From be0c2a424b68e5470c20294bf09cf16c50345d73 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C5=ABdolfs=20O=C5=A1i=C5=86=C5=A1?= <rudolfs@osins.org>
Date: Wed, 30 Sep 2026 15:50:40 +0200
Subject: [PATCH] Don't throw on empty or invalid frontmatter

Since js-yaml 5 an empty or comment-only block throws instead of returning
undefined, as does invalid YAML. Markdown renders the content from the
same parse, so one such block made the whole document fail to render.
---
 src/lib/frontmatter.ts         |  7 ++++-
 tests/unit/frontmatter.test.ts | 50 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 tests/unit/frontmatter.test.ts

diff --git a/src/lib/frontmatter.ts b/src/lib/frontmatter.ts
index d39e53899..ad40b285a 100644
--- a/src/lib/frontmatter.ts
+++ b/src/lib/frontmatter.ts
@@ -12,7 +12,12 @@ export function parseFrontmatter(input: string): ParsedFrontmatter {
   if (!match) {
     return { data: {}, content: input };
   }
-  const parsed = load(match[1]);
+  let parsed: unknown;
+  try {
+    parsed = load(match[1]);
+  } catch {
+    parsed = undefined;
+  }
   const data =
     parsed && typeof parsed === "object" && !Array.isArray(parsed)
       ? (parsed as Record<string, unknown>)
diff --git a/tests/unit/frontmatter.test.ts b/tests/unit/frontmatter.test.ts
new file mode 100644
index 000000000..3c0cce095
--- /dev/null
+++ b/tests/unit/frontmatter.test.ts
@@ -0,0 +1,50 @@
+import { expect, test } from "vitest";
+
+import { parseFrontmatter } from "@app/lib/frontmatter";
+
+test.each([
+  ["LF", "---\ntitle: Hello\nn: 1\n---\n# Body\n"],
+  ["CRLF", "---\r\ntitle: Hello\r\nn: 1\r\n---\r\n# Body\n"],
+])("splits %s frontmatter from the content", (_, input) => {
+  expect(parseFrontmatter(input)).toEqual({
+    data: { title: "Hello", n: 1 },
+    content: "# Body\n",
+  });
+});
+
+test("accepts a closing fence at the end of the input", () => {
+  expect(parseFrontmatter("---\na: 1\n---")).toEqual({
+    data: { a: 1 },
+    content: "",
+  });
+});
+
+test("stops at the first closing fence", () => {
+  expect(parseFrontmatter("---\na: 1\n---\ntext\n---\nmore")).toEqual({
+    data: { a: 1 },
+    content: "text\n---\nmore",
+  });
+});
+
+test.each([
+  "# Title\n---\na: 1\n---\n",
+  " ---\na: 1\n---\n",
+  "---\na: 1\n",
+  "---\n---\n",
+])("leaves %j without frontmatter as is", input => {
+  expect(parseFrontmatter(input)).toEqual({ data: {}, content: input });
+});
+
+test.each([
+  ["a scalar", "just text"],
+  ["a list", "- a\n- b"],
+  ["null", "~"],
+  ["nothing", ""],
+  ["a comment", "# draft"],
+  ["invalid YAML", "Note: see: below"],
+])("drops a block holding %s but strips it", (_, yaml) => {
+  expect(parseFrontmatter(`---\n${yaml}\n---\nbody`)).toEqual({
+    data: {},
+    content: "body",
+  });
+});