Add specific error for unclosed string interpolations

Author: istathar

src/parsing/parser.rs

@@ -27,6 +27,7 @@ pub enum ParsingError {
     Unrecognized(usize), // improve this
     Expected(usize, &'static str),
     ExpectedMatchingChar(usize, &'static str, char, char),
+    UnclosedInterpolation(usize),
     InvalidHeader(usize),
     InvalidCharacter(usize, char),
     UnexpectedEndOfInput(usize),
@@ -60,6 +61,7 @@ impl ParsingError {
             ParsingError::Unrecognized(offset) => *offset,
             ParsingError::Expected(offset, _) => *offset,
             ParsingError::ExpectedMatchingChar(offset, _, _, _) => *offset,
+            ParsingError::UnclosedInterpolation(offset) => *offset,
             ParsingError::InvalidHeader(offset) => *offset,
             ParsingError::InvalidCharacter(offset, _) => *offset,
             ParsingError::UnexpectedEndOfInput(offset) => *offset,
@@ -1479,12 +1481,9 @@ impl<'i> Parser<'i> {
                         current_pos = end_pos + 1;
                     }
                     None => {
-                        // Unmatched brace - point to end of string content (at closing quote)
-                        return Err(ParsingError::ExpectedMatchingChar(
-                            self.offset + raw.len(),
-                            "an interpolation",
-                            '{',
-                            '}',
+                        // Unmatched brace - point to the opening brace position
+                        return Err(ParsingError::UnclosedInterpolation(
+                            self.offset + absolute_brace_start,
                         ));
                     }
                 }

src/problem/messages.rs

@@ -35,6 +35,16 @@ there was no more input remaining in the current scope.
             .trim_ascii()
             .to_string(),
         ),
+        ParsingError::UnclosedInterpolation(_) => (
+            "Unclosed string interpolation".to_string(),
+            r#"
+Every '{' that starts an interpolation within a string must have a
+corresponding '}' to mark where the interpolation ends and the string
+literal resumes.
+            "#
+            .trim_ascii()
+            .to_string(),
+        ),
         ParsingError::InvalidHeader(_) => {
             // Format the sample metadata using the same code as the formatter
             let mut formatted_example = String::new();