1 files changed, 131 insertions, 0 deletions
diff --git a/src/util/mdx.rs b/src/util/mdx.rs
new file mode 100644
index 0000000..712b2c7
--- /dev/null
+++ b/src/util/mdx.rs
@@ -0,0 +1,131 @@
+extern crate alloc;
+
+use alloc::string::String;
+
+/// Signal used as feedback when parsing MDX ESM/expressions.
+#[derive(Clone, Debug)]
+pub enum Signal {
+    /// A syntax error.
+    ///
+    /// `markdown-rs` will crash with error message `String`, and convert the
+    /// `usize` (byte offset into `&str` passed to `MdxExpressionParse` or
+    /// `MdxEsmParse`) to where it happened in the whole document.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust ignore
+    /// Signal::Error("Unexpected `\"`, expected identifier".into(), 1)
+    /// ```
+    Error(String, usize),
+    /// An error at the end of the (partial?) expression.
+    ///
+    /// `markdown-rs` will either crash with error message `String` if it
+    /// doesn’t have any more text, or it will try again later when more text
+    /// is available.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust ignore
+    /// Signal::Eof("Unexpected end of file in string literal".into())
+    /// ```
+    Eof(String),
+    /// Done, successfully.
+    ///
+    /// `markdown-rs` knows that this is the end of a valid expression/esm and
+    /// continues with markdown.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust ignore
+    /// Signal::Ok
+    /// ```
+    Ok,
+}
+
+/// Signature of a function that parses MDX ESM.
+///
+/// Can be passed as `mdx_esm_parse` in [`ParseOptions`][] to support
+/// ESM according to a certain grammar (typically, a programming language).
+pub type EsmParse = dyn Fn(&str) -> Signal;
+
+/// Expression kind.
+#[derive(Clone, Debug)]
+pub enum ExpressionKind {
+    /// Kind of expressions in prose.
+    ///
+    /// ```mdx
+    /// > | # {Math.PI}
+    ///       ^^^^^^^^^
+    ///   |
+    /// > | {Math.PI}
+    ///     ^^^^^^^^^
+    /// ```
+    Expression,
+    /// Kind of expressions as attributes.
+    ///
+    /// ```mdx
+    /// > | <a {...b}>
+    ///        ^^^^^^
+    /// ```
+    AttributeExpression,
+    /// Kind of expressions as attribute values.
+    ///
+    /// ```mdx
+    /// > | <a b={c}>
+    ///          ^^^
+    /// ```
+    AttributeValueExpression,
+}
+
+/// Signature of a function that parses MDX expressions.
+///
+/// Can be passed as `mdx_expression_parse` in [`ParseOptions`][] to support
+/// expressions according to a certain grammar (typically, a programming
+/// language).
+///
+pub type ExpressionParse = dyn Fn(&str, &ExpressionKind) -> Signal;
+
+#[cfg(test)]
+mod tests {
+    extern crate std;
+    use super::*;
+    use alloc::boxed::Box;
+
+    #[test]
+    fn test_mdx_expression_parse() {
+        fn func(_value: &str, _kind: &ExpressionKind) -> Signal {
+            Signal::Ok
+        }
+
+        let func_accepting = |_a: Box<ExpressionParse>| true;
+
+        assert!(
+            matches!(func("a", &ExpressionKind::Expression), Signal::Ok),
+            "should expose an `ExpressionParse` type (1)"
+        );
+
+        assert!(
+            func_accepting(Box::new(func)),
+            "should expose an `ExpressionParse` type (2)"
+        );
+    }
+
+    #[test]
+    fn test_mdx_esm_parse() {
+        fn func(_value: &str) -> Signal {
+            Signal::Ok
+        }
+
+        let func_accepting = |_a: Box<EsmParse>| true;
+
+        assert!(
+            matches!(func("a"), Signal::Ok),
+            "should expose an `EsmParse` type (1)"
+        );
+
+        assert!(
+            func_accepting(Box::new(func)),
+            "should expose an `EsmParse` type (2)"
+        );
+    }
+}