Add TODO list support for Blackfriday

* Add CSS class to TODO list and list items
* Add a flag to turn task list support off

Fixes #2269

1 files changed, 38 insertions, 0 deletions

diff --git a/helpers/content_renderer.go b/helpers/content_renderer.go
index 02a9e9c83..6bd2212e1 100644
--- a/helpers/content_renderer.go
+++ b/helpers/content_renderer.go
@@ -72,6 +72,44 @@ func (renderer *HugoHTMLRenderer) Image(out *bytes.Buffer, link []byte, title []
 	}
 }
 
+// ListItem adds task list support to the Blackfriday renderer.
+func (renderer *HugoHTMLRenderer) ListItem(out *bytes.Buffer, text []byte, flags int) {
+	if !renderer.Config.TaskLists {
+		renderer.Renderer.ListItem(out, text, flags)
+		return
+	}
+
+	switch {
+	case bytes.HasPrefix(text, []byte("[ ] ")):
+		text = append([]byte(`<input type="checkbox" disabled class="task-list-item">`), text[3:]...)
+
+	case bytes.HasPrefix(text, []byte("[x] ")) || bytes.HasPrefix(text, []byte("[X] ")):
+		text = append([]byte(`<input type="checkbox" checked disabled class="task-list-item">`), text[3:]...)
+	}
+
+	renderer.Renderer.ListItem(out, text, flags)
+}
+
+// List adds task list support to the Blackfriday renderer.
+func (renderer *HugoHTMLRenderer) List(out *bytes.Buffer, text func() bool, flags int) {
+	if !renderer.Config.TaskLists {
+		renderer.Renderer.List(out, text, flags)
+		return
+	}
+	marker := out.Len()
+	renderer.Renderer.List(out, text, flags)
+	if out.Len() > marker {
+		list := out.Bytes()[marker:]
+		if bytes.Contains(list, []byte("task-list-item")) {
+			// Rewrite the buffer from the marker
+			out.Truncate(marker)
+			// May be either dl, ul or ol
+			list := append(list[:4], append([]byte(` class="task-list"`), list[4:]...)...)
+			out.Write(list)
+		}
+	}
+}
+
 // HugoMmarkHTMLRenderer wraps a mmark.Renderer, typically a mmark.html
 // Enabling Hugo to customise the rendering experience
 type HugoMmarkHTMLRenderer struct {