From 53a6210d82eaa2cff7c802df88ff08dac5e7dced Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B8rn=20Erik=20Pedersen?=
 <bjorn.erik.pedersen@gmail.com>
Date: Tue, 8 Mar 2022 20:10:19 +0100
Subject: [PATCH] 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
---
 hugolib/page.go                               |  5 +++
 .../goldmark/codeblocks/integration_test.go   | 37 +++++++++++++++++++
 2 files changed, 42 insertions(+)

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()