chore: fix unterminated block comment (#1958)

fix unterminated block comment

crates/noirc_frontend/src/lexer/errors.rs

@@ -19,6 +19,8 @@ pub enum LexerErrorKind {
     TooManyBits { span: Span, max: u32, got: u32 },
     #[error("LogicalAnd used instead of bitwise and")]
     LogicalAnd { span: Span },
+    #[error("Unterminated block comment")]
+    UnterminatedBlockComment { span: Span },
 }
 
 impl LexerErrorKind {
@@ -30,6 +32,7 @@ impl LexerErrorKind {
             LexerErrorKind::MalformedFuncAttribute { span, .. } => *span,
             LexerErrorKind::TooManyBits { span, .. } => *span,
             LexerErrorKind::LogicalAnd { span } => *span,
+            LexerErrorKind::UnterminatedBlockComment { span } => *span,
         }
     }
 
@@ -77,6 +80,7 @@ impl LexerErrorKind {
                 "Try `&` instead, or use `if` only if you require short-circuiting".to_string(),
                 *span,
             ),
+            LexerErrorKind::UnterminatedBlockComment { span } => ("unterminated block comment".to_string(), "Unterminated block comment".to_string(), *span),
         }
     }
 }

crates/noirc_frontend/src/lexer/lexer.rs

@@ -339,6 +339,7 @@ impl<'a> Lexer<'a> {
     }
 
     fn parse_block_comment(&mut self) -> SpannedTokenResult {
+        let span = Span::new(self.position..self.position + 1);
         let mut depth = 1usize;
 
         while let Some(ch) = self.next_char() {
@@ -352,6 +353,8 @@ impl<'a> Lexer<'a> {
                     depth -= 1;
 
                     // This block comment is closed, so for a construction like "/* */ */"
+                    // there will be a successfully parsed block comment "/* */"
+                    // and " */" will be processed separately.
                     if depth == 0 {
                         break;
                     }
@@ -360,7 +363,11 @@ impl<'a> Lexer<'a> {
             }
         }
 
-        self.next_token()
+        if depth == 0 {
+            self.next_token()
+        } else {
+            Err(LexerErrorKind::UnterminatedBlockComment { span })
+        }
     }
 
     /// Skips white space. They are not significant in the source language
@@ -497,6 +504,16 @@ fn test_arithmetic_sugar() {
     }
 }
 
+#[test]
+fn unterminated_block_comment() {
+    let input = "/*/";
+
+    let mut lexer = Lexer::new(input);
+    let token = lexer.next().unwrap();
+
+    assert!(token.is_err());
+}
+
 #[test]
 fn test_comment() {
     let input = "// hello