From 0c10c6593c9119a1ef669cfdd0c568654529ccb2 Mon Sep 17 00:00:00 2001
From: SecPan <qq2579937786@gmail.com>
Date: Wed, 8 Jul 2026 13:32:54 -0700
Subject: [PATCH] Port upstream mermaid export resilience fix

---
 .../__tests__/mermaidExportResilience.spec.ts | 81 +++++++++++++++++++
 third_party/muya/src/state/markdownToHtml.ts  | 19 ++++-
 2 files changed, 97 insertions(+), 3 deletions(-)
 create mode 100644 third_party/muya/src/state/__tests__/mermaidExportResilience.spec.ts

diff --git a/third_party/muya/src/state/__tests__/mermaidExportResilience.spec.ts b/third_party/muya/src/state/__tests__/mermaidExportResilience.spec.ts
new file mode 100644
index 0000000..59609ba
--- /dev/null
+++ b/third_party/muya/src/state/__tests__/mermaidExportResilience.spec.ts
@@ -0,0 +1,81 @@
+// @vitest-environment jsdom
+
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const mermaidRun = vi.fn();
+
+vi.mock('../../utils/diagram', () => ({
+    default: vi.fn(async (name: string) => {
+        if (name === 'mermaid') {
+            return {
+                initialize: vi.fn(),
+                run: mermaidRun,
+            };
+        }
+        throw new Error(`unexpected renderer ${name}`);
+    }),
+}));
+
+// Import after the mock is registered so MarkdownToHtml uses the fake renderer.
+const { MarkdownToHtml } = await import('../markdownToHtml');
+
+beforeEach(() => {
+    mermaidRun.mockReset();
+});
+
+const INVALID_MERMAID = [
+    '# Title',
+    '',
+    'Intro paragraph.',
+    '',
+    '```mermaid',
+    'graph LR',
+    'H[a|b|c]',
+    '```',
+    '',
+    'Trailing paragraph.',
+    '',
+].join('\n');
+
+describe('#4812: mermaid syntax error must not abort export', () => {
+    it('renderHtml resolves even when a mermaid diagram fails to parse', async () => {
+        mermaidRun.mockRejectedValue(new Error('Parse error'));
+
+        const html = await new MarkdownToHtml(INVALID_MERMAID).renderHtml();
+
+        expect(html).toContain('Title');
+        expect(html).toContain('Intro paragraph.');
+        expect(html).toContain('Trailing paragraph.');
+        expect(html).toContain('&lt; Invalid Diagram &gt;');
+    });
+
+    it('one broken diagram does not stop a later valid diagram from rendering', async () => {
+        mermaidRun
+            .mockRejectedValueOnce(new Error('Parse error'))
+            .mockResolvedValueOnce(undefined);
+
+        const markdown = [
+            '```mermaid',
+            'graph LR',
+            'H[a|b|c]',
+            '```',
+            '',
+            '```mermaid',
+            'graph TD; A-->B',
+            '```',
+            '',
+        ].join('\n');
+
+        const html = await new MarkdownToHtml(markdown).renderHtml();
+
+        expect(mermaidRun).toHaveBeenCalledTimes(2);
+        expect(html).toContain('&lt; Invalid Diagram &gt;');
+    });
+
+    it('does not load mermaid when the document contains no mermaid diagrams', async () => {
+        const html = await new MarkdownToHtml('plain paragraph').renderHtml();
+
+        expect(html).toContain('plain paragraph');
+        expect(mermaidRun).not.toHaveBeenCalled();
+    });
+});
diff --git a/third_party/muya/src/state/markdownToHtml.ts b/third_party/muya/src/state/markdownToHtml.ts
index 58de94b..615f480 100644
--- a/third_party/muya/src/state/markdownToHtml.ts
+++ b/third_party/muya/src/state/markdownToHtml.ts
@@ -49,6 +49,10 @@ export class MarkdownToHtml {
             mermaidContainer.classList.add('mermaid');
             preEle.replaceWith(mermaidContainer);
         }
+        const nodes = [...this._exportContainer!.querySelectorAll('div.mermaid')];
+        if (nodes.length === 0)
+            return;
+
         const mermaid = await loadRenderer('mermaid');
         // We only export light theme, so set mermaid theme to `default`, in the future, we can choose which theme to export.
         mermaid.initialize({
@@ -56,9 +60,18 @@ export class MarkdownToHtml {
             securityLevel: 'strict',
             theme: 'default',
         });
-        await mermaid.run({
-            nodes: [...this._exportContainer!.querySelectorAll('div.mermaid')],
-        });
+        // Render each diagram in isolation: `mermaid.run` rejects the whole
+        // batch on the first parse error, so one invalid diagram used to abort
+        // the entire export (#4812). Contain the failure to that diagram and
+        // fall back to the same placeholder the other diagram renderers use.
+        for (const node of nodes) {
+            try {
+                await mermaid.run({ nodes: [node] });
+            }
+            catch {
+                node.innerHTML = '< Invalid Diagram >';
+            }
+        }
         if (this._muya) {
             mermaid.initialize({
                 securityLevel: 'strict',