From bc7c8e3c845de4e789d6dfe0285889dbd3e6fc11 Mon Sep 17 00:00:00 2001
From: Mathieu Fenniak <mathieu@fenniak.net>
Date: Wed, 29 Apr 2026 19:49:55 +0200
Subject: [PATCH] fix: markdown rendering panic when code blocks do not have
 languages (#12325)

When attempting to render a markdown code block that does not have a language set in it, Forgejo will fail to render and log an error:
```
2026/04/29 08:47:47 ...markdown/markdown.go:162:func1() [W] Unable to render markdown due to panic in goldmark: runtime error: invalid memory address or nil pointer dereference
```

This is a regression introduced by #12056.

## Checklist

The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. All work and communication must conform to Forgejo's [AI Agreement](https://codeberg.org/forgejo/governance/src/branch/main/AIAgreement.md). There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).

### Tests for Go changes

- I added test coverage for Go changes...
  - [x] in their respective `*_test.go` for unit tests.
  - [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
  - [x] `make pr-go` before pushing

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [ ] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [x] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.
    - pre-release regression

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12325
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
---
 modules/markup/markdown/markdown_test.go            | 8 ++++++++
 modules/markup/markdown/transform_codeblock_lang.go | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/modules/markup/markdown/markdown_test.go b/modules/markup/markdown/markdown_test.go
index fc4a515f72..1f75799900 100644
--- a/modules/markup/markdown/markdown_test.go
+++ b/modules/markup/markdown/markdown_test.go
@@ -1511,4 +1511,12 @@ func TestCodeblockLanguageStripping(t *testing.T) {
 			"```",
 		`<pre class="code-block"><code class="chroma language-rust display"><span class="k">fn</span> <span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{}</span><span class="w">
 </span></code></pre>`)
+
+	// No language identifier
+	test(
+		"```\n"+
+			"fn main() {}\n"+
+			"```",
+		`<pre class="code-block"><code class="chroma language-text display">fn main() {}
+</code></pre>`)
 }
diff --git a/modules/markup/markdown/transform_codeblock_lang.go b/modules/markup/markdown/transform_codeblock_lang.go
index 2c90373c4e..5263ec4ffc 100644
--- a/modules/markup/markdown/transform_codeblock_lang.go
+++ b/modules/markup/markdown/transform_codeblock_lang.go
@@ -11,6 +11,9 @@ import (
 )
 
 func (g *ASTTransformer) transformCodeblockLanguage(v *ast.FencedCodeBlock, reader text.Reader) {
+	if v.Info == nil {
+		return
+	}
 	src := reader.Source()
 	info := v.Info.Segment.Value(src)
 	// Strip language after commas