From 9b59f6bf1973fe3f502f66c92650ffe517805e66 Mon Sep 17 00:00:00 2001
From: Jake Fecher <jfecher11@gmail.com>
Date: Mon, 24 Jun 2024 12:41:16 -0500
Subject: [PATCH] Add unclosed quote error

---
 compiler/noirc_frontend/src/lexer/errors.rs |  8 +++++-
 compiler/noirc_frontend/src/lexer/lexer.rs  | 27 ++++++++++++++++++---
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/compiler/noirc_frontend/src/lexer/errors.rs b/compiler/noirc_frontend/src/lexer/errors.rs
index dbaf2f3a81e..2452e034c1c 100644
--- a/compiler/noirc_frontend/src/lexer/errors.rs
+++ b/compiler/noirc_frontend/src/lexer/errors.rs
@@ -29,6 +29,8 @@ pub enum LexerErrorKind {
     InvalidEscape { escaped: char, span: Span },
     #[error("Invalid quote delimiter `{delimiter}`, valid delimiters are `{{`, `[`, and `(`")]
     InvalidQuoteDelimiter { delimiter: SpannedToken },
+    #[error("Expected `{end_delim}` to close this {start_delim}")]
+    UnclosedQuote { start_delim: SpannedToken, end_delim: Token },
 }
 
 impl From<LexerErrorKind> for ParserError {
@@ -50,6 +52,7 @@ impl LexerErrorKind {
             LexerErrorKind::UnterminatedStringLiteral { span } => *span,
             LexerErrorKind::InvalidEscape { span, .. } => *span,
             LexerErrorKind::InvalidQuoteDelimiter { delimiter } => delimiter.to_span(),
+            LexerErrorKind::UnclosedQuote { start_delim, .. } => start_delim.to_span(),
         }
     }
 
@@ -96,8 +99,11 @@ impl LexerErrorKind {
             LexerErrorKind::InvalidEscape { escaped, span } =>
                 (format!("'\\{escaped}' is not a valid escape sequence. Use '\\' for a literal backslash character."), "Invalid escape sequence".to_string(), *span),
             LexerErrorKind::InvalidQuoteDelimiter { delimiter } => {
-                ("Invalid quote delimiter `{delimiter}`".to_string(), "Valid delimiters are `{`, `[`, and `(`".to_string(), delimiter.to_span())
+                (format!("Invalid quote delimiter `{delimiter}`"), "Valid delimiters are `{`, `[`, and `(`".to_string(), delimiter.to_span())
             },
+            LexerErrorKind::UnclosedQuote { start_delim, end_delim } => {
+                ("Unclosed `quote` expression".to_string(), format!("Expected a `{end_delim}` to close this `{start_delim}`"), start_delim.to_span())
+            }
         }
     }
 }
diff --git a/compiler/noirc_frontend/src/lexer/lexer.rs b/compiler/noirc_frontend/src/lexer/lexer.rs
index 249103b3d15..d2bc3d0f519 100644
--- a/compiler/noirc_frontend/src/lexer/lexer.rs
+++ b/compiler/noirc_frontend/src/lexer/lexer.rs
@@ -536,15 +536,21 @@ impl<'a> Lexer<'a> {
         };
 
         let mut tokens = Vec::new();
-        let mut nested_delimiters = 1;
 
-        while nested_delimiters != 0 {
+        // Keep track of each nested delimiter we need to close.
+        let mut nested_delimiters = vec![delimiter];
+
+        while !nested_delimiters.is_empty() {
             let token = self.next_token()?;
 
             if *token.token() == start_delim {
-                nested_delimiters += 1;
+                nested_delimiters.push(token.clone());
             } else if *token.token() == end_delim {
-                nested_delimiters -= 1;
+                nested_delimiters.pop();
+            } else if *token.token() == Token::EOF {
+                let start_delim =
+                    nested_delimiters.pop().expect("If this were empty, we wouldn't be looping");
+                return Err(LexerErrorKind::UnclosedQuote { start_delim, end_delim });
             }
 
             tokens.push(token);
@@ -1312,4 +1318,17 @@ mod tests {
             }
         }
     }
+
+    #[test]
+    fn test_unclosed_quote() {
+        let cases = vec!["quote {", "quote { {  }", "quote [ []", "quote (((((((())))"];
+
+        for source in cases {
+            // `quote` is not itself a keyword so if the token stream fails to
+            // parse we don't expect any valid tokens from the quote construct
+            for token in Lexer::new(source) {
+                assert!(token.is_err(), "Expected Err, found {token:?}");
+            }
+        }
+    }
 }