markup/goldmark: Add the Hugo Goldmark Extras "delete" extension

With Goldmark v1.7.1 and earlier, the Goldmark "strikethrough" extension was
triggered by wrapping text within a pair of double-tilde characters. With
Goldmark v1.7.2 and later, to provide full GFM compatibility, the Goldmark
"strikethrough" extension is triggered by wrapping text within a pair of
single- or double-tilde characters.

This change created a conflict with the Hugo Goldmark Extras "subscript"
extension.

When enabling the Hugo Goldmark Extras "subscript" extension, if you
want to render subscript and strikethrough text concurrently, you must:

1. Disable the Goldmark "strikethrough" extension
2. Enable the Hugo Goldmark Extras "delete" extension

Closes #12597

3 files changed, 21 insertions, 4 deletions

diff --git a/markup/goldmark/convert.go b/markup/goldmark/convert.go
index 7c00433d5..1c0d228ed 100644
--- a/markup/goldmark/convert.go
+++ b/markup/goldmark/convert.go
@@ -116,6 +116,7 @@ func newMarkdown(pcfg converter.ProviderConfig) goldmark.Markdown {
 
 	extensions = append(extensions, extras.New(
 		extras.Config{
+			Delete:      extras.DeleteConfig{Enable: cfg.Extensions.Extras.Delete.Enable},
 			Insert:      extras.InsertConfig{Enable: cfg.Extensions.Extras.Insert.Enable},
 			Mark:        extras.MarkConfig{Enable: cfg.Extensions.Extras.Mark.Enable},
 			Subscript:   extras.SubscriptConfig{Enable: cfg.Extensions.Extras.Subscript.Enable},
diff --git a/markup/goldmark/goldmark_config/config.go b/markup/goldmark/goldmark_config/config.go
index 620475c48..c6e0bcd3d 100644
--- a/markup/goldmark/goldmark_config/config.go
+++ b/markup/goldmark/goldmark_config/config.go
@@ -50,10 +50,7 @@ var Default = Config{
 			EscapedSpace:             false,
 		},
 		Extras: Extras{
-			Superscript: Superscript{
-				Enable: false,
-			},
-			Subscript: Subscript{
+			Delete: Delete{
 				Enable: false,
 			},
 			Insert: Insert{
@@ -62,6 +59,12 @@ var Default = Config{
 			Mark: Mark{
 				Enable: false,
 			},
+			Subscript: Subscript{
+				Enable: false,
+			},
+			Superscript: Superscript{
+				Enable: false,
+			},
 		},
 		Passthrough: Passthrough{
 			Enable: false,
@@ -168,12 +171,17 @@ type Typographer struct {
 // Extras holds extras configuration.
 // github.com/hugoio/hugo-goldmark-extensions/extras
 type Extras struct {
+	Delete      Delete
 	Insert      Insert
 	Mark        Mark
 	Subscript   Subscript
 	Superscript Superscript
 }
 
+type Delete struct {
+	Enable bool
+}
+
 type Insert struct {
 	Enable bool
 }
diff --git a/markup/goldmark/goldmark_integration_test.go b/markup/goldmark/goldmark_integration_test.go
index 82b41cc67..19338310c 100644
--- a/markup/goldmark/goldmark_integration_test.go
+++ b/markup/goldmark/goldmark_integration_test.go
@@ -751,6 +751,10 @@ func TestExtrasExtension(t *testing.T) {
 	files := `
 -- hugo.toml --
 disableKinds = ['page','rss','section','sitemap','taxonomy','term']
+[markup.goldmark.extensions]
+strikethrough = false
+[markup.goldmark.extensions.extras.delete]
+enable = false
 [markup.goldmark.extensions.extras.insert]
 enable = false
 [markup.goldmark.extensions.extras.mark]
@@ -765,6 +769,8 @@ enable = false
 ---
 title: home
 ---
+~~delete~~
+
 ++insert++
 
 ==mark==
@@ -777,6 +783,7 @@ H~2~0
 	b := hugolib.Test(t, files)
 
 	b.AssertFileContent("public/index.html",
+		"<p>~~delete~~</p>",
 		"<p>++insert++</p>",
 		"<p>==mark==</p>",
 		"<p>H~2~0</p>",
@@ -788,6 +795,7 @@ H~2~0
 	b = hugolib.Test(t, files)
 
 	b.AssertFileContent("public/index.html",
+		"<p><del>delete</del></p>",
 		"<p><ins>insert</ins></p>",
 		"<p><mark>mark</mark></p>",
 		"<p>H<sub>2</sub>0</p>",