add citations

Signed-off-by: Miek Gieben <miek@miek.nl>

ast/node.go

@@ -39,6 +39,16 @@ const (
 	DocumentMatterBack
 )
 
+// CitationTypes holds the type of a citation, informative, normative or suppressed
+type CitationTypes int
+
+const (
+	CitationTypeNone CitationTypes = iota
+	CitationTypeSuppressed
+	CitationTypeInformative
+	CitationTypeNormative
+)
+
 // Node defines an ast node
 type Node interface {
 	AsContainer() *Container
@@ -240,6 +250,14 @@ type CrossReference struct {
 	Destination []byte // Destination is where the reference points to
 }
 
+// Citation is a citation node.
+type Citation struct {
+	Container
+
+	Destination [][]byte        // Destination is where the citation points to. Multiple ones are allowed.
+	Type        []CitationTypes // 1:1 mapping of destination and citation type
+}
+
 // Image represents markdown image node
 type Image struct {
 	Container

parser/citation.go

@@ -0,0 +1 @@
+package parser

parser/inline.go

@@ -177,6 +177,7 @@ const (
 	linkImg
 	linkDeferredFootnote
 	linkInlineFootnote
+	linkCitation
 )
 
 func isReferenceStyleLink(data []byte, pos int, t linkType) bool {
@@ -200,7 +201,7 @@ func maybeInlineFootnote(p *Parser, data []byte, offset int) (int, ast.Node) {
 	return 0, nil
 }
 
-// '[': parse a link or an image or a footnote
+// '[': parse a link or an image or a footnote or a citation
 func link(p *Parser, data []byte, offset int) (int, ast.Node) {
 	// no links allowed inside regular links, footnote, and deferred footnotes
 	if p.insideLink && (offset > 0 && data[offset-1] == '[' || len(data)-1 > offset && data[offset+1] == '^') {
@@ -226,6 +227,14 @@ func link(p *Parser, data []byte, offset int) (int, ast.Node) {
 		} else if len(data)-1 > offset && data[offset+1] == '^' {
 			t = linkDeferredFootnote
 		}
+	// [@citation], [-@citation] support
+	case p.extensions&Mmark != 0:
+		if len(data)-1 > offset && data[offset+1] == '@' {
+			t = linkCitation
+		}
+		if len(data)-2 > offset && data[offset+1] == '-' && data[offset+2] == '@' {
+			t = linkCitation
+		}
 	// [text] == regular link
 	default:
 		t = linkNormal
@@ -233,6 +242,10 @@ func link(p *Parser, data []byte, offset int) (int, ast.Node) {
 
 	data = data[offset:]
 
+	if t == linkCitation {
+		return citation(p, data, 0)
+	}
+
 	var (
 		i                       = 1
 		noteID                  int