perf: optimize advance() with lazy line/column tracking

src/parse-anplusb.ts

@@ -30,8 +30,7 @@ export class ANplusBParser {
 	 */
 	parse_anplusb(start: number, end: number, line: number = 1): number | null {
 		this.expr_end = end
-		this.lexer.pos = start
-		this.lexer.line = line
+		this.lexer.seek(start, line)
 
 		let b: string | null = null
 		let a_start = start

src/parse-atrule-prelude.ts

@@ -56,9 +56,7 @@ export class AtRulePreludeParser {
 		this.prelude_end = end
 
 		// Position lexer at prelude start
-		this.lexer.pos = start
-		this.lexer.line = line
-		this.lexer.column = column
+		this.lexer.seek(start, line, column)
 
 		return this.parse_prelude_dispatch(at_rule_name)
 	}
@@ -745,9 +743,7 @@ export class AtRulePreludeParser {
 	private parse_feature_value(start: number, end: number): number[] {
 		// Use a temporary lexer for this range to avoid corrupting main lexer position state
 		let temp_lexer = new Lexer(this.source)
-		temp_lexer.pos = start
-		temp_lexer.line = this.lexer.line
-		temp_lexer.column = this.lexer.column
+		temp_lexer.seek(start, this.lexer.line, this.lexer.column)
 
 		let nodes: number[] = []
 		let saved_lexer = this.lexer

src/parse-declaration.ts

@@ -40,9 +40,7 @@ export class DeclarationParser {
 	parse_declaration(start: number, end: number, line: number = 1, column: number = 1): number | null {
 		// Create a fresh lexer instance for standalone parsing
 		const lexer = new Lexer(this.source)
-		lexer.pos = start
-		lexer.line = line
-		lexer.column = column
+		lexer.seek(start, line, column)
 		lexer.next_token_fast(true) // skip whitespace like Parser does
 
 		return this.parse_declaration_with_lexer(lexer, end)

src/parse-selector.ts

@@ -89,9 +89,7 @@ export class SelectorParser {
 		this.selector_end = end
 
 		// Position lexer at selector start
-		this.lexer.pos = start
-		this.lexer.line = line
-		this.lexer.column = column
+		this.lexer.seek(start, line, column)
 
 		// Parse selector list (comma-separated selectors)
 		// Returns NODE_SELECTOR_LIST directly (no wrapper)
@@ -827,9 +825,7 @@ export class SelectorParser {
 	private parse_lang_identifiers(start: number, end: number, parent_node: number): void {
 		// Use a temporary lexer for this range to avoid corrupting main lexer position state
 		let temp_lexer = new Lexer(this.source)
-		temp_lexer.pos = start
-		temp_lexer.line = this.lexer.line
-		temp_lexer.column = this.lexer.column
+		temp_lexer.seek(start, this.lexer.line, this.lexer.column)
 
 		// Save current parser state
 		let saved_selector_end = this.selector_end

src/parse-value.ts

@@ -40,9 +40,7 @@ export class ValueParser {
 		this.value_end = end
 
 		// Position lexer at value start with provided line/column
-		this.lexer.pos = start
-		this.lexer.line = start_line
-		this.lexer.column = start_column
+		this.lexer.seek(start, start_line, start_column)
 
 		// Parse individual value tokens
 		let value_nodes = this.parse_value_tokens()

src/tokenize.ts

@@ -3,12 +3,16 @@ import {
 	is_ident_start,
 	is_ident_char,
 	is_whitespace,
-	is_newline,
 	char_types,
 	CHAR_DIGIT,
 	CHAR_WHITESPACE,
 	CHAR_NEWLINE,
 } from './char-types'
+
+// Local inline version for hot paths that still need it
+function is_newline(ch: number): boolean {
+	return ch < 128 && (char_types[ch] & CHAR_NEWLINE) !== 0
+}
 import {
 	TOKEN_IDENT,
 	TOKEN_FUNCTION,
@@ -74,6 +78,7 @@ export interface LexerPosition {
 	pos: number
 	line: number
 	column: number
+	_line_offset: number
 	token_type: TokenType
 	token_start: number
 	token_end: number
@@ -93,8 +98,8 @@ export interface CommentInfo {
 export class Lexer {
 	source: string
 	pos: number
-	line: number
-	column: number
+	private _line: number
+	private _line_offset: number
 	on_comment: ((info: CommentInfo) => void) | undefined
 	// Current token properties (avoiding object allocation)
 	token_type: TokenType
@@ -106,8 +111,8 @@ export class Lexer {
 	constructor(source: string, on_comment?: (info: CommentInfo) => void) {
 		this.source = source
 		this.pos = 0
-		this.line = 1
-		this.column = 1
+		this._line = 1
+		this._line_offset = 0
 		this.on_comment = on_comment
 		this.token_type = TOKEN_EOF
 		this.token_start = 0
@@ -116,6 +121,20 @@ export class Lexer {
 		this.token_column = 1
 	}
 
+	get line(): number {
+		return this._line
+	}
+
+	get column(): number {
+		return this.pos - this._line_offset + 1
+	}
+
+	seek(pos: number, line: number, column: number = 1): void {
+		this.pos = pos
+		this._line = line
+		this._line_offset = pos - column + 1
+	}
+
 	// Fast token advancing without object allocation (for internal parser use)
 	next_token_fast(skip_whitespace: boolean = false): TokenType {
 		// Fast path: skip whitespace if requested
@@ -597,15 +616,14 @@ export class Lexer {
 			let ch = this.source.charCodeAt(this.pos)
 			this.pos++
 
-			if (is_newline(ch)) {
+			// Inline newline check - only update on newline
+			if (ch < 128 && (char_types[ch] & CHAR_NEWLINE) !== 0) {
 				// Handle \r\n as single newline
 				if (ch === CHAR_CARRIAGE_RETURN && this.pos < this.source.length && this.source.charCodeAt(this.pos) === CHAR_LINE_FEED) {
 					this.pos++
 				}
-				this.line++
-				this.column = 1
-			} else {
-				this.column++
+				this._line++
+				this._line_offset = this.pos
 			}
 			return
 		}
@@ -617,16 +635,15 @@ export class Lexer {
 			let ch = this.source.charCodeAt(this.pos)
 			this.pos++
 
-			if (is_newline(ch)) {
+			// Inline newline check - only update on newline
+			if (ch < 128 && (char_types[ch] & CHAR_NEWLINE) !== 0) {
 				// Handle \r\n as single newline
 				if (ch === CHAR_CARRIAGE_RETURN && this.pos < this.source.length && this.source.charCodeAt(this.pos) === CHAR_LINE_FEED) {
 					this.pos++
 					i++ // Count \r\n as 2 characters for advance(count)
 				}
-				this.line++
-				this.column = 1
-			} else {
-				this.column++
+				this._line++
+				this._line_offset = this.pos
 			}
 		}
 	}
@@ -665,8 +682,9 @@ export class Lexer {
 	save_position(): LexerPosition {
 		return {
 			pos: this.pos,
-			line: this.line,
+			line: this._line,
 			column: this.column,
+			_line_offset: this._line_offset,
 			token_type: this.token_type,
 			token_start: this.token_start,
 			token_end: this.token_end,
@@ -681,8 +699,8 @@ export class Lexer {
 	 */
 	restore_position(saved: LexerPosition): void {
 		this.pos = saved.pos
-		this.line = saved.line
-		this.column = saved.column
+		this._line = saved.line
+		this._line_offset = saved._line_offset
 		this.token_type = saved.token_type
 		this.token_start = saved.token_start
 		this.token_end = saved.token_end