feat(ui): Fix comma separated attributes in code blocks language preventing syntax-highlighting (#12056)

Currently, forgejo does not support syntax highlighting code-blocks that have comma separated attributes after the language. This is a pattern sometimes seen in Rust code blocks, with tests like this:

\`\`\`rust
#[test]
fn run_this_test() { /* ... */ }
\`\`\`

\`\`\`rust,ignore
#[test]
fn skip_this_test() { /* ... */ }
\`\`\`

Currently, forgejo only does syntax highlighting in the first case:

```rust
#[test]
fn run_this_test() { /* ... */ }
```

```rust,ignore
#[test]
fn skip_this_test() { /* ... */ }
```

An example of this causing problems can be seen in this commit (5be9c5b7d2) causing the following issue (https://codeberg.org/zesterer/ariadne/issues/188).

This PR fixes fixes the second case not getting proper syntax highlighting.

Co-authored-by: TurtleArmy <44322335+TurtleArmyMc@users.noreply.github.com>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12056
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Reviewed-by: Ellen Εμίλια Άννα Zscheile <fogti@noreply.codeberg.org>
Co-authored-by: TurtleArmy <turtlearmy@noreply.codeberg.org>
Co-committed-by: TurtleArmy <turtlearmy@noreply.codeberg.org>

modules/markup/markdown/goldmark.go

@@ -90,6 +90,8 @@ func (g *ASTTransformer) Transform(node *ast.Document, reader text.Reader, pc pa
 			}
 		case *ast.RawHTML:
 			g.transformRawHTML(ctx, v, reader)
+		case *ast.FencedCodeBlock:
+			g.transformCodeblockLanguage(v, reader)
 		}
 		return ast.WalkContinue, nil
 	})

modules/markup/markdown/markdown_test.go

@@ -1488,3 +1488,27 @@ func TestCallout(t *testing.T) {
 <p>Bad stuff is brewing here</p>
 </blockquote>`)
 }
+
+func TestCodeblockLanguageStripping(t *testing.T) {
+	test := func(input, expected string) {
+		buffer, err := markdown.RenderString(&markup.RenderContext{Ctx: git.DefaultContext}, input)
+		require.NoError(t, err)
+		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(string(buffer)))
+	}
+
+	// Unstripped
+	test(
+		"```rust\n"+
+			"fn main() {}\n"+
+			"```",
+		`<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>`)
+
+	// Stripped
+	test(
+		"```rust,ignore\n"+
+			"fn main() {}\n"+
+			"```",
+		`<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>`)
+}

modules/markup/markdown/transform_codeblock_lang.go

@@ -0,0 +1,27 @@
+// Copyright 2026 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package markdown
+
+import (
+	"bytes"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/text"
+)
+
+func (g *ASTTransformer) transformCodeblockLanguage(v *ast.FencedCodeBlock, reader text.Reader) {
+	src := reader.Source()
+	info := v.Info.Segment.Value(src)
+	// Strip language after commas
+	//
+	// For example,
+	// ```rust,ignore
+	// ...
+	// ```
+	// Should have a language of "rust", not "rust,ignore"
+	if i := bytes.IndexByte(info, ','); i != -1 {
+		start := v.Info.Segment.Start
+		v.Info = ast.NewTextSegment(text.NewSegment(start, start+i))
+	}
+}