strconv: change Quote to be Unicode-friendly,

add QuoteToASCII.
The Quote and QuoteRune functions now let printable
runes (as defined by unicode.IsPrint) through.  When
true 7-bit clean stuff is necessary, there are now two
new functions: QuoteToASCII and QuoteRuneToASCII.

Printf("%q") uses Quote. To get the old behavior, it
will now be necessary to say
        Printf("%s", strconv.QuoteToASCII(s))
but that should rarely be necessary.

R=golang-dev, gri, r
CC=golang-dev
https://golang.org/cl/4561061

4 files changed, 125 insertions, 72 deletions

diff --git a/src/pkg/fmt/fmt_test.go b/src/pkg/fmt/fmt_test.go
index caecb6fb84..122b9516ba 100644
--- a/src/pkg/fmt/fmt_test.go
+++ b/src/pkg/fmt/fmt_test.go
@@ -132,15 +132,15 @@ var fmttests = []struct {
 	{"%q", `"`, `"\""`},
 	{"%q", "\a\b\f\r\n\t\v", `"\a\b\f\r\n\t\v"`},
 	{"%q", "abc\xffdef", `"abc\xffdef"`},
-	{"%q", "\u263a", `"\u263a"`},
+	{"%q", "\u263a", `"☺"`},
 	{"%q", "\U0010ffff", `"\U0010ffff"`},
 
 	// escaped characters
 	{"%q", 'x', `'x'`},
 	{"%q", 0, `'\x00'`},
 	{"%q", '\n', `'\n'`},
-	{"%q", '\u1234', `'\u1234'`},
-	{"%q", '\U00012345', `'\U00012345'`},
+	{"%q", '\u0e00', `'\u0e00'`},         // not a printable rune.
+	{"%q", '\U000c2345', `'\U000c2345'`}, // not a printable rune.
 	{"%q", int64(0x7FFFFFFF), `%!q(int64=2147483647)`},
 	{"%q", uint64(0xFFFFFFFF), `%!q(uint64=4294967295)`},
 	{"%q", '"', `'"'`},
@@ -148,7 +148,7 @@ var fmttests = []struct {
 
 	// width
 	{"%5s", "abc", "  abc"},
-	{"%2s", "\u263a", " \u263a"},
+	{"%2s", "\u263a", " ☺"},
 	{"%-5s", "abc", "abc  "},
 	{"%-8q", "abc", `"abc"   `},
 	{"%05s", "abc", "00abc"},
@@ -158,9 +158,9 @@ var fmttests = []struct {
 	{"%.5s", "日本語日本語", "日本語日本"},
 	{"%.5s", []byte("日本語日本語"), "日本語日本"},
 	{"%.5q", "abcdefghijklmnopqrstuvwxyz", `"abcde"`},
-	{"%.3q", "日本語日本語", `"\u65e5\u672c\u8a9e"`},
-	{"%.3q", []byte("日本語日本語"), `"\u65e5\u672c\u8a9e"`},
-	{"%10.1q", "日本語日本語", `  "\u65e5"`},
+	{"%.3q", "日本語日本語", `"日本語"`},
+	{"%.3q", []byte("日本語日本語"), `"日本語"`},
+	{"%10.1q", "日本語日本語", `       "日"`},
 
 	// integers
 	{"%d", 12345, "12345"},
diff --git a/src/pkg/go/scanner/scanner_test.go b/src/pkg/go/scanner/scanner_test.go
index 8af972838d..ee1e830a18 100644
--- a/src/pkg/go/scanner/scanner_test.go
+++ b/src/pkg/go/scanner/scanner_test.go
@@ -652,7 +652,7 @@ var errors = []struct {
 }{
 	{"\a", token.ILLEGAL, 0, "illegal character '\\a'"},
 	{`#`, token.ILLEGAL, 0, "illegal character '#'"},
-	{`…`, token.ILLEGAL, 0, "illegal character '\\u2026'"},
+	{`…`, token.ILLEGAL, 0, "illegal character '…'"},
 	{`' '`, token.CHAR, 0, ""},
 	{`''`, token.CHAR, 0, "illegal character literal"},
 	{`'\8'`, token.CHAR, 2, "unknown escape sequence"},
diff --git a/src/pkg/strconv/quote.go b/src/pkg/strconv/quote.go
index bbc0b2658e..98b19d3a2b 100644
--- a/src/pkg/strconv/quote.go
+++ b/src/pkg/strconv/quote.go
@@ -14,56 +14,68 @@ import (
 
 const lowerhex = "0123456789abcdef"
 
-func quoteWith(s string, quote byte) string {
+func quoteWith(s string, quote byte, ASCIIonly bool) string {
 	var buf bytes.Buffer
 	buf.WriteByte(quote)
-	for ; len(s) > 0; s = s[1:] {
-		switch c := s[0]; {
-		case c == quote:
+	for width := 0; len(s) > 0; s = s[width:] {
+		rune := int(s[0])
+		width = 1
+		if rune >= utf8.RuneSelf {
+			rune, width = utf8.DecodeRuneInString(s)
+		}
+		if width == 1 && rune == utf8.RuneError {
+			goto printEscX
+		}
+		if rune == int(quote) || rune == '\\' { // always backslashed
 			buf.WriteByte('\\')
-			buf.WriteByte(quote)
-		case c == '\\':
-			buf.WriteString(`\\`)
-		case ' ' <= c && c <= '~':
-			buf.WriteString(string(c))
-		case c == '\a':
+			buf.WriteByte(byte(rune))
+			continue
+		}
+		if ASCIIonly {
+			if rune <= unicode.MaxASCII && unicode.IsPrint(rune) {
+				buf.WriteRune(rune)
+				continue
+			}
+		} else if unicode.IsPrint(rune) {
+			buf.WriteRune(rune)
+			continue
+		}
+		switch rune {
+		case '\a':
 			buf.WriteString(`\a`)
-		case c == '\b':
+		case '\b':
 			buf.WriteString(`\b`)
-		case c == '\f':
+		case '\f':
 			buf.WriteString(`\f`)
-		case c == '\n':
+		case '\n':
 			buf.WriteString(`\n`)
-		case c == '\r':
+		case '\r':
 			buf.WriteString(`\r`)
-		case c == '\t':
+		case '\t':
 			buf.WriteString(`\t`)
-		case c == '\v':
+		case '\v':
 			buf.WriteString(`\v`)
-
-		case c >= utf8.RuneSelf && utf8.FullRuneInString(s):
-			r, size := utf8.DecodeRuneInString(s)
-			if r == utf8.RuneError && size == 1 {
-				goto EscX
-			}
-			s = s[size-1:] // next iteration will slice off 1 more
-			if r < 0x10000 {
+		default:
+			switch {
+			case rune < ' ':
+			printEscX:
+				buf.WriteString(`\x`)
+				buf.WriteByte(lowerhex[s[0]>>4])
+				buf.WriteByte(lowerhex[s[0]&0xF])
+			case rune > unicode.MaxRune:
+				rune = 0xFFFD
+				fallthrough
+			case rune < 0x10000:
 				buf.WriteString(`\u`)
-				for j := uint(0); j < 4; j++ {
-					buf.WriteByte(lowerhex[(r>>(12-4*j))&0xF])
+				for s := 12; s >= 0; s -= 4 {
+					buf.WriteByte(lowerhex[rune>>uint(s)&0xF])
 				}
-			} else {
+			default:
 				buf.WriteString(`\U`)
-				for j := uint(0); j < 8; j++ {
-					buf.WriteByte(lowerhex[(r>>(28-4*j))&0xF])
+				for s := 28; s >= 0; s -= 4 {
+					buf.WriteByte(lowerhex[rune>>uint(s)&0xF])
 				}
 			}
-
-		default:
-		EscX:
-			buf.WriteString(`\x`)
-			buf.WriteByte(lowerhex[c>>4])
-			buf.WriteByte(lowerhex[c&0xF])
 		}
 	}
 	buf.WriteByte(quote)
@@ -71,21 +83,38 @@ func quoteWith(s string, quote byte) string {
 
 }
 
-// Quote returns a double-quoted Go string literal
-// representing s.  The returned string uses Go escape
-// sequences (\t, \n, \xFF, \u0100) for control characters
-// and non-ASCII characters.
+// Quote returns a double-quoted Go string literal representing s.  The
+// returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for
+// control characters and non-printable characters as defined by
+// unicode.IsPrint.
 func Quote(s string) string {
-	return quoteWith(s, '"')
+	return quoteWith(s, '"', false)
+}
+
+// QuoteToASCII returns a double-quoted Go string literal representing s.
+// The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for
+// non-ASCII characters and non-printable characters as defined by
+// unicode.IsPrint.
+func QuoteToASCII(s string) string {
+	return quoteWith(s, '"', true)
 }
 
-// QuoteRune returns a single-quoted Go character literal
-// representing the rune.  The returned string uses Go escape
-// sequences (\t, \n, \xFF, \u0100) for control characters
-// and non-ASCII characters.
+// QuoteRune returns a single-quoted Go character literal representing the
+// rune.  The returned string uses Go escape sequences (\t, \n, \xFF, \u0100)
+// for control characters and non-printable characters as defined by
+// unicode.IsPrint.
 func QuoteRune(rune int) string {
 	// TODO: avoid the allocation here.
-	return quoteWith(string(rune), '\'')
+	return quoteWith(string(rune), '\'', false)
+}
+
+// QuoteRuneToASCII returns a single-quoted Go character literal representing
+// the rune.  The returned string uses Go escape sequences (\t, \n, \xFF,
+// \u0100) for non-ASCII characters and non-printable characters as defined
+// by unicode.IsPrint.
+func QuoteRuneToASCII(rune int) string {
+	// TODO: avoid the allocation here.
+	return quoteWith(string(rune), '\'', true)
 }
 
 // CanBackquote returns whether the string s would be
diff --git a/src/pkg/strconv/quote_test.go b/src/pkg/strconv/quote_test.go
index 3232d611cf..4d615db443 100644
--- a/src/pkg/strconv/quote_test.go
+++ b/src/pkg/strconv/quote_test.go
@@ -11,17 +11,18 @@ import (
 )
 
 type quoteTest struct {
-	in  string
-	out string
+	in    string
+	out   string
+	ascii string
 }
 
 var quotetests = []quoteTest{
-	{"\a\b\f\r\n\t\v", `"\a\b\f\r\n\t\v"`},
-	{"\\", `"\\"`},
-	{"abc\xffdef", `"abc\xffdef"`},
-	{"\u263a", `"\u263a"`},
-	{"\U0010ffff", `"\U0010ffff"`},
-	{"\x04", `"\x04"`},
+	{"\a\b\f\r\n\t\v", `"\a\b\f\r\n\t\v"`, `"\a\b\f\r\n\t\v"`},
+	{"\\", `"\\"`, `"\\"`},
+	{"abc\xffdef", `"abc\xffdef"`, `"abc\xffdef"`},
+	{"\u263a", `"☺"`, `"\u263a"`},
+	{"\U0010ffff", `"\U0010ffff"`, `"\U0010ffff"`},
+	{"\x04", `"\x04"`, `"\x04"`},
 }
 
 func TestQuote(t *testing.T) {
@@ -32,20 +33,30 @@ func TestQuote(t *testing.T) {
 	}
 }
 
+func TestQuoteToASCII(t *testing.T) {
+	for _, tt := range quotetests {
+		if out := QuoteToASCII(tt.in); out != tt.ascii {
+			t.Errorf("QuoteToASCII(%s) = %s, want %s", tt.in, out, tt.ascii)
+		}
+	}
+}
+
 type quoteRuneTest struct {
-	in  int
-	out string
+	in    int
+	out   string
+	ascii string
 }
 
 var quoterunetests = []quoteRuneTest{
-	{'a', `'a'`},
-	{'\a', `'\a'`},
-	{'\\', `'\\'`},
-	{0xFF, `'\u00ff'`},
-	{0x263a, `'\u263a'`},
-	{0x0010ffff, `'\U0010ffff'`},
-	{0x0010ffff + 1, `'\ufffd'`},
-	{0x04, `'\x04'`},
+	{'a', `'a'`, `'a'`},
+	{'\a', `'\a'`, `'\a'`},
+	{'\\', `'\\'`, `'\\'`},
+	{0xFF, `'ÿ'`, `'\u00ff'`},
+	{0x263a, `'☺'`, `'\u263a'`},
+	{0xfffd, `'�'`, `'\ufffd'`},
+	{0x0010ffff, `'\U0010ffff'`, `'\U0010ffff'`},
+	{0x0010ffff + 1, `'�'`, `'\ufffd'`},
+	{0x04, `'\x04'`, `'\x04'`},
 }
 
 func TestQuoteRune(t *testing.T) {
@@ -56,6 +67,14 @@ func TestQuoteRune(t *testing.T) {
 	}
 }
 
+func TestQuoteRuneToASCII(t *testing.T) {
+	for _, tt := range quoterunetests {
+		if out := QuoteRuneToASCII(tt.in); out != tt.ascii {
+			t.Errorf("QuoteRuneToASCII(%U) = %s, want %s", tt.in, out, tt.ascii)
+		}
+	}
+}
+
 type canBackquoteTest struct {
 	in  string
 	out bool
@@ -110,7 +129,12 @@ func TestCanBackquote(t *testing.T) {
 	}
 }
 
-var unquotetests = []quoteTest{
+type unQuoteTest struct {
+	in  string
+	out string
+}
+
+var unquotetests = []unQuoteTest{
 	{`""`, ""},
 	{`"a"`, "a"},
 	{`"abc"`, "abc"},