godoc/static: use a stable quote function

Printf(%q) aka strconv.AppendQuote depends on the Unicode tables du
jour, which means gen_test breaks after a Go release in which Unicode
evolves. This change uses a very dumb quotation function that emits
only ASCII and is independent of the Go release.

Perhaps an even better fix would have been to parse the generated file.

Change-Id: I197942f1c36a8b53d6a37be4bb2b1e63a208f7e2
Reviewed-on: https://go-review.googlesource.com/119157
Reviewed-by: Ian Lance Taylor <iant@golang.org>

godoc/static/gen.go

@@ -12,7 +12,7 @@ import (
 	"go/format"
 	"io/ioutil"
 	"time"
-	"unicode/utf8"
+	"unicode"
 )
 
 var files = []string{
@@ -80,35 +80,28 @@ func Generate() ([]byte, error) {
 			return b, err
 		}
 		fmt.Fprintf(buf, "\t%q: ", fn)
-		if utf8.Valid(b) {
-			fmt.Fprintf(buf, "`%s`", sanitize(b))
-		} else {
-			fmt.Fprintf(buf, "%q", b)
-		}
+		appendQuote(buf, b)
 		fmt.Fprintf(buf, ",\n\n")
 	}
 	fmt.Fprintln(buf, "}")
-
-	b := buf.Bytes()
-
-	// The 鿥 U+9FE5 character became printable in go 1.10,
-	// causing it to appear literally in newer output.
-	// Force the old behavior.
-	b = bytes.Replace(b, []byte("\u9fe5"), []byte(`\u9fe5`), -1)
-
-	return format.Source(b)
+	return format.Source(buf.Bytes())
 }
 
-// sanitize prepares a valid UTF-8 string as a raw string constant.
-func sanitize(b []byte) []byte {
-	// Replace ` with `+"`"+`
-	b = bytes.Replace(b, []byte("`"), []byte("`+\"`\"+`"), -1)
-
-	// Replace BOM with `+"\xEF\xBB\xBF"+`
-	// (A BOM is valid UTF-8 but not permitted in Go source files.
-	// I wouldn't bother handling this, but for some insane reason
-	// jquery.js has a BOM somewhere in the middle.)
-	return bytes.Replace(b, []byte("\xEF\xBB\xBF"), []byte("`+\"\\xEF\\xBB\\xBF\"+`"), -1)
+// appendQuote is like strconv.AppendQuote, but we avoid the latter
+// because it changes when Unicode evolves, breaking gen_test.go.
+func appendQuote(out *bytes.Buffer, data []byte) {
+	out.WriteByte('"')
+	for _, b := range data {
+		if b == '\\' || b == '"' {
+			out.WriteByte('\\')
+			out.WriteByte(b)
+		} else if b <= unicode.MaxASCII && unicode.IsPrint(rune(b)) && !unicode.IsSpace(rune(b)) {
+			out.WriteByte(b)
+		} else {
+			fmt.Fprintf(out, "\\x%02x", b)
+		}
+	}
+	out.WriteByte('"')
 }
 
 const warning = `// Code generated by "makestatic"; DO NOT EDIT.`

godoc/static/gen_test.go

@@ -7,7 +7,9 @@ package static
 import (
 	"bytes"
 	"io/ioutil"
+	"strconv"
 	"testing"
+	"unicode"
 )
 
 func TestStaticIsUpToDate(t *testing.T) {
@@ -29,3 +31,19 @@ to see the differences.`)
 
 	}
 }
+
+// TestAppendQuote ensures that AppendQuote produces a valid literal.
+func TestAppendQuote(t *testing.T) {
+	var in, out bytes.Buffer
+	for r := rune(0); r < unicode.MaxRune; r++ {
+		in.WriteRune(r)
+	}
+	appendQuote(&out, in.Bytes())
+	in2, err := strconv.Unquote(out.String())
+	if err != nil {
+		t.Fatalf("AppendQuote produced invalid string literal: %v", err)
+	}
+	if got, want := in2, in.String(); got != want {
+		t.Fatal("AppendQuote modified string") // no point printing got/want: huge
+	}
+}