Update Go library to r60.

From-SVN: r178910

6 files changed, 332 insertions, 65 deletions

diff --git a/libgo/go/fmt/doc.go b/libgo/go/fmt/doc.go
index e4d4f18..35a11e1 100644
--- a/libgo/go/fmt/doc.go
+++ b/libgo/go/fmt/doc.go
@@ -25,9 +25,10 @@
 		%c	the character represented by the corresponding Unicode code point
 		%d	base 10
 		%o	base 8
+		%q	a single-quoted character literal safely escaped with Go syntax.
 		%x	base 16, with lower-case letters for a-f
 		%X	base 16, with upper-case letters for A-F
-		%U	Unicode format: U+1234; same as "U+%0.4X"
+		%U	Unicode format: U+1234; same as "U+%04X"
 	Floating-point and complex constituents:
 		%b	decimalless scientific notation with exponent a power
 			of two, in the manner of strconv.Ftoa32, e.g. -123456p-78
@@ -62,11 +63,13 @@
 	number of characters to output, truncating if necessary.
 
 	Other flags:
-		+	always print a sign for numeric values
+		+	always print a sign for numeric values;
+			guarantee ASCII-only output for %q (%+q)
 		-	pad with spaces on the right rather than the left (left-justify the field)
 		#	alternate format: add leading 0 for octal (%#o), 0x for hex (%#x);
 			0X for hex (%#X); suppress 0x for %p (%#p);
-			print a raw (backquoted) string if possible for %q (%#q)
+			print a raw (backquoted) string if possible for %q (%#q);
+			write e.g. U+0078 'x' if the character is printable for %U (%#U).
 		' '	(space) leave a space for elided sign in numbers (% d);
 			put spaces between bytes printing strings or slices in hex (% x, % X)
 		0	pad with leading zeros rather than spaces
@@ -134,10 +137,10 @@
 	The formats behave analogously to those of Printf with the
 	following exceptions:
 
-	%p is not implemented
-	%T is not implemented
-	%e %E %f %F %g %g are all equivalent and scan any floating point or complex value
-	%s and %v on strings scan a space-delimited token
+		%p is not implemented
+		%T is not implemented
+		%e %E %f %F %g %G are all equivalent and scan any floating point or complex value
+		%s and %v on strings scan a space-delimited token
 
 	The familiar base-setting prefixes 0 (octal) and 0x
 	(hexadecimal) are accepted when scanning integers without a
diff --git a/libgo/go/fmt/fmt_test.go b/libgo/go/fmt/fmt_test.go
index b3c0c5a..1142c9f 100644
--- a/libgo/go/fmt/fmt_test.go
+++ b/libgo/go/fmt/fmt_test.go
@@ -43,7 +43,6 @@ func TestFmtInterface(t *testing.T) {
 	}
 }
 
-
 const b32 uint32 = 1<<32 - 1
 const b64 uint64 = 1<<64 - 1
 
@@ -132,12 +131,26 @@ 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", "\u263a", `"\u263a"`},
 	{"%q", "\U0010ffff", `"\U0010ffff"`},
 
+	// escaped characters
+	{"%q", 'x', `'x'`},
+	{"%q", 0, `'\x00'`},
+	{"%q", '\n', `'\n'`},
+	{"%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", '"', `'"'`},
+	{"%q", '\'', `'\''`},
+	{"%q", "\u263a", `"☺"`},
+	{"%+q", "\u263a", `"\u263a"`},
+
 	// width
 	{"%5s", "abc", "  abc"},
-	{"%2s", "\u263a", " \u263a"},
+	{"%2s", "\u263a", " ☺"},
 	{"%-5s", "abc", "abc  "},
 	{"%-8q", "abc", `"abc"   `},
 	{"%05s", "abc", "00abc"},
@@ -147,9 +160,9 @@ 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"},
@@ -167,6 +180,8 @@ var fmttests = []struct {
 	{"%+d", 0, "+0"},
 	{"% d", 0, " 0"},
 	{"% d", 12345, " 12345"},
+	{"%.0d", 0, ""},
+	{"%.d", 0, ""},
 
 	// unicode format
 	{"%U", 0x1, "U+0001"},
@@ -176,6 +191,12 @@ var fmttests = []struct {
 	{"%U", 0x12345, "U+12345"},
 	{"%10.6U", 0xABC, "  U+000ABC"},
 	{"%-10.6U", 0xABC, "U+000ABC  "},
+	{"%U", '\n', `U+000A`},
+	{"%#U", '\n', `U+000A`},
+	{"%U", 'x', `U+0078`},
+	{"%#U", 'x', `U+0078 'x'`},
+	{"%U", '\u263a', `U+263A`},
+	{"%#U", '\u263a', `U+263A '☺'`},
 
 	// floats
 	{"%+.3e", 0.0, "+0.000e+00"},
@@ -456,28 +477,36 @@ func TestCountMallocs(t *testing.T) {
 	if testing.Short() {
 		return
 	}
+	runtime.UpdateMemStats()
 	mallocs := 0 - runtime.MemStats.Mallocs
 	for i := 0; i < 100; i++ {
 		Sprintf("")
 	}
+	runtime.UpdateMemStats()
 	mallocs += runtime.MemStats.Mallocs
 	Printf("mallocs per Sprintf(\"\"): %d\n", mallocs/100)
+	runtime.UpdateMemStats()
 	mallocs = 0 - runtime.MemStats.Mallocs
 	for i := 0; i < 100; i++ {
 		Sprintf("xxx")
 	}
+	runtime.UpdateMemStats()
 	mallocs += runtime.MemStats.Mallocs
 	Printf("mallocs per Sprintf(\"xxx\"): %d\n", mallocs/100)
+	runtime.UpdateMemStats()
 	mallocs = 0 - runtime.MemStats.Mallocs
 	for i := 0; i < 100; i++ {
 		Sprintf("%x", i)
 	}
+	runtime.UpdateMemStats()
 	mallocs += runtime.MemStats.Mallocs
 	Printf("mallocs per Sprintf(\"%%x\"): %d\n", mallocs/100)
+	runtime.UpdateMemStats()
 	mallocs = 0 - runtime.MemStats.Mallocs
 	for i := 0; i < 100; i++ {
 		Sprintf("%x %x", i, i)
 	}
+	runtime.UpdateMemStats()
 	mallocs += runtime.MemStats.Mallocs
 	Printf("mallocs per Sprintf(\"%%x %%x\"): %d\n", mallocs/100)
 }
@@ -614,7 +643,6 @@ func TestBlankln(t *testing.T) {
 	}
 }
 
-
 // Check Formatter with Sprint, Sprintln, Sprintf
 func TestFormatterPrintln(t *testing.T) {
 	f := F(1)
@@ -663,3 +691,56 @@ func TestWidthAndPrecision(t *testing.T) {
 		}
 	}
 }
+
+// A type that panics in String.
+type Panic struct {
+	message interface{}
+}
+
+// Value receiver.
+func (p Panic) GoString() string {
+	panic(p.message)
+}
+
+// Value receiver.
+func (p Panic) String() string {
+	panic(p.message)
+}
+
+// A type that panics in Format.
+type PanicF struct {
+	message interface{}
+}
+
+// Value receiver.
+func (p PanicF) Format(f State, c int) {
+	panic(p.message)
+}
+
+var panictests = []struct {
+	fmt string
+	in  interface{}
+	out string
+}{
+	// String
+	{"%d", (*Panic)(nil), "<nil>"}, // nil pointer special case
+	{"%d", Panic{io.ErrUnexpectedEOF}, "%d(PANIC=unexpected EOF)"},
+	{"%d", Panic{3}, "%d(PANIC=3)"},
+	// GoString
+	{"%#v", (*Panic)(nil), "<nil>"}, // nil pointer special case
+	{"%#v", Panic{io.ErrUnexpectedEOF}, "%v(PANIC=unexpected EOF)"},
+	{"%#v", Panic{3}, "%v(PANIC=3)"},
+	// Format
+	{"%s", (*PanicF)(nil), "<nil>"}, // nil pointer special case
+	{"%s", PanicF{io.ErrUnexpectedEOF}, "%s(PANIC=unexpected EOF)"},
+	{"%s", PanicF{3}, "%s(PANIC=3)"},
+}
+
+func TestPanics(t *testing.T) {
+	for _, tt := range panictests {
+		s := Sprintf(tt.fmt, tt.in)
+		if s != tt.out {
+			t.Errorf("%q: got %q expected %q", tt.fmt, s, tt.out)
+		}
+	}
+}
diff --git a/libgo/go/fmt/format.go b/libgo/go/fmt/format.go
index f9d2b4f..24b15a2 100644
--- a/libgo/go/fmt/format.go
+++ b/libgo/go/fmt/format.go
@@ -7,6 +7,7 @@ package fmt
 import (
 	"bytes"
 	"strconv"
+	"unicode"
 	"utf8"
 )
 
@@ -50,6 +51,7 @@ type fmt struct {
 	sharp       bool
 	space       bool
 	unicode     bool
+	uniQuote    bool // Use 'x'= prefix for %U if printable.
 	zero        bool
 }
 
@@ -63,6 +65,7 @@ func (f *fmt) clearflags() {
 	f.sharp = false
 	f.space = false
 	f.unicode = false
+	f.uniQuote = false
 	f.zero = false
 }
 
@@ -163,6 +166,11 @@ func (f *fmt) fmt_boolean(v bool) {
 // integer; interprets prec but not wid.  Once formatted, result is sent to pad()
 // and then flags are cleared.
 func (f *fmt) integer(a int64, base uint64, signedness bool, digits string) {
+	// precision of 0 and value of 0 means "print nothing"
+	if f.precPresent && f.prec == 0 && a == 0 {
+		return
+	}
+
 	var buf []byte = f.intbuf[0:]
 	negative := signedness == signed && a < 0
 	if negative {
@@ -232,6 +240,24 @@ func (f *fmt) integer(a int64, base uint64, signedness bool, digits string) {
 		i--
 		buf[i] = ' '
 	}
+
+	// If we want a quoted char for %#U, move the data up to make room.
+	if f.unicode && f.uniQuote && a >= 0 && a <= unicode.MaxRune && unicode.IsPrint(int(a)) {
+		runeWidth := utf8.RuneLen(int(a))
+		width := 1 + 1 + runeWidth + 1 // space, quote, rune, quote
+		copy(buf[i-width:], buf[i:])   // guaranteed to have enough room.
+		i -= width
+		// Now put " 'x'" at the end.
+		j := len(buf) - width
+		buf[j] = ' '
+		j++
+		buf[j] = '\''
+		j++
+		utf8.EncodeRune(buf[j:], int(a))
+		j += runeWidth
+		buf[j] = '\''
+	}
+
 	f.pad(buf[i:])
 }
 
@@ -291,7 +317,23 @@ func (f *fmt) fmt_q(s string) {
 	if f.sharp && strconv.CanBackquote(s) {
 		quoted = "`" + s + "`"
 	} else {
-		quoted = strconv.Quote(s)
+		if f.plus {
+			quoted = strconv.QuoteToASCII(s)
+		} else {
+			quoted = strconv.Quote(s)
+		}
+	}
+	f.padString(quoted)
+}
+
+// fmt_qc formats the integer as a single-quoted, escaped Go character constant.
+// If the character is not valid Unicode, it will print '\ufffd'.
+func (f *fmt) fmt_qc(c int64) {
+	var quoted string
+	if f.plus {
+		quoted = strconv.QuoteRuneToASCII(int(c))
+	} else {
+		quoted = strconv.QuoteRune(int(c))
 	}
 	f.padString(quoted)
 }
diff --git a/libgo/go/fmt/print.go b/libgo/go/fmt/print.go
index 10e0fe7..7387349 100644
--- a/libgo/go/fmt/print.go
+++ b/libgo/go/fmt/print.go
@@ -9,6 +9,7 @@ import (
 	"io"
 	"os"
 	"reflect"
+	"unicode"
 	"utf8"
 )
 
@@ -21,6 +22,7 @@ var (
 	nilBytes        = []byte("nil")
 	mapBytes        = []byte("map[")
 	missingBytes    = []byte("(MISSING)")
+	panicBytes      = []byte("(PANIC=")
 	extraBytes      = []byte("%!(EXTRA ")
 	irparenBytes    = []byte("i)")
 	bytesBytes      = []byte("[]byte{")
@@ -41,7 +43,7 @@ type State interface {
 	Precision() (prec int, ok bool)
 
 	// Flag returns whether the flag c, a character, has been set.
-	Flag(int) bool
+	Flag(c int) bool
 }
 
 // Formatter is the interface implemented by values with a custom formatter.
@@ -51,7 +53,7 @@ type Formatter interface {
 	Format(f State, c int)
 }
 
-// Stringer is implemented by any value that has a String method(),
+// Stringer is implemented by any value that has a String method,
 // which defines the ``native'' format for that value.
 // The String method is used to print values passed as an operand
 // to a %s or %v format or to an unformatted printer such as Print.
@@ -59,7 +61,7 @@ type Stringer interface {
 	String() string
 }
 
-// GoStringer is implemented by any value that has a GoString() method,
+// GoStringer is implemented by any value that has a GoString method,
 // which defines the Go syntax for that value.
 // The GoString method is used to print values passed as an operand
 // to a %#v format.
@@ -68,10 +70,11 @@ type GoStringer interface {
 }
 
 type pp struct {
-	n       int
-	buf     bytes.Buffer
-	runeBuf [utf8.UTFMax]byte
-	fmt     fmt
+	n         int
+	panicking bool
+	buf       bytes.Buffer
+	runeBuf   [utf8.UTFMax]byte
+	fmt       fmt
 }
 
 // A cache holds a set of reusable objects.
@@ -110,6 +113,7 @@ var ppFree = newCache(func() interface{} { return new(pp) })
 // Allocate a new pp struct or grab a cached one.
 func newPrinter() *pp {
 	p := ppFree.get().(*pp)
+	p.panicking = false
 	p.fmt.init(&p.buf)
 	return p
 }
@@ -158,19 +162,18 @@ func (p *pp) Write(b []byte) (ret int, err os.Error) {
 
 // Fprintf formats according to a format specifier and writes to w.
 // It returns the number of bytes written and any write error encountered.
-func Fprintf(w io.Writer, format string, a ...interface{}) (n int, error os.Error) {
+func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err os.Error) {
 	p := newPrinter()
 	p.doPrintf(format, a)
-	n64, error := p.buf.WriteTo(w)
+	n64, err := p.buf.WriteTo(w)
 	p.free()
-	return int(n64), error
+	return int(n64), err
 }
 
 // Printf formats according to a format specifier and writes to standard output.
 // It returns the number of bytes written and any write error encountered.
-func Printf(format string, a ...interface{}) (n int, errno os.Error) {
-	n, errno = Fprintf(os.Stdout, format, a...)
-	return n, errno
+func Printf(format string, a ...interface{}) (n int, err os.Error) {
+	return Fprintf(os.Stdout, format, a...)
 }
 
 // Sprintf formats according to a format specifier and returns the resulting string.
@@ -185,7 +188,7 @@ func Sprintf(format string, a ...interface{}) string {
 // Errorf formats according to a format specifier and returns the string 
 // converted to an os.ErrorString, which satisfies the os.Error interface.
 func Errorf(format string, a ...interface{}) os.Error {
-	return os.ErrorString(Sprintf(format, a...))
+	return os.NewError(Sprintf(format, a...))
 }
 
 // These routines do not take a format string
@@ -193,20 +196,19 @@ func Errorf(format string, a ...interface{}) os.Error {
 // Fprint formats using the default formats for its operands and writes to w.
 // Spaces are added between operands when neither is a string.
 // It returns the number of bytes written and any write error encountered.
-func Fprint(w io.Writer, a ...interface{}) (n int, error os.Error) {
+func Fprint(w io.Writer, a ...interface{}) (n int, err os.Error) {
 	p := newPrinter()
 	p.doPrint(a, false, false)
-	n64, error := p.buf.WriteTo(w)
+	n64, err := p.buf.WriteTo(w)
 	p.free()
-	return int(n64), error
+	return int(n64), err
 }
 
 // Print formats using the default formats for its operands and writes to standard output.
 // Spaces are added between operands when neither is a string.
 // It returns the number of bytes written and any write error encountered.
-func Print(a ...interface{}) (n int, errno os.Error) {
-	n, errno = Fprint(os.Stdout, a...)
-	return n, errno
+func Print(a ...interface{}) (n int, err os.Error) {
+	return Fprint(os.Stdout, a...)
 }
 
 // Sprint formats using the default formats for its operands and returns the resulting string.
@@ -226,20 +228,19 @@ func Sprint(a ...interface{}) string {
 // Fprintln formats using the default formats for its operands and writes to w.
 // Spaces are always added between operands and a newline is appended.
 // It returns the number of bytes written and any write error encountered.
-func Fprintln(w io.Writer, a ...interface{}) (n int, error os.Error) {
+func Fprintln(w io.Writer, a ...interface{}) (n int, err os.Error) {
 	p := newPrinter()
 	p.doPrint(a, true, true)
-	n64, error := p.buf.WriteTo(w)
+	n64, err := p.buf.WriteTo(w)
 	p.free()
-	return int(n64), error
+	return int(n64), err
 }
 
 // Println formats using the default formats for its operands and writes to standard output.
 // Spaces are always added between operands and a newline is appended.
 // It returns the number of bytes written and any write error encountered.
-func Println(a ...interface{}) (n int, errno os.Error) {
-	n, errno = Fprintln(os.Stdout, a...)
-	return n, errno
+func Println(a ...interface{}) (n int, err os.Error) {
+	return Fprintln(os.Stdout, a...)
 }
 
 // Sprintln formats using the default formats for its operands and returns the resulting string.
@@ -252,7 +253,6 @@ func Sprintln(a ...interface{}) string {
 	return s
 }
 
-
 // Get the i'th arg of the struct value.
 // If the arg itself is an interface, return a value for
 // the thing inside the interface, not the interface itself.
@@ -332,6 +332,12 @@ func (p *pp) fmtInt64(v int64, verb int, value interface{}) {
 		p.fmt.integer(v, 10, signed, ldigits)
 	case 'o':
 		p.fmt.integer(v, 8, signed, ldigits)
+	case 'q':
+		if 0 <= v && v <= unicode.MaxRune {
+			p.fmt.fmt_qc(v)
+		} else {
+			p.badVerb(verb, value)
+		}
 	case 'x':
 		p.fmt.integer(v, 16, signed, ldigits)
 	case 'U':
@@ -356,6 +362,8 @@ func (p *pp) fmt0x64(v uint64, leading0x bool) {
 // temporarily turning on the unicode flag and tweaking the precision.
 func (p *pp) fmtUnicode(v int64) {
 	precPresent := p.fmt.precPresent
+	sharp := p.fmt.sharp
+	p.fmt.sharp = false
 	prec := p.fmt.prec
 	if !precPresent {
 		// If prec is already set, leave it alone; otherwise 4 is minimum.
@@ -363,10 +371,13 @@ func (p *pp) fmtUnicode(v int64) {
 		p.fmt.precPresent = true
 	}
 	p.fmt.unicode = true // turn on U+
+	p.fmt.uniQuote = sharp
 	p.fmt.integer(int64(v), 16, unsigned, udigits)
 	p.fmt.unicode = false
+	p.fmt.uniQuote = false
 	p.fmt.prec = prec
 	p.fmt.precPresent = precPresent
+	p.fmt.sharp = sharp
 }
 
 func (p *pp) fmtUint64(v uint64, verb int, goSyntax bool, value interface{}) {
@@ -385,6 +396,12 @@ func (p *pp) fmtUint64(v uint64, verb int, goSyntax bool, value interface{}) {
 		}
 	case 'o':
 		p.fmt.integer(int64(v), 8, unsigned, ldigits)
+	case 'q':
+		if 0 <= v && v <= unicode.MaxRune {
+			p.fmt.fmt_qc(int64(v))
+		} else {
+			p.badVerb(verb, value)
+		}
 	case 'x':
 		p.fmt.integer(int64(v), 16, unsigned, ldigits)
 	case 'X':
@@ -548,6 +565,31 @@ var (
 	uintptrBits = reflect.TypeOf(uintptr(0)).Bits()
 )
 
+func (p *pp) catchPanic(val interface{}, verb int) {
+	if err := recover(); err != nil {
+		// If it's a nil pointer, just say "<nil>". The likeliest causes are a
+		// Stringer that fails to guard against nil or a nil pointer for a
+		// value receiver, and in either case, "<nil>" is a nice result.
+		if v := reflect.ValueOf(val); v.Kind() == reflect.Ptr && v.IsNil() {
+			p.buf.Write(nilAngleBytes)
+			return
+		}
+		// Otherwise print a concise panic message. Most of the time the panic
+		// value will print itself nicely.
+		if p.panicking {
+			// Nested panics; the recursion in printField cannot succeed.
+			panic(err)
+		}
+		p.buf.WriteByte('%')
+		p.add(verb)
+		p.buf.Write(panicBytes)
+		p.panicking = true
+		p.printField(err, 'v', false, false, 0)
+		p.panicking = false
+		p.buf.WriteByte(')')
+	}
+}
+
 func (p *pp) printField(field interface{}, verb int, plus, goSyntax bool, depth int) (wasString bool) {
 	if field == nil {
 		if verb == 'T' || verb == 'v' {
@@ -570,6 +612,7 @@ func (p *pp) printField(field interface{}, verb int, plus, goSyntax bool, depth
 	}
 	// Is it a Formatter?
 	if formatter, ok := field.(Formatter); ok {
+		defer p.catchPanic(field, verb)
 		formatter.Format(p, verb)
 		return false // this value is not a string
 
@@ -582,6 +625,7 @@ func (p *pp) printField(field interface{}, verb int, plus, goSyntax bool, depth
 	if goSyntax {
 		p.fmt.sharp = false
 		if stringer, ok := field.(GoStringer); ok {
+			defer p.catchPanic(field, verb)
 			// Print the result of GoString unadorned.
 			p.fmtString(stringer.GoString(), 's', false, field)
 			return false // this value is not a string
@@ -589,6 +633,7 @@ func (p *pp) printField(field interface{}, verb int, plus, goSyntax bool, depth
 	} else {
 		// Is it a Stringer?
 		if stringer, ok := field.(Stringer); ok {
+			defer p.catchPanic(field, verb)
 			p.printField(stringer.String(), verb, plus, false, depth)
 			return false // this value is not a string
 		}
@@ -883,6 +928,10 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 				}
 			} else {
 				p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i+1, end)
+				if !p.fmt.precPresent {
+					p.fmt.prec = 0
+					p.fmt.precPresent = true
+				}
 			}
 		}
 		if i >= end {
diff --git a/libgo/go/fmt/scan.go b/libgo/go/fmt/scan.go
index 42bc52c..259451d 100644
--- a/libgo/go/fmt/scan.go
+++ b/libgo/go/fmt/scan.go
@@ -35,6 +35,10 @@ type ScanState interface {
 	ReadRune() (rune int, size int, err os.Error)
 	// UnreadRune causes the next call to ReadRune to return the same rune.
 	UnreadRune() os.Error
+	// SkipSpace skips space in the input. Newlines are treated as space 
+	// unless the scan operation is Scanln, Fscanln or Sscanln, in which case 
+	// a newline is treated as EOF.
+	SkipSpace()
 	// Token skips space in the input if skipSpace is true, then returns the
 	// run of Unicode code points c satisfying f(c).  If f is nil,
 	// !unicode.IsSpace(c) is used; that is, the token will hold non-space
@@ -167,7 +171,7 @@ type ssave struct {
 // satisfies io.Reader. It will never be called when used as
 // intended, so there is no need to make it actually work.
 func (s *ss) Read(buf []byte) (n int, err os.Error) {
-	return 0, os.ErrorString("ScanState's Read should not be called. Use ReadRune")
+	return 0, os.NewError("ScanState's Read should not be called. Use ReadRune")
 }
 
 func (s *ss) ReadRune() (rune int, size int, err os.Error) {
@@ -231,6 +235,7 @@ func (s *ss) UnreadRune() os.Error {
 	} else {
 		s.peekRune = s.prevRune
 	}
+	s.prevRune = -1
 	s.count--
 	return nil
 }
@@ -240,7 +245,7 @@ func (s *ss) error(err os.Error) {
 }
 
 func (s *ss) errorString(err string) {
-	panic(scanError{os.ErrorString(err)})
+	panic(scanError{os.NewError(err)})
 }
 
 func (s *ss) Token(skipSpace bool, f func(int) bool) (tok []byte, err os.Error) {
@@ -266,6 +271,12 @@ func notSpace(r int) bool {
 	return !unicode.IsSpace(r)
 }
 
+// skipSpace provides Scan() methods the ability to skip space and newline characters 
+// in keeping with the current scanning mode set by format strings and Scan()/Scanln().
+func (s *ss) SkipSpace() {
+	s.skipSpace(false)
+}
+
 // readRune is a structure to enable reading UTF-8 encoded code points
 // from an io.Reader.  It is used if the Reader given to the scanner does
 // not already implement io.RuneReader.
@@ -324,7 +335,6 @@ func (r *readRune) ReadRune() (rune int, size int, err os.Error) {
 	return
 }
 
-
 var ssFree = newCache(func() interface{} { return new(ss) })
 
 // Allocate a new ss struct or grab a cached one.
@@ -398,7 +408,6 @@ func (s *ss) skipSpace(stopAtNewline bool) {
 	}
 }
 
-
 // token returns the next space-delimited string from the input.  It
 // skips white space.  For Scanln, it stops at newlines.  For Scan,
 // newlines are treated as spaces.
@@ -426,8 +435,8 @@ func (s *ss) typeError(field interface{}, expected string) {
 	s.errorString("expected field of type pointer to " + expected + "; found " + reflect.TypeOf(field).String())
 }
 
-var complexError = os.ErrorString("syntax error scanning complex number")
-var boolError = os.ErrorString("syntax error scanning boolean")
+var complexError = os.NewError("syntax error scanning complex number")
+var boolError = os.NewError("syntax error scanning boolean")
 
 // consume reads the next rune in the input and reports whether it is in the ok string.
 // If accept is true, it puts the character into the input token.
@@ -457,6 +466,14 @@ func (s *ss) peek(ok string) bool {
 	return strings.IndexRune(ok, rune) >= 0
 }
 
+func (s *ss) notEOF() {
+	// Guarantee there is data to be read.
+	if rune := s.getRune(); rune == eof {
+		panic(os.EOF)
+	}
+	s.UnreadRune()
+}
+
 // accept checks the next rune in the input.  If it's a byte (sic) in the string, it puts it in the
 // buffer and returns true. Otherwise it return false.
 func (s *ss) accept(ok string) bool {
@@ -476,11 +493,13 @@ func (s *ss) okVerb(verb int, okVerbs, typ string) bool {
 
 // scanBool returns the value of the boolean represented by the next token.
 func (s *ss) scanBool(verb int) bool {
+	s.skipSpace(false)
+	s.notEOF()
 	if !s.okVerb(verb, "tv", "boolean") {
 		return false
 	}
 	// Syntax-checking a boolean is annoying.  We're not fastidious about case.
-	switch s.mustReadRune() {
+	switch s.getRune() {
 	case '0':
 		return false
 	case '1':
@@ -531,8 +550,11 @@ func (s *ss) getBase(verb int) (base int, digits string) {
 
 // scanNumber returns the numerical string with specified digits starting here.
 func (s *ss) scanNumber(digits string, haveDigits bool) string {
-	if !haveDigits && !s.accept(digits) {
-		s.errorString("expected integer")
+	if !haveDigits {
+		s.notEOF()
+		if !s.accept(digits) {
+			s.errorString("expected integer")
+		}
 	}
 	for s.accept(digits) {
 	}
@@ -541,7 +563,8 @@ func (s *ss) scanNumber(digits string, haveDigits bool) string {
 
 // scanRune returns the next rune value in the input.
 func (s *ss) scanRune(bitSize int) int64 {
-	rune := int64(s.mustReadRune())
+	s.notEOF()
+	rune := int64(s.getRune())
 	n := uint(bitSize)
 	x := (rune << (64 - n)) >> (64 - n)
 	if x != rune {
@@ -575,6 +598,7 @@ func (s *ss) scanInt(verb int, bitSize int) int64 {
 		return s.scanRune(bitSize)
 	}
 	s.skipSpace(false)
+	s.notEOF()
 	base, digits := s.getBase(verb)
 	haveDigits := false
 	if verb == 'U' {
@@ -607,6 +631,7 @@ func (s *ss) scanUint(verb int, bitSize int) uint64 {
 		return uint64(s.scanRune(bitSize))
 	}
 	s.skipSpace(false)
+	s.notEOF()
 	base, digits := s.getBase(verb)
 	haveDigits := false
 	if verb == 'U' {
@@ -727,6 +752,7 @@ func (s *ss) scanComplex(verb int, n int) complex128 {
 		return 0
 	}
 	s.skipSpace(false)
+	s.notEOF()
 	sreal, simag := s.complexTokens()
 	real := s.convertFloat(sreal, n/2)
 	imag := s.convertFloat(simag, n/2)
@@ -740,6 +766,7 @@ func (s *ss) convertString(verb int) (str string) {
 		return ""
 	}
 	s.skipSpace(false)
+	s.notEOF()
 	switch verb {
 	case 'q':
 		str = s.quotedString()
@@ -748,16 +775,13 @@ func (s *ss) convertString(verb int) (str string) {
 	default:
 		str = string(s.token(true, notSpace)) // %s and %v just return the next word
 	}
-	// Empty strings other than with %q are not OK.
-	if len(str) == 0 && verb != 'q' && s.maxWid > 0 {
-		s.errorString("Scan: no data for string")
-	}
 	return
 }
 
 // quotedString returns the double- or back-quoted string represented by the next input characters.
 func (s *ss) quotedString() string {
-	quote := s.mustReadRune()
+	s.notEOF()
+	quote := s.getRune()
 	switch quote {
 	case '`':
 		// Back-quoted: Anything goes until EOF or back quote.
@@ -827,6 +851,7 @@ func (s *ss) hexByte() (b byte, ok bool) {
 
 // hexString returns the space-delimited hexpair-encoded string.
 func (s *ss) hexString() string {
+	s.notEOF()
 	for {
 		b, ok := s.hexByte()
 		if !ok {
@@ -860,6 +885,7 @@ func (s *ss) scanOne(verb int, field interface{}) {
 		}
 		return
 	}
+
 	switch v := field.(type) {
 	case *bool:
 		*v = s.scanBool(verb)
@@ -894,11 +920,13 @@ func (s *ss) scanOne(verb int, field interface{}) {
 	case *float32:
 		if s.okVerb(verb, floatVerbs, "float32") {
 			s.skipSpace(false)
+			s.notEOF()
 			*v = float32(s.convertFloat(s.floatToken(), 32))
 		}
 	case *float64:
 		if s.okVerb(verb, floatVerbs, "float64") {
 			s.skipSpace(false)
+			s.notEOF()
 			*v = s.convertFloat(s.floatToken(), 64)
 		}
 	case *string:
@@ -927,7 +955,7 @@ func (s *ss) scanOne(verb int, field interface{}) {
 			// For now, can only handle (renamed) []byte.
 			typ := v.Type()
 			if typ.Elem().Kind() != reflect.Uint8 {
-				goto CantHandle
+				s.errorString("Scan: can't handle type: " + val.Type().String())
 			}
 			str := s.convertString(verb)
 			v.Set(reflect.MakeSlice(typ, len(str), len(str)))
@@ -936,23 +964,23 @@ func (s *ss) scanOne(verb int, field interface{}) {
 			}
 		case reflect.Float32, reflect.Float64:
 			s.skipSpace(false)
+			s.notEOF()
 			v.SetFloat(s.convertFloat(s.floatToken(), v.Type().Bits()))
 		case reflect.Complex64, reflect.Complex128:
 			v.SetComplex(s.scanComplex(verb, v.Type().Bits()))
 		default:
-		CantHandle:
 			s.errorString("Scan: can't handle type: " + val.Type().String())
 		}
 	}
 }
 
-// errorHandler turns local panics into error returns.  EOFs are benign.
+// errorHandler turns local panics into error returns.
 func errorHandler(errp *os.Error) {
 	if e := recover(); e != nil {
 		if se, ok := e.(scanError); ok { // catch local error
-			if se.err != os.EOF {
-				*errp = se.err
-			}
+			*errp = se.err
+		} else if eof, ok := e.(os.Error); ok && eof == os.EOF { // out of input
+			*errp = eof
 		} else {
 			panic(e)
 		}
diff --git a/libgo/go/fmt/scan_test.go b/libgo/go/fmt/scan_test.go
index da13eb2..3f06e57 100644
--- a/libgo/go/fmt/scan_test.go
+++ b/libgo/go/fmt/scan_test.go
@@ -94,7 +94,7 @@ func (x *Xs) Scan(state ScanState, verb int) os.Error {
 	}
 	s := string(tok)
 	if !regexp.MustCompile("^" + string(verb) + "+$").MatchString(s) {
-		return os.ErrorString("syntax error for xs")
+		return os.NewError("syntax error for xs")
 	}
 	*x = Xs(s)
 	return nil
@@ -298,6 +298,8 @@ var scanfTests = []ScanfTest{
 	// Fixed bugs
 	{"%d\n", "27\n", &intVal, 27},  // ok
 	{"%d\n", "28 \n", &intVal, 28}, // was: "unexpected newline"
+	{"%v", "0", &intVal, 0},        // was: "EOF"; 0 was taken as base prefix and not counted.
+	{"%v", "0", &uintVal, uint(0)}, // was: "EOF"; 0 was taken as base prefix and not counted.
 }
 
 var overflowTests = []ScanTest{
@@ -660,6 +662,68 @@ func TestEOF(t *testing.T) {
 	}
 }
 
+// Verify that we see an EOF error if we run out of input.
+// This was a buglet: we used to get "expected integer".
+func TestEOFAtEndOfInput(t *testing.T) {
+	var i, j int
+	n, err := Sscanf("23", "%d %d", &i, &j)
+	if n != 1 || i != 23 {
+		t.Errorf("Sscanf expected one value of 23; got %d %d", n, i)
+	}
+	if err != os.EOF {
+		t.Errorf("Sscanf expected EOF; got %q", err)
+	}
+	n, err = Sscan("234", &i, &j)
+	if n != 1 || i != 234 {
+		t.Errorf("Sscan expected one value of 234; got %d %d", n, i)
+	}
+	if err != os.EOF {
+		t.Errorf("Sscan expected EOF; got %q", err)
+	}
+	// Trailing space is tougher.
+	n, err = Sscan("234 ", &i, &j)
+	if n != 1 || i != 234 {
+		t.Errorf("Sscan expected one value of 234; got %d %d", n, i)
+	}
+	if err != os.EOF {
+		t.Errorf("Sscan expected EOF; got %q", err)
+	}
+}
+
+var eofTests = []struct {
+	format string
+	v      interface{}
+}{
+	{"%s", &stringVal},
+	{"%q", &stringVal},
+	{"%x", &stringVal},
+	{"%v", &stringVal},
+	{"%v", &bytesVal},
+	{"%v", &intVal},
+	{"%v", &uintVal},
+	{"%v", &boolVal},
+	{"%v", &float32Val},
+	{"%v", &complex64Val},
+	{"%v", &renamedStringVal},
+	{"%v", &renamedBytesVal},
+	{"%v", &renamedIntVal},
+	{"%v", &renamedUintVal},
+	{"%v", &renamedBoolVal},
+	{"%v", &renamedFloat32Val},
+	{"%v", &renamedComplex64Val},
+}
+
+func TestEOFAllTypes(t *testing.T) {
+	for i, test := range eofTests {
+		if _, err := Sscanf("", test.format, test.v); err != os.EOF {
+			t.Errorf("#%d: %s %T not eof on empty string: %s", i, test.format, test.v, err)
+		}
+		if _, err := Sscanf("   ", test.format, test.v); err != os.EOF {
+			t.Errorf("#%d: %s %T not eof on trailing blanks: %s", i, test.format, test.v, err)
+		}
+	}
+}
+
 // Verify that, at least when using bufio, successive calls to Fscan do not lose runes.
 func TestUnreadRuneWithBufio(t *testing.T) {
 	r := bufio.NewReader(strings.NewReader("123αb"))
@@ -756,7 +820,7 @@ func (r *RecursiveInt) Scan(state ScanState, verb int) (err os.Error) {
 	next := new(RecursiveInt)
 	_, err = Fscanf(state, ".%v", next)
 	if err != nil {
-		if err == os.ErrorString("input does not match format") || err == io.ErrUnexpectedEOF {
+		if err == os.NewError("input does not match format") || err == io.ErrUnexpectedEOF {
 			err = nil
 		}
 		return