fix: re-assign tokenizer.lexer and renderer.parser at start of each parse call (#3907)

Author: VeerShah41

src/Lexer.ts

@@ -105,6 +105,7 @@ export class _Lexer<ParserOutput = string, RendererOutput = string> {
   blockTokens(src: string, tokens?: Token[], lastParagraphClipped?: boolean): Token[];
   blockTokens(src: string, tokens?: TokensList, lastParagraphClipped?: boolean): TokensList;
   blockTokens(src: string, tokens: Token[] = [], lastParagraphClipped = false) {
+    this.tokenizer.lexer = this;
     if (this.options.pedantic) {
       src = src.replace(other.tabCharGlobal, '    ').replace(other.spaceLine, '');
     }
@@ -297,6 +298,7 @@ export class _Lexer<ParserOutput = string, RendererOutput = string> {
    * Lexing/Compiling
    */
   inlineTokens(src: string, tokens: Token[] = []): Token[] {
+    this.tokenizer.lexer = this;
     // String with links masked to avoid interference with em and strong
     let maskedSrc = src;
     let match: RegExpExecArray | null = null;

src/Parser.ts

@@ -40,6 +40,7 @@ export class _Parser<ParserOutput = string, RendererOutput = string> {
    * Parse Loop
    */
   parse(tokens: Token[]): ParserOutput {
+    this.renderer.parser = this;
     let out = '';
 
     for (let i = 0; i < tokens.length; i++) {
@@ -126,6 +127,7 @@ export class _Parser<ParserOutput = string, RendererOutput = string> {
    * Parse Inline Tokens
    */
   parseInline(tokens: Token[], renderer: _Renderer<ParserOutput, RendererOutput> | _TextRenderer<RendererOutput> = this.renderer): ParserOutput {
+    this.renderer.parser = this;
     let out = '';
 
     for (let i = 0; i < tokens.length; i++) {

test/unit/Lexer.test.js

@@ -1929,4 +1929,27 @@ paragraph
       });
     });
   });
+
+  describe('multiple instances', () => {
+    it('should produce identical tokens when multiple Lexer instances lex the same input (issue #3854)', () => {
+      // Create the first instance and lex — this may mutate shared _defaults.tokenizer.lexer
+      const lexer1 = new Lexer();
+      const tokensA = lexer1.lex('Test');
+
+      // Create a second instance after the first — previously tokensB.tokens would be empty
+      // because lexer1's constructor overwrote _defaults.tokenizer.lexer to point to lexer1
+      const lexer2 = new Lexer();
+      const tokensB = lexer2.lex('Test');
+
+      assert.deepEqual(tokensA, tokensB);
+    });
+
+    it('should produce identical tokens using static lex and instance lex (issue #3854)', () => {
+      const lexer = new Lexer();
+      const tokensA = Lexer.lex('Test');
+      const tokensB = lexer.lex('Test');
+
+      assert.deepEqual(tokensA, tokensB);
+    });
+  });
 });