Remove `must_use` if tarpaulin doesn’t understand them

Also moves some code to separate files, in the hopes that
tarpaulin understands them.

3 files changed, 262 insertions, 0 deletions

diff --git a/src/util/line_ending.rs b/src/util/line_ending.rs
new file mode 100644
index 0000000..a018fe8
--- /dev/null
+++ b/src/util/line_ending.rs
@@ -0,0 +1,129 @@
+extern crate alloc;
+
+use alloc::{str::FromStr, string::String};
+
+/// Type of line endings in markdown.
+///
+/// Particularly when working with Windows, you might want to use
+/// `LineEnding::CarriageReturnLineFeed`.
+///
+/// ## Examples
+///
+/// ```
+/// use markdown::LineEnding;
+/// # fn main() {
+///
+/// // Use a CR + LF combination:
+/// let crlf = LineEnding::CarriageReturnLineFeed;
+/// # }
+/// ```
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
+pub enum LineEnding {
+    /// Both a carriage return (`\r`) and a line feed (`\n`).
+    ///
+    /// ## Example
+    ///
+    /// ```markdown
+    /// a␍␊
+    /// b
+    /// ```
+    CarriageReturnLineFeed,
+    /// Sole carriage return (`\r`).
+    ///
+    /// ## Example
+    ///
+    /// ```markdown
+    /// a␍
+    /// b
+    /// ```
+    CarriageReturn,
+    /// Sole line feed (`\n`).
+    ///
+    /// ## Example
+    ///
+    /// ```markdown
+    /// a␊
+    /// b
+    /// ```
+    #[default]
+    LineFeed,
+}
+
+// xxxxxxxxxxxxxxx
+impl LineEnding {
+    /// Turn the line ending into a [str].
+    #[must_use]
+    pub fn as_str(&self) -> &str {
+        match self {
+            LineEnding::CarriageReturnLineFeed => "\r\n",
+            LineEnding::CarriageReturn => "\r",
+            LineEnding::LineFeed => "\n",
+        }
+    }
+}
+
+impl FromStr for LineEnding {
+    type Err = String;
+
+    /// Turn a string into a line ending.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if `code` is not `\r\n`, `\r`, or `\n`.
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "\r\n" => Ok(LineEnding::CarriageReturnLineFeed),
+            "\r" => Ok(LineEnding::CarriageReturn),
+            "\n" => Ok(LineEnding::LineFeed),
+            _ => Err("Expected CR, LF, or CRLF".into()),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    extern crate std;
+    use super::*;
+
+    #[test]
+    fn test_line_ending() {
+        assert_eq!(
+            "\r".parse(),
+            Ok(LineEnding::CarriageReturn),
+            "should support turning a string into a carriage return"
+        );
+        assert_eq!(
+            LineEnding::CarriageReturn.as_str(),
+            "\r",
+            "should support turning a carriage return into a string"
+        );
+
+        assert_eq!(
+            "\n".parse(),
+            Ok(LineEnding::LineFeed),
+            "should support turning a string into a line feed"
+        );
+        assert_eq!(
+            LineEnding::LineFeed.as_str(),
+            "\n",
+            "should support turning a line feed into a string"
+        );
+
+        assert_eq!(
+            "\r\n".parse(),
+            Ok(LineEnding::CarriageReturnLineFeed),
+            "should support turning a string into a carriage return + line feed"
+        );
+        assert_eq!(
+            LineEnding::CarriageReturnLineFeed.as_str(),
+            "\r\n",
+            "should support turning a carriage return + line feed into a string"
+        );
+
+        assert_eq!(
+            "aaa".parse::<LineEnding>(),
+            Err("Expected CR, LF, or CRLF".into()),
+            "should error when parsing a non-eol"
+        );
+    }
+}
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)"
+        );
+    }
+}
diff --git a/src/util/mod.rs b/src/util/mod.rs
index f44e183..cb9a40b 100644
--- a/src/util/mod.rs
+++ b/src/util/mod.rs
@@ -8,7 +8,9 @@ pub mod encode;
 pub mod gfm_tagfilter;
 pub mod identifier;
 pub mod infer;
+pub mod line_ending;
 pub mod location;
+pub mod mdx;
 pub mod mdx_collect;
 pub mod normalize_identifier;
 pub mod sanitize_uri;