Strict Mode Lex/Parse (#717)

* Add strict mode to lex trait

* Lexer reserved keyword identifier strict mode lexing

* Prevent with statement in strict mode

* Add strict_mode flag to parse methods

* Enable function scope strict mode

* Script scope strict mode

* Delete statement strict mode

* Function decl in block in strict mode

* Fix merge

* Strict mode code tests

* Move strict_mode flag onto Lexer

* Move strict_mode lex flag to Lexer Cursor

* Isolated failing test parts

* Fixed bug in func decl in block in strict mode

* BindingIdentifier strict mode

* use to_string

* Remove dbg

* Add missing spec ref

* Missing spec ref for dup func params

* Remove clone

* .to_string -> .as_ref

boa/src/exec/tests.rs

@@ -1383,3 +1383,124 @@ fn test_identifier_op() {
     let scenario = "break = 1";
     assert_eq!(&exec(scenario), "\"SyntaxError\": \"expected token \'identifier\', got \'=\' in binding identifier at line 1, col 7\"");
 }
+
+#[test]
+fn test_strict_mode_octal() {
+    // Checks as per https://tc39.es/ecma262/#sec-literals-numeric-literals that 0 prefix
+    // octal number literal syntax is a syntax error in strict mode.
+
+    let scenario = r#"
+    'use strict';
+    var n = 023;
+    "#;
+
+    let mut engine = Context::new();
+
+    let string = dbg!(forward(&mut engine, scenario));
+
+    assert!(string.starts_with("Uncaught \"SyntaxError\": "));
+}
+
+#[test]
+fn test_strict_mode_with() {
+    // Checks as per https://tc39.es/ecma262/#sec-with-statement-static-semantics-early-errors
+    // that a with statement is an error in strict mode code.
+
+    let scenario = r#"
+    'use strict';
+    function f(x, o) {
+        with (o) {
+            console.log(x);
+        }
+    }
+    "#;
+
+    let mut engine = Context::new();
+
+    let string = dbg!(forward(&mut engine, scenario));
+
+    assert!(string.starts_with("Uncaught \"SyntaxError\": "));
+}
+
+#[test]
+fn test_strict_mode_delete() {
+    // Checks as per https://tc39.es/ecma262/#sec-delete-operator-static-semantics-early-errors
+    // that delete on a variable name is an error in strict mode code.
+
+    let scenario = r#"
+    'use strict';
+    let x = 10;
+    delete x;
+    "#;
+
+    let mut engine = Context::new();
+
+    let string = dbg!(forward(&mut engine, scenario));
+
+    assert!(string.starts_with("Uncaught \"SyntaxError\": "));
+}
+
+#[test]
+fn test_strict_mode_reserved_name() {
+    // Checks that usage of a reserved keyword for an identifier name is
+    // an error in strict mode code as per https://tc39.es/ecma262/#sec-strict-mode-of-ecmascript.
+
+    let test_cases = [
+        "var implements = 10;",
+        "var interface = 10;",
+        "var package = 10;",
+        "var private = 10;",
+        "var protected = 10;",
+        "var public = 10;",
+        "var static = 10;",
+        "var eval = 10;",
+        "var arguments = 10;",
+        "var let = 10;",
+        "var yield = 10;",
+    ];
+
+    for case in test_cases.iter() {
+        let mut engine = Context::new();
+        let scenario = format!("'use strict'; \n {}", case);
+
+        let string = dbg!(forward(&mut engine, &scenario));
+
+        assert!(string.starts_with("Uncaught \"SyntaxError\": "));
+    }
+}
+
+#[test]
+fn test_strict_mode_func_decl_in_block() {
+    // Checks that a function declaration in a block is an error in
+    // strict mode code as per https://tc39.es/ecma262/#early-error.
+
+    let scenario = r#"
+    'use strict';
+    let a = 4;
+    let b = 5;
+    if (a < b) { function f() {} }
+    "#;
+
+    let mut engine = Context::new();
+
+    let string = dbg!(forward(&mut engine, scenario));
+
+    assert!(string.starts_with("Uncaught \"SyntaxError\": "));
+}
+
+#[test]
+fn test_strict_mode_dup_func_parameters() {
+    // Checks that a function cannot contain duplicate parameter
+    // names in strict mode code as per https://tc39.es/ecma262/#sec-function-definitions-static-semantics-early-errors.
+
+    let scenario = r#"
+    'use strict';
+    function f(a, b, b) {}
+    "#;
+
+    let mut engine = Context::new();
+
+    let string = dbg!(forward(&mut engine, scenario));
+
+    assert!(string.starts_with("Uncaught \"SyntaxError\": "));
+}

boa/src/syntax/lexer/cursor.rs

@@ -9,6 +9,7 @@ pub(super) struct Cursor<R> {
     iter: InnerIter<R>,
     peeked: Option<Option<char>>,
     pos: Position,
+    strict_mode: bool,
 }
 
 impl<R> Cursor<R> {
@@ -38,6 +39,16 @@ impl<R> Cursor<R> {
         let current_line = self.pos.line_number();
         self.pos = Position::new(current_line, 1);
     }
+
+    #[inline]
+    pub(super) fn strict_mode(&self) -> bool {
+        self.strict_mode
+    }
+
+    #[inline]
+    pub(super) fn set_strict_mode(&mut self, strict_mode: bool) {
+        self.strict_mode = strict_mode
+    }
 }
 
 impl<R> Cursor<R>
@@ -51,6 +62,7 @@ where
             iter: InnerIter::new(inner.bytes()),
             peeked: None,
             pos: Position::new(1, 1),
+            strict_mode: false,
         }
     }
 

boa/src/syntax/lexer/identifier.rs

@@ -4,12 +4,26 @@ use super::{Cursor, Error, Tokenizer};
 use crate::{
     profiler::BoaProfiler,
     syntax::{
-        ast::{Position, Span},
+        ast::{Keyword, Position, Span},
         lexer::{Token, TokenKind},
     },
 };
 use std::io::Read;
 
+const STRICT_FORBIDDEN_IDENTIFIERS: [&str; 11] = [
+    "eval",
+    "arguments",
+    "implements",
+    "interface",
+    "let",
+    "package",
+    "private",
+    "protected",
+    "public",
+    "static",
+    "yield",
+];
+
 /// Identifier lexing.
 ///
 /// More information:
@@ -49,8 +63,24 @@ impl<R> Tokenizer<R> for Identifier {
             "null" => TokenKind::NullLiteral,
             slice => {
                 if let Ok(keyword) = slice.parse() {
+                    if cursor.strict_mode() && keyword == Keyword::With {
+                        return Err(Error::Syntax(
+                            "using 'with' statement not allowed in strict mode".into(),
+                            start_pos,
+                        ));
+                    }
                     TokenKind::Keyword(keyword)
                 } else {
+                    if cursor.strict_mode() && STRICT_FORBIDDEN_IDENTIFIERS.contains(&slice) {
+                        return Err(Error::Syntax(
+                            format!(
+                                "using future reserved keyword '{}' not allowed in strict mode",
+                                slice
+                            )
+                            .into(),
+                            start_pos,
+                        ));
+                    }
                     TokenKind::identifier(slice)
                 }
             }

boa/src/syntax/lexer/mod.rs

@@ -90,6 +90,16 @@ impl<R> Lexer<R> {
         self.goal_symbol
     }
 
+    #[inline]
+    pub(super) fn strict_mode(&self) -> bool {
+        self.cursor.strict_mode()
+    }
+
+    #[inline]
+    pub(super) fn set_strict_mode(&mut self, strict_mode: bool) {
+        self.cursor.set_strict_mode(strict_mode)
+    }
+
     /// Creates a new lexer.
     #[inline]
     pub fn new(reader: R) -> Self
@@ -180,9 +190,6 @@ impl<R> Lexer<R> {
             }
         };
 
-        // TODO, setting strict mode on/off.
-        let strict_mode = false;
-
         let token = match next_chr {
             '\r' | '\n' | '\u{2028}' | '\u{2029}' => Ok(Token::new(
                 TokenKind::LineTerminator,
@@ -190,9 +197,7 @@ impl<R> Lexer<R> {
             )),
             '"' | '\'' => StringLiteral::new(next_chr).lex(&mut self.cursor, start),
             '`' => TemplateLiteral.lex(&mut self.cursor, start),
-            _ if next_chr.is_digit(10) => {
+            _ if next_chr.is_digit(10) => NumberLiteral::new(next_chr).lex(&mut self.cursor, start),
-                NumberLiteral::new(next_chr, strict_mode).lex(&mut self.cursor, start)
-            }
             _ if next_chr.is_alphabetic() || next_chr == '$' || next_chr == '_' => {
                 Identifier::new(next_chr).lex(&mut self.cursor, start)
             }

boa/src/syntax/lexer/number.rs

@@ -24,13 +24,12 @@ use std::{io::Read, str::FromStr};
 #[derive(Debug, Clone, Copy)]
 pub(super) struct NumberLiteral {
     init: char,
-    strict_mode: bool,
 }
 
 impl NumberLiteral {
     /// Creates a new string literal lexer.
-    pub(super) fn new(init: char, strict_mode: bool) -> Self {
+    pub(super) fn new(init: char) -> Self {
-        Self { init, strict_mode }
+        Self { init }
     }
 }
 
@@ -187,7 +186,7 @@ impl<R> Tokenizer<R> for NumberLiteral {
                     ch => {
                         if ch.is_digit(8) {
                             // LegacyOctalIntegerLiteral
-                            if self.strict_mode {
+                            if cursor.strict_mode() {
                                 // LegacyOctalIntegerLiteral is forbidden with strict mode true.
                                 return Err(Error::syntax(
                                     "implicit octal literals are not allowed in strict mode",
@@ -205,7 +204,7 @@ impl<R> Tokenizer<R> for NumberLiteral {
                             // Indicates a numerical digit comes after then 0 but it isn't an octal digit
                             // so therefore this must be a number with an unneeded leading 0. This is
                             // forbidden in strict mode.
-                            if self.strict_mode {
+                            if cursor.strict_mode() {
                                 return Err(Error::syntax(
                                     "leading 0's are not allowed in strict mode",
                                     start_pos,

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

@@ -82,6 +82,16 @@ where
         self.lexer.lex_slash_token(start).map_err(|e| e.into())
     }
 
+    #[inline]
+    pub(super) fn strict_mode(&self) -> bool {
+        self.lexer.strict_mode()
+    }
+
+    #[inline]
+    pub(super) fn set_strict_mode(&mut self, strict_mode: bool) {
+        self.lexer.set_strict_mode(strict_mode)
+    }
+
     /// Fills the peeking buffer with the next token.
     ///
     /// It will not fill two line terminators one after the other.

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

@@ -56,6 +56,16 @@ where
         self.buffered_lexer.peek(skip_n, true)
     }
 
+    #[inline]
+    pub(super) fn strict_mode(&self) -> bool {
+        self.buffered_lexer.strict_mode()
+    }
+
+    #[inline]
+    pub(super) fn set_strict_mode(&mut self, strict_mode: bool) {
+        self.buffered_lexer.set_strict_mode(strict_mode)
+    }
+
     /// Returns an error if the next token is not of kind `kind`.
     ///
     /// Note: it will consume the next token only if the next token is the expected type.

boa/src/syntax/parser/expression/mod.rs

@@ -61,7 +61,7 @@ macro_rules! expression { ($name:ident, $lower:ident, [$( $op:path ),*], [$( $lo
     {
         type Output = Node;
 
-        fn parse(self, cursor: &mut Cursor<R>) -> ParseResult {
+        fn parse(self, cursor: &mut Cursor<R>)-> ParseResult {
             let _timer = BoaProfiler::global().start_event($profile, "Parsing");
 
             if $goal.is_some() {

boa/src/syntax/parser/expression/unary.rs

@@ -15,7 +15,7 @@ use crate::{
             op::UnaryOp,
             Keyword, Punctuator,
         },
-        lexer::TokenKind,
+        lexer::{Error as LexError, TokenKind},
         parser::{
             expression::update::UpdateExpression, AllowAwait, AllowYield, Cursor, ParseError,
             ParseResult, TokenParser,
@@ -62,10 +62,22 @@ where
         let _timer = BoaProfiler::global().start_event("UnaryExpression", "Parsing");
 
         let tok = cursor.peek(0)?.ok_or(ParseError::AbruptEnd)?;
+        let token_start = tok.span().start();
         match tok.kind() {
             TokenKind::Keyword(Keyword::Delete) => {
                 cursor.next()?.expect("Delete keyword vanished"); // Consume the token.
-                Ok(node::UnaryOp::new(UnaryOp::Delete, self.parse(cursor)?).into())
+                let val = self.parse(cursor)?;
+
+                if cursor.strict_mode() {
+                    if let Node::Identifier(_) = val {
+                        return Err(ParseError::lex(LexError::Syntax(
+                            "Delete <variable> statements not allowed in strict mode".into(),
+                            token_start,
+                        )));
+                    }
+                }
+
+                Ok(node::UnaryOp::new(UnaryOp::Delete, val).into())
             }
             TokenKind::Keyword(Keyword::Void) => {
                 cursor.next()?.expect("Void keyword vanished"); // Consume the token.

boa/src/syntax/parser/function/mod.rs

@@ -259,12 +259,27 @@ where
 
     fn parse(self, cursor: &mut Cursor<R>) -> Result<Self::Output, ParseError> {
         let _timer = BoaProfiler::global().start_event("FunctionStatementList", "Parsing");
+
+        let global_strict_mode = cursor.strict_mode();
         if let Some(tk) = cursor.peek(0)? {
-            if tk.kind() == &Punctuator::CloseBlock.into() {
+            match tk.kind() {
-                return Ok(Vec::new().into());
+                TokenKind::Punctuator(Punctuator::CloseBlock) => {
+                    return Ok(Vec::new().into());
+                }
+                TokenKind::StringLiteral(string) | TokenKind::TemplateLiteral(string) => {
+                    if string == &"use strict".into() {
+                        cursor.set_strict_mode(true);
+                    }
+                }
+                _ => {}
             }
         }
 
-        StatementList::new(self.allow_yield, self.allow_await, true, true).parse(cursor)
+        let stmlist =
+            StatementList::new(self.allow_yield, self.allow_await, true, true, true).parse(cursor);
+
+        // Reset strict mode back to the global scope.
+        cursor.set_strict_mode(global_strict_mode);
+        stmlist
     }
 }

boa/src/syntax/parser/mod.rs

@@ -9,7 +9,7 @@ mod statement;
 mod tests;
 
 pub use self::error::{ParseError, ParseResult};
-use crate::syntax::ast::node::StatementList;
+use crate::syntax::{ast::node::StatementList, lexer::TokenKind};
 
 use cursor::Cursor;
 
@@ -121,10 +121,19 @@ where
     type Output = StatementList;
 
     fn parse(self, cursor: &mut Cursor<R>) -> Result<Self::Output, ParseError> {
-        if cursor.peek(0)?.is_some() {
+        match cursor.peek(0)? {
-            ScriptBody.parse(cursor)
+            Some(tok) => {
-        } else {
+                match tok.kind() {
-            Ok(StatementList::from(Vec::new()))
+                    TokenKind::StringLiteral(string) | TokenKind::TemplateLiteral(string) => {
+                        if string.as_ref() == "use strict" {
+                            cursor.set_strict_mode(true);
+                        }
+                    }
+                    _ => {}
+                }
+                ScriptBody.parse(cursor)
+            }
+            None => Ok(StatementList::from(Vec::new())),
         }
     }
 }
@@ -145,6 +154,6 @@ where
     type Output = StatementList;
 
     fn parse(self, cursor: &mut Cursor<R>) -> Result<Self::Output, ParseError> {
-        self::statement::StatementList::new(false, false, false, false).parse(cursor)
+        self::statement::StatementList::new(false, false, false, false, true).parse(cursor)
     }
 }

boa/src/syntax/parser/statement/block/mod.rs

@@ -78,10 +78,15 @@ where
             }
         }
 
-        let statement_list =
+        let statement_list = StatementList::new(
-            StatementList::new(self.allow_yield, self.allow_await, self.allow_return, true)
+            self.allow_yield,
-                .parse(cursor)
+            self.allow_await,
-                .map(node::Block::from)?;
+            self.allow_return,
+            true,
+            true,
+        )
+        .parse(cursor)
+        .map(node::Block::from)?;
         cursor.expect(Punctuator::CloseBlock, "block")?;
 
         Ok(statement_list)

boa/src/syntax/parser/statement/mod.rs

@@ -41,7 +41,7 @@ use super::{AllowAwait, AllowReturn, AllowYield, Cursor, ParseError, TokenParser
 use crate::{
     syntax::{
         ast::{node, Keyword, Node, Punctuator},
-        lexer::{InputElement, TokenKind},
+        lexer::{Error as LexError, InputElement, TokenKind},
     },
     BoaProfiler,
 };
@@ -215,6 +215,7 @@ pub(super) struct StatementList {
     allow_await: AllowAwait,
     allow_return: AllowReturn,
     break_when_closingbraces: bool,
+    in_block: bool,
 }
 
 impl StatementList {
@@ -224,6 +225,7 @@ impl StatementList {
         allow_await: A,
         allow_return: R,
         break_when_closingbraces: bool,
+        in_block: bool,
     ) -> Self
     where
         Y: Into<AllowYield>,
@@ -235,6 +237,7 @@ impl StatementList {
             allow_await: allow_await.into(),
             allow_return: allow_return.into(),
             break_when_closingbraces,
+            in_block,
         }
     }
 
@@ -268,9 +271,13 @@ impl StatementList {
                 return Err(ParseError::AbruptEnd);
             }
 
-            let item =
+            let item = StatementListItem::new(
-                StatementListItem::new(self.allow_yield, self.allow_await, self.allow_return)
+                self.allow_yield,
-                    .parse(cursor)?;
+                self.allow_await,
+                self.allow_return,
+                self.in_block,
+            )
+            .parse(cursor)?;
 
             items.push(item);
 
@@ -313,9 +320,13 @@ where
                 _ => {}
             }
 
-            let item =
+            let item = StatementListItem::new(
-                StatementListItem::new(self.allow_yield, self.allow_await, self.allow_return)
+                self.allow_yield,
-                    .parse(cursor)?;
+                self.allow_await,
+                self.allow_return,
+                self.in_block,
+            )
+            .parse(cursor)?;
             items.push(item);
 
             // move the cursor forward for any consecutive semicolon.
@@ -343,11 +354,12 @@ struct StatementListItem {
     allow_yield: AllowYield,
     allow_await: AllowAwait,
     allow_return: AllowReturn,
+    in_block: bool,
 }
 
 impl StatementListItem {
     /// Creates a new `StatementListItem` parser.
-    fn new<Y, A, R>(allow_yield: Y, allow_await: A, allow_return: R) -> Self
+    fn new<Y, A, R>(allow_yield: Y, allow_await: A, allow_return: R, in_block: bool) -> Self
     where
         Y: Into<AllowYield>,
         A: Into<AllowAwait>,
@@ -357,6 +369,7 @@ impl StatementListItem {
             allow_yield: allow_yield.into(),
             allow_await: allow_await.into(),
             allow_return: allow_return.into(),
+            in_block,
         }
     }
 }
@@ -369,12 +382,20 @@ where
 
     fn parse(self, cursor: &mut Cursor<R>) -> Result<Self::Output, ParseError> {
         let _timer = BoaProfiler::global().start_event("StatementListItem", "Parsing");
+        let strict_mode = cursor.strict_mode();
         let tok = cursor.peek(0)?.ok_or(ParseError::AbruptEnd)?;
 
         match *tok.kind() {
-            TokenKind::Keyword(Keyword::Function)
+            TokenKind::Keyword(Keyword::Function) => {
-            | TokenKind::Keyword(Keyword::Const)
+                if strict_mode && self.in_block {
-            | TokenKind::Keyword(Keyword::Let) => {
+                    return Err(ParseError::lex(LexError::Syntax(
+                        "Function declaration in blocks not allowed in strict mode".into(),
+                        tok.span().start(),
+                    )));
+                }
+                Declaration::new(self.allow_yield, self.allow_await, true).parse(cursor)
+            }
+            TokenKind::Keyword(Keyword::Const) | TokenKind::Keyword(Keyword::Let) => {
                 Declaration::new(self.allow_yield, self.allow_await, true).parse(cursor)
             }
             _ => {
@@ -426,16 +447,34 @@ where
 {
     type Output = Box<str>;
 
+    /// Strict mode parsing as per https://tc39.es/ecma262/#sec-identifiers-static-semantics-early-errors.
     fn parse(self, cursor: &mut Cursor<R>) -> Result<Self::Output, ParseError> {
         let _timer = BoaProfiler::global().start_event("BindingIdentifier", "Parsing");
-        // TODO: strict mode.
 
         let next_token = cursor.next()?.ok_or(ParseError::AbruptEnd)?;
 
         match next_token.kind() {
             TokenKind::Identifier(ref s) => Ok(s.clone()),
-            TokenKind::Keyword(k @ Keyword::Yield) if !self.allow_yield.0 => Ok(k.as_str().into()),
+            TokenKind::Keyword(k @ Keyword::Yield) if !self.allow_yield.0 => {
-            TokenKind::Keyword(k @ Keyword::Await) if !self.allow_await.0 => Ok(k.as_str().into()),
+                if cursor.strict_mode() {
+                    Err(ParseError::lex(LexError::Syntax(
+                        "yield keyword in binding identifier not allowed in strict mode".into(),
+                        next_token.span().start(),
+                    )))
+                } else {
+                    Ok(k.as_str().into())
+                }
+            }
+            TokenKind::Keyword(k @ Keyword::Await) if !self.allow_await.0 => {
+                if cursor.strict_mode() {
+                    Err(ParseError::lex(LexError::Syntax(
+                        "await keyword in binding identifier not allowed in strict mode".into(),
+                        next_token.span().start(),
+                    )))
+                } else {
+                    Ok(k.as_str().into())
+                }
+            }
             _ => Err(ParseError::expected(
                 vec![TokenKind::identifier("identifier")],
                 next_token,

boa/src/syntax/parser/statement/switch/mod.rs

@@ -130,6 +130,7 @@ where
                         self.allow_await,
                         self.allow_return,
                         true,
+                        false,
                     )
                     .parse_generalised(cursor, &CASE_BREAK_TOKENS)?;
 
@@ -151,6 +152,7 @@ where
                         self.allow_await,
                         self.allow_return,
                         true,
+                        false,
                     )
                     .parse_generalised(cursor, &CASE_BREAK_TOKENS)?;