Add support for alt-text in preformatted blocks ⚠️

⚠️  Breaking Change ⚠️

This adds support for parsing and rendering alt-text in preformatted blocks.  This changes the public API both around the `Node` enum and the `preformatted()` method of the builder.  I cannot think of a way to avoid this that is not needlessly overcomplicated, except maybe merging the preformatted & body into a single newline delimited string but that's hella gross and i don't think anyone wants that.  Lemme know if you can think of a better way of doing this

Preformatted blocks without alt text can still be created by passing in an empty string.  Because alt text isn't separated by a space, this does not add any unnecessary padding.  I chose not to accept Option<String> here because an empty string serves the same function but encourages users to use alt-text in their documents, which is very important for increasing accessibility.

gemtext/src/lib.rs

@@ -26,8 +26,12 @@ impl Builder {
         self
     }
 
-    pub fn preformatted<T: Into<String>>(mut self, data: T) -> Builder {
+    pub fn preformatted<A, T>(mut self, alt_text: T, data: T) -> Builder
-        self.nodes.push(Node::Preformatted(data.into()));
+    where
+        A: Into<String>,
+        T: Into<String>,
+    {
+        self.nodes.push(Node::Preformatted { alt: alt_text.into(), body: data.into() });
         self
     }
 
@@ -113,7 +117,7 @@ pub fn render(nodes: impl AsRef<[Node]>, out: &mut impl Write) -> io::Result<()>
                 Some(name) => write!(out, "=> {} {}\n", to, name)?,
                 None => write!(out, "=> {}\n", to)?,
             },
-            Preformatted(body) => write!(out, "```\n{}\n```\n", body)?,
+            Preformatted { alt, body } => write!(out, "```{}\n{}\n```\n", alt, body)?,
             Heading { level, body } => write!(out, "{} {}\n", "#".repeat(*level as usize), body)?,
             ListItem(body) => write!(out, "* {}\n", body)?,
             Quote(body) => write!(out, "> {}\n", body)?,
@@ -165,7 +169,19 @@ pub enum Node {
     /// (e.g. Python) should be able to be copied and pasted from the client into
     /// a file and interpreted/compiled without any problems arising from the
     /// client's manner of displaying them.
-    Preformatted(String),
+    ///
+    /// The first preformatted toggle of a document is often followed by a short
+    /// string, which acts as alt-text for the preformatted block.  This is also
+    /// often used to denote the language of code in a block of text.  For example,
+    /// a block starting with the text `\`\`\`rust` may be interpreted as rust
+    /// code, and a block starting with `\`\`\` An ascii art owl` would be
+    /// described aptly to visually impaired users using a screen reader.  The alt
+    /// text may be separated from the toggle by whitespace.  `gemtext` currently
+    /// renders alt text without this separation.
+    ///
+    /// To create a preformatted block with no alt text, simply pass a zero-length
+    /// string as alt text.
+    Preformatted { alt: String, body: String },
 
     /// Lines beginning with "#" are heading lines. Heading lines consist of one,
     /// two or three consecutive "#" characters, followed by optional whitespace,
@@ -224,7 +240,10 @@ impl Node {
     /// # use gemtext::Node;
     /// let simple_text = Node::Text(String::from("Henlo worl"));
     /// let linky_link = Node::Link { to: "gemini://cetacean.club/maj/".to_string(), name: Some("Maj".to_string()) };
-    /// let human_rights = Node::Preformatted("trans rights! 🏳️‍⚧️".to_string());;
+    /// let human_rights = Node::Preformatted {
+    ///     alt: "".to_string(),
+    ///     body: "trans rights! 🏳️‍⚧️".to_string(),
+    /// };
     ///
     /// assert_eq!(
     ///     simple_text.estimate_len(),
@@ -244,7 +263,8 @@ impl Node {
             Self::Text(text) => text.len(),
             Self::Link { to, name } => 3 + to.as_bytes().len() +
                 name.as_ref().map(|n| n.as_bytes().len() + 1).unwrap_or(0),
-            Self::Preformatted(text) => text.as_bytes().len() + 8,
+            Self::Preformatted { alt, body } => alt.as_bytes().len()
+                + body.as_bytes().len() + 8,
             Self::Heading { level, body } => *level as usize + 1 + body.as_bytes().len(),
             Self::ListItem(item) | Self::Quote(item)=> 2 + item.as_bytes().len(),
         }
@@ -255,18 +275,22 @@ pub fn parse(doc: &str) -> Vec<Node> {
     let mut result: Vec<Node> = vec![];
     let mut collect_preformatted: bool = false;
     let mut preformatted_buffer: Vec<u8> = vec![];
+    let mut alt = "";
 
     for line in doc.lines() {
-        if line.starts_with("```") {
+        if let Some(trailing) = line.strip_prefix("```") {
             collect_preformatted = !collect_preformatted;
             if !collect_preformatted {
-                result.push(Node::Preformatted(
+                result.push(Node::Preformatted {
-                    String::from_utf8(preformatted_buffer)
+                    alt: alt.to_string(),
+                    body: String::from_utf8(preformatted_buffer)
                         .unwrap()
                         .trim_end()
                         .to_string(),
-                ));
+                });
                 preformatted_buffer = vec![];
+            } else {
+                alt = trailing.trim();
             }
             continue;
         }
@@ -365,13 +389,13 @@ mod tests {
     #[test]
     fn preformatted() {
         let _ = pretty_env_logger::try_init();
-        let msg = "```\n\
+        let msg = "```hi there\n\
-                   hi there\n\
+                   obi-wan kenobi\n\
                    ```\n\
                    \n\
                    Test\n";
         let expected: Vec<Node> = vec![
-            Node::Preformatted("hi there".to_string()),
+            Node::Preformatted{ alt: "hi there".to_string(), body: "obi-wan kenobi".to_string() },
             Node::Text(String::new()),
             Node::Text("Test".to_string()),
         ];
@@ -421,7 +445,7 @@ mod tests {
         let _ = pretty_env_logger::try_init();
         let msg = include_str!("../../testdata/ambig_preformatted.gmi");
         let expected: Vec<Node> = vec![
-            Node::Preformatted("FOO".to_string()),
+            Node::Preformatted { alt: "foo".to_string(), body: "FOO".to_string() },
             Node::Text("Foo bar".to_string()),
         ];
         assert_eq!(expected, parse(msg));