Documents: inline formulas typeset in text; \( and \[ read as math

src/documents/document/format/clear.rs

@@ -5,7 +5,7 @@ use std::ops::Range;
 use markdown::mdast::Node;
 
 use super::{Change, EditRefusal, after, block, cut, holder, marks, room};
-use crate::documents::{markdown::span, tree::inside};
+use crate::documents::markdown::{math_inside, span};
 
 /// The backslashes of escapes in a text node's span.
 fn escapes(text: &str, whole: Range<usize>) -> Vec<Range<usize>> {
@@ -33,7 +33,7 @@ fn meta(node: &Node, text: &str, autolinks: &[Range<usize>]) -> Vec<Range<usize>
         Node::Text(_) if holder(autolinks, &whole).is_some() => Vec::new(),
         Node::Text(_) => escapes(text, whole),
         Node::InlineMath(_) => {
-            let inner = inside(text, whole.clone(), '$');
+            let inner = math_inside(text, whole.clone());
             vec![whole.start..inner.start, inner.end..whole.end]
         }
         Node::FootnoteReference(_) => vec![whole.start..whole.start + 2, whole.end - 1..whole.end],

src/documents/markdown.rs

@@ -1,4 +1,4 @@
-use std::ops::Range;
+use std::{borrow::Cow, ops::Range};
 
 use gpui::App;
 use markdown::{Constructs, ParseOptions, mdast};
@@ -20,19 +20,92 @@ pub(crate) fn options() -> ParseOptions {
 
 /// `text` as a syntax tree.
 pub(crate) fn tree(text: &str) -> mdast::Node {
-    markdown::to_mdast(text, &options()).expect("markdown without MDX always parses")
+    parsed(text, &options())
+}
+
+fn parsed(text: &str, options: &ParseOptions) -> mdast::Node {
+    let text = tex_math(text, options);
+    markdown::to_mdast(&text, options).expect("markdown without MDX always parses")
+}
+
+/// `\(` and `\[` delimiters as `$`, byte for byte.
+fn tex_math<'a>(text: &'a str, options: &ParseOptions) -> Cow<'a, str> {
+    if !text.contains("\\(") && !text.contains("\\[") {
+        return Cow::Borrowed(text);
+    }
+    let root = markdown::to_mdast(text, options).expect("markdown without MDX always parses");
+    let mut nodes = Vec::new();
+    walk(&root, &mut nodes);
+    let mut kept = vec![false; text.len()];
+    for node in nodes {
+        use mdast::Node::{Code, Html, InlineCode, InlineMath, Math, Toml, Yaml};
+        if matches!(
+            node,
+            Code(_) | InlineCode(_) | Math(_) | InlineMath(_) | Html(_) | Yaml(_) | Toml(_)
+        ) {
+            kept[span(node)].fill(true);
+        }
+    }
+    let bytes = text.as_bytes();
+    let mut out = bytes.to_vec();
+    let mut open: Option<(usize, u8)> = None;
+    let mut at = 0;
+    while at + 1 < bytes.len() {
+        match bytes[at] {
+            // A blank line ends a paragraph and its formula.
+            b'\n' if blank_after(&bytes[at + 1..]) => open = None,
+            b'\\' if !kept[at] => {
+                match (bytes[at + 1], open) {
+                    (b'(', None) => open = Some((at, b')')),
+                    (b'[', None) => open = Some((at, b']')),
+                    (close, Some((start, wanted)))
+                        if close == wanted && at > start + 2 && !text[start..at].contains('$') =>
+                    {
+                        out[start..start + 2].copy_from_slice(b"$ ");
+                        out[at..at + 2].copy_from_slice(b" $");
+                        open = None;
+                    }
+                    _ => {}
+                }
+                // An escaped backslash escapes nothing after it.
+                at += 2;
+                continue;
+            }
+            _ => {}
+        }
+        at += 1;
+    }
+    match out == bytes {
+        true => Cow::Borrowed(text),
+        false => Cow::Owned(String::from_utf8(out).expect("ASCII swaps keep UTF-8")),
+    }
+}
+
+/// Whether the line `rest` starts holds only white space.
+fn blank_after(rest: &[u8]) -> bool {
+    rest.iter()
+        .take_while(|byte| **byte != b'\n')
+        .all(u8::is_ascii_whitespace)
+}
+
+/// An inline formula's TeX: inside `$` runs or `\(` pairs.
+pub(crate) fn math_inside(source: &str, whole: Range<usize>) -> Range<usize> {
+    match source[whole.clone()].starts_with('$') {
+        true => crate::documents::tree::inside(source, whole, '$'),
+        false => whole.start + 2..whole.end - 2,
+    }
 }
 
 /// How a whole file parses: front matter too.
-pub fn file_options() -> ParseOptions {
+pub(crate) fn file_options() -> ParseOptions {
     let mut options = options();
     options.constructs.frontmatter = true;
     options
 }
 
 /// A whole file as a syntax tree.
-pub(crate) fn file_tree(text: &str) -> mdast::Node {
-    markdown::to_mdast(text, &file_options()).expect("markdown without MDX always parses")
+pub fn file_tree(text: &str) -> mdast::Node {
+    parsed(text, &file_options())
 }
 
 /// The bytes of the source a parsed node spans.

src/documents/mod.rs

@@ -46,7 +46,7 @@ pub(crate) use history::Change;
 pub use history::{PageHistoryDiff, Version, VersionHistory};
 pub use knowledge::{Backlink, Backlinks, Favorite, Favorites, TrashBin, Trashed};
 pub use link::LinkEditor;
-pub use markdown::file_options as markdown_options;
+pub use markdown::file_tree as markdown_tree;
 pub use markdown::markdown_highlights;
 pub use modes::{MarkdownEditor, MarkdownMode};
 pub use pages::{PageCover, PageIcon};

src/documents/render.rs

@@ -3,7 +3,7 @@ use std::{path::Path, rc::Rc, sync::Arc};
 use gpui::{
     AnyElement, App, ElementId, Entity, FontStyle, FontWeight, HighlightStyle, InteractiveText,
     IntoElement, ParentElement, Pixels, RenderOnce, SharedString, StrikethroughStyle, Styled,
-    StyledText, UnderlineStyle, Window, div, prelude::*, relative,
+    StyledText, TextLayout, UnderlineStyle, Window, div, prelude::*, relative,
 };
 
 use super::{
@@ -21,6 +21,7 @@ use crate::{
 };
 
 mod blocks;
+mod math_text;
 mod point;
 mod table;
 
@@ -170,6 +171,38 @@ fn highlight(style: &Style, colors: &Palette, rule: Pixels) -> HighlightStyle {
     }
 }
 
+/// `inline` as text; `hidden` ranges lose their highlight.
+fn drawn_text(
+    inline: &Inline,
+    hidden: &[std::ops::Range<usize>],
+    links: Option<ElementId>,
+    on_link: &Option<OnLink>,
+    cx: &App,
+) -> (AnyElement, TextLayout) {
+    let theme = cx.theme();
+    let colors = &theme.colors;
+    let rule = theme.underline_thickness();
+    let styles: Vec<_> = (inline.styles.iter())
+        .filter(|(range, _)| !hidden.contains(range))
+        .map(|(range, style)| (range.clone(), highlight(style, colors, rule)))
+        .collect();
+    let styled = StyledText::new(inline.text.clone()).with_highlights(crate::editor::stack(styles));
+    let layout = styled.layout().clone();
+    let drawn = match links {
+        None => styled.into_any_element(),
+        Some(id) => {
+            let (ranges, urls): (Vec<_>, Vec<_>) = inline.links.iter().cloned().unzip();
+            let on_link = on_link.clone();
+            InteractiveText::new(id, styled)
+                .on_click(ranges, move |ix, window, cx| {
+                    open_link(&on_link, &urls[ix], window, cx)
+                })
+                .into_any_element()
+        }
+    };
+    (drawn, layout)
+}
+
 /// Draws nodes under one owner's ids and hooks.
 struct Draw<'a> {
     id: &'a ElementId,
@@ -198,30 +231,20 @@ impl Draw<'_> {
     }
 
     fn inline(&self, inline: &Inline, cx: &App) -> AnyElement {
-        let theme = cx.theme();
-        let colors = &theme.colors;
-        let rule = theme.underline_thickness();
-        let styles: Vec<_> = inline
-            .styles
-            .iter()
-            .map(|(range, style)| (range.clone(), highlight(style, colors, rule)))
-            .collect();
-        let styled =
-            StyledText::new(inline.text.clone()).with_highlights(crate::editor::stack(styles));
-        let layout = styled.layout().clone();
-        let drawn = match inline.links.is_empty() {
-            true => styled.into_any_element(),
-            false => {
-                let (ranges, urls): (Vec<_>, Vec<_>) = inline.links.iter().cloned().unzip();
-                let on_link = self.hooks.on_link.clone();
-                InteractiveText::new(self.key("links"), styled)
-                    .on_click(ranges, move |ix, window, cx| {
-                        open_link(&on_link, &urls[ix], window, cx)
-                    })
-                    .into_any_element()
-            }
-        };
-        self.point_text(drawn, layout, inline)
+        let links = (!inline.links.is_empty()).then(|| self.key("links"));
+        if !inline.styles.iter().any(|(_, style)| *style == Style::Math) {
+            let (drawn, layout) = drawn_text(inline, &[], links, self.hooks.on_link, cx);
+            let at = move |position| {
+                layout
+                    .index_for_position(position)
+                    .unwrap_or_else(|near| near)
+            };
+            return self.point_text(drawn, at, inline);
+        }
+        let on_link = self.hooks.on_link.clone();
+        let (drawn, at) =
+            math_text::MathText::new(self.key("math"), inline.clone(), links, on_link);
+        self.point_text(drawn.into_any_element(), at, inline)
     }
 
     fn nodes(&self, nodes: &[Node], cx: &App) -> Vec<AnyElement> {

src/documents/render/math_text.rs

@@ -0,0 +1,355 @@
+//! Inline formulas typeset among a paragraph's words.
+
+use std::{cell::RefCell, ops::Range, rc::Rc, sync::Arc};
+
+use gpui::{
+    AnyElement, App, Bounds, Corners, Element, ElementId, GlobalElementId, InspectorElementId,
+    IntoElement, LayoutId, Pixels, Point, RenderImage, SharedString, Size, TextLayout,
+    TextStyleRefinement, Window, point,
+};
+
+use super::{OnLink, drawn_text};
+use crate::{
+    documents::tree::{Inline, Style},
+    typography::typeset,
+};
+
+/// Glue that reserves a formula's width and never breaks.
+const GLUE: char = '\u{00A0}';
+
+/// An original span and the drawn span standing for it.
+type Swap = (Range<usize>, Range<usize>);
+
+/// The drawn text and how its bytes map back.
+struct Shown {
+    layout: TextLayout,
+    swaps: Vec<Swap>,
+}
+
+/// Paragraph text whose formulas draw typeset over reserved glue.
+pub(super) struct MathText {
+    id: ElementId,
+    inline: Inline,
+    links: Option<ElementId>,
+    on_link: Option<OnLink>,
+    shown: Rc<RefCell<Option<Shown>>>,
+    text: Option<AnyElement>,
+    /// Each picture, its size, and the drawn span it covers.
+    pictures: Vec<(Arc<RenderImage>, Size<Pixels>, Range<usize>)>,
+}
+
+impl MathText {
+    /// The element and how a point finds its original byte.
+    pub(super) fn new(
+        id: ElementId,
+        inline: Inline,
+        links: Option<ElementId>,
+        on_link: Option<OnLink>,
+    ) -> (Self, impl Fn(Point<Pixels>) -> usize + 'static) {
+        let shown = Rc::new(RefCell::new(None));
+        let read = shown.clone();
+        let at = move |position| match &*read.borrow() {
+            Some(Shown { layout, swaps }) => back(
+                swaps,
+                layout
+                    .index_for_position(position)
+                    .unwrap_or_else(|near| near),
+            ),
+            None => 0,
+        };
+        let text = Self {
+            id,
+            inline,
+            links,
+            on_link,
+            shown,
+            text: None,
+            pictures: Vec::new(),
+        };
+        (text, at)
+    }
+}
+
+/// Where original byte `at` is drawn.
+fn forward(swaps: &[Swap], at: usize) -> usize {
+    let mut shift = 0isize;
+    for (written, drawn) in swaps {
+        if at < written.start {
+            break;
+        }
+        if at < written.end {
+            return drawn.start;
+        }
+        shift = drawn.end as isize - written.end as isize;
+    }
+    (at as isize + shift) as usize
+}
+
+/// The original byte drawn byte `at` stands for.
+fn back(swaps: &[Swap], at: usize) -> usize {
+    let mut shift = 0isize;
+    for (written, drawn) in swaps {
+        if at < drawn.start {
+            break;
+        }
+        if at < drawn.end {
+            return written.start;
+        }
+        shift = written.end as isize - drawn.end as isize;
+    }
+    (at as isize + shift) as usize
+}
+
+/// `inline` with each swapped span drawn as `glue[ix]` glue.
+fn shown(inline: &Inline, swaps: &mut [Swap], glue: &[usize]) -> Inline {
+    let mut text = String::new();
+    let mut from = 0;
+    for ((written, drawn), count) in swaps.iter_mut().zip(glue) {
+        text.push_str(&inline.text[from..written.start]);
+        let start = text.len();
+        text.extend(std::iter::repeat_n(GLUE, *count));
+        *drawn = start..text.len();
+        from = written.end;
+    }
+    text.push_str(&inline.text[from..]);
+    let span = |range: &Range<usize>| forward(swaps, range.start)..forward(swaps, range.end);
+    Inline {
+        text,
+        styles: (inline.styles.iter())
+            .map(|(range, style)| (span(range), *style))
+            .collect(),
+        links: (inline.links.iter())
+            .map(|(range, url)| (span(range), url.clone()))
+            .collect(),
+        sources: Vec::new(),
+    }
+}
+
+impl IntoElement for MathText {
+    type Element = Self;
+
+    fn into_element(self) -> Self {
+        self
+    }
+}
+
+impl Element for MathText {
+    type RequestLayoutState = ();
+    type PrepaintState = ();
+
+    fn id(&self) -> Option<ElementId> {
+        Some(self.id.clone())
+    }
+
+    fn source_location(&self) -> Option<&'static core::panic::Location<'static>> {
+        None
+    }
+
+    fn request_layout(
+        &mut self,
+        _: Option<&GlobalElementId>,
+        _: Option<&InspectorElementId>,
+        window: &mut Window,
+        cx: &mut App,
+    ) -> (LayoutId, ()) {
+        let style = window.text_style();
+        let rem = window.rem_size();
+        let font = style.font_size.to_pixels(rem);
+        let glue = String::from(GLUE);
+        let run = style.to_run(glue.len());
+        let width = window
+            .text_system()
+            .shape_line(glue.into(), font, &[run], None)
+            .width;
+        let mut maths: Vec<Range<usize>> = (self.inline.styles.iter())
+            .filter(|(_, style)| *style == Style::Math)
+            .map(|(range, _)| range.clone())
+            .collect();
+        maths.sort_by_key(|range| range.start);
+        let mut swaps = Vec::new();
+        let mut counts = Vec::new();
+        let mut pictures = Vec::new();
+        for (ix, range) in maths.into_iter().enumerate() {
+            let source = SharedString::from(self.inline.text[range.clone()].to_string());
+            match typeset(
+                (self.id.clone(), SharedString::from(format!("formula-{ix}"))),
+                (&source, false),
+                font,
+                window,
+                cx,
+            ) {
+                Some(Ok((image, size))) => {
+                    counts.push((size.width / width).ceil().max(1.0) as usize);
+                    pictures.push((image, size));
+                    swaps.push((range, 0..0));
+                }
+                // The formula is the user's text: not logged.
+                Some(Err(_)) => log::warn!("markdown: an inline formula shows as TeX, unset"),
+                None => {}
+            }
+        }
+        let inline = shown(&self.inline, &mut swaps, &counts);
+        let hidden: Vec<Range<usize>> = swaps.iter().map(|(_, drawn)| drawn.clone()).collect();
+        let (mut text, layout) =
+            drawn_text(&inline, &hidden, self.links.clone(), &self.on_link, cx);
+        let tallest = pictures
+            .iter()
+            .map(|(_, size)| size.height)
+            .fold(Pixels::ZERO, Pixels::max);
+        // A tall formula opens the paragraph's lines.
+        let taller = (tallest > style.line_height_in_pixels(rem)).then(|| TextStyleRefinement {
+            line_height: Some(tallest.into()),
+            ..TextStyleRefinement::default()
+        });
+        let id = window.with_text_style(taller, |window| text.request_layout(window, cx));
+        self.pictures = (pictures.into_iter().zip(&hidden))
+            .map(|((image, size), drawn)| (image, size, drawn.clone()))
+            .collect();
+        *self.shown.borrow_mut() = Some(Shown { layout, swaps });
+        self.text = Some(text);
+        (id, ())
+    }
+
+    fn prepaint(
+        &mut self,
+        _: Option<&GlobalElementId>,
+        _: Option<&InspectorElementId>,
+        _: Bounds<Pixels>,
+        _: &mut (),
+        window: &mut Window,
+        cx: &mut App,
+    ) {
+        if let Some(text) = &mut self.text {
+            text.prepaint(window, cx);
+        }
+    }
+
+    fn paint(
+        &mut self,
+        _: Option<&GlobalElementId>,
+        _: Option<&InspectorElementId>,
+        _: Bounds<Pixels>,
+        _: &mut (),
+        _: &mut (),
+        window: &mut Window,
+        cx: &mut App,
+    ) {
+        let Some(text) = &mut self.text else {
+            return;
+        };
+        text.paint(window, cx);
+        let shown = self.shown.borrow();
+        let Some(Shown { layout, .. }) = &*shown else {
+            return;
+        };
+        let line = layout.line_height();
+        for (image, size, drawn) in &self.pictures {
+            let (Some(start), Some(end)) = (
+                layout.position_for_index(drawn.start),
+                layout.position_for_index(drawn.end),
+            ) else {
+                continue;
+            };
+            // Glue at a line's end ends there.
+            let room = if end.y == start.y {
+                end.x - start.x
+            } else {
+                size.width
+            };
+            let origin = start + point((room - size.width) / 2.0, (line - size.height) / 2.0);
+            let bounds = Bounds {
+                origin,
+                size: *size,
+            };
+            if let Err(error) =
+                window.paint_image(bounds, bounds, Corners::default(), image.clone(), 0, false)
+            {
+                log::error!("markdown: an inline formula did not paint: {error}");
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn bytes_map_both_ways_around_a_formula() {
+        let inline = Inline {
+            text: "a x^2 b".into(),
+            styles: vec![(2..5, Style::Math), (6..7, Style::Strong)],
+            ..Inline::default()
+        };
+        let mut swaps = vec![(2..5, 0..0)];
+        let drawn = shown(&inline, &mut swaps, &[4]);
+        assert_eq!(drawn.text, format!("a {} b", GLUE.to_string().repeat(4)));
+        let glue = GLUE.len_utf8() * 4;
+        assert_eq!(swaps[0].1, 2..2 + glue);
+        assert_eq!(
+            drawn.styles[1].0,
+            3 + glue..4 + glue,
+            "the bold b moves past the glue"
+        );
+        assert_eq!(back(&swaps, 3), 2, "glue reads back to its formula");
+        assert_eq!(back(&swaps, 3 + glue), 6);
+        assert_eq!(forward(&swaps, 6), 3 + glue);
+    }
+
+    type Found = Rc<
+        RefCell<
+            Option<(
+                Rc<RefCell<Option<Shown>>>,
+                Box<dyn Fn(Point<Pixels>) -> usize>,
+            )>,
+        >,
+    >;
+
+    struct Probe(Found);
+
+    impl gpui::Render for Probe {
+        fn render(&mut self, _: &mut Window, _: &mut gpui::Context<Self>) -> impl IntoElement {
+            use gpui::{ParentElement as _, Styled as _};
+            let inline = Inline {
+                text: "a x^2 b".into(),
+                styles: vec![(2..5, Style::Math)],
+                ..Inline::default()
+            };
+            let (text, at) = MathText::new("probe".into(), inline, None, None);
+            *self.0.borrow_mut() = Some((text.shown.clone(), Box::new(at)));
+            gpui::div().text_size(gpui::px(16.0)).child(text)
+        }
+    }
+
+    #[gpui::test]
+    fn a_formula_draws_over_glue_and_reads_back(cx: &mut gpui::TestAppContext) {
+        cx.update(crate::theme::Theme::init);
+        let found = Found::default();
+        let held = found.clone();
+        let (_, cx) = cx.add_window_view(move |_, _| Probe(held));
+        for _ in 0..4 {
+            cx.run_until_parked();
+            cx.update(|window, _| window.refresh());
+        }
+        let found = found.borrow();
+        let (shown, at) = found.as_ref().expect("drawn");
+        let shown = shown.borrow();
+        let Shown { layout, swaps } = shown.as_ref().expect("laid out");
+        assert_eq!(swaps.len(), 1, "the formula typeset in place");
+        let drawn = swaps[0].1.clone();
+        let (start, end) = (
+            layout.position_for_index(drawn.start),
+            layout.position_for_index(drawn.end),
+        );
+        let (start, end) = (start.expect("its start"), end.expect("its end"));
+        assert!(
+            end.x - start.x > gpui::px(10.0),
+            "glue holds the picture's width"
+        );
+        let middle = point(
+            (start.x + end.x) / 2.0,
+            start.y + layout.line_height() / 2.0,
+        );
+        assert_eq!(at(middle), 2, "a press on the picture is the formula");
+    }
+}

src/documents/render/point.rs

@@ -140,11 +140,11 @@ impl Draw<'_> {
         })
     }
 
-    /// Drawn `inline`; a press finds its byte through `layout`.
+    /// Drawn `inline`; a press finds its byte through `at`.
     pub(super) fn point_text(
         &self,
         element: AnyElement,
-        layout: TextLayout,
+        at: impl Fn(gpui::Point<gpui::Pixels>) -> usize + 'static,
         inline: &Inline,
     ) -> AnyElement {
         if self.hooks.on_point.is_none() {
@@ -152,9 +152,7 @@ impl Draw<'_> {
         }
         let inline = Rc::new(inline.clone());
         self.pointable(element, move |event| {
-            let at = layout
-                .index_for_position(event.position)
-                .unwrap_or_else(|near| near);
+            let at = at(event.position);
             let link = inline.links.iter().find(|(range, _)| range.contains(&at));
             Pointed {
                 link: link.map(|(_, url)| url.clone()),

src/documents/tree/mod.rs

@@ -318,12 +318,14 @@ impl<'a> Reader<'a> {
         }
     }
 
-    /// Text split at its images; lone `$$` math is block.
+    /// Text split at its images; lone `$$` or `\[` math is block.
     fn paragraph(&self, node: &mdast::Node, children: &[mdast::Node], out: &mut Vec<Node>) {
         if let [mdast::Node::InlineMath(math)] = children
-            && self.source[span(node)].starts_with("$$")
+            && ["$$", "\\["]
+                .iter()
+                .any(|open| self.source[span(node)].starts_with(open))
         {
-            return out.push(Node::Math(math.value.clone()));
+            return out.push(Node::Math(math.value.trim().to_string()));
         }
         let mut run = Run {
             table: matches!(node, mdast::Node::TableCell(_)),

src/documents/tree/sources.rs

@@ -32,7 +32,10 @@ pub(super) fn written(node: &Node, source: &str) -> Option<(Range<usize>, Escape
     Some(match node {
         Node::Text(_) => (whole, Escapes::Markdown),
         Node::InlineCode(_) => (inside(source, whole, '`'), Escapes::Plain),
-        Node::InlineMath(_) => (inside(source, whole, '$'), Escapes::Plain),
+        Node::InlineMath(_) => (
+            crate::documents::markdown::math_inside(source, whole),
+            Escapes::Plain,
+        ),
         _ => (whole, Escapes::Plain),
     })
 }

src/documents/tree/tests.rs

@@ -416,3 +416,41 @@ fn the_first_shortcode_decides_its_text_node() {
         assert_eq!(line(source).text, shown, "{source:?}");
     }
 }
+
+#[test]
+fn latex_delimiters_read_as_math() {
+    assert_eq!(parse(r"\[c = 1\]"), [Node::Math("c = 1".into())]);
+    assert_eq!(parse("\\[\nc = 1\n\\]"), [Node::Math("c = 1".into())]);
+    let Node::Paragraph(inline) = &parse(r"so \(c\) holds")[0] else {
+        panic!("inline math stays in its paragraph")
+    };
+    assert_eq!(inline.text, "so c holds");
+    assert_eq!(inline.styles, [(3..4, Style::Math)]);
+    let Node::Paragraph(alone) = &parse(r"\(c\)")[0] else {
+        panic!("a lone formula stays inline")
+    };
+    assert_eq!(alone.styles, [(0..1, Style::Math)]);
+}
+
+#[test]
+fn latex_delimiters_leave_code_escapes_and_open_pairs() {
+    let text = |source: &str| match &parse(source)[0] {
+        Node::Paragraph(inline) => (inline.text.clone(), inline.styles.clone()),
+        other => panic!("a paragraph, not {other:?}"),
+    };
+    assert_eq!(text(r"`\(c\)`").1, [(0..5, Style::Code)], "code stays code");
+    assert_eq!(
+        text(r"\\(c\\)"),
+        (r"\(c\)".into(), Vec::new()),
+        "escaped backslashes"
+    );
+    assert_eq!(text(r"a \(c").0, "a (c", "no closing, no formula");
+    let split = parse("a \\(c\n\nd\\) e");
+    assert!(
+        split.iter().all(|node| match node {
+            Node::Paragraph(inline) => inline.styles.is_empty(),
+            _ => false,
+        }),
+        "a blank line ends the formula: {split:?}"
+    );
+}

src/typography/math.rs

@@ -96,7 +96,7 @@ struct Formula {
 }
 
 /// A typeset formula: its picture and logical size.
-type Typeset = Result<(Arc<RenderImage>, Size<Pixels>), MathError>;
+pub(crate) type Typeset = Result<(Arc<RenderImage>, Size<Pixels>), MathError>;
 
 enum Typesetter {}
 
@@ -201,27 +201,39 @@ fn framed(svg: &str, width: f32, height: f32) -> Result<(String, Size<Pixels>),
     Ok((reframed, size(px(w), px(h))))
 }
 
-impl Latex {
-    /// The asset key this formula draws from in `window`.
-    fn formula(&self, window: &Window, cx: &App) -> (Formula, Pixels) {
-        let theme = cx.theme();
-        let font = theme.text_size(self.size).to_pixels(window.rem_size());
-        let formula = Formula {
-            source: self.source.clone(),
-            display: self.display,
-            rgba: u32::from(theme.colors.fg.to_rgb()),
-            font: (font.as_f32() * 100.0).round() as u32,
-            scale: (window.scale_factor() * 100.0).round() as u32,
-        };
-        (formula, font)
+/// The asset key for `source` at `font` in `window`.
+fn formula(
+    (source, display): (&SharedString, bool),
+    font: Pixels,
+    window: &Window,
+    cx: &App,
+) -> Formula {
+    Formula {
+        source: source.clone(),
+        display,
+        rgba: u32::from(cx.theme().colors.fg.to_rgb()),
+        font: (font.as_f32() * 100.0).round() as u32,
+        scale: (window.scale_factor() * 100.0).round() as u32,
     }
 }
 
+/// `source` typeset at `font` in `window`; None while it loads.
+pub(crate) fn typeset(
+    id: impl Into<ElementId>,
+    (source, display): (&SharedString, bool),
+    font: Pixels,
+    window: &mut Window,
+    cx: &mut App,
+) -> Option<Typeset> {
+    let formula = formula((source, display), font, window, cx);
+    let picture = |typeset: &Typeset| typeset.as_ref().ok().map(|(image, _)| image.clone());
+    hold::<Typesetter>(id, &formula, picture, window, cx)
+}
+
 impl RenderOnce for Latex {
     fn render(self, window: &mut Window, cx: &mut App) -> impl IntoElement {
-        let (formula, font) = self.formula(window, cx);
-        let picture = |typeset: &Typeset| typeset.as_ref().ok().map(|(image, _)| image.clone());
-        match hold::<Typesetter>(self.id, &formula, picture, window, cx) {
+        let font = cx.theme().text_size(self.size).to_pixels(window.rem_size());
+        match typeset(self.id, (&self.source, self.display), font, window, cx) {
             Some(Ok((picture, shape))) => img(picture)
                 .w(shape.width)
                 .h(shape.height)

src/typography/math/tests.rs

@@ -114,8 +114,11 @@ fn flush(cx: &mut gpui::VisualTestContext) {
 /// Whether `source`'s picture sits in the asset cache.
 fn cached(source: &str, cx: &mut gpui::VisualTestContext) -> bool {
     cx.update(|window, cx| {
-        let latex = Latex::parse("probe", source).expect("parses");
-        let (formula, _) = latex.formula(window, cx);
+        let font = cx
+            .theme()
+            .text_size(TextSize::Lg)
+            .to_pixels(window.rem_size());
+        let formula = super::formula((&source.to_string().into(), false), font, window, cx);
         cx.has_asset::<Typesetter>(&formula)
     })
 }

src/typography/mod.rs

@@ -26,6 +26,7 @@ pub use formatted::{
 pub use inline::{Blockquote, Code, Highlight, Kbd, KbdCombo};
 pub use link::{ExternalLink, Link};
 pub(crate) use math::failed;
+pub(crate) use math::typeset;
 pub use math::{Latex, MathError, formula_svg};
 pub use rolling::AnimatedNumber;
 pub use select::SelectableText;