appview/pages/markup: smart commit autolink renderer

Implemented tangled link extension. This can be extended for other link
types like issue/pull references in future.

The `tangled.org` host is hardcoded right now.

Close: <https://tangled.org/tangled.org/core/issues/382>

Signed-off-by: Seongmin Lee <[e-mail]>

appview/pages/markup/extension/tangledlink.go

···
+package extension
+
+import (
+	"net/url"
+	"strings"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+// KindTangledLink is a NodeKind of the TangledLink node.
+var KindTangledLink = ast.NewNodeKind("TangledLink")
+
+type TangledLinkNode struct {
+	ast.BaseInline
+	Destination string
+	Commit      *TangledCommitLink
+	// TODO: add more Tangled-link types
+}
+
+type TangledCommitLink struct {
+	Sha string
+}
+
+var _ ast.Node = new(TangledLinkNode)
+
+// Dump implements [ast.Node].
+func (n *TangledLinkNode) Dump(source []byte, level int) {
+	ast.DumpHelper(n, source, level, nil, nil)
+}
+
+// Kind implements [ast.Node].
+func (n *TangledLinkNode) Kind() ast.NodeKind {
+	return KindTangledLink
+}
+
+type tangledLinkTransformer struct {
+	host string
+}
+
+var _ parser.ASTTransformer = new(tangledLinkTransformer)
+
+// Transform implements [parser.ASTTransformer].
+func (t *tangledLinkTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
+	ast.Walk(node, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+
+		var dest string
+
+		switch n := n.(type) {
+		case *ast.AutoLink:
+			dest = string(n.URL(reader.Source()))
+		case *ast.Link:
+			// maybe..? not sure
+		default:
+			return ast.WalkContinue, nil
+		}
+
+		if sha := t.parseLinkCommitSha(dest); sha != "" {
+			newLink := &TangledLinkNode{
+				Destination: dest,
+				Commit: &TangledCommitLink{
+					Sha: sha,
+				},
+			}
+			n.Parent().ReplaceChild(n.Parent(), n, newLink)
+		}
+
+		return ast.WalkContinue, nil
+	})
+}
+
+func (t *tangledLinkTransformer) parseLinkCommitSha(raw string) string {
+	u, err := url.Parse(raw)
+	if err != nil || u.Host != "tangled.org" {
+		return ""
+	}
+
+	// /{owner}/{repo}/commit/<sha>
+	parts := strings.Split(strings.Trim(u.Path, "/"), "/")
+	if len(parts) != 4 || parts[2] != "commit" {
+		return ""
+	}
+
+	sha := parts[3]
+
+	// basic sha validation
+	if len(sha) < 7 {
+		return ""
+	}
+	for _, c := range sha {
+		if !strings.ContainsRune("0123456789abcdef", c) {
+			return ""
+		}
+	}
+
+	return sha[:8]
+}
+
+type tangledLinkRenderer struct{}
+
+var _ renderer.NodeRenderer = new(tangledLinkRenderer)
+
+// RegisterFuncs implements [renderer.NodeRenderer].
+func (r *tangledLinkRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(KindTangledLink, r.renderTangledLink)
+}
+
+func (r *tangledLinkRenderer) renderTangledLink(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	link := node.(*TangledLinkNode)
+
+	if link.Commit != nil {
+		if entering {
+			w.WriteString(`<a href="`)
+			w.WriteString(link.Destination)
+			w.WriteString(`"><code>`)
+			w.WriteString(link.Commit.Sha)
+		} else {
+			w.WriteString(`</code></a>`)
+		}
+	}
+
+	return ast.WalkContinue, nil
+}
+
+type tangledLinkExt struct {
+	host string
+}
+
+var _ goldmark.Extender = new(tangledLinkExt)
+
+func (e *tangledLinkExt) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(parser.WithASTTransformers(
+		util.Prioritized(&tangledLinkTransformer{host: e.host}, 500),
+	))
+	m.Renderer().AddOptions(renderer.WithNodeRenderers(
+		util.Prioritized(&tangledLinkRenderer{}, 500),
+	))
+}
+
+func NewTangledLinkExt(host string) goldmark.Extender {
+	return &tangledLinkExt{host}
+}

appview/pages/markup/extension/tangledlink_test.go

···
+package extension_test
+
+import (
+	"bytes"
+	"testing"
+
+	"tangled.org/core/appview/pages/markup"
+)
+
+func TestTangledLinkExtension_Rendering(t *testing.T) {
+	tests := []struct {
+		name     string
+		markdown string
+		expected string
+	}{
+		{
+			name:     "renders simple commit link from commonmark autolink",
+			markdown: "This is a commit: <https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0>",
+			expected: `<p>This is a commit: <a href="https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0"><code>cde47050</code></a></p>`,
+		},
+		{
+			name:     "renders simple commit link from gfm autolink",
+			markdown: "This is a commit: https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0",
+			expected: `<p>This is a commit: <a href="https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0"><code>cde47050</code></a></p>`,
+		},
+		{
+			name:     "skip non-autolink links",
+			markdown: "This is a commit: [a commit](https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0)",
+			expected: `<p>This is a commit: <a href="https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0">a commit</a></p>`,
+		},
+		{
+			name:     "skip non-autolink links with content same as dest",
+			markdown: "This is a commit: [https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0](https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0)",
+			expected: `<p>This is a commit: <a href="https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0">https://tangled.org/alice.tngl.sh/cool-repo/commit/cde4705021a07e3cb11322fb9ef78a6c786b41c0</a></p>`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			md := markup.NewMarkdown()
+
+			var buf bytes.Buffer
+			if err := md.Convert([]byte(tt.markdown), &buf); err != nil {
+				t.Fatalf("failed to convert markdown: %v", err)
+			}
+
+			result := buf.String()
+			if result != tt.expected+"\n" {
+				t.Errorf("expected:\n%s\ngot:\n%s", tt.expected, result)
+			}
+		})
+	}
+}

appview/pages/markup/markdown.go

···
 			),
 			callout.CalloutExtention,
 			textension.AtExt,
+			textension.NewTangledLinkExt("tangled.org"),
 			emoji.Emoji,
 		),
 		goldmark.WithParserOptions(