Reduced boilerplate code in the parser

boa_engine/src/syntax/parser/cursor/buffered_lexer/mod.rs

@@ -1,6 +1,6 @@
 use crate::syntax::{
     lexer::{InputElement, Lexer, Token, TokenKind},
-    parser::error::ParseError,
+    parser::{error::ParseError, ParseResult},
 };
 use boa_ast::Position;
 use boa_interner::Interner;
@@ -83,7 +83,7 @@ where
         &mut self,
         start: Position,
         interner: &mut Interner,
-    ) -> Result<Token, ParseError> {
+    ) -> ParseResult<Token> {
         let _timer = Profiler::global().start_event("cursor::lex_regex()", "Parsing");
         self.set_goal(InputElement::RegExp);
         self.lexer
@@ -97,7 +97,7 @@ where
         &mut self,
         start: Position,
         interner: &mut Interner,
-    ) -> Result<Token, ParseError> {
+    ) -> ParseResult<Token> {
         self.lexer
             .lex_template(start, interner)
             .map_err(ParseError::from)
@@ -116,7 +116,7 @@ where
     /// Fills the peeking buffer with the next token.
     ///
     /// It will not fill two line terminators one after the other.
-    fn fill(&mut self, interner: &mut Interner) -> Result<(), ParseError> {
+    fn fill(&mut self, interner: &mut Interner) -> ParseResult<()> {
         debug_assert!(
             self.write_index < PEEK_BUF_SIZE,
             "write index went out of bounds"
@@ -166,12 +166,12 @@ where
     ///
     /// This follows iterator semantics in that a `peek(0, false)` followed by a `next(false)` will
     /// return the same value. Note that because a `peek(n, false)` may return a line terminator a
-    // subsequent `next(true)` may not return the same value.
+    /// subsequent `next(true)` may not return the same value.
     pub(super) fn next(
         &mut self,
         skip_line_terminators: bool,
         interner: &mut Interner,
-    ) -> Result<Option<Token>, ParseError> {
+    ) -> ParseResult<Option<Token>> {
         if self.read_index == self.write_index {
             self.fill(interner)?;
         }
@@ -217,7 +217,7 @@ where
         skip_n: usize,
         skip_line_terminators: bool,
         interner: &mut Interner,
-    ) -> Result<Option<&Token>, ParseError> {
+    ) -> ParseResult<Option<&Token>> {
         assert!(
             skip_n <= MAX_PEEK_SKIP,
             "you cannot skip more than {} elements",

boa_engine/src/syntax/parser/cursor/mod.rs

@@ -1,7 +1,7 @@
 //! Cursor implementation for the parser.
 mod buffered_lexer;
 
-use super::{statement::PrivateElement, ParseError};
+use super::{statement::PrivateElement, OrAbrupt, ParseError, ParseResult};
 use crate::syntax::lexer::{InputElement, Lexer, Token, TokenKind};
 use boa_ast::{Position, Punctuator};
 use boa_interner::{Interner, Sym};
@@ -54,7 +54,7 @@ where
         &mut self,
         start: Position,
         interner: &mut Interner,
-    ) -> Result<Token, ParseError> {
+    ) -> ParseResult<Token> {
         self.buffered_lexer.lex_regex(start, interner)
     }
 
@@ -63,35 +63,55 @@ where
         &mut self,
         start: Position,
         interner: &mut Interner,
-    ) -> Result<Token, ParseError> {
+    ) -> ParseResult<Token> {
         self.buffered_lexer.lex_template(start, interner)
     }
 
+    /// Advances the cursor and returns the next token.
     #[inline]
-    pub(super) fn next(&mut self, interner: &mut Interner) -> Result<Option<Token>, ParseError> {
+    pub(super) fn next(&mut self, interner: &mut Interner) -> ParseResult<Option<Token>> {
         self.buffered_lexer.next(true, interner)
     }
 
+    /// Advances the cursor without returning the next token.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if there is no further token in the cursor.
+    #[inline]
+    #[track_caller]
+    #[allow(clippy::let_underscore_drop)]
+    pub(super) fn advance(&mut self, interner: &mut Interner) {
+        let _ = self
+            .next(interner)
+            .expect("tried to advance cursor, but the buffer was empty");
+    }
+
+    /// Peeks a future token, without consuming it or advancing the cursor.
+    ///
+    /// You can skip some tokens with the `skip_n` option.
     #[inline]
     pub(super) fn peek(
         &mut self,
         skip_n: usize,
         interner: &mut Interner,
-    ) -> Result<Option<&Token>, ParseError> {
+    ) -> ParseResult<Option<&Token>> {
         self.buffered_lexer.peek(skip_n, true, interner)
     }
 
+    /// Gets the current strict mode for the cursor.
     #[inline]
     pub(super) fn strict_mode(&self) -> bool {
         self.buffered_lexer.strict_mode()
     }
 
+    /// Sets the strict mode to strict or non-strict.
     #[inline]
     pub(super) fn set_strict_mode(&mut self, strict_mode: bool) {
         self.buffered_lexer.set_strict_mode(strict_mode);
     }
 
-    /// Returns if the cursor is currently in a arrow function declaration.
+    /// Returns if the cursor is currently in an arrow function declaration.
     #[inline]
     pub(super) fn arrow(&self) -> bool {
         self.arrow
@@ -116,7 +136,7 @@ where
         &mut self,
         identifier: Sym,
         position: Position,
-    ) -> Result<(), ParseError> {
+    ) -> ParseResult<()> {
         if let Some(env) = self.private_environments_stack.last_mut() {
             env.entry(identifier).or_insert(position);
             Ok(())
@@ -136,7 +156,7 @@ where
     pub(super) fn pop_private_environment(
         &mut self,
         identifiers: &FxHashMap<Sym, PrivateElement>,
-    ) -> Result<(), ParseError> {
+    ) -> ParseResult<()> {
         let last = self
             .private_environments_stack
             .pop()
@@ -163,11 +183,11 @@ where
         kind: K,
         context: &'static str,
         interner: &mut Interner,
-    ) -> Result<Token, ParseError>
+    ) -> ParseResult<Token>
     where
         K: Into<TokenKind>,
     {
-        let next_token = self.next(interner)?.ok_or(ParseError::AbruptEnd)?;
+        let next_token = self.next(interner).or_abrupt()?;
         let kind = kind.into();
 
         if next_token.kind() == &kind {
@@ -191,7 +211,7 @@ where
     pub(super) fn peek_semicolon(
         &mut self,
         interner: &mut Interner,
-    ) -> Result<SemicolonResult<'_>, ParseError> {
+    ) -> ParseResult<SemicolonResult<'_>> {
         match self.buffered_lexer.peek(0, false, interner)? {
             Some(tk) => match tk.kind() {
                 TokenKind::Punctuator(Punctuator::Semicolon | Punctuator::CloseBlock)
@@ -212,7 +232,7 @@ where
         &mut self,
         context: &'static str,
         interner: &mut Interner,
-    ) -> Result<(), ParseError> {
+    ) -> ParseResult<()> {
         match self.peek_semicolon(interner)? {
             SemicolonResult::Found(Some(tk)) => match *tk.kind() {
                 TokenKind::Punctuator(Punctuator::Semicolon) | TokenKind::LineTerminator => {
@@ -243,19 +263,20 @@ where
         skip_n: usize,
         context: &'static str,
         interner: &mut Interner,
-    ) -> Result<&Token, ParseError> {
-        if let Some(t) = self.buffered_lexer.peek(skip_n, false, interner)? {
-            if t.kind() == &TokenKind::LineTerminator {
-                Err(ParseError::unexpected(
-                    t.to_string(interner),
-                    t.span(),
-                    context,
-                ))
-            } else {
-                Ok(t)
-            }
+    ) -> ParseResult<&Token> {
+        let tok = self
+            .buffered_lexer
+            .peek(skip_n, false, interner)
+            .or_abrupt()?;
+
+        if tok.kind() == &TokenKind::LineTerminator {
+            Err(ParseError::unexpected(
+                tok.to_string(interner),
+                tok.span(),
+                context,
+            ))
         } else {
-            Err(ParseError::AbruptEnd)
+            Ok(tok)
         }
     }
 
@@ -265,7 +286,7 @@ where
         &mut self,
         skip_n: usize,
         interner: &mut Interner,
-    ) -> Result<Option<bool>, ParseError> {
+    ) -> ParseResult<Option<bool>> {
         if let Some(t) = self.buffered_lexer.peek(skip_n, false, interner)? {
             Ok(Some(t.kind() == &TokenKind::LineTerminator))
         } else {
@@ -283,7 +304,7 @@ where
         &mut self,
         kind: K,
         interner: &mut Interner,
-    ) -> Result<Option<Token>, ParseError>
+    ) -> ParseResult<Option<Token>>
     where
         K: Into<TokenKind>,
     {

boa_engine/src/syntax/parser/error.rs

@@ -12,13 +12,15 @@ pub(crate) trait ErrorContext {
     fn context(self, context: &'static str) -> Self;
 }
 
-impl<T> ErrorContext for Result<T, ParseError> {
+impl<T> ErrorContext for ParseResult<T> {
+    #[inline]
     fn context(self, context: &'static str) -> Self {
         self.map_err(|e| e.context(context))
     }
 }
 
 impl From<LexError> for ParseError {
+    #[inline]
     fn from(e: LexError) -> Self {
         Self::lex(e)
     }

boa_engine/src/syntax/parser/expression/assignment/arrow_function.rs

@@ -14,7 +14,8 @@ use crate::syntax::{
         error::{ErrorContext, ParseError, ParseResult},
         expression::BindingIdentifier,
         function::{FormalParameters, FunctionBody},
-        name_in_lexically_declared_names, AllowAwait, AllowIn, AllowYield, Cursor, TokenParser,
+        name_in_lexically_declared_names, AllowAwait, AllowIn, AllowYield, Cursor, OrAbrupt,
+        TokenParser,
     },
 };
 use ast::operations::{bound_names, top_level_lexically_declared_names};
@@ -78,7 +79,7 @@ where
 
     fn parse(self, cursor: &mut Cursor<R>, interner: &mut Interner) -> ParseResult<Self::Output> {
         let _timer = Profiler::global().start_event("ArrowFunction", "Parsing");
-        let next_token = cursor.peek(0, interner)?.ok_or(ParseError::AbruptEnd)?;
+        let next_token = cursor.peek(0, interner).or_abrupt()?;
 
         let (params, params_start_position) = if let TokenKind::Punctuator(Punctuator::OpenParen) =
             &next_token.kind()
@@ -191,13 +192,9 @@ where
     type Output = StatementList;
 
     fn parse(self, cursor: &mut Cursor<R>, interner: &mut Interner) -> ParseResult<Self::Output> {
-        match cursor
-            .peek(0, interner)?
-            .ok_or(ParseError::AbruptEnd)?
-            .kind()
-        {
+        match cursor.peek(0, interner).or_abrupt()?.kind() {
             TokenKind::Punctuator(Punctuator::OpenBlock) => {
-                let _next = cursor.next(interner)?;
+                cursor.advance(interner);
                 let body = FunctionBody::new(false, false).parse(cursor, interner)?;
                 cursor.expect(Punctuator::CloseBlock, "arrow function", interner)?;
                 Ok(body)

boa_engine/src/syntax/parser/expression/assignment/async_arrow_function.rs

@@ -14,7 +14,7 @@ use crate::syntax::{
         error::{ErrorContext, ParseError, ParseResult},
         expression::BindingIdentifier,
         function::{FormalParameters, FunctionBody},
-        name_in_lexically_declared_names, AllowIn, AllowYield, Cursor, TokenParser,
+        name_in_lexically_declared_names, AllowIn, AllowYield, Cursor, OrAbrupt, TokenParser,
     },
 };
 use ast::{
@@ -76,7 +76,7 @@ where
         cursor.expect((Keyword::Async, false), "async arrow function", interner)?;
         cursor.peek_expect_no_lineterminator(0, "async arrow function", interner)?;
 
-        let next_token = cursor.peek(0, interner)?.ok_or(ParseError::AbruptEnd)?;
+        let next_token = cursor.peek(0, interner).or_abrupt()?;
         let (params, params_start_position) = if let TokenKind::Punctuator(Punctuator::OpenParen) =
             &next_token.kind()
         {
@@ -180,13 +180,9 @@ where
     type Output = StatementList;
 
     fn parse(self, cursor: &mut Cursor<R>, interner: &mut Interner) -> ParseResult<Self::Output> {
-        match cursor
-            .peek(0, interner)?
-            .ok_or(ParseError::AbruptEnd)?
-            .kind()
-        {
+        match cursor.peek(0, interner).or_abrupt()?.kind() {
             TokenKind::Punctuator(Punctuator::OpenBlock) => {
-                cursor.next(interner)?;
+                cursor.advance(interner);
                 let body = FunctionBody::new(false, true).parse(cursor, interner)?;
                 cursor.expect(Punctuator::CloseBlock, "async arrow function", interner)?;
                 Ok(body)

boa_engine/src/syntax/parser/expression/assignment/conditional.rs

@@ -79,7 +79,7 @@ where
 
         if let Some(tok) = cursor.peek(0, interner)? {
             if tok.kind() == &TokenKind::Punctuator(Punctuator::Question) {
-                cursor.next(interner)?.expect("? character vanished"); // Consume the token.
+                cursor.advance(interner);
                 let then_clause =
                     AssignmentExpression::new(None, true, self.allow_yield, self.allow_await)
                         .parse(cursor, interner)?;

boa_engine/src/syntax/parser/expression/assignment/exponentiation.rs

@@ -7,12 +7,11 @@
 //! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Exponentiation
 //! [spec]: https://tc39.es/ecma262/#sec-exp-operator
 
-use super::ParseError;
 use crate::syntax::{
     lexer::TokenKind,
     parser::{
         expression::{unary::UnaryExpression, update::UpdateExpression},
-        AllowAwait, AllowYield, Cursor, ParseResult, TokenParser,
+        AllowAwait, AllowYield, Cursor, OrAbrupt, ParseResult, TokenParser,
     },
 };
 use boa_ast::{
@@ -70,7 +69,7 @@ where
     fn parse(self, cursor: &mut Cursor<R>, interner: &mut Interner) -> ParseResult<Self::Output> {
         let _timer = Profiler::global().start_event("ExponentiationExpression", "Parsing");
 
-        let next = cursor.peek(0, interner)?.ok_or(ParseError::AbruptEnd)?;
+        let next = cursor.peek(0, interner).or_abrupt()?;
         match next.kind() {
             TokenKind::Keyword((Keyword::Delete | Keyword::Void | Keyword::TypeOf, _))
             | TokenKind::Punctuator(
@@ -90,7 +89,7 @@ where
             .parse(cursor, interner)?;
         if let Some(tok) = cursor.peek(0, interner)? {
             if let TokenKind::Punctuator(Punctuator::Exp) = tok.kind() {
-                cursor.next(interner)?.expect("** token vanished"); // Consume the token.
+                cursor.advance(interner);
                 return Ok(Binary::new(
                     ArithmeticOp::Exp.into(),
                     lhs,