fix: trim trailing whitespace from lheading text (#3920)

Author: VeerShah41

src/Tokenizer.ts

@@ -574,12 +574,13 @@ export class _Tokenizer<ParserOutput = string, RendererOutput = string> {
   lheading(src: string): Tokens.Heading | undefined {
     const cap = this.rules.block.lheading.exec(src);
     if (cap) {
+      const text = cap[1].trim();
       return {
         type: 'heading',
         raw: cap[0],
         depth: cap[2].charAt(0) === '=' ? 1 : 2,
-        text: cap[1],
-        tokens: this.lexer.inline(cap[1]),
+        text,
+        tokens: this.lexer.inline(text),
       };
     }
   }

test/unit/Lexer.test.js

@@ -165,6 +165,19 @@ lheading 2
       });
     });
 
+    it('lheading should trim trailing whitespace from text', () => {
+      expectTokens({
+        md: 'heading with trailing spaces   \n==============================',
+        tokens: [{
+          type: 'heading',
+          raw: 'heading with trailing spaces   \n==============================',
+          depth: 1,
+          text: 'heading with trailing spaces',
+          tokens: [{ type: 'text', raw: 'heading with trailing spaces', text: 'heading with trailing spaces', escaped: false }],
+        }],
+      });
+    });
+
     it('should not be heading if depth > 6', () => {
       expectTokens({
         md: '####### heading 7',