From 42d03b6457090425084cffc81535e16e408a16e4 Mon Sep 17 00:00:00 2001
From: Andreas Fuchs <asf@boinkor.net>
Date: Thu, 30 Jan 2025 08:38:33 -0500
Subject: [PATCH] Use "id" of elements for anchors instead of auto-generating a
 tag

This improves the accuracy of anchor locations in large documents like
the nixpkgs manual, where on occasion the autoanchor counter gets out
of sync. It also seems like the right thing to do.
---
 dashing.go | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/dashing.go b/dashing.go
index 1edf295..6112346 100644
--- a/dashing.go
+++ b/dashing.go
@@ -628,14 +628,27 @@ func attr(node *html.Node, key string) string {
 // NOTE: NOT THREADSAFE. If we switch to goroutines, swith to atom int.
 var tcounter int
 
-func anchor(node *html.Node) string {
-	if node.Type == html.ElementNode && node.Data == "a" {
-		for _, a := range node.Attr {
-			if a.Key == "name" {
-				return a.Val
-			}
+// nodeAttrValue returns the value for a node attribute, and a flag
+// indicating whether that node has the attribute.
+func nodeAttrValue(node *html.Node, attrName string) (string, bool) {
+	if node.Type != html.ElementNode {
+		return "", false
+	}
+	for _, a := range node.Attr {
+		if a.Key == attrName {
+			return a.Val, true
 		}
 	}
+	return "", false
+}
+
+func anchor(node *html.Node) string {
+	if idVal, ok := nodeAttrValue(node, "id"); ok {
+		return idVal
+	}
+	if nameVal, ok := nodeAttrValue(node, "name"); ok && node.Data == "a" {
+		return nameVal
+	}
 	tname := fmt.Sprintf("autolink-%d", tcounter)
 	link := autolink(tname)
 	node.Parent.InsertBefore(link, node)