Merge js-lexer: fix line continuation escape in string and template literals

crates/js/src/lexer.rs

···
                 }
                 Some(b'\\') => {
                     self.advance(); // backslash
-                    let ch = self.scan_escape_sequence()?;
-                    value.push(ch);
+                    if let Some(ch) = self.scan_escape_sequence()? {
+                        value.push(ch);
+                    }
                 }
                 Some(_) => {
                     let ch = self.advance_char();
···
         Ok(TokenKind::String(value))
     }
 
-    fn scan_escape_sequence(&mut self) -> Result<char, LexError> {
+    /// Scan an escape sequence after the backslash has been consumed.
+    /// Returns `None` for line continuations (`\<newline>`), which produce no character.
+    fn scan_escape_sequence(&mut self) -> Result<Option<char>, LexError> {
         let pos = self.current_pos();
         match self.advance() {
-            Some(b'n') => Ok('\n'),
-            Some(b'r') => Ok('\r'),
-            Some(b't') => Ok('\t'),
-            Some(b'b') => Ok('\u{0008}'),
-            Some(b'f') => Ok('\u{000C}'),
-            Some(b'v') => Ok('\u{000B}'),
-            Some(b'0') if !matches!(self.peek(), Some(b'0'..=b'9')) => Ok('\0'),
-            Some(b'\\') => Ok('\\'),
-            Some(b'\'') => Ok('\''),
-            Some(b'"') => Ok('"'),
-            Some(b'`') => Ok('`'),
-            Some(b'\n') => Ok('\n'),
+            Some(b'n') => Ok(Some('\n')),
+            Some(b'r') => Ok(Some('\r')),
+            Some(b't') => Ok(Some('\t')),
+            Some(b'b') => Ok(Some('\u{0008}')),
+            Some(b'f') => Ok(Some('\u{000C}')),
+            Some(b'v') => Ok(Some('\u{000B}')),
+            Some(b'0') if !matches!(self.peek(), Some(b'0'..=b'9')) => Ok(Some('\0')),
+            Some(b'\\') => Ok(Some('\\')),
+            Some(b'\'') => Ok(Some('\'')),
+            Some(b'"') => Ok(Some('"')),
+            Some(b'`') => Ok(Some('`')),
+            // Line continuation: \<newline> produces no character
+            Some(b'\n') => Ok(None),
             Some(b'\r') => {
                 self.advance_if(b'\n');
-                Ok('\n')
+                Ok(None)
             }
             Some(b'x') => {
                 let hi = self.advance().and_then(hex_digit_val).ok_or(LexError {
···
                     pos,
                 })?;
                 let code = (hi << 4) | lo;
-                Ok(code as char)
+                Ok(Some(code as char))
             }
-            Some(b'u') => self.scan_unicode_escape(pos),
+            Some(b'u') => self.scan_unicode_escape(pos).map(Some),
             Some(b) => {
                 // identity escape
-                Ok(b as char)
+                Ok(Some(b as char))
             }
             None => Err(LexError {
                 message: "unexpected end of input in escape sequence".into(),
···
                 }
                 Some(b'\\') => {
                     self.advance();
-                    let ch = self.scan_escape_sequence()?;
-                    value.push(ch);
+                    if let Some(ch) = self.scan_escape_sequence()? {
+                        value.push(ch);
+                    }
                 }
                 Some(_) => {
                     let ch = self.advance_char();
···
                 }
                 Some(b'\\') => {
                     self.advance();
-                    let ch = self.scan_escape_sequence()?;
-                    value.push(ch);
+                    if let Some(ch) = self.scan_escape_sequence()? {
+                        value.push(ch);
+                    }
                 }
                 Some(_) => {
                     let ch = self.advance_char();
···
         assert_eq!(
             kind(r#""\u{1F600}""#),
             TokenKind::String("\u{1F600}".into())
+        );
+    }
+
+    #[test]
+    fn test_string_line_continuation() {
+        // \<newline> is a line continuation producing no character
+        assert_eq!(
+            kind("\"line1\\\nline2\""),
+            TokenKind::String("line1line2".into())
         );
     }