Add support for headline CUSTOM_ID property & linking

this introduces the PropertyDrawer node to make it easier to access the
properties associated to a headline - normal drawers don't parse their content
into kv pairs

org/drawer.go

@@ -10,8 +10,13 @@ type Drawer struct {
 	Children []Node
 }
 
+type PropertyDrawer struct {
+	Properties [][]string
+}
+
 var beginDrawerRegexp = regexp.MustCompile(`^(\s*):(\S+):\s*$`)
 var endDrawerRegexp = regexp.MustCompile(`^(\s*):END:\s*$`)
+var propertyRegexp = regexp.MustCompile(`^(\s*):(\S+):(\s+(.*)$|\s*$)`)
 
 func lexDrawer(line string) (token, bool) {
 	if m := endDrawerRegexp.FindStringSubmatch(line); m != nil {
@@ -23,7 +28,11 @@ func lexDrawer(line string) (token, bool) {
 }
 
 func (d *Document) parseDrawer(i int, parentStop stopFn) (int, Node) {
-	drawer, start := Drawer{Name: strings.ToUpper(d.tokens[i].content)}, i
+	name := strings.ToUpper(d.tokens[i].content)
+	if name == "PROPERTIES" {
+		return d.parsePropertyDrawer(i, parentStop)
+	}
+	drawer, start := Drawer{Name: name}, i
 	i++
 	stop := func(d *Document, i int) bool {
 		if parentStop(d, i) {
@@ -49,3 +58,34 @@ func (d *Document) parseDrawer(i int, parentStop stopFn) (int, Node) {
 	}
 	return i - start, drawer
 }
+
+func (d *Document) parsePropertyDrawer(i int, parentStop stopFn) (int, Node) {
+	drawer, start := PropertyDrawer{}, i
+	i++
+	stop := func(d *Document, i int) bool {
+		return parentStop(d, i) || (d.tokens[i].kind != "text" && d.tokens[i].kind != "beginDrawer")
+	}
+	for ; !stop(d, i); i++ {
+		m := propertyRegexp.FindStringSubmatch(d.tokens[i].matches[0])
+		k, v := strings.ToUpper(m[2]), strings.TrimSpace(m[4])
+		drawer.Properties = append(drawer.Properties, []string{k, v})
+	}
+	if i < len(d.tokens) && d.tokens[i].kind == "endDrawer" {
+		i++
+	} else {
+		return 0, nil
+	}
+	return i - start, drawer
+}
+
+func (d *PropertyDrawer) Get(key string) (string, bool) {
+	if d == nil {
+		return "", false
+	}
+	for _, kvPair := range d.Properties {
+		if kvPair[0] == key {
+			return kvPair[1], true
+		}
+	}
+	return "", false
+}

org/headline.go

@@ -10,7 +10,7 @@ type Headline struct {
 	Lvl        int
 	Status     string
 	Priority   string
-	Properties Node
+	Properties *PropertyDrawer
 	Title      []Node
 	Tags       []string
 	Children   []Node
@@ -62,8 +62,8 @@ func (d *Document) parseHeadline(i int, parentStop stopFn) (int, Node) {
 	}
 	consumed, nodes := d.parseMany(i+1, stop)
 	if len(nodes) > 0 {
-		if d, ok := nodes[0].(Drawer); ok && d.Name == "PROPERTIES" {
-			headline.Properties = d
+		if d, ok := nodes[0].(PropertyDrawer); ok {
+			headline.Properties = &d
 			nodes = nodes[1:]
 		}
 	}

org/html.go

@@ -89,6 +89,8 @@ func (w *HTMLWriter) writeNodes(ns ...Node) {
 			w.writeBlock(n)
 		case Drawer:
 			w.writeDrawer(n)
+		case PropertyDrawer:
+			continue
 
 		case FootnoteDefinition:
 			w.writeFootnoteDefinition(n)
@@ -207,7 +209,13 @@ func (w *HTMLWriter) writeHeadline(h Headline) {
 	if h.Lvl == 1 && title == w.FootnotesHeadingTitle {
 		return
 	}
-	w.WriteString(fmt.Sprintf("<h%d>\n", h.Lvl))
+
+	if id, ok := h.Properties.Get("CUSTOM_ID"); ok {
+		w.WriteString(fmt.Sprintf(`<h%d id="%s">`, h.Lvl, id) + "\n")
+	} else {
+		w.WriteString(fmt.Sprintf("<h%d>\n", h.Lvl))
+	}
+
 	if h.Status != "" {
 		w.WriteString(fmt.Sprintf(`<span class="todo">%s</span>`, h.Status) + "\n")
 	}

org/org.go

@@ -63,6 +63,8 @@ func (w *OrgWriter) writeNodes(ns ...Node) {
 			w.writeBlock(n)
 		case Drawer:
 			w.writeDrawer(n)
+		case PropertyDrawer:
+			w.writePropertyDrawer(n)
 
 		case FootnoteDefinition:
 			w.writeFootnoteDefinition(n)
@@ -132,7 +134,7 @@ func (w *OrgWriter) writeHeadline(h Headline) {
 		w.WriteString(w.indent)
 	}
 	if h.Properties != nil {
-		w.writeNodes(h.Properties)
+		w.writeNodes(*h.Properties)
 	}
 	w.writeNodes(h.Children...)
 }
@@ -159,6 +161,18 @@ func (w *OrgWriter) writeDrawer(d Drawer) {
 	w.WriteString(w.indent + ":END:\n")
 }
 
+func (w *OrgWriter) writePropertyDrawer(d PropertyDrawer) {
+	w.WriteString(":PROPERTIES:\n")
+	for _, kvPair := range d.Properties {
+		k, v := kvPair[0], kvPair[1]
+		if v != "" {
+			v = " " + v
+		}
+		w.WriteString(fmt.Sprintf(":%s:%s\n", k, v))
+	}
+	w.WriteString(":END:\n")
+}
+
 func (w *OrgWriter) writeFootnoteDefinition(f FootnoteDefinition) {
 	w.WriteString(fmt.Sprintf("[fn:%s]", f.Name))
 	if !(len(f.Children) >= 1 && isEmptyLineParagraph(f.Children[0])) {

org/testdata/headlines.html

@@ -25,12 +25,12 @@ not just where they are actually meant to be - even here &gt; <code class="stati
 <span class="priority">[B]</span>
 Headline with todo status &amp; priority
 </h1>
-<h1>
+<h1 id="this-will-be-the-id-of-the-headline">
 <span class="todo">DONE</span>
 Headline with TODO status
 </h1>
 <p>
-the <strong>content</strong>
+we can link to headlines that define a custom_id: <a href="#this-will-be-the-id-of-the-headline">#this-will-be-the-id-of-the-headline</a>
 </p>
 <h1>
 <span class="priority">[A]</span>

org/testdata/headlines.org

@@ -7,10 +7,11 @@
 * TODO [#B] Headline with todo status & priority
 * DONE Headline with TODO status
 :PROPERTIES:
-:Note: property drawers are not exported as html like other drawers
+:custom_id: this-will-be-the-id-of-the-headline
+:note: property drawers are not exported as html like other drawers
 :END:
 
-the *content*
+we can link to headlines that define a custom_id: [[#this-will-be-the-id-of-the-headline]]
 * [#A] Headline with tags & priority                                :foo:bar:
 Still outside the drawer
 :DRAWERNAME:

org/testdata/headlines.pretty_org

@@ -7,10 +7,11 @@
 * TODO [#B] Headline with todo status & priority
 * DONE Headline with TODO status
 :PROPERTIES:
-:Note: property drawers are not exported as html like other drawers
+:CUSTOM_ID: this-will-be-the-id-of-the-headline
+:NOTE: property drawers are not exported as html like other drawers
 :END:
 
-the *content*
+we can link to headlines that define a custom_id: [[#this-will-be-the-id-of-the-headline]]
 * [#A] Headline with tags & priority                                :foo:bar:
 Still outside the drawer
 :DRAWERNAME:

org/testdata/misc.html

@@ -52,10 +52,11 @@ src block
 * TODO [#B] Headline with todo status & priority
 * DONE Headline with TODO status
 :PROPERTIES:
-:Note: property drawers are not exported as html like other drawers
+:custom_id: this-will-be-the-id-of-the-headline
+:note: property drawers are not exported as html like other drawers
 :END:
 
-the *content*
+we can link to headlines that define a custom_id: [[#this-will-be-the-id-of-the-headline]]
 * [#A] Headline with tags & priority                                :foo:bar:
 Still outside the drawer
 :DRAWERNAME: