Add direct link to a footnote from it's referer

Some renderers might not care to have an explicit list of footnotes at
the end of the document, instead they're interested in the content of
the footnote at the location of a referer. Make their lives easier by
providing such a link

inline.go

@@ -297,6 +297,7 @@ func link(p *parser, data []byte, offset int) (int, *Node) {
 
 	txtE := i
 	i++
+	var footnoteNode *Node
 
 	// skip any amount of whitespace or newline
 	// (this is much more lax than original markdown syntax)
@@ -476,6 +477,7 @@ func link(p *parser, data []byte, offset int) (int, *Node) {
 			}
 		}
 
+		footnoteNode = NewNode(Item)
 		if t == linkInlineFootnote {
 			// create a new reference
 			noteID = len(p.notes) + 1
@@ -497,6 +499,7 @@ func link(p *parser, data []byte, offset int) (int, *Node) {
 				hasBlock: false,
 				link:     fragment,
 				title:    id,
+				footnote: footnoteNode,
 			}
 
 			p.notes = append(p.notes, ref)
@@ -512,6 +515,7 @@ func link(p *parser, data []byte, offset int) (int, *Node) {
 
 			if t == linkDeferredFootnote {
 				lr.noteID = len(p.notes) + 1
+				lr.footnote = footnoteNode
 				p.notes = append(p.notes, lr)
 			}
 
@@ -570,6 +574,7 @@ func link(p *parser, data []byte, offset int) (int, *Node) {
 		linkNode.Destination = link
 		linkNode.Title = title
 		linkNode.NoteID = noteID
+		linkNode.Footnote = footnoteNode
 		if t == linkInlineFootnote {
 			i++
 		}

markdown.go

@@ -213,14 +213,16 @@ func (p *parser) finalize(block *Node) {
 }
 
 func (p *parser) addChild(node NodeType, offset uint32) *Node {
-	for !p.tip.canContain(node) {
+	return p.addExistingChild(NewNode(node), offset)
+}
+
+func (p *parser) addExistingChild(node *Node, offset uint32) *Node {
+	for !p.tip.canContain(node.Type) {
 		p.finalize(p.tip)
 	}
-	newNode := NewNode(node)
-	newNode.content = []byte{}
-	p.tip.AppendChild(newNode)
-	p.tip = newNode
-	return newNode
+	p.tip.AppendChild(node)
+	p.tip = node
+	return node
 }
 
 func (p *parser) closeUnmatchedBlocks() {
@@ -419,7 +421,8 @@ func (p *parser) parseRefsToAST() {
 	// the fixed initial set.
 	for i := 0; i < len(p.notes); i++ {
 		ref := p.notes[i]
-		block := p.addBlock(Item, nil)
+		p.addExistingChild(ref.footnote, 0)
+		block := ref.footnote
 		block.ListFlags = flags | ListTypeOrdered
 		block.RefLink = ref.link
 		if ref.hasBlock {
@@ -570,6 +573,7 @@ type reference struct {
 	title    []byte
 	noteID   int // 0 if not a footnote ref
 	hasBlock bool
+	footnote *Node // a link to the Item node within a list of footnotes
 
 	text []byte // only gets populated by refOverride feature with Reference.Text
 }

node.go

@@ -84,6 +84,7 @@ type LinkData struct {
 	Destination []byte // Destination is what goes into a href
 	Title       []byte // Title is the tooltip thing that goes in a title attribute
 	NoteID      int    // NoteID contains a serial number of a footnote, zero if it's not a footnote
+	Footnote    *Node  // If it's a footnote, this is a direct link to the footnote Node. Otherwise nil.
 }
 
 // CodeBlockData contains fields relevant to a CodeBlock node type.