markup/goldmark: Add attributes support for blocks (tables etc.)

E.g.:

```
> foo
> bar
{.myclass}
```

There are some current limitations: For tables you can currently only apply it to the full table, and for lists the ul/ol-nodes only, e.g.:

```
* Fruit
  * Apple
  * Orange
  * Banana
  {.fruits}
* Dairy
  * Milk
  * Cheese
  {.dairies}
{.list}
```

Fixes #7548

4 files changed, 237 insertions, 3 deletions

diff --git a/markup/goldmark/convert.go b/markup/goldmark/convert.go
index 50e7bcb8a..629e2b15a 100644
--- a/markup/goldmark/convert.go
+++ b/markup/goldmark/convert.go
@@ -21,6 +21,8 @@ import (
 	"path/filepath"
 	"runtime/debug"
 
+	"github.com/gohugoio/hugo/markup/goldmark/internal/extensions/attributes"
+
 	"github.com/gohugoio/hugo/identity"
 
 	"github.com/pkg/errors"
@@ -137,10 +139,14 @@ func newMarkdown(pcfg converter.ProviderConfig) goldmark.Markdown {
 		parserOptions = append(parserOptions, parser.WithAutoHeadingID())
 	}
 
-	if cfg.Parser.Attribute {
+	if cfg.Parser.Attribute.Title {
 		parserOptions = append(parserOptions, parser.WithAttribute())
 	}
 
+	if cfg.Parser.Attribute.Block {
+		extensions = append(extensions, attributes.New())
+	}
+
 	md := goldmark.New(
 		goldmark.WithExtensions(
 			extensions...,
diff --git a/markup/goldmark/convert_test.go b/markup/goldmark/convert_test.go
index f105afdc4..d35d4d1fd 100644
--- a/markup/goldmark/convert_test.go
+++ b/markup/goldmark/convert_test.go
@@ -17,6 +17,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/spf13/cast"
+
 	"github.com/gohugoio/hugo/markup/goldmark/goldmark_config"
 
 	"github.com/gohugoio/hugo/markup/highlight"
@@ -193,6 +195,103 @@ func TestConvertAutoIDBlackfriday(t *testing.T) {
 	c.Assert(got, qt.Contains, "<h2 id=\"let-s-try-this-shall-we\">")
 }
 
+func TestConvertAttributes(t *testing.T) {
+	c := qt.New(t)
+
+	withBlockAttributes := func(conf *markup_config.Config) {
+		conf.Goldmark.Parser.Attribute.Block = true
+		conf.Goldmark.Parser.Attribute.Title = false
+	}
+
+	withTitleAndBlockAttributes := func(conf *markup_config.Config) {
+		conf.Goldmark.Parser.Attribute.Block = true
+		conf.Goldmark.Parser.Attribute.Title = true
+	}
+
+	for _, test := range []struct {
+		name       string
+		withConfig func(conf *markup_config.Config)
+		input      string
+		expect     interface{}
+	}{
+		{
+			"Title",
+			nil,
+			"## heading {#id .className attrName=attrValue class=\"class1 class2\"}",
+			"<h2 id=\"id\" class=\"className class1 class2\" attrName=\"attrValue\">heading</h2>\n",
+		},
+		{
+			"Blockquote",
+			withBlockAttributes,
+			"> foo\n> bar\n{#id .className attrName=attrValue class=\"class1 class2\"}\n",
+			"<blockquote id=\"id\" class=\"className class1 class2\"><p>foo\nbar</p>\n</blockquote>\n",
+		},
+		{
+			"Paragraph",
+			withBlockAttributes,
+			"\nHi there.\n{.myclass }",
+			"<p class=\"myclass\">Hi there.</p>\n",
+		},
+		{
+			"Ordered list",
+			withBlockAttributes,
+			"\n1. First\n2. Second\n{.myclass }",
+			"<ol class=\"myclass\">\n<li>First</li>\n<li>Second</li>\n</ol>\n",
+		},
+		{
+			"Unordered list",
+			withBlockAttributes,
+			"\n* First\n* Second\n{.myclass }",
+			"<ul class=\"myclass\">\n<li>First</li>\n<li>Second</li>\n</ul>\n",
+		},
+		{
+			"Unordered list, indented",
+			withBlockAttributes,
+			`* Fruit
+  * Apple
+  * Orange
+  * Banana
+  {.fruits}
+* Dairy
+  * Milk
+  * Cheese
+  {.dairies}
+{.list}`,
+			[]string{"<ul class=\"list\">\n<li>Fruit\n<ul class=\"fruits\">", "<li>Dairy\n<ul class=\"dairies\">"},
+		},
+		{
+			"Table",
+			withBlockAttributes,
+			`| A        | B           |
+| ------------- |:-------------:| -----:|
+| AV      | BV |
+{.myclass }`,
+			"<table class=\"myclass\">\n<thead>",
+		},
+		{
+			"Title and Blockquote",
+			withTitleAndBlockAttributes,
+			"## heading {#id .className attrName=attrValue class=\"class1 class2\"}\n> foo\n> bar\n{.myclass}",
+			"<h2 id=\"id\" class=\"className class1 class2\" attrName=\"attrValue\">heading</h2>\n<blockquote class=\"myclass\"><p>foo\nbar</p>\n</blockquote>\n",
+		},
+	} {
+		c.Run(test.name, func(c *qt.C) {
+			mconf := markup_config.Default
+			if test.withConfig != nil {
+				test.withConfig(&mconf)
+			}
+			b := convert(c, mconf, test.input)
+			got := string(b.Bytes())
+
+			for _, s := range cast.ToStringSlice(test.expect) {
+				c.Assert(got, qt.Contains, s)
+			}
+
+		})
+	}
+
+}
+
 func TestConvertIssues(t *testing.T) {
 	c := qt.New(t)
 
diff --git a/markup/goldmark/goldmark_config/config.go b/markup/goldmark/goldmark_config/config.go
index af33e03dc..82b8d9630 100644
--- a/markup/goldmark/goldmark_config/config.go
+++ b/markup/goldmark/goldmark_config/config.go
@@ -37,7 +37,10 @@ var Default = Config{
 	Parser: Parser{
 		AutoHeadingID:     true,
 		AutoHeadingIDType: AutoHeadingIDTypeGitHub,
-		Attribute:         true,
+		Attribute: ParserAttribute{
+			Title: true,
+			Block: false,
+		},
 	},
 }
 
@@ -82,5 +85,12 @@ type Parser struct {
 	AutoHeadingIDType string
 
 	// Enables custom attributes.
-	Attribute bool
+	Attribute ParserAttribute
+}
+
+type ParserAttribute struct {
+	// Enables custom attributes for titles.
+	Title bool
+	// Enables custom attributeds for blocks.
+	Block bool
 }
diff --git a/markup/goldmark/internal/extensions/attributes/attributes.go b/markup/goldmark/internal/extensions/attributes/attributes.go
new file mode 100644
index 000000000..ce745295c
--- /dev/null
+++ b/markup/goldmark/internal/extensions/attributes/attributes.go
@@ -0,0 +1,119 @@
+package attributes
+
+import (
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+// This extenion is based on/inspired by https://github.com/mdigger/goldmark-attributes
+// MIT License
+// Copyright (c) 2019 Dmitry Sedykh
+
+var (
+	kindAttributesBlock = ast.NewNodeKind("AttributesBlock")
+
+	defaultParser                        = new(attrParser)
+	defaultTransformer                   = new(transformer)
+	attributes         goldmark.Extender = new(attrExtension)
+)
+
+func New() goldmark.Extender {
+	return attributes
+}
+
+type attrExtension struct{}
+
+func (a *attrExtension) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(
+		parser.WithBlockParsers(
+			util.Prioritized(defaultParser, 100)),
+		parser.WithASTTransformers(
+			util.Prioritized(defaultTransformer, 100),
+		),
+	)
+}
+
+type attrParser struct{}
+
+func (a *attrParser) CanAcceptIndentedLine() bool {
+	return false
+}
+
+func (a *attrParser) CanInterruptParagraph() bool {
+	return true
+}
+
+func (a *attrParser) Close(node ast.Node, reader text.Reader, pc parser.Context) {
+}
+
+func (a *attrParser) Continue(node ast.Node, reader text.Reader, pc parser.Context) parser.State {
+	return parser.Close
+}
+
+func (a *attrParser) Open(parent ast.Node, reader text.Reader, pc parser.Context) (ast.Node, parser.State) {
+	if attrs, ok := parser.ParseAttributes(reader); ok {
+		// add attributes
+		var node = &attributesBlock{
+			BaseBlock: ast.BaseBlock{},
+		}
+		for _, attr := range attrs {
+			node.SetAttribute(attr.Name, attr.Value)
+		}
+		return node, parser.NoChildren
+	}
+	return nil, parser.RequireParagraph
+}
+
+func (a *attrParser) Trigger() []byte {
+	return []byte{'{'}
+}
+
+type attributesBlock struct {
+	ast.BaseBlock
+}
+
+func (a *attributesBlock) Dump(source []byte, level int) {
+	attrs := a.Attributes()
+	list := make(map[string]string, len(attrs))
+	for _, attr := range attrs {
+		var (
+			name  = util.BytesToReadOnlyString(attr.Name)
+			value = util.BytesToReadOnlyString(util.EscapeHTML(attr.Value.([]byte)))
+		)
+		list[name] = value
+	}
+	ast.DumpHelper(a, source, level, list, nil)
+}
+
+func (a *attributesBlock) Kind() ast.NodeKind {
+	return kindAttributesBlock
+}
+
+type transformer struct{}
+
+func (a *transformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
+	var attributes = make([]ast.Node, 0, 500)
+	ast.Walk(node, func(node ast.Node, entering bool) (ast.WalkStatus, error) {
+		if entering && node.Kind() == kindAttributesBlock && !node.HasBlankPreviousLines() {
+			attributes = append(attributes, node)
+			return ast.WalkSkipChildren, nil
+		}
+		return ast.WalkContinue, nil
+	})
+
+	for _, attr := range attributes {
+		if prev := attr.PreviousSibling(); prev != nil &&
+			prev.Type() == ast.TypeBlock {
+			for _, attr := range attr.Attributes() {
+				if _, found := prev.Attribute(attr.Name); !found {
+					prev.SetAttribute(attr.Name, attr.Value)
+				}
+			}
+		}
+		// remove attributes node
+		attr.Parent().RemoveChild(attr.Parent(), attr)
+	}
+}