_overlay: Option<markdown::ImageOverlay>,
    image_overlay_corner: markdown::ImageOverlayCorner,
    _document: gpui::Subscription,
}

impl Editor {
    /// An editor on a document of its own.
    pub fn new(source: &str, cx: &mut Context<Self>) -> Self {
        let document = cx.new(|cx| Document::new(source, cx));
        Self::for_document(document, cx)
    }

    /// An editor on `document`, beside any others already on it.
    pub fn for_document(document: Entity<Document>, cx: &mut Context<Self>) -> Self {
        let (doc, mode, marks, synced, anchors) = {
            let document = document.read(cx);
            (
                document.doc.clone(),
                document.mode,
                document.marks.clone(),
                document.synced.clone(),
                document.anchors.clone(),
            )
        };
        let subscription = cx.subscribe(&document, |this, document, event: &DocumentEvent, cx| {
            if event.by != Some(cx.entity_id()) {
                this.take_document(&document, &event.change, cx);
            }
        });
        Self {
            document,
            marks,
            // Clamped, not defaulted: a document opening on a fence or a table
            // has no body at block zero, and a caret claiming one resolves
            // against nothing until something moves it.
            selection: Selection::at(Cursor::default().clamp(&doc)),
            doc,
            mode,
            synced,
            anchors,
            source_view: None,
            source_spans: None,
            chrome: Chrome::default(),
            focus_handle: cx.focus_handle(),
            marked: None,
            layouts: BlockLayouts::default(),
            run: Run::default(),
            caret_on: true,
            blink: None,
            washes: Vec::new(),
            stored: Vec::new(),
            slash: None,
            mention: None,
            pasted: None,
            url_prompt: None,
            dropping: None,
            hovered: None,
            hovered_cell: None,
            table_menu: Default::default(),
            text_menu: Default::default(),
            image_menu: Default::default(),
            table_drag: None,
            table_dragged: false,
            lifted: None,
            resizing: None,
            sizing: None,
            block_menu: MenuPopup::default(),
            language_menu: MenuPopup::default(),
            press_claimed: false,
            origin: gpui::Point::default(),
            width: gpui::Pixels::ZERO,
            dragging: None,
            over_text: false,
            over_anchor: None,
            scroll: None,
            reveal: None,
            drag_at: None,
            edge_scroll: None,
            goal: None,
            handle_at: None,
            text_size: None,
            typography: None,
            text_color: None,
            base: None,
            image_overlay: None,
            image_overlay_corner: markdown::ImageOverlayCorner::default(),
            _document: subscription,
        }
    }

    /// The document this editor is a view of.
    pub fn document(&self) -> &Entity<Document> {
        &self.document
    }

    /// Which of the editor's own affordances to paint. See [`Chrome`].
    pub fn with_chrome(mut self, chrome: Chrome) -> Self {
        self.chrome = chrome;
        self
    }

    /// Adds an app-provided hover control to pictures in rich mode.
    pub fn with_image_overlay(mut self, overlay: markdown::ImageOverlay) -> Self {
        self.image_overlay = Some(overlay);
        self
    }

    /// Replaces or removes the picture hover control.
    pub fn set_image_overlay(
        &mut self,
        overlay: Option<markdown::ImageOverlay>,
        cx: &mut Context<Self>,
    ) {
        self.image_overlay = overlay;
        cx.notify();
    }

    /// Positions picture hover controls; bottom-right by default.
    pub fn with_image_overlay_corner(mut self, corner: markdown::ImageOverlayCorner) -> Self {
        self.image_overlay_corner = corner;
        self
    }

    /// Repositions the picture hover control.
    pub fn set_image_overlay_corner(
        &mut self,
        corner: markdown::ImageOverlayCorner,
        cx: &mut Context<Self>,
    ) {
        self.image_overlay_corner = corner;
        cx.notify();
    }

    /// What is painting now, for an app whose own bar mirrors it.
    pub fn chrome(&self) -> Chrome {
        self.chrome
    }

    /// Open the document at a size of its own, in points — the app's settings
    /// field for prose. Unset, it is set at the app's own text size.
    ///
    /// The base, not the current size: `cmd-+` moves a shared adjustment over
    /// this, and `cmd-0` clears that adjustment to come back here.
    pub fn with_text_size(mut self, points: f32) -> Self {
        self.text_size = Some(points);
        self
    }

    /// Update the configured base size without changing the temporary zoom.
    pub fn set_text_size(&mut self, points: f32, cx: &mut Context<Self>) {
        if self.text_size != Some(points) {
            self.text_size = Some(points);
            cx.notify();
        }
    }

    /// The base the app set, if any. Add
    /// [`crate::AppExt::editor_text_size_adjustment`](crate::AppExt::editor_text_size_adjustment) for what is on
    /// screen.
    pub fn text_size(&self) -> Option<f32> {
        self.text_size
    }

    pub fn resolved_typography(&self, cx: &App) -> Typography {
        self.typography.unwrap_or_else(|| {
            cx.typography()
                .scaled(text_size::resolve(self.text_size, cx) / theme::base_text_size())
        })
    }

    /// Resolve relative image paths against `dir` — the document's own folder,
    /// for a document that keeps its pictures beside it. The stored URL stays
    /// as written.
    pub fn with_base(mut self, dir: impl Into<std::path::PathBuf>) -> Self {
        self.base = Some(dir.into());
        self
    }

    /// Change or clear the directory relative image paths resolve against.
    pub fn set_base(&mut self, dir: Option<std::path::PathBuf>, cx: &mut Context<Self>) {
        if self.base != dir {
            self.base = dir;
            cx.notify();
        }
    }

    /// The directory relative image paths resolve against, if one is set.
    pub fn base(&self) -> Option<&std::path::Path> {
        self.base.as_deref()
    }

    /// The box the document scrolls in, so typing off the bottom follows the
    /// caret down and a drag held past its top or bottom scrolls it.
    ///
    /// The host's rather than the editor's: a document goes in whatever pane
    /// the app gives it, and the gutter handle, the drop indicator and the
    /// menus are all placed absolutely against this editor's own origin — put
    /// the scroll box here and every one of them would be offset twice.
    pub fn with_scroll(mut self, handle: gpui::ScrollHandle) -> Self {
        self.scroll = Some(handle);
        self
    }

    pub fn doc(&self) -> &Doc {
        &self.doc
    }

    pub fn selection(&self) -> Selection {
        self.selection
    }

    /// Put the selection somewhere — what a thread in a sidebar does when it is
    /// clicked, and what a caret restored with a document needs.
    ///
    /// Clamped, because the caller's range came from somewhere the document may
    /// have moved on from.
    pub fn select(&mut self, selection: Selection, cx: &mut Context<Self>) {
        self.select_revealing(selection, Reveal::Nearest, cx);
    }

    /// [`Self::select`], scrolling the caret's row to the top of the scroll
    /// box — what a jump to a heading wants, from either side of it.
    pub fn select_to_top(&mut self, selection: Selection, cx: &mut Context<Self>) {
        self.select_revealing(selection, Reveal::Top, cx);
    }

    fn select_revealing(&mut self, selection: Selection, reveal: Reveal, cx: &mut Context<Self>) {
        self.selection = selection.clamp(&self.doc);
        self.run.interrupt();
        self.reveal = Some(reveal);
        self.caret_moved();
        cx.notify();
    }

    /// Where everything landed last frame — blocks, pictures, a fence's
    /// language label, and the row rects of any range.
    ///
    /// Handed out whole rather than a method per question: an app placing
    /// chrome of its own asks the geometry, and which question it needs is not
    /// this crate's to guess. See [`markdown::BlockLayouts`].
    pub fn layouts(&self) -> &BlockLayouts {
        &self.layouts
    }

    /// Where the selection sits on screen, in window coordinates, so a host can
    /// float a toolbar at it.
    ///
    /// The head's row only — a selection spanning ten blocks wants its bubble
    /// where the pointer left off, not centred over the whole span. `None` when
    /// nothing is selected or the caret has not painted yet.
    pub fn selection_bounds(&self) -> Option<gpui::Bounds<gpui::Pixels>> {
        // The head alone. A bar centred over the whole selection wants
        // `layouts().rects(selection)`, which is every painted row of it.
        if self.selection.is_collapsed() {
            return None;
        }
        let (point, line_height) = self
            .layouts
            .position(self.selection.head, self.selection.affinity)?;
        Some(gpui::Bounds::new(
            point,
            gpui::size(gpui::px(0.0), line_height),
        ))
    }
}

impl EventEmitter<EditorEvent> for Editor {}

impl Focusable for Editor {
    fn focus_handle(&self, _: &App) -> FocusHandle {
        self.focus_handle.clone()
    }
}