* gcc-interface/decl.c (warn_on_field_placement): Issue the warning

[official-gcc.git] / libgo / go / fmt / print.go

// Copyright 2009 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 fmt

import (
        "errors"
        "io"
        "os"
        "reflect"
        "sync"
        "unicode/utf8"
)

// Strings for use with buffer.WriteString.
// This is less overhead than using buffer.Write with byte arrays.
const (
        commaSpaceString  = ", "
        nilAngleString    = "<nil>"
        nilParenString    = "(nil)"
        nilString         = "nil"
        mapString         = "map["
        percentBangString = "%!"
        missingString     = "(MISSING)"
        badIndexString    = "(BADINDEX)"
        panicString       = "(PANIC="
        extraString       = "%!(EXTRA "
        badWidthString    = "%!(BADWIDTH)"
        badPrecString     = "%!(BADPREC)"
        noVerbString      = "%!(NOVERB)"
        invReflectString  = "<invalid reflect.Value>"
)

// State represents the printer state passed to custom formatters.
// It provides access to the io.Writer interface plus information about
// the flags and options for the operand's format specifier.
type State interface {
        // Write is the function to call to emit formatted output to be printed.
        Write(b []byte) (n int, err error)
        // Width returns the value of the width option and whether it has been set.
        Width() (wid int, ok bool)
        // Precision returns the value of the precision option and whether it has been set.
        Precision() (prec int, ok bool)

        // Flag reports whether the flag c, a character, has been set.
        Flag(c int) bool
}

// Formatter is the interface implemented by values with a custom formatter.
// The implementation of Format may call Sprint(f) or Fprint(f) etc.
// to generate its output.
type Formatter interface {
        Format(f State, c rune)
}

// 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 any format that accepts a string or to an unformatted printer
// such as Print.
type Stringer interface {
        String() string
}

// 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.
type GoStringer interface {
        GoString() string
}

// Use simple []byte instead of bytes.Buffer to avoid large dependency.
type buffer []byte

func (b *buffer) Write(p []byte) {
        *b = append(*b, p...)
}

func (b *buffer) WriteString(s string) {
        *b = append(*b, s...)
}

func (b *buffer) WriteByte(c byte) {
        *b = append(*b, c)
}

func (bp *buffer) WriteRune(r rune) {
        if r < utf8.RuneSelf {
                *bp = append(*bp, byte(r))
                return
        }

        b := *bp
        n := len(b)
        for n+utf8.UTFMax > cap(b) {
                b = append(b, 0)
        }
        w := utf8.EncodeRune(b[n:n+utf8.UTFMax], r)
        *bp = b[:n+w]
}

// pp is used to store a printer's state and is reused with sync.Pool to avoid allocations.
type pp struct {
        buf buffer

        // arg holds the current item, as an interface{}.
        arg interface{}

        // value is used instead of arg for reflect values.
        value reflect.Value

        // fmt is used to format basic items such as integers or strings.
        fmt fmt

        // reordered records whether the format string used argument reordering.
        reordered bool
        // goodArgNum records whether the most recent reordering directive was valid.
        goodArgNum bool
        // panicking is set by catchPanic to avoid infinite panic, recover, panic, ... recursion.
        panicking bool
        // erroring is set when printing an error string to guard against calling handleMethods.
        erroring bool
}

var ppFree = sync.Pool{
        New: func() interface{} { return new(pp) },
}

// newPrinter allocates a new pp struct or grabs a cached one.
func newPrinter() *pp {
        p := ppFree.Get().(*pp)
        p.panicking = false
        p.erroring = false
        p.fmt.init(&p.buf)
        return p
}

// free saves used pp structs in ppFree; avoids an allocation per invocation.
func (p *pp) free() {
        p.buf = p.buf[:0]
        p.arg = nil
        p.value = reflect.Value{}
        ppFree.Put(p)
}

func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }

func (p *pp) Precision() (prec int, ok bool) { return p.fmt.prec, p.fmt.precPresent }

func (p *pp) Flag(b int) bool {
        switch b {
        case '-':
                return p.fmt.minus
        case '+':
                return p.fmt.plus || p.fmt.plusV
        case '#':
                return p.fmt.sharp || p.fmt.sharpV
        case ' ':
                return p.fmt.space
        case '0':
                return p.fmt.zero
        }
        return false
}

// Implement Write so we can call Fprintf on a pp (through State), for
// recursive use in custom verbs.
func (p *pp) Write(b []byte) (ret int, err error) {
        p.buf.Write(b)
        return len(b), nil
}

// These routines end in 'f' and take a format string.

// 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, err error) {
        p := newPrinter()
        p.doPrintf(format, a)
        n, err = w.Write(p.buf)
        p.free()
        return
}

// 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, err error) {
        return Fprintf(os.Stdout, format, a...)
}

// Sprintf formats according to a format specifier and returns the resulting string.
func Sprintf(format string, a ...interface{}) string {
        p := newPrinter()
        p.doPrintf(format, a)
        s := string(p.buf)
        p.free()
        return s
}

// Errorf formats according to a format specifier and returns the string
// as a value that satisfies error.
func Errorf(format string, a ...interface{}) error {
        return errors.New(Sprintf(format, a...))
}

// These routines do not take a format string

// 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, err error) {
        p := newPrinter()
        p.doPrint(a)
        n, err = w.Write(p.buf)
        p.free()
        return
}

// 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, err error) {
        return Fprint(os.Stdout, a...)
}

// Sprint formats using the default formats for its operands and returns the resulting string.
// Spaces are added between operands when neither is a string.
func Sprint(a ...interface{}) string {
        p := newPrinter()
        p.doPrint(a)
        s := string(p.buf)
        p.free()
        return s
}

// These routines end in 'ln', do not take a format string,
// always add spaces between operands, and add a newline
// after the last operand.

// 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, err error) {
        p := newPrinter()
        p.doPrintln(a)
        n, err = w.Write(p.buf)
        p.free()
        return
}

// 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, err error) {
        return Fprintln(os.Stdout, a...)
}

// Sprintln formats using the default formats for its operands and returns the resulting string.
// Spaces are always added between operands and a newline is appended.
func Sprintln(a ...interface{}) string {
        p := newPrinter()
        p.doPrintln(a)
        s := string(p.buf)
        p.free()
        return s
}

// getField gets the i'th field of the struct value.
// If the field is itself is an interface, return a value for
// the thing inside the interface, not the interface itself.
func getField(v reflect.Value, i int) reflect.Value {
        val := v.Field(i)
        if val.Kind() == reflect.Interface && !val.IsNil() {
                val = val.Elem()
        }
        return val
}

// tooLarge reports whether the magnitude of the integer is
// too large to be used as a formatting width or precision.
func tooLarge(x int) bool {
        const max int = 1e6
        return x > max || x < -max
}

// parsenum converts ASCII to integer.  num is 0 (and isnum is false) if no number present.
func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
        if start >= end {
                return 0, false, end
        }
        for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
                if tooLarge(num) {
                        return 0, false, end // Overflow; crazy long number most likely.
                }
                num = num*10 + int(s[newi]-'0')
                isnum = true
        }
        return
}

func (p *pp) unknownType(v reflect.Value) {
        if !v.IsValid() {
                p.buf.WriteString(nilAngleString)
                return
        }
        p.buf.WriteByte('?')
        p.buf.WriteString(v.Type().String())
        p.buf.WriteByte('?')
}

func (p *pp) badVerb(verb rune) {
        p.erroring = true
        p.buf.WriteString(percentBangString)
        p.buf.WriteRune(verb)
        p.buf.WriteByte('(')
        switch {
        case p.arg != nil:
                p.buf.WriteString(reflect.TypeOf(p.arg).String())
                p.buf.WriteByte('=')
                p.printArg(p.arg, 'v')
        case p.value.IsValid():
                p.buf.WriteString(p.value.Type().String())
                p.buf.WriteByte('=')
                p.printValue(p.value, 'v', 0)
        default:
                p.buf.WriteString(nilAngleString)
        }
        p.buf.WriteByte(')')
        p.erroring = false
}

func (p *pp) fmtBool(v bool, verb rune) {
        switch verb {
        case 't', 'v':
                p.fmt.fmt_boolean(v)
        default:
                p.badVerb(verb)
        }
}

// fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
// not, as requested, by temporarily setting the sharp flag.
func (p *pp) fmt0x64(v uint64, leading0x bool) {
        sharp := p.fmt.sharp
        p.fmt.sharp = leading0x
        p.fmt.fmt_integer(v, 16, unsigned, ldigits)
        p.fmt.sharp = sharp
}

// fmtInteger formats a signed or unsigned integer.
func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
        switch verb {
        case 'v':
                if p.fmt.sharpV && !isSigned {
                        p.fmt0x64(v, true)
                } else {
                        p.fmt.fmt_integer(v, 10, isSigned, ldigits)
                }
        case 'd':
                p.fmt.fmt_integer(v, 10, isSigned, ldigits)
        case 'b':
                p.fmt.fmt_integer(v, 2, isSigned, ldigits)
        case 'o':
                p.fmt.fmt_integer(v, 8, isSigned, ldigits)
        case 'x':
                p.fmt.fmt_integer(v, 16, isSigned, ldigits)
        case 'X':
                p.fmt.fmt_integer(v, 16, isSigned, udigits)
        case 'c':
                p.fmt.fmt_c(v)
        case 'q':
                if v <= utf8.MaxRune {
                        p.fmt.fmt_qc(v)
                } else {
                        p.badVerb(verb)
                }
        case 'U':
                p.fmt.fmt_unicode(v)
        default:
                p.badVerb(verb)
        }
}

// fmtFloat formats a float. The default precision for each verb
// is specified as last argument in the call to fmt_float.
func (p *pp) fmtFloat(v float64, size int, verb rune) {
        switch verb {
        case 'v':
                p.fmt.fmt_float(v, size, 'g', -1)
        case 'b', 'g', 'G':
                p.fmt.fmt_float(v, size, verb, -1)
        case 'f', 'e', 'E':
                p.fmt.fmt_float(v, size, verb, 6)
        case 'F':
                p.fmt.fmt_float(v, size, 'f', 6)
        default:
                p.badVerb(verb)
        }
}

// fmtComplex formats a complex number v with
// r = real(v) and j = imag(v) as (r+ji) using
// fmtFloat for r and j formatting.
func (p *pp) fmtComplex(v complex128, size int, verb rune) {
        // Make sure any unsupported verbs are found before the
        // calls to fmtFloat to not generate an incorrect error string.
        switch verb {
        case 'v', 'b', 'g', 'G', 'f', 'F', 'e', 'E':
                oldPlus := p.fmt.plus
                p.buf.WriteByte('(')
                p.fmtFloat(real(v), size/2, verb)
                // Imaginary part always has a sign.
                p.fmt.plus = true
                p.fmtFloat(imag(v), size/2, verb)
                p.buf.WriteString("i)")
                p.fmt.plus = oldPlus
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtString(v string, verb rune) {
        switch verb {
        case 'v':
                if p.fmt.sharpV {
                        p.fmt.fmt_q(v)
                } else {
                        p.fmt.fmt_s(v)
                }
        case 's':
                p.fmt.fmt_s(v)
        case 'x':
                p.fmt.fmt_sx(v, ldigits)
        case 'X':
                p.fmt.fmt_sx(v, udigits)
        case 'q':
                p.fmt.fmt_q(v)
        default:
                p.badVerb(verb)
        }
}

func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
        switch verb {
        case 'v', 'd':
                if p.fmt.sharpV {
                        p.buf.WriteString(typeString)
                        if v == nil {
                                p.buf.WriteString(nilParenString)
                                return
                        }
                        p.buf.WriteByte('{')
                        for i, c := range v {
                                if i > 0 {
                                        p.buf.WriteString(commaSpaceString)
                                }
                                p.fmt0x64(uint64(c), true)
                        }
                        p.buf.WriteByte('}')
                } else {
                        p.buf.WriteByte('[')
                        for i, c := range v {
                                if i > 0 {
                                        p.buf.WriteByte(' ')
                                }
                                p.fmt.fmt_integer(uint64(c), 10, unsigned, ldigits)
                        }
                        p.buf.WriteByte(']')
                }
        case 's':
                p.fmt.fmt_s(string(v))
        case 'x':
                p.fmt.fmt_bx(v, ldigits)
        case 'X':
                p.fmt.fmt_bx(v, udigits)
        case 'q':
                p.fmt.fmt_q(string(v))
        default:
                p.printValue(reflect.ValueOf(v), verb, 0)
        }
}

func (p *pp) fmtPointer(value reflect.Value, verb rune) {
        var u uintptr
        switch value.Kind() {
        case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
                u = value.Pointer()
        default:
                p.badVerb(verb)
                return
        }

        switch verb {
        case 'v':
                if p.fmt.sharpV {
                        p.buf.WriteByte('(')
                        p.buf.WriteString(value.Type().String())
                        p.buf.WriteString(")(")
                        if u == 0 {
                                p.buf.WriteString(nilString)
                        } else {
                                p.fmt0x64(uint64(u), true)
                        }
                        p.buf.WriteByte(')')
                } else {
                        if u == 0 {
                                p.fmt.padString(nilAngleString)
                        } else {
                                p.fmt0x64(uint64(u), !p.fmt.sharp)
                        }
                }
        case 'p':
                p.fmt0x64(uint64(u), !p.fmt.sharp)
        case 'b', 'o', 'd', 'x', 'X':
                p.fmtInteger(uint64(u), unsigned, verb)
        default:
                p.badVerb(verb)
        }
}

func (p *pp) catchPanic(arg interface{}, verb rune) {
        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(arg); v.Kind() == reflect.Ptr && v.IsNil() {
                        p.buf.WriteString(nilAngleString)
                        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 printArg cannot succeed.
                        panic(err)
                }

                oldFlags := p.fmt.fmtFlags
                // For this output we want default behavior.
                p.fmt.clearflags()

                p.buf.WriteString(percentBangString)
                p.buf.WriteRune(verb)
                p.buf.WriteString(panicString)
                p.panicking = true
                p.printArg(err, 'v')
                p.panicking = false
                p.buf.WriteByte(')')

                p.fmt.fmtFlags = oldFlags
        }
}

func (p *pp) handleMethods(verb rune) (handled bool) {
        if p.erroring {
                return
        }
        // Is it a Formatter?
        if formatter, ok := p.arg.(Formatter); ok {
                handled = true
                defer p.catchPanic(p.arg, verb)
                formatter.Format(p, verb)
                return
        }

        // If we're doing Go syntax and the argument knows how to supply it, take care of it now.
        if p.fmt.sharpV {
                if stringer, ok := p.arg.(GoStringer); ok {
                        handled = true
                        defer p.catchPanic(p.arg, verb)
                        // Print the result of GoString unadorned.
                        p.fmt.fmt_s(stringer.GoString())
                        return
                }
        } else {
                // If a string is acceptable according to the format, see if
                // the value satisfies one of the string-valued interfaces.
                // Println etc. set verb to %v, which is "stringable".
                switch verb {
                case 'v', 's', 'x', 'X', 'q':
                        // Is it an error or Stringer?
                        // The duplication in the bodies is necessary:
                        // setting handled and deferring catchPanic
                        // must happen before calling the method.
                        switch v := p.arg.(type) {
                        case error:
                                handled = true
                                defer p.catchPanic(p.arg, verb)
                                p.fmtString(v.Error(), verb)
                                return

                        case Stringer:
                                handled = true
                                defer p.catchPanic(p.arg, verb)
                                p.fmtString(v.String(), verb)
                                return
                        }
                }
        }
        return false
}

func (p *pp) printArg(arg interface{}, verb rune) {
        p.arg = arg
        p.value = reflect.Value{}

        if arg == nil {
                switch verb {
                case 'T', 'v':
                        p.fmt.padString(nilAngleString)
                default:
                        p.badVerb(verb)
                }
                return
        }

        // Special processing considerations.
        // %T (the value's type) and %p (its address) are special; we always do them first.
        switch verb {
        case 'T':
                p.fmt.fmt_s(reflect.TypeOf(arg).String())
                return
        case 'p':
                p.fmtPointer(reflect.ValueOf(arg), 'p')
                return
        }

        // Some types can be done without reflection.
        switch f := arg.(type) {
        case bool:
                p.fmtBool(f, verb)
        case float32:
                p.fmtFloat(float64(f), 32, verb)
        case float64:
                p.fmtFloat(f, 64, verb)
        case complex64:
                p.fmtComplex(complex128(f), 64, verb)
        case complex128:
                p.fmtComplex(f, 128, verb)
        case int:
                p.fmtInteger(uint64(f), signed, verb)
        case int8:
                p.fmtInteger(uint64(f), signed, verb)
        case int16:
                p.fmtInteger(uint64(f), signed, verb)
        case int32:
                p.fmtInteger(uint64(f), signed, verb)
        case int64:
                p.fmtInteger(uint64(f), signed, verb)
        case uint:
                p.fmtInteger(uint64(f), unsigned, verb)
        case uint8:
                p.fmtInteger(uint64(f), unsigned, verb)
        case uint16:
                p.fmtInteger(uint64(f), unsigned, verb)
        case uint32:
                p.fmtInteger(uint64(f), unsigned, verb)
        case uint64:
                p.fmtInteger(f, unsigned, verb)
        case uintptr:
                p.fmtInteger(uint64(f), unsigned, verb)
        case string:
                p.fmtString(f, verb)
        case []byte:
                p.fmtBytes(f, verb, "[]byte")
        case reflect.Value:
                // Handle extractable values with special methods
                // since printValue does not handle them at depth 0.
                if f.IsValid() && f.CanInterface() {
                        p.arg = f.Interface()
                        if p.handleMethods(verb) {
                                return
                        }
                }
                p.printValue(f, verb, 0)
        default:
                // If the type is not simple, it might have methods.
                if !p.handleMethods(verb) {
                        // Need to use reflection, since the type had no
                        // interface methods that could be used for formatting.
                        p.printValue(reflect.ValueOf(f), verb, 0)
                }
        }
}

var byteType = reflect.TypeOf(byte(0))

// printValue is similar to printArg but starts with a reflect value, not an interface{} value.
// It does not handle 'p' and 'T' verbs because these should have been already handled by printArg.
func (p *pp) printValue(value reflect.Value, verb rune, depth int) {
        // Handle values with special methods if not already handled by printArg (depth == 0).
        if depth > 0 && value.IsValid() && value.CanInterface() {
                p.arg = value.Interface()
                if p.handleMethods(verb) {
                        return
                }
        }
        p.arg = nil
        p.value = value

        switch f := value; value.Kind() {
        case reflect.Invalid:
                if depth == 0 {
                        p.buf.WriteString(invReflectString)
                } else {
                        switch verb {
                        case 'v':
                                p.buf.WriteString(nilAngleString)
                        default:
                                p.badVerb(verb)
                        }
                }
        case reflect.Bool:
                p.fmtBool(f.Bool(), verb)
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                p.fmtInteger(uint64(f.Int()), signed, verb)
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                p.fmtInteger(f.Uint(), unsigned, verb)
        case reflect.Float32:
                p.fmtFloat(f.Float(), 32, verb)
        case reflect.Float64:
                p.fmtFloat(f.Float(), 64, verb)
        case reflect.Complex64:
                p.fmtComplex(f.Complex(), 64, verb)
        case reflect.Complex128:
                p.fmtComplex(f.Complex(), 128, verb)
        case reflect.String:
                p.fmtString(f.String(), verb)
        case reflect.Map:
                if p.fmt.sharpV {
                        p.buf.WriteString(f.Type().String())
                        if f.IsNil() {
                                p.buf.WriteString(nilParenString)
                                return
                        }
                        p.buf.WriteByte('{')
                } else {
                        p.buf.WriteString(mapString)
                }
                keys := f.MapKeys()
                for i, key := range keys {
                        if i > 0 {
                                if p.fmt.sharpV {
                                        p.buf.WriteString(commaSpaceString)
                                } else {
                                        p.buf.WriteByte(' ')
                                }
                        }
                        p.printValue(key, verb, depth+1)
                        p.buf.WriteByte(':')
                        p.printValue(f.MapIndex(key), verb, depth+1)
                }
                if p.fmt.sharpV {
                        p.buf.WriteByte('}')
                } else {
                        p.buf.WriteByte(']')
                }
        case reflect.Struct:
                if p.fmt.sharpV {
                        p.buf.WriteString(f.Type().String())
                }
                p.buf.WriteByte('{')
                for i := 0; i < f.NumField(); i++ {
                        if i > 0 {
                                if p.fmt.sharpV {
                                        p.buf.WriteString(commaSpaceString)
                                } else {
                                        p.buf.WriteByte(' ')
                                }
                        }
                        if p.fmt.plusV || p.fmt.sharpV {
                                if name := f.Type().Field(i).Name; name != "" {
                                        p.buf.WriteString(name)
                                        p.buf.WriteByte(':')
                                }
                        }
                        p.printValue(getField(f, i), verb, depth+1)
                }
                p.buf.WriteByte('}')
        case reflect.Interface:
                value := f.Elem()
                if !value.IsValid() {
                        if p.fmt.sharpV {
                                p.buf.WriteString(f.Type().String())
                                p.buf.WriteString(nilParenString)
                        } else {
                                p.buf.WriteString(nilAngleString)
                        }
                } else {
                        p.printValue(value, verb, depth+1)
                }
        case reflect.Array, reflect.Slice:
                switch verb {
                case 's', 'q', 'x', 'X':
                        // Handle byte and uint8 slices and arrays special for the above verbs.
                        t := f.Type()
                        if t.Elem().Kind() == reflect.Uint8 {
                                var bytes []byte
                                if f.Kind() == reflect.Slice {
                                        bytes = f.Bytes()
                                } else if f.CanAddr() {
                                        bytes = f.Slice(0, f.Len()).Bytes()
                                } else {
                                        // We have an array, but we cannot Slice() a non-addressable array,
                                        // so we build a slice by hand. This is a rare case but it would be nice
                                        // if reflection could help a little more.
                                        bytes = make([]byte, f.Len())
                                        for i := range bytes {
                                                bytes[i] = byte(f.Index(i).Uint())
                                        }
                                }
                                p.fmtBytes(bytes, verb, t.String())
                                return
                        }
                }
                if p.fmt.sharpV {
                        p.buf.WriteString(f.Type().String())
                        if f.Kind() == reflect.Slice && f.IsNil() {
                                p.buf.WriteString(nilParenString)
                                return
                        }
                        p.buf.WriteByte('{')
                        for i := 0; i < f.Len(); i++ {
                                if i > 0 {
                                        p.buf.WriteString(commaSpaceString)
                                }
                                p.printValue(f.Index(i), verb, depth+1)
                        }
                        p.buf.WriteByte('}')
                } else {
                        p.buf.WriteByte('[')
                        for i := 0; i < f.Len(); i++ {
                                if i > 0 {
                                        p.buf.WriteByte(' ')
                                }
                                p.printValue(f.Index(i), verb, depth+1)
                        }
                        p.buf.WriteByte(']')
                }
        case reflect.Ptr:
                // pointer to array or slice or struct?  ok at top level
                // but not embedded (avoid loops)
                if depth == 0 && f.Pointer() != 0 {
                        switch a := f.Elem(); a.Kind() {
                        case reflect.Array, reflect.Slice, reflect.Struct, reflect.Map:
                                p.buf.WriteByte('&')
                                p.printValue(a, verb, depth+1)
                                return
                        }
                }
                fallthrough
        case reflect.Chan, reflect.Func, reflect.UnsafePointer:
                p.fmtPointer(f, verb)
        default:
                p.unknownType(f)
        }
}

// intFromArg gets the argNumth element of a. On return, isInt reports whether the argument has integer type.
func intFromArg(a []interface{}, argNum int) (num int, isInt bool, newArgNum int) {
        newArgNum = argNum
        if argNum < len(a) {
                num, isInt = a[argNum].(int) // Almost always OK.
                if !isInt {
                        // Work harder.
                        switch v := reflect.ValueOf(a[argNum]); v.Kind() {
                        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                                n := v.Int()
                                if int64(int(n)) == n {
                                        num = int(n)
                                        isInt = true
                                }
                        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                                n := v.Uint()
                                if int64(n) >= 0 && uint64(int(n)) == n {
                                        num = int(n)
                                        isInt = true
                                }
                        default:
                                // Already 0, false.
                        }
                }
                newArgNum = argNum + 1
                if tooLarge(num) {
                        num = 0
                        isInt = false
                }
        }
        return
}

// parseArgNumber returns the value of the bracketed number, minus 1
// (explicit argument numbers are one-indexed but we want zero-indexed).
// The opening bracket is known to be present at format[0].
// The returned values are the index, the number of bytes to consume
// up to the closing paren, if present, and whether the number parsed
// ok. The bytes to consume will be 1 if no closing paren is present.
func parseArgNumber(format string) (index int, wid int, ok bool) {
        // There must be at least 3 bytes: [n].
        if len(format) < 3 {
                return 0, 1, false
        }

        // Find closing bracket.
        for i := 1; i < len(format); i++ {
                if format[i] == ']' {
                        width, ok, newi := parsenum(format, 1, i)
                        if !ok || newi != i {
                                return 0, i + 1, false
                        }
                        return width - 1, i + 1, true // arg numbers are one-indexed and skip paren.
                }
        }
        return 0, 1, false
}

// argNumber returns the next argument to evaluate, which is either the value of the passed-in
// argNum or the value of the bracketed integer that begins format[i:]. It also returns
// the new value of i, that is, the index of the next byte of the format to process.
func (p *pp) argNumber(argNum int, format string, i int, numArgs int) (newArgNum, newi int, found bool) {
        if len(format) <= i || format[i] != '[' {
                return argNum, i, false
        }
        p.reordered = true
        index, wid, ok := parseArgNumber(format[i:])
        if ok && 0 <= index && index < numArgs {
                return index, i + wid, true
        }
        p.goodArgNum = false
        return argNum, i + wid, ok
}

func (p *pp) badArgNum(verb rune) {
        p.buf.WriteString(percentBangString)
        p.buf.WriteRune(verb)
        p.buf.WriteString(badIndexString)
}

func (p *pp) missingArg(verb rune) {
        p.buf.WriteString(percentBangString)
        p.buf.WriteRune(verb)
        p.buf.WriteString(missingString)
}

func (p *pp) doPrintf(format string, a []interface{}) {
        end := len(format)
        argNum := 0         // we process one argument per non-trivial format
        afterIndex := false // previous item in format was an index like [3].
        p.reordered = false
formatLoop:
        for i := 0; i < end; {
                p.goodArgNum = true
                lasti := i
                for i < end && format[i] != '%' {
                        i++
                }
                if i > lasti {
                        p.buf.WriteString(format[lasti:i])
                }
                if i >= end {
                        // done processing format string
                        break
                }

                // Process one verb
                i++

                // Do we have flags?
                p.fmt.clearflags()
        simpleFormat:
                for ; i < end; i++ {
                        c := format[i]
                        switch c {
                        case '#':
                                p.fmt.sharp = true
                        case '0':
                                p.fmt.zero = !p.fmt.minus // Only allow zero padding to the left.
                        case '+':
                                p.fmt.plus = true
                        case '-':
                                p.fmt.minus = true
                                p.fmt.zero = false // Do not pad with zeros to the right.
                        case ' ':
                                p.fmt.space = true
                        default:
                                // Fast path for common case of ascii lower case simple verbs
                                // without precision or width or argument indices.
                                if 'a' <= c && c <= 'z' && argNum < len(a) {
                                        if c == 'v' {
                                                // Go syntax
                                                p.fmt.sharpV = p.fmt.sharp
                                                p.fmt.sharp = false
                                                // Struct-field syntax
                                                p.fmt.plusV = p.fmt.plus
                                                p.fmt.plus = false
                                        }
                                        p.printArg(a[argNum], rune(c))
                                        argNum++
                                        i++
                                        continue formatLoop
                                }
                                // Format is more complex than simple flags and a verb or is malformed.
                                break simpleFormat
                        }
                }

                // Do we have an explicit argument index?
                argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))

                // Do we have width?
                if i < end && format[i] == '*' {
                        i++
                        p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)

                        if !p.fmt.widPresent {
                                p.buf.WriteString(badWidthString)
                        }

                        // We have a negative width, so take its value and ensure
                        // that the minus flag is set
                        if p.fmt.wid < 0 {
                                p.fmt.wid = -p.fmt.wid
                                p.fmt.minus = true
                                p.fmt.zero = false // Do not pad with zeros to the right.
                        }
                        afterIndex = false
                } else {
                        p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
                        if afterIndex && p.fmt.widPresent { // "%[3]2d"
                                p.goodArgNum = false
                        }
                }

                // Do we have precision?
                if i+1 < end && format[i] == '.' {
                        i++
                        if afterIndex { // "%[3].2d"
                                p.goodArgNum = false
                        }
                        argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
                        if i < end && format[i] == '*' {
                                i++
                                p.fmt.prec, p.fmt.precPresent, argNum = intFromArg(a, argNum)
                                // Negative precision arguments don't make sense
                                if p.fmt.prec < 0 {
                                        p.fmt.prec = 0
                                        p.fmt.precPresent = false
                                }
                                if !p.fmt.precPresent {
                                        p.buf.WriteString(badPrecString)
                                }
                                afterIndex = false
                        } else {
                                p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i, end)
                                if !p.fmt.precPresent {
                                        p.fmt.prec = 0
                                        p.fmt.precPresent = true
                                }
                        }
                }

                if !afterIndex {
                        argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
                }

                if i >= end {
                        p.buf.WriteString(noVerbString)
                        break
                }

                verb, w := utf8.DecodeRuneInString(format[i:])
                i += w

                switch {
                case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
                        p.buf.WriteByte('%')
                case !p.goodArgNum:
                        p.badArgNum(verb)
                case argNum >= len(a): // No argument left over to print for the current verb.
                        p.missingArg(verb)
                case verb == 'v':
                        // Go syntax
                        p.fmt.sharpV = p.fmt.sharp
                        p.fmt.sharp = false
                        // Struct-field syntax
                        p.fmt.plusV = p.fmt.plus
                        p.fmt.plus = false
                        fallthrough
                default:
                        p.printArg(a[argNum], verb)
                        argNum++
                }
        }

        // Check for extra arguments unless the call accessed the arguments
        // out of order, in which case it's too expensive to detect if they've all
        // been used and arguably OK if they're not.
        if !p.reordered && argNum < len(a) {
                p.fmt.clearflags()
                p.buf.WriteString(extraString)
                for i, arg := range a[argNum:] {
                        if i > 0 {
                                p.buf.WriteString(commaSpaceString)
                        }
                        if arg == nil {
                                p.buf.WriteString(nilAngleString)
                        } else {
                                p.buf.WriteString(reflect.TypeOf(arg).String())
                                p.buf.WriteByte('=')
                                p.printArg(arg, 'v')
                        }
                }
                p.buf.WriteByte(')')
        }
}

func (p *pp) doPrint(a []interface{}) {
        prevString := false
        for argNum, arg := range a {
                isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
                // Add a space between two non-string arguments.
                if argNum > 0 && !isString && !prevString {
                        p.buf.WriteByte(' ')
                }
                p.printArg(arg, 'v')
                prevString = isString
        }
}

// doPrintln is like doPrint but always adds a space between arguments
// and a newline after the last argument.
func (p *pp) doPrintln(a []interface{}) {
        for argNum, arg := range a {
                if argNum > 0 {
                        p.buf.WriteByte(' ')
                }
                p.printArg(arg, 'v')
        }
        p.buf.WriteByte('\n')
}