1 files changed, 170 insertions, 0 deletions
diff --git a/internal/api/render.go b/internal/api/render.go
new file mode 100644
index 00000000..47b157af
--- /dev/null
+++ b/internal/api/render.go
@@ -0,0 +1,170 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package api
+
+import (
+	"fmt"
+	"go/ast"
+	"go/doc"
+	"go/doc/comment"
+	"go/format"
+	"go/token"
+	"io"
+	"slices"
+	"strings"
+)
+
+// A renderer prints symbol documentation for a package.
+// An error that occurs during rendering is saved and returned
+// by the end method.
+type renderer interface {
+	start(*doc.Package)
+	end() error
+	// startSection start a section, like the one for functions.
+	startSection(name string)
+	endSection()
+
+	// emit prints documentation for particular node, like a const
+	// or function.
+	emit(comment string, node ast.Node)
+	// TODO(jba): support examples
+}
+
+type textRenderer struct {
+	fset    *token.FileSet
+	w       io.Writer
+	pkg     *doc.Package
+	parser  *comment.Parser
+	printer *comment.Printer
+	err     error
+}
+
+func (r *textRenderer) start(pkg *doc.Package) {
+	r.pkg = pkg
+	r.parser = pkg.Parser()
+	// Configure the printer for symbol comments here,
+	// so we only do it once.
+	r.printer = pkg.Printer()
+	r.printer.TextPrefix = "\t"
+	r.printer.TextCodePrefix = "\t\t"
+
+	r.printf("package %s\n", pkg.Name)
+	if pkg.Doc != "" {
+		r.printf("\n")
+		// The package doc is not indented, so don't use r.printer.
+		_, err := r.w.Write(pkg.Text(pkg.Doc))
+		if err != nil {
+			r.err = err
+		}
+	}
+	r.printf("\n")
+}
+
+func (r *textRenderer) end() error { return r.err }
+
+func (r *textRenderer) startSection(name string) {
+	r.printf("%s\n\n", strings.ToUpper(name))
+}
+
+func (r *textRenderer) endSection() {}
+
+func (r *textRenderer) emit(comment string, node ast.Node) {
+	if r.err != nil {
+		return
+	}
+	err := format.Node(r.w, r.fset, node)
+	if err != nil {
+		r.err = err
+		return
+	}
+	r.printf("\n")
+	formatted := r.printer.Text(r.parser.Parse(comment))
+	if len(formatted) > 0 {
+		_, err = r.w.Write(formatted)
+		if err != nil {
+			r.err = err
+			return
+		}
+	}
+	r.printf("\n")
+}
+
+func (r *textRenderer) printf(format string, args ...any) {
+	if r.err != nil {
+		return
+	}
+	_, err := fmt.Fprintf(r.w, format, args...)
+	if err != nil {
+		r.err = err
+	}
+}
+
+// renderDoc renders the documentation for dpkg using the given renderer.
+// TODO(jba): support examples.
+func renderDoc(dpkg *doc.Package, r renderer) error {
+	r.start(dpkg)
+
+	renderValues(dpkg.Consts, r, "constants")
+	renderValues(dpkg.Vars, r, "variables")
+	renderFuncs(dpkg.Funcs, r, "functions")
+
+	started := false
+	for _, t := range dpkg.Types {
+		if !ast.IsExported(t.Name) {
+			continue
+		}
+		if !started {
+			r.startSection("types")
+			started = true
+		}
+		r.emit(t.Doc, t.Decl)
+		renderValues(t.Consts, r, "")
+		renderValues(t.Vars, r, "")
+		renderFuncs(t.Funcs, r, "")
+		renderFuncs(t.Methods, r, "")
+	}
+	if started {
+		r.endSection()
+	}
+	return r.end()
+}
+
+func renderValues(vals []*doc.Value, r renderer, section string) {
+	started := false
+	for _, v := range vals {
+		// Render a group if at least one is exported.
+		if slices.IndexFunc(v.Names, ast.IsExported) >= 0 {
+			if !started {
+				if section != "" {
+					r.startSection(section)
+				}
+				started = true
+			}
+			r.emit(v.Doc, v.Decl)
+		}
+	}
+	if started && section != "" {
+		r.endSection()
+	}
+}
+
+func renderFuncs(funcs []*doc.Func, r renderer, section string) {
+	started := false
+	for _, f := range funcs {
+		if !ast.IsExported(f.Name) {
+			continue
+		}
+		if !started {
+			if section != "" {
+				r.startSection(section)
+			}
+			started = true
+		}
+		r.emit(f.Doc, f.Decl)
+	}
+	if started && section != "" {
+		r.endSection()
+	}
+}