@@ -8,6 +8,8 @@ import (
 	"os"
 	"regexp"
 	"strings"
+
+	xhtml "golang.org/x/net/html"
 )
 
 type apiDocumentation struct {
package api

import (
	"bytes"
	"encoding/json"
	"fmt"
	"html"
	"os"
	"regexp"
	"strings"
)

type apiDocumentation struct {
	*API
	Operations map[string]string
	Service    string
	Shapes     map[string]shapeDocumentation
}

type shapeDocumentation struct {
	Base string
	Refs map[string]string
}

// AttachDocs attaches documentation from a JSON filename.
func (a *API) AttachDocs(filename string) {
	d := apiDocumentation{API: a}

	f, err := os.Open(filename)
	defer f.Close()
	if err != nil {
		panic(err)
	}
	err = json.NewDecoder(f).Decode(&d)
	if err != nil {
		panic(err)
	}

	d.setup()

}

func (d *apiDocumentation) setup() {
	d.API.Documentation = docstring(d.Service)
	if d.Service == "" {
		d.API.Documentation =
			fmt.Sprintf("// %s is a client for %s.\n", d.API.StructName(), d.API.NiceName())
	}

	for op, doc := range d.Operations {
		d.API.Operations[op].Documentation = strings.TrimSpace(docstring(doc))
	}

	for shape, info := range d.Shapes {
		if sh := d.API.Shapes[shape]; sh != nil {
			sh.Documentation = docstring(info.Base)
		}

		for ref, doc := range info.Refs {
			if doc == "" {
				continue
			}

			parts := strings.Split(ref, "$")
			if sh := d.API.Shapes[parts[0]]; sh != nil {
				if m := sh.MemberRefs[parts[1]]; m != nil {
					m.Documentation = docstring(doc)
				}
			}
		}
	}
}

var reNewline = regexp.MustCompile(`\r?\n`)
var reMultiSpace = regexp.MustCompile(`\s+`)
var reComments = regexp.MustCompile(`<!--.*?-->`)
var reFullname = regexp.MustCompile(`\s*<fullname?>.+?<\/fullname?>\s*`)
var reExamples = regexp.MustCompile(`<examples?>.+?<\/examples?>`)
var rePara = regexp.MustCompile(`<(?:p|h\d)>(.+?)</(?:p|h\d)>`)
var reLink = regexp.MustCompile(`<a href="(.+?)">(.+?)</a>`)
var reTag = regexp.MustCompile(`<.+?>`)
var reEndNL = regexp.MustCompile(`\n+$`)

// docstring rewrites a string to insert godocs formatting.
func docstring(doc string) string {
	doc = reNewline.ReplaceAllString(doc, "")
	doc = reMultiSpace.ReplaceAllString(doc, " ")
	doc = reComments.ReplaceAllString(doc, "")
	doc = reFullname.ReplaceAllString(doc, "")
	doc = reExamples.ReplaceAllString(doc, "")
	doc = rePara.ReplaceAllString(doc, "$1\n\n")
	doc = reLink.ReplaceAllString(doc, "$2 ($1)")
	doc = reTag.ReplaceAllString(doc, "$1")
	doc = reEndNL.ReplaceAllString(doc, "")
	doc = strings.TrimSpace(doc)
	if doc == "" {
		return "\n"
	}

	doc = html.UnescapeString(doc)
	doc = wrap(doc, 72)

	return commentify(doc)
}

// commentify converts a string to a Go comment
func commentify(doc string) string {
	lines := strings.Split(doc, "\n")
	out := []string{}
	for i, line := range lines {
		if i > 0 && line == "" && lines[i-1] == "" {
			continue
		}
		out = append(out, "// "+line)
	}

	return strings.Join(out, "\n") + "\n"
}

// wrap returns a rewritten version of text to have line breaks
// at approximately length characters. Line breaks will only be
// inserted into whitespace.
func wrap(text string, length int) string {
	var buf bytes.Buffer
	var last rune
	var lastNL bool
	var col int

	for _, c := range text {
		switch c {
		case '\r': // ignore this
			continue // and also don't track `last`
		case '\n': // ignore this too, but reset col
			if col >= length || last == '\n' {
				buf.WriteString("\n\n")
			}
			col = 0
		case ' ', '\t': // opportunity to split
			if col >= length {
				buf.WriteByte('\n')
				col = 0
			} else {
				if !lastNL {
					buf.WriteRune(c)
				}
				col++ // count column
			}
		default:
			buf.WriteRune(c)
			col++
		}
		lastNL = c == '\n'
		last = c
	}
	return buf.String()
}

Need to take a look at how to prevent the `golang.org/x/net/html` being included as a runtime dependency. I have PR #891 to add `codegen` build tags to the `/private/mode/api` packages to prevent them causing their dependencies to leak into the runtime. Though I think this is a strong argument for splitting the code generator logic out of the SDK. Doing so would prevent polluting the SDK's runtime environment with code gen deps.