Port upstream code fence info string fix

third_party/muya/src/state/__tests__/codeFenceInfoString.spec.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from 'vitest';
+import { MarkdownToState } from '../markdownToState';
+import ExportMarkdown from '../stateToMarkdown';
+
+function roundTrip(markdown: string): string {
+    const states = new MarkdownToState().generate(markdown);
+    return new ExportMarkdown({ listIndentation: 1 }).generate(states);
+}
+
+describe('#4770: fenced code block info string round-trip', () => {
+    it('preserves a Pandoc/RMarkdown-style attribute info string', () => {
+        const markdown = '```{example, listing1-name}\nlabel for code listing 1\n```\n';
+
+        expect(roundTrip(markdown)).toContain('```{example, listing1-name}');
+    });
+
+    it('preserves a language followed by attributes', () => {
+        const markdown = '```js title="app.js"\nconst a = 1\n```\n';
+
+        expect(roundTrip(markdown)).toContain('```js title="app.js"');
+    });
+
+    it('leaves a plain single-word language unchanged', () => {
+        const output = roundTrip('```js\nconst a = 1\n```\n');
+
+        expect(output).toContain('```js\n');
+    });
+
+    it('leaves a language-less fence unchanged', () => {
+        const output = roundTrip('```\nplain\n```\n');
+
+        expect(output).toContain('```\n');
+        expect(output).not.toContain('```undefined');
+    });
+
+    it('uses the edited language when a stored info string is now stale', () => {
+        const states = [
+            {
+                name: 'code-block' as const,
+                meta: { type: 'fenced', lang: 'python', info: '{example, listing1-name}' },
+                text: 'x',
+            },
+        ];
+
+        const output = new ExportMarkdown({ listIndentation: 1 }).generate(states);
+
+        expect(output).toContain('```python\n');
+        expect(output).not.toContain('example');
+    });
+});

third_party/muya/src/state/markdownToState.ts

@@ -458,12 +458,14 @@ export class MarkdownToState {
         // but `'fenced'` reaches us at runtime via the
         // walkTokens assignment — hence the cast.
         const isFenced = (codeBlockStyle as 'indented' | 'fenced' | undefined) === 'fenced';
+        const info = infoString || '';
         return {
             name: 'code-block' as const,
             meta: {
                 type: isFenced ? 'fenced' : 'indented',
                 lang,
                 ...(isFenced && fenceLength && fenceLength > 3 ? { fenceLength } : {}),
+                ...(isFenced && info !== lang ? { info } : {}),
             },
             text: value,
         };

third_party/muya/src/state/stateToMarkdown.ts

@@ -354,10 +354,11 @@ export default class ExportMarkdown {
         const { text, meta } = state;
         const textList = text.split('\n');
         const { type, lang } = meta;
+        const info = meta.info && meta.info.match(/\S*/)?.[0] === lang ? meta.info : lang;
 
         if (type === 'fenced') {
             const fence = '`'.repeat(this._codeFenceLength(text, meta.fenceLength));
-            result.push(`${indent}${lang ? `${fence}${lang}\n` : `${fence}\n`}`);
+            result.push(`${indent}${info ? `${fence}${info}\n` : `${fence}\n`}`);
             textList.forEach((text) => {
                 result.push(`${indent}${text}\n`);
             });

third_party/muya/src/state/types.ts

@@ -31,6 +31,7 @@ export interface ICodeBlockState {
         type: string; // "indented" | "fenced";
         lang: string;
         fenceLength?: number;
+        info?: string;
     };
     text: string;
 }