markup/goldmark: Support extras extension

Enables inclusion of these HTML elements in Markdown:

- Inserted Text (++inserted++)
- Mark Text (==marked==)
- Subscript (H~2~O)
- Superscript (1^st^)

6 files changed, 113 insertions, 1 deletions

diff --git a/docs/data/docs.yaml b/docs/data/docs.yaml
index dcc96c590..036c21285 100644
--- a/docs/data/docs.yaml
+++ b/docs/data/docs.yaml
@@ -1065,6 +1065,15 @@ config:
           enable: false
           escapedSpace: false
         definitionList: true
+        extras:
+          insert:
+            enable: false
+          mark:
+            enable: false
+          subscript:
+            enable: false
+          superscript:
+            enable: false
         footnote: true
         linkify: true
         linkifyProtocol: https
diff --git a/go.mod b/go.mod
index c441df5af..affe8f528 100644
--- a/go.mod
+++ b/go.mod
@@ -35,6 +35,7 @@ require (
 	github.com/gobuffalo/flect v1.0.2
 	github.com/gobwas/glob v0.2.3
 	github.com/gohugoio/go-i18n/v2 v2.1.3-0.20230805085216-e63c13218d0e
+	github.com/gohugoio/hugo-goldmark-extensions/extras v0.1.0
 	github.com/gohugoio/hugo-goldmark-extensions/passthrough v0.2.0
 	github.com/gohugoio/locales v0.14.0
 	github.com/gohugoio/localescompressed v1.0.1
diff --git a/go.sum b/go.sum
index f9b71ddff..60fe686ae 100644
--- a/go.sum
+++ b/go.sum
@@ -213,6 +213,8 @@ github.com/gobwas/glob v0.2.3 h1:A4xDbljILXROh+kObIiy5kIaPYD8e96x1tgBhUI5J+Y=
 github.com/gobwas/glob v0.2.3/go.mod h1:d3Ez4x06l9bZtSvzIay5+Yzi0fmZzPgnTbPcKjJAkT8=
 github.com/gohugoio/go-i18n/v2 v2.1.3-0.20230805085216-e63c13218d0e h1:QArsSubW7eDh8APMXkByjQWvuljwPGAGQpJEFn0F0wY=
 github.com/gohugoio/go-i18n/v2 v2.1.3-0.20230805085216-e63c13218d0e/go.mod h1:3Ltoo9Banwq0gOtcOwxuHG6omk+AwsQPADyw2vQYOJQ=
+github.com/gohugoio/hugo-goldmark-extensions/extras v0.1.0 h1:YhxZNU8y2vxV6Ibr7QJzzUlpr8oHHWX/l+Q1R/a5Zao=
+github.com/gohugoio/hugo-goldmark-extensions/extras v0.1.0/go.mod h1:0cuvOnGKW7WeXA3i7qK6IS07FH1bgJ2XzOjQ7BMJYH4=
 github.com/gohugoio/hugo-goldmark-extensions/passthrough v0.2.0 h1:PCtO5l++psZf48yen2LxQ3JiOXxaRC6v0594NeHvGZg=
 github.com/gohugoio/hugo-goldmark-extensions/passthrough v0.2.0/go.mod h1:g9CCh+Ci2IMbPUrVJuXbBTrA+rIIx5+hDQ4EXYaQDoM=
 github.com/gohugoio/locales v0.14.0 h1:Q0gpsZwfv7ATHMbcTNepFd59H7GoykzWJIxi113XGDc=
diff --git a/markup/goldmark/convert.go b/markup/goldmark/convert.go
index d7180140d..7c00433d5 100644
--- a/markup/goldmark/convert.go
+++ b/markup/goldmark/convert.go
@@ -17,6 +17,7 @@ package goldmark
 import (
 	"bytes"
 
+	"github.com/gohugoio/hugo-goldmark-extensions/extras"
 	"github.com/gohugoio/hugo-goldmark-extensions/passthrough"
 	"github.com/gohugoio/hugo/markup/goldmark/hugocontext"
 	"github.com/yuin/goldmark/util"
@@ -113,6 +114,15 @@ func newMarkdown(pcfg converter.ProviderConfig) goldmark.Markdown {
 
 	extensions = append(extensions, images.New(cfg.Parser.WrapStandAloneImageWithinParagraph))
 
+	extensions = append(extensions, extras.New(
+		extras.Config{
+			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},
+			Superscript: extras.SuperscriptConfig{Enable: cfg.Extensions.Extras.Superscript.Enable},
+		},
+	))
+
 	if mcfg.Highlight.CodeFences {
 		extensions = append(extensions, codeblocks.New())
 	}
diff --git a/markup/goldmark/goldmark_config/config.go b/markup/goldmark/goldmark_config/config.go
index c22852b29..620475c48 100644
--- a/markup/goldmark/goldmark_config/config.go
+++ b/markup/goldmark/goldmark_config/config.go
@@ -49,6 +49,20 @@ var Default = Config{
 			EastAsianLineBreaksStyle: "simple",
 			EscapedSpace:             false,
 		},
+		Extras: Extras{
+			Superscript: Superscript{
+				Enable: false,
+			},
+			Subscript: Subscript{
+				Enable: false,
+			},
+			Insert: Insert{
+				Enable: false,
+			},
+			Mark: Mark{
+				Enable: false,
+			},
+		},
 		Passthrough: Passthrough{
 			Enable: false,
 			Delimiters: DelimitersConfig{
@@ -112,6 +126,7 @@ type Extensions struct {
 	Typographer    Typographer
 	Footnote       bool
 	DefinitionList bool
+	Extras         Extras
 	Passthrough    Passthrough
 
 	// GitHub flavored markdown
@@ -150,7 +165,32 @@ type Typographer struct {
 	Apostrophe string
 }
 
-// Passthrough hold passthrough configuration.
+// Extras holds extras configuration.
+// github.com/hugoio/hugo-goldmark-extensions/extras
+type Extras struct {
+	Insert      Insert
+	Mark        Mark
+	Subscript   Subscript
+	Superscript Superscript
+}
+
+type Insert struct {
+	Enable bool
+}
+
+type Mark struct {
+	Enable bool
+}
+
+type Subscript struct {
+	Enable bool
+}
+
+type Superscript struct {
+	Enable bool
+}
+
+// Passthrough holds passthrough configuration.
 // github.com/hugoio/hugo-goldmark-extensions/passthrough
 type Passthrough struct {
 	// Whether to enable the extension
diff --git a/markup/goldmark/goldmark_integration_test.go b/markup/goldmark/goldmark_integration_test.go
index ffeb763a7..82b41cc67 100644
--- a/markup/goldmark/goldmark_integration_test.go
+++ b/markup/goldmark/goldmark_integration_test.go
@@ -744,3 +744,53 @@ a^*=x-b^*
 %!%
 	`)
 }
+
+func TestExtrasExtension(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['page','rss','section','sitemap','taxonomy','term']
+[markup.goldmark.extensions.extras.insert]
+enable = false
+[markup.goldmark.extensions.extras.mark]
+enable = false
+[markup.goldmark.extensions.extras.subscript]
+enable = false
+[markup.goldmark.extensions.extras.superscript]
+enable = false
+-- layouts/index.html --
+{{ .Content }}
+-- content/_index.md --
+---
+title: home
+---
+++insert++
+
+==mark==
+
+H~2~0
+
+1^st^
+`
+
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html",
+		"<p>++insert++</p>",
+		"<p>==mark==</p>",
+		"<p>H~2~0</p>",
+		"<p>1^st^</p>",
+	)
+
+	files = strings.ReplaceAll(files, "enable = false", "enable = true")
+
+	b = hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html",
+		"<p><ins>insert</ins></p>",
+		"<p><mark>mark</mark></p>",
+		"<p>H<sub>2</sub>0</p>",
+		"<p>1<sup>st</sup></p>",
+	)
+}