fix: LaTeX diagnostics halt after unmatched inline math ($) inside a macro

harper-tex/src/masker.rs

@@ -61,14 +61,12 @@ fn math_mode_at_cursor(cursor: usize, source: &[char]) -> Option<usize> {
         return None;
     }
 
-    Some(
-        source
-            .iter()
-            .skip(cursor + 1)
-            .take_while(|t| **t != '$')
-            .count()
-            + 2,
-    )
+    let closing_delimiter = source
+        .iter()
+        .skip(cursor + 1)
+        .position(|character| *character == '$')?;
+
+    Some(closing_delimiter + 2)
 }
 
 /// Check whether there is a command at the current cursor. If so, this function will update the action queue to mask out the hidden elements.
@@ -242,6 +240,16 @@ mod tests {
 
     use super::{Masker, deconstruct_command};
 
+    fn allowed_text(source: &str) -> Vec<String> {
+        let source: Vec<_> = source.chars().collect();
+
+        Masker::default()
+            .create_mask(&source)
+            .iter_allowed(&source)
+            .map(|(_, chars)| chars.iter().collect())
+            .collect()
+    }
+
     #[test]
     fn ignores_many_comment_signs() {
         let source: Vec<_> = "%%%".chars().collect();
@@ -274,6 +282,36 @@ mod tests {
         assert_eq!(mask.iter_allowed(&source).count(), 2)
     }
 
+    #[test]
+    fn leaves_text_after_unmatched_inline_math_allowed() {
+        assert_eq!(allowed_text("before $after"), ["before $after"]);
+    }
+
+    #[test]
+    fn masks_paired_inline_math() {
+        assert_eq!(allowed_text("before $x$ after"), ["before ", " after"]);
+    }
+
+    #[test]
+    fn masks_text_between_escaped_dollars() {
+        assert_eq!(allowed_text(r"before \$x\$ after"), ["before ", " after"]);
+    }
+
+    #[test]
+    fn masks_text_between_parenthesized_math_delimiters() {
+        assert_eq!(allowed_text(r"before \(x\) after"), ["before ", " after"]);
+    }
+
+    #[test]
+    fn masks_empty_inline_math() {
+        assert_eq!(allowed_text("before $$ after"), ["before ", " after"]);
+    }
+
+    #[test]
+    fn leaves_trailing_dollar_allowed() {
+        assert_eq!(allowed_text("before $"), ["before $"]);
+    }
+
     #[test]
     fn emits_all_command_components_correctly() {
         let source: Vec<_> = r"\begin[some]{math}".chars().collect();

harper-tex/tests/run_tests.rs

@@ -44,3 +44,4 @@ create_test!(many_tags.tex, 6);
 create_test!(many_more_tags.tex, 11);
 create_test!(em_dash.tex, 0);
 create_test!(issue_2835.tex, 3);
+create_test!(issue_3791.tex, 2);

harper-tex/tests/test_sources/issue_3791.tex

@@ -0,0 +1,9 @@
+\documentclass[11pt]{article}
+
+\begin{document}
+errawr
+\begin{figure}
+\caption{A sample ($N_{THC}$).}
+\end{figure}
+errawr
+\end{document}