feat: add markdown alert support (#423)

This adds supports for markdown alerts (github/gitlab style) as support
for these was recently added to comrak. This for now looks close a block
quote except it also contains a title colored the same color as the
vertical bar prefix that shows up on the left of the block quote.

See kivikakk/comrak#519 and
kivikakk/comrak#521 for syntax but basically
this:

```markdown
> [!note]
> this is a note

> [!tip]
> this is a tip

> [!important]
> this is important

> [!warning]
> this is warning!

> [!caution]
> this advises caution!

>>> [!note] other title
ez
multiline
>>>
```

Renders like this:


![image](https://github.com/user-attachments/assets/219024ae-b635-4bf2-87ba-e252b64ebd67)

src/markdown/elements.rs

@@ -1,4 +1,5 @@
 use super::text_style::TextStyle;
+use comrak::nodes::AlertType;
 use std::{fmt, iter, path::PathBuf, str::FromStr};
 use unicode_width::UnicodeWidthStr;
 
@@ -51,6 +52,18 @@ pub(crate) enum MarkdownElement {
 
     /// A block quote containing a list of lines.
     BlockQuote(Vec<Line>),
+
+    /// An alert.
+    Alert {
+        /// The alert's type.
+        alert_type: AlertType,
+
+        /// The optional title.
+        title: Option<String>,
+
+        /// The content lines in this alert.
+        lines: Vec<Line>,
+    },
 }
 
 #[derive(Clone, Copy, Debug, Default)]

src/markdown/parse.rs

@@ -8,8 +8,8 @@ use comrak::{
     arena_tree::Node,
     format_commonmark,
     nodes::{
-        Ast, AstNode, ListDelimType, ListType, NodeCodeBlock, NodeHeading, NodeHtmlBlock, NodeList, NodeValue,
-        Sourcepos,
+        Ast, AstNode, ListDelimType, ListType, NodeAlert, NodeCodeBlock, NodeHeading, NodeHtmlBlock, NodeList,
+        NodeValue, Sourcepos,
     },
     parse_document,
 };
@@ -31,6 +31,7 @@ impl Default for ParserOptions {
         options.extension.table = true;
         options.extension.strikethrough = true;
         options.extension.multiline_block_quotes = true;
+        options.extension.alerts = true;
         Self(options)
     }
 }
@@ -76,6 +77,7 @@ impl<'a> MarkdownParser<'a> {
             NodeValue::ThematicBreak => MarkdownElement::ThematicBreak,
             NodeValue::HtmlBlock(block) => self.parse_html_block(block, data.sourcepos)?,
             NodeValue::BlockQuote | NodeValue::MultilineBlockQuote(_) => self.parse_block_quote(node)?,
+            NodeValue::Alert(alert) => self.parse_alert(alert, node)?,
             other => return Err(ParseErrorKind::UnsupportedElement(other.identifier()).with_sourcepos(data.sourcepos)),
         };
         Ok(vec![element])
@@ -106,19 +108,19 @@ impl<'a> MarkdownParser<'a> {
     }
 
     fn parse_block_quote(&self, node: &'a AstNode<'a>) -> ParseResult<MarkdownElement> {
-        let mut elements = Vec::new();
+        let mut lines = Vec::new();
         let inlines = InlinesParser::new(self.arena, SoftBreak::Newline, StringifyImages::Yes).parse(node)?;
         for inline in inlines {
             match inline {
-                Inline::Text(text) => elements.push(text),
-                Inline::LineBreak => elements.push(Line::from("")),
+                Inline::Text(text) => lines.push(text),
+                Inline::LineBreak => lines.push(Line::from("")),
                 Inline::Image { .. } => {}
             }
         }
-        if elements.last() == Some(&Line::from("")) {
-            elements.pop();
+        if lines.last() == Some(&Line::from("")) {
+            lines.pop();
         }
-        Ok(MarkdownElement::BlockQuote(elements))
+        Ok(MarkdownElement::BlockQuote(lines))
     }
 
     fn parse_code_block(block: &NodeCodeBlock, sourcepos: Sourcepos) -> ParseResult<MarkdownElement> {
@@ -132,6 +134,11 @@ impl<'a> MarkdownParser<'a> {
         })
     }
 
+    fn parse_alert(&self, alert: &NodeAlert, node: &'a AstNode<'a>) -> ParseResult<MarkdownElement> {
+        let MarkdownElement::BlockQuote(lines) = self.parse_block_quote(node)? else { panic!("not a block quote") };
+        Ok(MarkdownElement::Alert { alert_type: alert.alert_type, title: alert.title.clone(), lines })
+    }
+
     fn parse_heading(&self, heading: &NodeHeading, node: &'a AstNode<'a>) -> ParseResult<MarkdownElement> {
         let text = self.parse_text(node)?;
         if heading.setext {
@@ -973,4 +980,17 @@ mom
         let expected = format!("hi{nl}mom{nl}");
         assert_eq!(contents, &expected);
     }
+
+    #[test]
+    fn parse_alert() {
+        let input = r"
+> [!note]
+> hi mom
+> bye **mom**
+";
+        let MarkdownElement::Alert { lines, .. } = parse_single(&input) else {
+            panic!("not an alert");
+        };
+        assert_eq!(lines.len(), 2);
+    }
 }

src/presentation/builder.rs

@@ -43,6 +43,7 @@ use crate::{
         separator::RenderSeparator,
     },
 };
+use comrak::nodes::AlertType;
 use image::DynamicImage;
 use serde::Deserialize;
 use std::{borrow::Cow, cell::RefCell, fmt::Display, iter, mem, path::PathBuf, rc::Rc, str::FromStr};
@@ -287,6 +288,7 @@ impl<'a> PresentationBuilder<'a> {
             MarkdownElement::Image { path, title, source_position } => {
                 self.push_image_from_path(path, title, source_position)?
             }
+            MarkdownElement::Alert { alert_type, title, lines } => self.push_alert(alert_type, title, lines),
         };
         if should_clear_last {
             self.slide_state.last_element = LastElement::Other;
@@ -716,8 +718,30 @@ impl<'a> PresentationBuilder<'a> {
 
     fn push_block_quote(&mut self, lines: Vec<Line>) {
         let prefix = self.theme.block_quote.prefix.clone().unwrap_or_default();
-        let block_length = lines.iter().map(|line| line.width() + prefix.width()).max().unwrap_or(0) as u16;
         let prefix_color = self.theme.block_quote.colors.prefix.or(self.theme.block_quote.colors.base.foreground);
+        self.push_quoted_text(lines, prefix, self.theme.block_quote.colors.base, prefix_color);
+    }
+
+    fn push_alert(&mut self, alert_type: AlertType, title: Option<String>, mut lines: Vec<Line>) {
+        let (default_title, prefix_color) = match alert_type {
+            AlertType::Note => ("Note", self.theme.alert.colors.types.note),
+            AlertType::Tip => ("Tip", self.theme.alert.colors.types.tip),
+            AlertType::Important => ("Important", self.theme.alert.colors.types.important),
+            AlertType::Warning => ("Warning", self.theme.alert.colors.types.warning),
+            AlertType::Caution => ("Caution", self.theme.alert.colors.types.caution),
+        };
+        let prefix_color = prefix_color.or(self.theme.alert.colors.base.foreground);
+        let title = title.unwrap_or_else(|| default_title.to_string());
+        let title_colors = Colors { foreground: prefix_color, background: self.theme.alert.colors.base.background };
+        lines.insert(0, Line::from(Text::from("")));
+        lines.insert(0, Line::from(Text::new(title, TextStyle::default().colors(title_colors))));
+
+        let prefix = self.theme.block_quote.prefix.clone().unwrap_or_default();
+        self.push_quoted_text(lines, prefix, self.theme.alert.colors.base, prefix_color);
+    }
+
+    fn push_quoted_text(&mut self, lines: Vec<Line>, prefix: String, base_colors: Colors, prefix_color: Option<Color>) {
+        let block_length = lines.iter().map(|line| line.width() + prefix.width()).max().unwrap_or(0) as u16;
         let prefix = Text::new(
             prefix,
             TextStyle::default()
@@ -728,9 +752,11 @@ impl<'a> PresentationBuilder<'a> {
         for mut line in lines {
             // Apply our colors to each chunk in this line.
             for text in &mut line.0 {
-                text.style.colors = self.theme.block_quote.colors.base;
-                if text.style.is_code() {
-                    text.style.colors = self.theme.inline_code.colors;
+                if text.style.colors.background.is_none() && text.style.colors.foreground.is_none() {
+                    text.style.colors = base_colors;
+                    if text.style.is_code() {
+                        text.style.colors = self.theme.inline_code.colors;
+                    }
                 }
             }
             self.chunk_operations.push(RenderOperation::RenderBlockLine(BlockLine {
@@ -740,7 +766,7 @@ impl<'a> PresentationBuilder<'a> {
                 text: line.into(),
                 block_length,
                 alignment: alignment.clone(),
-                block_color: self.theme.block_quote.colors.base.background,
+                block_color: base_colors.background,
             }));
             self.push_line_break();
         }

src/theme.rs

@@ -150,6 +150,10 @@ pub struct PresentationTheme {
     #[serde(default)]
     pub(crate) block_quote: BlockQuoteStyle,
 
+    /// The style for an alert.
+    #[serde(default)]
+    pub(crate) alert: AlertStyle,
+
     /// The default style.
     #[serde(rename = "default", default)]
     pub(crate) default_style: DefaultStyle,
@@ -325,9 +329,64 @@ pub(crate) struct BlockQuoteColors {
     pub(crate) base: Colors,
 
     /// The color of the vertical bar that prefixes each line in the quote.
+    #[serde(default)]
     pub(crate) prefix: Option<Color>,
 }
 
+/// The style of an alert.
+#[derive(Clone, Debug, Default, Deserialize, Serialize)]
+pub(crate) struct AlertStyle {
+    /// The alignment.
+    #[serde(flatten, default)]
+    pub(crate) alignment: Option<Alignment>,
+
+    /// The prefix to be added to this block quote.
+    ///
+    /// This allows adding something like a vertical bar before the text.
+    #[serde(default)]
+    pub(crate) prefix: Option<String>,
+
+    /// The colors to be used.
+    #[serde(default)]
+    pub(crate) colors: AlertColors,
+}
+
+/// The colors of an alert.
+#[derive(Clone, Debug, Default, Deserialize, Serialize)]
+pub(crate) struct AlertColors {
+    /// The foreground/background colors.
+    #[serde(flatten)]
+    pub(crate) base: Colors,
+
+    /// The color of the vertical bar that prefixes each line in the quote.
+    #[serde(default)]
+    pub(crate) types: AlertTypeColors,
+}
+
+/// The colors of each alert type.
+#[derive(Clone, Debug, Default, Deserialize, Serialize)]
+pub(crate) struct AlertTypeColors {
+    /// The color for note type alerts.
+    #[serde(default)]
+    pub(crate) note: Option<Color>,
+
+    /// The color for tip type alerts.
+    #[serde(default)]
+    pub(crate) tip: Option<Color>,
+
+    /// The color for important type alerts.
+    #[serde(default)]
+    pub(crate) important: Option<Color>,
+
+    /// The color for warning type alerts.
+    #[serde(default)]
+    pub(crate) warning: Option<Color>,
+
+    /// The color for caution type alerts.
+    #[serde(default)]
+    pub(crate) caution: Option<Color>,
+}
+
 /// The style for the presentation introduction slide.
 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 pub(crate) struct IntroSlideStyle {

src/ui/footer.rs

@@ -38,6 +38,7 @@ impl FooterGenerator {
         colors: Colors,
         alignment: Alignment,
     ) -> RenderOperation {
+        #[allow(unknown_lints)]
         #[allow(clippy::literal_string_with_formatting_args)]
         let contents = template
             .replace("{current_slide}", current_slide)

themes/catppuccin-frappe.yaml

@@ -103,6 +103,18 @@ block_quote:
     background: "414559"
     prefix: "e5c890"
 
+alert:
+  prefix: "▍ "
+  colors:
+    foreground: "c6d0f5"
+    background: "414559"
+    types:
+      note: "8caaee"
+      tip: "a6d189"
+      important: "ca9ee6"
+      warning: "e5c890"
+      caution: "e78284"
+
 typst:
   colors:
     foreground: "c6d0f5"

themes/catppuccin-latte.yaml

@@ -103,6 +103,18 @@ block_quote:
     background: "ccd0da"
     prefix: "df8e1d"
 
+alert:
+  prefix: "▍ "
+  colors:
+    foreground: "4c4f69"
+    background: "ccd0da"
+    types:
+      note: "1e66f5"
+      tip: "40a02b"
+      important: "8839ef"
+      warning: "df8e1d"
+      caution: "d20f39"
+
 typst:
   colors:
     foreground: "4c4f69"

themes/catppuccin-macchiato.yaml

@@ -103,6 +103,18 @@ block_quote:
     background: "363a4f"
     prefix: "eed49f"
 
+alert:
+  prefix: "▍ "
+  colors:
+    foreground: "cad3f5"
+    background: "363a4f"
+    types:
+      note: "8aadf4"
+      tip: "a6da95"
+      important: "c6a0f6"
+      warning: "f5a97f"
+      caution: "ed8796"
+
 typst:
   colors:
     foreground: "cad3f5"

themes/catppuccin-mocha.yaml

@@ -103,6 +103,18 @@ block_quote:
     background: "313244"
     prefix: "f9e2af"
 
+alert:
+  prefix: "▍ "
+  colors:
+    foreground: "cdd6f4"
+    background: "313244"
+    types:
+      note: "89b4fa"
+      tip: "a6e3a1"
+      important: "cba6f7"
+      warning: "fab387"
+      caution: "f38ba8"
+
 typst:
   colors:
     foreground: "cdd6f4"

themes/dark.yaml

@@ -104,6 +104,18 @@ block_quote:
     background: "292e42"
     prefix: "ee9322"
 
+alert:
+  prefix: "▍ "
+  colors:
+    foreground: "f0f0f0"
+    background: "292e42"
+    types:
+      note: "3085c3"
+      tip: "a8df8e"
+      important: "986ee2"
+      warning: "ee9322"
+      caution: "f78ca2"
+
 typst:
   colors:
     foreground: "f0f0f0"

themes/light.yaml

@@ -104,6 +104,18 @@ block_quote:
     background: "e9ecef"
     prefix: "f77f00"
 
+alert:
+  prefix: "▍ "
+  colors:
+    foreground: "212529"
+    background: "e9ecef"
+    types:
+      note: "1e66f5"
+      tip: "40a02b"
+      important: "8839ef"
+      warning: "df8e1d"
+      caution: "d20f39"
+
 typst:
   colors:
     foreground: "212529"

themes/terminal-dark.yaml

@@ -102,6 +102,18 @@ block_quote:
     background: black
     prefix: yellow
 
+alert:
+  prefix: "▍ "
+  colors:
+    foreground: white
+    background: black
+    types:
+      note: blue
+      tip: green
+      important: magenta
+      warning: yellow
+      caution: red
+
 typst:
   colors:
     foreground: "f0f0f0"