Merge pull request #9 from Tcode-Motion/bolt-parser-optimization-9269391063391972267

⚡ Bolt: Remove unnecessary Token cloning in parser

Author: Tcode-Motion

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2024-01-20 - Lifetime Refactoring in Parser to Eliminate Token Cloning
+**Learning:** In the Rust parser (`compiler/parser/src/parser.rs`), methods like `advance()` and `previous()` originally returned a reference tied to `&mut self`. Because `Token` was still borrowing `self` mutably, the parser couldn't call methods like `self.parse_prefix` (which requires another `&mut self` borrow) without first calling `.clone()` on the token to drop the initial borrow.
+**Action:** By explicitly defining the return lifetime as `&'a Token` (tied to the lifetime of the underlying token slice `&'a [Token]`, rather than the `Parser` instance), the mutable borrow of `self` ends immediately. This elegantly satisfies the borrow checker while removing the overhead of cloning tokens throughout `expressions.rs` and `statements.rs`. Look for similar lifetime constraints elsewhere in the compiler that force unnecessary copies.

compiler/parser/src/expressions.rs

@@ -14,8 +14,8 @@ impl<'a> Parser<'a> {
         precedence: Precedence,
         reporter: &mut DiagnosticReporter,
     ) -> ParseResult<Expression> {
-        let token = self.advance().clone();
-        let mut left = self.parse_prefix(&token, reporter)?;
+        let token = self.advance();
+        let mut left = self.parse_prefix(token, reporter)?;
 
         while !self.is_at_end() {
             let next_prec = self.peek().kind.precedence();
@@ -41,8 +41,8 @@ impl<'a> Parser<'a> {
                 break;
             }
 
-            let next_token = self.advance().clone();
-            left = self.parse_infix(left, &next_token, reporter)?;
+            let next_token = self.advance();
+            left = self.parse_infix(left, next_token, reporter)?;
         }
 
         Ok(left)

compiler/parser/src/parser.rs

@@ -162,15 +162,15 @@ impl<'a> Parser<'a> {
     }
 
     /// Advances the cursor and returns the previous token.
-    pub(crate) fn advance(&mut self) -> &Token {
+    pub(crate) fn advance(&mut self) -> &'a Token {
         if !self.is_at_end() {
             self.pos += 1;
         }
         &self.tokens[self.pos - 1]
     }
 
     /// Returns the previous token.
-    pub(crate) fn previous(&self) -> &Token {
+    pub(crate) fn previous(&self) -> &'a Token {
         &self.tokens[self.pos - 1]
     }
 

compiler/parser/src/statements.rs

@@ -67,7 +67,7 @@ impl<'a> Parser<'a> {
             || self.check(TokenKind::Send)
         {
             let start_pos = self.peek().span.start;
-            let kw_token = self.peek().clone();
+            let kw_token = self.peek();
             if kw_token.kind == TokenKind::Return {
                 reporter.report(techscript_errors::Diagnostic::new(
                     techscript_errors::DiagnosticLevel::Warning,

patch_expressions.diff

@@ -0,0 +1,17 @@
+--- compiler/parser/src/expressions.rs
++++ compiler/parser/src/expressions.rs
+@@ -17,7 +17,7 @@
+         let token = self.advance();
+-        let mut left = self.parse_prefix(&token, reporter)?;
++        let mut left = self.parse_prefix(token, reporter)?;
+
+         while !self.is_at_end() {
+             let next_prec = self.peek().kind.precedence();
+@@ -44,7 +44,7 @@
+
+             let next_token = self.advance();
+-            left = self.parse_infix(left, &next_token, reporter)?;
++            left = self.parse_infix(left, next_token, reporter)?;
+         }
+
+         Ok(left)