markup/goldmark/codeblocks: Fix slice bounds out of range

For the Position in code blocks we try to match the .Inner with the original source. This isn't always possible.

This commits avoids panics in these situations.

Fixes #9627

2 files changed, 42 insertions, 0 deletions

diff --git a/hugolib/page.go b/hugolib/page.go
index 175e1fc3b..c4f30de9d 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -784,6 +784,11 @@ func (p *pageState) posFromPage(offset int) text.Position {
 }
 
 func (p *pageState) posFromInput(input []byte, offset int) text.Position {
+	if offset < 0 {
+		return text.Position{
+			Filename: p.pathOrTitle(),
+		}
+	}
 	lf := []byte("\n")
 	input = input[:offset]
 	lineNumber := bytes.Count(input, lf) + 1
diff --git a/markup/goldmark/codeblocks/integration_test.go b/markup/goldmark/codeblocks/integration_test.go
index 1a70b0bf0..7362ef297 100644
--- a/markup/goldmark/codeblocks/integration_test.go
+++ b/markup/goldmark/codeblocks/integration_test.go
@@ -164,6 +164,43 @@ fmt.Println("Hello, World!");
 	)
 }
 
+func TestCodeblocksBugs(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- config.toml --
+-- layouts/_default/_markup/render-codeblock.html --
+{{ .Position | safeHTML }}
+-- layouts/_default/single.html --
+{{ .Content }}
+-- content/p1.md --
+---
+title: "p1"
+---
+
+## Issue 9627
+
+§§§text
+{{</* foo */>}}
+§§§
+
+`
+
+	b := hugolib.NewIntegrationTestBuilder(
+		hugolib.IntegrationTestConfig{
+			T:           t,
+			TxtarString: files,
+			NeedsOsFS:   false,
+		},
+	).Build()
+
+	b.AssertFileContent("public/p1/index.html", `
+# Issue 9627: For the Position in code blocks we try to match the .Inner with the original source. This isn't always possible.
+p1.md:0:0
+	`,
+	)
+}
+
 func TestCodeChomp(t *testing.T) {
 	t.Parallel()