From 47d4c391453bdeb407bac69c19441e2bf0d6a876 Mon Sep 17 00:00:00 2001
From: Athitheya Gobinathan <athith.g@gmail.com>
Date: Sat, 14 Mar 2026 11:07:30 -0700
Subject: [PATCH] FIX(rslib/cloze): Ignore `}}` inside MathJax when tokenizing
 clozes

* FIX premature cloze termination inside MathJax

* ADD regression test for MathJax cloze parsing
---
 CONTRIBUTORS       |  1 +
 rslib/src/cloze.rs | 53 ++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index a3b1b1c6f84..6c0658d68ec 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -266,6 +266,7 @@ Yuuki Gabriele Patriarca <yuukigpatriarca@gmail.com>
 SecretX <https://github.com/SecretX33>
 Daniel Pechersky <danny.pechersky@gmail.com>
 fernandolins <1887601+fernandolins@users.noreply.github.com>
+Athitheya Gobinathan <athith.g@gmail.com>
 
 ********************
 
diff --git a/rslib/src/cloze.rs b/rslib/src/cloze.rs
index 70a5d1703a8..ab6f2dfc99c 100644
--- a/rslib/src/cloze.rs
+++ b/rslib/src/cloze.rs
@@ -91,16 +91,44 @@ fn tokenize(mut text: &str) -> impl Iterator<Item = Token<'_>> {
                 nom::error::ErrorKind::Eof,
             )));
         }
-        let mut other_token = alt((open_cloze, close_cloze));
-        // start with the no-match case
         let mut index = text.len();
-        for (idx, _) in text.char_indices() {
-            if other_token.parse(&text[idx..]).is_ok() {
-                index = idx;
+        let mut i = 0;
+        let mut mathjax_end: Option<&str> = None;
+        while i < text.len() {
+            let rest = &text[i..];
+            // Cloze openings should be recognized everywhere, including inside MathJax.
+            if open_cloze(rest).is_ok() {
+                index = i;
                 break;
             }
+            // Cloze closings should only be recognized outside MathJax.
+            if mathjax_end.is_none() && close_cloze(rest).is_ok() {
+                index = i;
+                break;
+            }
+            // Enter MathJax when not already inside it.
+            if mathjax_end.is_none() {
+                if rest.starts_with(r"\(") {
+                    mathjax_end = Some(r"\)");
+                    i += 2;
+                    continue;
+                }
+                if rest.starts_with(r"\[") {
+                    mathjax_end = Some(r"\]");
+                    i += 2;
+                    continue;
+                }
+            } else if let Some(end) = mathjax_end {
+                // Exit MathJax when we hit the matching delimiter.
+                if rest.starts_with(end) {
+                    mathjax_end = None;
+                    i += 2;
+                    continue;
+                }
+            }
+            i += rest.chars().next().unwrap().len_utf8();
         }
-        Ok((&text[index..], Token::Text(&text[0..index])))
+        Ok((&text[index..], Token::Text(&text[..index])))
     }
 
     std::iter::from_fn(move || {
@@ -665,6 +693,19 @@ mod test {
         );
     }
 
+    #[test]
+    fn cloze_with_mathjax_braces() {
+        let text = r"{{c1:: \( \frac{1}{\sqrt{\pi}} \) }}";
+        assert_eq!(
+            strip_html(reveal_cloze_text(text, 1, true).as_ref()),
+            "[...]"
+        );
+        assert_eq!(
+            strip_html(reveal_cloze_text(text, 1, false).as_ref()),
+            r" \( \frac{1}{\sqrt{\pi}} \) "
+        );
+    }
+
     #[test]
     fn non_latin() {
         assert!(cloze_numbers_in_string("öaöaöööaö").is_empty());