Add color preview to markdown

Signed-off-by: Yarden Shoham <hrsi88@gmail.com>

modules/markup/markdown/ast.go

@@ -144,3 +144,39 @@ func IsIcon(node ast.Node) bool {
 	_, ok := node.(*Icon)
 	return ok
 }
+
+// ColorPreview is an inline for a color preview
+type ColorPreview struct {
+	ast.BaseInline
+	Color []byte
+}
+
+// Dump implements Node.Dump.
+func (n *ColorPreview) Dump(source []byte, level int) {
+	m := map[string]string{}
+	m["Color"] = string(n.Color)
+	ast.DumpHelper(n, source, level, m, nil)
+}
+
+// KindColorPreview is the NodeKind for ColorPreview
+var KindColorPreview = ast.NewNodeKind("ColorPreview")
+
+// Kind implements Node.Kind.
+func (n *ColorPreview) Kind() ast.NodeKind {
+	return KindColorPreview
+}
+
+// NewColorPreview returns a new Span node.
+func NewColorPreview(color []byte) *ColorPreview {
+	return &ColorPreview{
+		BaseInline: ast.BaseInline{},
+		Color:      color,
+	}
+}
+
+// IsColorPreview returns true if the given node implements the ColorPreview interface,
+// otherwise false.
+func IsColorPreview(node ast.Node) bool {
+	_, ok := node.(*ColorPreview)
+	return ok
+}

modules/markup/markdown/goldmark.go

@@ -27,6 +27,8 @@ import (
 
 var byteMailto = []byte("mailto:")
 
+var cssColorRegex = regexp.MustCompile(`(?i)(#(?:[0-9a-f]{2}){2,4}$|(#[0-9a-f]{3}$)|(rgb|hsl)a?\((-?\d+%?[,\s]+){2,3}\s*[\d\.]+%?\))$`)
+
 // ASTTransformer is a default transformer of the goldmark tree.
 type ASTTransformer struct{}
 
@@ -178,6 +180,11 @@ func (g *ASTTransformer) Transform(node *ast.Document, reader text.Reader, pc pa
 					v.SetHardLineBreak(setting.Markdown.EnableHardLineBreakInDocuments)
 				}
 			}
+		case *ast.CodeSpan:
+			colorContent := n.Text(reader.Source())
+			if cssColorRegex.Match(colorContent) {
+				v.Parent().InsertAfter(v.Parent(), v, NewColorPreview(colorContent))
+			}
 		}
 		return ast.WalkContinue, nil
 	})
@@ -266,6 +273,7 @@ func (r *HTMLRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
 	reg.Register(KindDetails, r.renderDetails)
 	reg.Register(KindSummary, r.renderSummary)
 	reg.Register(KindIcon, r.renderIcon)
+	reg.Register(KindColorPreview, r.renderColorPreview)
 	reg.Register(KindTaskCheckBoxListItem, r.renderTaskCheckBoxListItem)
 	reg.Register(east.KindTaskCheckBox, r.renderTaskCheckBox)
 }
@@ -356,6 +364,22 @@ func (r *HTMLRenderer) renderIcon(w util.BufWriter, source []byte, node ast.Node
 	return ast.WalkContinue, nil
 }
 
+func (r *HTMLRenderer) renderColorPreview(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	var err error
+	n := node.(*ColorPreview)
+	if entering {
+		_, err = w.WriteString(fmt.Sprintf(`<code class="color-preview"><span class="repo-icon rounded" style="background-color: %v">`, string(n.Color)))
+	} else {
+		_, err = w.WriteString("</span></code>")
+	}
+
+	if err != nil {
+		return ast.WalkStop, err
+	}
+
+	return ast.WalkContinue, nil
+}
+
 func (r *HTMLRenderer) renderTaskCheckBoxListItem(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
 	n := node.(*TaskCheckBoxListItem)
 	if entering {

modules/markup/sanitizer.go

@@ -55,6 +55,10 @@ func createDefaultPolicy() *bluemonday.Policy {
 	// For JS code copy and Mermaid loading state
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^code-block( is-loading)?$`)).OnElements("pre")
 
+	// For color preview
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^repo-icon rounded$`)).OnElements("span")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^color-preview$")).OnElements("code")
+
 	// For Chroma markdown plugin
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(chroma )?language-[\w-]+( display)?( is-loading)?$`)).OnElements("code")
 
@@ -88,8 +92,8 @@ func createDefaultPolicy() *bluemonday.Policy {
 	// Allow 'style' attribute on text elements.
 	policy.AllowAttrs("style").OnElements("span", "p")
 
-	// Allow 'color' property for the style attribute on text elements.
-	policy.AllowStyles("color").OnElements("span", "p")
+	// Allow 'color' and 'background-color' properties for the style attribute on text elements.
+	policy.AllowStyles("color", "background-color").OnElements("span", "p")
 
 	// Allow generally safe attributes
 	generalSafeAttrs := []string{

web_src/less/_base.less

@@ -1371,6 +1371,22 @@ a.ui.card:hover,
   border-color: var(--color-secondary);
 }
 
+.color-preview {
+  padding-left: 0 !important;
+  border-top-left-radius: 0 !important;
+  border-bottom-left-radius: 0 !important;
+  span {
+    height: 7px;
+    width: 7px;
+  }
+}
+
+code:has(+ .color-preview) {
+  border-top-right-radius: 0;
+  border-bottom-right-radius: 0;
+  padding-right: 0.2em;
+}
+
 footer {
   background-color: var(--color-footer);
   border-top: 1px solid var(--color-secondary);