From 5bbda1a24e7f8174ecf5be824e682c4f4e15f025 Mon Sep 17 00:00:00 2001
From: Jeff <dev@jeffa.io>
Date: Sat, 12 Oct 2024 08:16:06 -0400
Subject: [PATCH] Disallow comparison chaining

---
 dust-lang/src/chunk.rs  | 10 +++-------
 dust-lang/src/parser.rs | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/dust-lang/src/chunk.rs b/dust-lang/src/chunk.rs
index 09d4158..3f5f8f7 100644
--- a/dust-lang/src/chunk.rs
+++ b/dust-lang/src/chunk.rs
@@ -215,13 +215,7 @@ impl Chunk {
         register_index: u8,
         position: Span,
     ) -> Result<u8, ChunkError> {
-        log::debug!(
-            "Declaring local: {:?} {:?} {:?} {:?}",
-            identifier,
-            r#type,
-            is_mutable,
-            register_index
-        );
+        log::debug!("Declare local {identifier}");
 
         let starting_length = self.locals.len();
 
@@ -253,6 +247,8 @@ impl Chunk {
             }
         })?;
 
+        log::debug!("Define local {}", local.identifier);
+
         local.register_index = Some(register_index);
 
         Ok(())
diff --git a/dust-lang/src/parser.rs b/dust-lang/src/parser.rs
index a9a3b59..de3fb7e 100644
--- a/dust-lang/src/parser.rs
+++ b/dust-lang/src/parser.rs
@@ -553,6 +553,14 @@ impl<'src> Parser<'src> {
     }
 
     fn parse_comparison_binary(&mut self) -> Result<(), ParseError> {
+        if let [Some(Operation::Jump), Some(Operation::Equal) | Some(Operation::Less) | Some(Operation::LessEqual)] =
+            self.chunk.get_last_n_operations()
+        {
+            return Err(ParseError::CannotChainComparison {
+                position: self.current_position,
+            });
+        }
+
         let (left_instruction, left_position) =
             self.chunk.pop_instruction(self.current_position)?;
         let (push_back_left, left_is_constant, _, left) =
@@ -1499,6 +1507,9 @@ impl From<&Token<'_>> for ParseRule<'_> {
 
 #[derive(Debug, PartialEq)]
 pub enum ParseError {
+    CannotChainComparison {
+        position: Span,
+    },
     CannotMutateImmutableVariable {
         identifier: Identifier,
         position: Span,
@@ -1565,6 +1576,7 @@ impl AnnotatedError for ParseError {
 
     fn description(&self) -> &'static str {
         match self {
+            Self::CannotChainComparison { .. } => "Cannot chain comparison",
             Self::CannotMutateImmutableVariable { .. } => "Cannot mutate immutable variable",
             Self::ExpectedExpression { .. } => "Expected an expression",
             Self::ExpectedToken { .. } => "Expected a specific token",
@@ -1584,6 +1596,9 @@ impl AnnotatedError for ParseError {
 
     fn details(&self) -> Option<String> {
         match self {
+            Self::CannotChainComparison { .. } => {
+                Some("Cannot chain comparison operations".to_string())
+            }
             Self::CannotMutateImmutableVariable { identifier, .. } => {
                 Some(format!("Cannot mutate immutable variable {identifier}"))
             }
@@ -1633,6 +1648,7 @@ impl AnnotatedError for ParseError {
 
     fn position(&self) -> Span {
         match self {
+            Self::CannotChainComparison { position } => *position,
             Self::CannotMutateImmutableVariable { position, .. } => *position,
             Self::ExpectedExpression { position, .. } => *position,
             Self::ExpectedToken { position, .. } => *position,