appview/pages/markup: insert anchor link in headings

Signed-off-by: oppiliappan <[e-mail]>

appview/pages/markup/markdown.go

···
 		switch a.rctx.RendererType {
 		case RendererTypeRepoMarkdown:
 			switch n := n.(type) {
+			case *ast.Heading:
+				a.rctx.anchorHeadingTransformer(n)
 			case *ast.Link:
 				a.rctx.relativeLinkTransformer(n)
 			case *ast.Image:
···
 			}
 		case RendererTypeDefault:
 			switch n := n.(type) {
+			case *ast.Heading:
+				a.rctx.anchorHeadingTransformer(n)
 			case *ast.Image:
 				a.rctx.imageFromKnotAstTransformer(n)
 				a.rctx.camoImageLinkAstTransformer(n)
···
 
 	dst := string(link.Destination)
 
-	if isAbsoluteUrl(dst) {
+	if isAbsoluteUrl(dst) || isFragment(dst) || isMail(dst) {
 		return
 	}
 
···
 	img.Destination = []byte(rctx.imageFromKnotTransformer(dst))
 }
 
+func (rctx *RenderContext) anchorHeadingTransformer(h *ast.Heading) {
+	idGeneric, exists := h.AttributeString("id")
+	if !exists {
+		return // no id, nothing to do
+	}
+	id, ok := idGeneric.([]byte)
+	if !ok {
+		return
+	}
+
+	// create anchor link
+	anchor := ast.NewLink()
+	anchor.Destination = fmt.Appendf(nil, "#%s", string(id))
+	anchor.SetAttribute([]byte("class"), []byte("anchor"))
+
+	// create icon text
+	iconText := ast.NewString([]byte("#"))
+	anchor.AppendChild(anchor, iconText)
+
+	// set class on heading
+	h.SetAttribute([]byte("class"), []byte("heading"))
+
+	// append anchor to heading
+	h.AppendChild(h, anchor)
+}
+
 // actualPath decides when to join the file path with the
 // current repository directory (essentially only when the link
 // destination is relative. if it's absolute then we assume the
···
 	}
 	return parsed.IsAbs()
 }
+
+func isFragment(link string) bool {
+	return strings.HasPrefix(link, "#")
+}
+
+func isMail(link string) bool {
+	return strings.HasPrefix(link, "mailto:")
+}

appview/pages/markup/sanitizer.go

···
 	// for code blocks
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`chroma`)).OnElements("pre")
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`anchor|footnote-ref|footnote-backref`)).OnElements("a")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`heading`)).OnElements("h1", "h2", "h3", "h4", "h5", "h6", "h7", "h8")
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(strings.Join(slices.Collect(maps.Values(chroma.StandardTypes)), "|"))).OnElements("span")
 
 	// centering content

input.css

···
           disabled:before:bg-green-400 dark:disabled:before:bg-green-600;
         }
 
+        .prose hr {
+          @apply my-2;
+        }
+
         .prose li:has(input) {
-          list-style: none;
+          @apply list-none;
+        }
+
+        .prose ul:has(input) {
+          @apply pl-2;
+        }
+
+        .prose .heading .anchor {
+          @apply no-underline mx-2 opacity-0;
+        }
+
+        .prose .heading:hover .anchor {
+          @apply opacity-70;
+        }
+
+        .prose .heading .anchor:hover {
+          @apply opacity-70;
+        }
+
         .prose a.footnote-backref {
           @apply no-underline;
         }