3 files changed, 248 insertions, 0 deletions
diff --git a/modules/markup/markdown/callout/ast.go b/modules/markup/markdown/callout/ast.go
new file mode 100644
index 0000000..a5b1bbc
--- /dev/null
+++ b/modules/markup/markdown/callout/ast.go
@@ -0,0 +1,37 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package callout
+
+import (
+	"github.com/yuin/goldmark/ast"
+)
+
+// Attention is an inline for an attention
+type Attention struct {
+	ast.BaseInline
+	AttentionType string
+}
+
+// Dump implements Node.Dump.
+func (n *Attention) Dump(source []byte, level int) {
+	m := map[string]string{}
+	m["AttentionType"] = n.AttentionType
+	ast.DumpHelper(n, source, level, m, nil)
+}
+
+// KindAttention is the NodeKind for Attention
+var KindAttention = ast.NewNodeKind("Attention")
+
+// Kind implements Node.Kind.
+func (n *Attention) Kind() ast.NodeKind {
+	return KindAttention
+}
+
+// NewAttention returns a new Attention node.
+func NewAttention(attentionType string) *Attention {
+	return &Attention{
+		BaseInline:    ast.BaseInline{},
+		AttentionType: attentionType,
+	}
+}
diff --git a/modules/markup/markdown/callout/github.go b/modules/markup/markdown/callout/github.go
new file mode 100644
index 0000000..9b8b611
--- /dev/null
+++ b/modules/markup/markdown/callout/github.go
@@ -0,0 +1,141 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Copyright 2024 The Forgejo Authors c/o Codeberg e.V.. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package callout
+
+import (
+	"strings"
+
+	"code.gitea.io/gitea/modules/svg"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/renderer/html"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+type GitHubCalloutTransformer struct{}
+
+// Transform transforms the given AST tree.
+func (g *GitHubCalloutTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
+	supportedAttentionTypes := map[string]bool{
+		"note":      true,
+		"tip":       true,
+		"important": true,
+		"warning":   true,
+		"caution":   true,
+	}
+
+	_ = ast.Walk(node, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+
+		if v, ok := n.(*ast.Blockquote); ok {
+			if v.ChildCount() == 0 {
+				return ast.WalkContinue, nil
+			}
+
+			// We only want attention blockquotes when the AST looks like:
+			// Text: "["
+			// Text: "!TYPE"
+			// Text(SoftLineBreak): "]"
+
+			// grab these nodes and make sure we adhere to the attention blockquote structure
+			firstParagraph := v.FirstChild()
+			if firstParagraph.ChildCount() < 3 {
+				return ast.WalkContinue, nil
+			}
+			firstTextNode, ok := firstParagraph.FirstChild().(*ast.Text)
+			if !ok || string(firstTextNode.Text(reader.Source())) != "[" {
+				return ast.WalkContinue, nil
+			}
+			secondTextNode, ok := firstTextNode.NextSibling().(*ast.Text)
+			if !ok {
+				return ast.WalkContinue, nil
+			}
+			// If the second node's text isn't one of the supported attention
+			// types, continue walking.
+			secondTextNodeText := secondTextNode.Text(reader.Source())
+			attentionType := strings.ToLower(strings.TrimPrefix(string(secondTextNodeText), "!"))
+			if _, has := supportedAttentionTypes[attentionType]; !has {
+				return ast.WalkContinue, nil
+			}
+
+			thirdTextNode, ok := secondTextNode.NextSibling().(*ast.Text)
+			if !ok || string(thirdTextNode.Text(reader.Source())) != "]" {
+				return ast.WalkContinue, nil
+			}
+
+			// color the blockquote
+			v.SetAttributeString("class", []byte("attention-header attention-"+attentionType))
+
+			// create an emphasis to make it bold
+			attentionParagraph := ast.NewParagraph()
+			attentionParagraph.SetAttributeString("class", []byte("attention-title"))
+			emphasis := ast.NewEmphasis(2)
+			emphasis.SetAttributeString("class", []byte("attention-"+attentionType))
+			firstParagraph.InsertBefore(firstParagraph, firstTextNode, emphasis)
+
+			// capitalize first letter
+			attentionText := ast.NewString([]byte(strings.ToUpper(string(attentionType[0])) + attentionType[1:]))
+
+			// replace the ![TYPE] with a dedicated paragraph of icon+Type
+			emphasis.AppendChild(emphasis, attentionText)
+			attentionParagraph.AppendChild(attentionParagraph, NewAttention(attentionType))
+			attentionParagraph.AppendChild(attentionParagraph, emphasis)
+			firstParagraph.Parent().InsertBefore(firstParagraph.Parent(), firstParagraph, attentionParagraph)
+			firstParagraph.RemoveChild(firstParagraph, firstTextNode)
+			firstParagraph.RemoveChild(firstParagraph, secondTextNode)
+			firstParagraph.RemoveChild(firstParagraph, thirdTextNode)
+		}
+		return ast.WalkContinue, nil
+	})
+}
+
+type GitHubCalloutHTMLRenderer struct {
+	html.Config
+}
+
+// RegisterFuncs implements renderer.NodeRenderer.RegisterFuncs.
+func (r *GitHubCalloutHTMLRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(KindAttention, r.renderAttention)
+}
+
+// renderAttention renders a quote marked with i.e. "> **Note**" or "> **Warning**" with a corresponding svg
+func (r *GitHubCalloutHTMLRenderer) renderAttention(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	if entering {
+		n := node.(*Attention)
+
+		var octiconName string
+		switch n.AttentionType {
+		case "note":
+			octiconName = "info"
+		case "tip":
+			octiconName = "light-bulb"
+		case "important":
+			octiconName = "report"
+		case "warning":
+			octiconName = "alert"
+		case "caution":
+			octiconName = "stop"
+		default:
+			octiconName = "info"
+		}
+		_, _ = w.WriteString(string(svg.RenderHTML("octicon-"+octiconName, 16, "attention-icon attention-"+n.AttentionType)))
+	}
+	return ast.WalkContinue, nil
+}
+
+func NewGitHubCalloutHTMLRenderer(opts ...html.Option) renderer.NodeRenderer {
+	r := &GitHubCalloutHTMLRenderer{
+		Config: html.NewConfig(),
+	}
+	for _, opt := range opts {
+		opt.SetHTMLOption(&r.Config)
+	}
+	return r
+}
diff --git a/modules/markup/markdown/callout/github_legacy.go b/modules/markup/markdown/callout/github_legacy.go
new file mode 100644
index 0000000..32a278b
--- /dev/null
+++ b/modules/markup/markdown/callout/github_legacy.go
@@ -0,0 +1,70 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Copyright 2024 The Forgejo Authors c/o Codeberg e.V.. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package callout
+
+import (
+	"strings"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+)
+
+// Transformer for GitHub's legacy callout markup.
+type GitHubLegacyCalloutTransformer struct{}
+
+func (g *GitHubLegacyCalloutTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
+	supportedCalloutTypes := map[string]bool{"Note": true, "Warning": true}
+
+	_ = ast.Walk(node, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+
+		if v, ok := n.(*ast.Blockquote); ok {
+			if v.ChildCount() == 0 {
+				return ast.WalkContinue, nil
+			}
+
+			// The first paragraph contains the callout type.
+			firstParagraph := v.FirstChild()
+			if firstParagraph.ChildCount() < 1 {
+				return ast.WalkContinue, nil
+			}
+
+			// In the legacy GitHub callout markup, the first node of the first
+			// paragraph should be an emphasis.
+			calloutNode, ok := firstParagraph.FirstChild().(*ast.Emphasis)
+			if !ok {
+				return ast.WalkContinue, nil
+			}
+			calloutText := string(calloutNode.Text(reader.Source()))
+			calloutType := strings.ToLower(calloutText)
+			// We only support "Note" and "Warning" callouts in legacy mode,
+			// match only those.
+			if _, has := supportedCalloutTypes[calloutText]; !has {
+				return ast.WalkContinue, nil
+			}
+
+			// Set the attention attribute on the emphasis
+			calloutNode.SetAttributeString("class", []byte("attention-"+calloutType))
+
+			// color the blockquote
+			v.SetAttributeString("class", []byte("attention-header attention-"+calloutType))
+
+			// Create new paragraph.
+			attentionParagraph := ast.NewParagraph()
+			attentionParagraph.SetAttributeString("class", []byte("attention-title"))
+
+			// Move the callout node to the paragraph and insert the paragraph.
+			attentionParagraph.AppendChild(attentionParagraph, NewAttention(calloutType))
+			attentionParagraph.AppendChild(attentionParagraph, calloutNode)
+			firstParagraph.Parent().InsertBefore(firstParagraph.Parent(), firstParagraph, attentionParagraph)
+			firstParagraph.RemoveChild(firstParagraph, calloutNode)
+		}
+
+		return ast.WalkContinue, nil
+	})
+}