Read SVG arc flags as single characters in path data (#1726)

Found while testing crates/io/src/svg_read.rs:892-894 (arc flags read via Numbers::next_num, 675-709)

Co-authored-by: Claude Haiku 5.5 <noreply@anthropic.com>

crates/io/src/svg_read.rs

@@ -756,17 +756,33 @@ enum Tok {
 struct Tokenizer<'a> {
     s: &'a [u8],
     i: usize,
+    /// Start of the most recently returned token.
+    tok_start: usize,
 }
 
 impl<'a> Tokenizer<'a> {
     fn new(s: &'a str) -> Self {
-        Tokenizer { s: s.as_bytes(), i: 0 }
+        Tokenizer { s: s.as_bytes(), i: 0, tok_start: 0 }
+    }
+
+    /// Read an arc flag: a single `0` or `1` character, which needs no separator after it.
+    fn next_flag(&mut self) -> Option<f64> {
+        let mut nums = Numbers { s: self.s, i: self.i };
+        nums.skip_seps();
+        let v = match self.s.get(nums.i)? {
+            b'0' => 0.0,
+            b'1' => 1.0,
+            _ => return None,
+        };
+        self.i = nums.i + 1;
+        Some(v)
     }
 
     fn next_tok(&mut self) -> Option<Tok> {
         let mut nums = Numbers { s: self.s, i: self.i };
         nums.skip_seps();
         self.i = nums.i;
+        self.tok_start = self.i;
         let c = self.s.get(self.i).copied()?;
         if c.is_ascii_alphabetic() {
             self.i += 1;
@@ -843,7 +859,18 @@ fn parse_path(d: &str) -> Result<Vec<Subpath>> {
             _ => return Err(IoError::Format(format!("SVG: unknown path command `{}`", cmd as char))),
         };
         let mut args = [0.0f64; 7];
-        for slot in args.iter_mut().take(count) {
+        for (idx, slot) in args.iter_mut().enumerate().take(count) {
+            if abs == b'A' && (idx == 3 || idx == 4) {
+                // Flags are single characters; re-scan a pending number token from its start.
+                if matches!(lookahead, Some(Tok::Num(_))) {
+                    lookahead = None;
+                    tk.i = tk.tok_start;
+                }
+                if lookahead.is_none() {
+                    *slot = tk.next_flag().ok_or_else(|| IoError::Format("SVG: path command is missing coordinates".into()))?;
+                    continue;
+                }
+            }
             *slot = next_num(&mut tk, &mut lookahead)?;
         }
         let point = |x: f64, y: f64| if rel { cur + Vec2::new(x, y) } else { Vec2::new(x, y) };
@@ -1030,3 +1057,25 @@ fn elliptical_params(p0: Vec2, p1: Vec2, rx: f64, ry: f64, phi: f64, large: bool
     let ccw = angle(ux, uy, vx, vy).rem_euclid(std::f64::consts::TAU);
     Some((center, theta, pick_sweep(ccw, large, sweep)))
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn arc_of(d: &str) -> (bool, bool, Vec2) {
+        let subs = parse_path(d).unwrap_or_else(|e| panic!("{d}: {e:?}"));
+        match &subs[0].segs[0] {
+            Seg::Arc { large, sweep, end, .. } => (*large, *sweep, *end),
+            _ => panic!("not an arc"),
+        }
+    }
+
+    #[test]
+    fn compact_arc_flags_read_as_single_characters() {
+        let spaced = arc_of("M10 10 a20 20 0 0 1 20 20");
+        assert_eq!(arc_of("M10 10 a20 20 0 01 20 20"), spaced);
+        assert_eq!(arc_of("M10 10 a20 20 0 0120 20"), spaced);
+        assert_eq!(arc_of("M10 10 a20 20 0 1 0 20 20"), (true, false, spaced.2));
+        assert!(arc_of("M10 10 a20 20 0 10-20 20").0);
+    }
+}