Source file src/fmt/print.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package fmt
     6  
     7  import (
     8  	"internal/fmtsort"
     9  	"io"
    10  	"os"
    11  	"reflect"
    12  	"sync"
    13  	"unicode/utf8"
    14  )
    15  
    16  // Strings for use with buffer.WriteString.
    17  // This is less overhead than using buffer.Write with byte arrays.
    18  const (
    19  	commaSpaceString  = ", "
    20  	nilAngleString    = "<nil>"
    21  	nilParenString    = "(nil)"
    22  	nilString         = "nil"
    23  	mapString         = "map["
    24  	percentBangString = "%!"
    25  	missingString     = "(MISSING)"
    26  	badIndexString    = "(BADINDEX)"
    27  	panicString       = "(PANIC="
    28  	extraString       = "%!(EXTRA "
    29  	badWidthString    = "%!(BADWIDTH)"
    30  	badPrecString     = "%!(BADPREC)"
    31  	noVerbString      = "%!(NOVERB)"
    32  	invReflectString  = "<invalid reflect.Value>"
    33  )
    34  
    35  // State represents the printer state passed to custom formatters.
    36  // It provides access to the io.Writer interface plus information about
    37  // the flags and options for the operand's format specifier.
    38  type State interface {
    39  	// Write is the function to call to emit formatted output to be printed.
    40  	Write(b []byte) (n int, err error)
    41  	// Width returns the value of the width option and whether it has been set.
    42  	Width() (wid int, ok bool)
    43  	// Precision returns the value of the precision option and whether it has been set.
    44  	Precision() (prec int, ok bool)
    45  
    46  	// Flag reports whether the flag c, a character, has been set.
    47  	Flag(c int) bool
    48  }
    49  
    50  // Formatter is implemented by any value that has a Format method.
    51  // The implementation controls how State and rune are interpreted,
    52  // and may call Sprint(f) or Fprint(f) etc. to generate its output.
    53  type Formatter interface {
    54  	Format(f State, verb rune)
    55  }
    56  
    57  // Stringer is implemented by any value that has a String method,
    58  // which defines the ``native'' format for that value.
    59  // The String method is used to print values passed as an operand
    60  // to any format that accepts a string or to an unformatted printer
    61  // such as Print.
    62  type Stringer interface {
    63  	String() string
    64  }
    65  
    66  // GoStringer is implemented by any value that has a GoString method,
    67  // which defines the Go syntax for that value.
    68  // The GoString method is used to print values passed as an operand
    69  // to a %#v format.
    70  type GoStringer interface {
    71  	GoString() string
    72  }
    73  
    74  // Use simple []byte instead of bytes.Buffer to avoid large dependency.
    75  type buffer []byte
    76  
    77  func (b *buffer) write(p []byte) {
    78  	*b = append(*b, p...)
    79  }
    80  
    81  func (b *buffer) writeString(s string) {
    82  	*b = append(*b, s...)
    83  }
    84  
    85  func (b *buffer) writeByte(c byte) {
    86  	*b = append(*b, c)
    87  }
    88  
    89  func (bp *buffer) writeRune(r rune) {
    90  	if r < utf8.RuneSelf {
    91  		*bp = append(*bp, byte(r))
    92  		return
    93  	}
    94  
    95  	b := *bp
    96  	n := len(b)
    97  	for n+utf8.UTFMax > cap(b) {
    98  		b = append(b, 0)
    99  	}
   100  	w := utf8.EncodeRune(b[n:n+utf8.UTFMax], r)
   101  	*bp = b[:n+w]
   102  }
   103  
   104  // pp is used to store a printer's state and is reused with sync.Pool to avoid allocations.
   105  type pp struct {
   106  	buf buffer
   107  
   108  	// arg holds the current item, as an interface{}.
   109  	arg interface{}
   110  
   111  	// value is used instead of arg for reflect values.
   112  	value reflect.Value
   113  
   114  	// fmt is used to format basic items such as integers or strings.
   115  	fmt fmt
   116  
   117  	// reordered records whether the format string used argument reordering.
   118  	reordered bool
   119  	// goodArgNum records whether the most recent reordering directive was valid.
   120  	goodArgNum bool
   121  	// panicking is set by catchPanic to avoid infinite panic, recover, panic, ... recursion.
   122  	panicking bool
   123  	// erroring is set when printing an error string to guard against calling handleMethods.
   124  	erroring bool
   125  	// wrapErrs is set when the format string may contain a %w verb.
   126  	wrapErrs bool
   127  	// wrappedErr records the target of the %w verb.
   128  	wrappedErr error
   129  }
   130  
   131  var ppFree = sync.Pool{
   132  	New: func() interface{} { return new(pp) },
   133  }
   134  
   135  // newPrinter allocates a new pp struct or grabs a cached one.
   136  func newPrinter() *pp {
   137  	p := ppFree.Get().(*pp)
   138  	p.panicking = false
   139  	p.erroring = false
   140  	p.wrapErrs = false
   141  	p.fmt.init(&p.buf)
   142  	return p
   143  }
   144  
   145  // free saves used pp structs in ppFree; avoids an allocation per invocation.
   146  func (p *pp) free() {
   147  	// Proper usage of a sync.Pool requires each entry to have approximately
   148  	// the same memory cost. To obtain this property when the stored type
   149  	// contains a variably-sized buffer, we add a hard limit on the maximum buffer
   150  	// to place back in the pool.
   151  	//
   152  	// See https://golang.org/issue/23199
   153  	if cap(p.buf) > 64<<10 {
   154  		return
   155  	}
   156  
   157  	p.buf = p.buf[:0]
   158  	p.arg = nil
   159  	p.value = reflect.Value{}
   160  	p.wrappedErr = nil
   161  	ppFree.Put(p)
   162  }
   163  
   164  func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }
   165  
   166  func (p *pp) Precision() (prec int, ok bool) { return p.fmt.prec, p.fmt.precPresent }
   167  
   168  func (p *pp) Flag(b int) bool {
   169  	switch b {
   170  	case '-':
   171  		return p.fmt.minus
   172  	case '+':
   173  		return p.fmt.plus || p.fmt.plusV
   174  	case '#':
   175  		return p.fmt.sharp || p.fmt.sharpV
   176  	case ' ':
   177  		return p.fmt.space
   178  	case '0':
   179  		return p.fmt.zero
   180  	}
   181  	return false
   182  }
   183  
   184  // Implement Write so we can call Fprintf on a pp (through State), for
   185  // recursive use in custom verbs.
   186  func (p *pp) Write(b []byte) (ret int, err error) {
   187  	p.buf.write(b)
   188  	return len(b), nil
   189  }
   190  
   191  // Implement WriteString so that we can call io.WriteString
   192  // on a pp (through state), for efficiency.
   193  func (p *pp) WriteString(s string) (ret int, err error) {
   194  	p.buf.writeString(s)
   195  	return len(s), nil
   196  }
   197  
   198  // These routines end in 'f' and take a format string.
   199  
   200  // Fprintf formats according to a format specifier and writes to w.
   201  // It returns the number of bytes written and any write error encountered.
   202  func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error) {
   203  	p := newPrinter()
   204  	p.doPrintf(format, a)
   205  	n, err = w.Write(p.buf)
   206  	p.free()
   207  	return
   208  }
   209  
   210  // Printf formats according to a format specifier and writes to standard output.
   211  // It returns the number of bytes written and any write error encountered.
   212  func Printf(format string, a ...interface{}) (n int, err error) {
   213  	return Fprintf(os.Stdout, format, a...)
   214  }
   215  
   216  // Sprintf formats according to a format specifier and returns the resulting string.
   217  func Sprintf(format string, a ...interface{}) string {
   218  	p := newPrinter()
   219  	p.doPrintf(format, a)
   220  	s := string(p.buf)
   221  	p.free()
   222  	return s
   223  }
   224  
   225  // These routines do not take a format string
   226  
   227  // Fprint formats using the default formats for its operands and writes to w.
   228  // Spaces are added between operands when neither is a string.
   229  // It returns the number of bytes written and any write error encountered.
   230  func Fprint(w io.Writer, a ...interface{}) (n int, err error) {
   231  	p := newPrinter()
   232  	p.doPrint(a)
   233  	n, err = w.Write(p.buf)
   234  	p.free()
   235  	return
   236  }
   237  
   238  // Print formats using the default formats for its operands and writes to standard output.
   239  // Spaces are added between operands when neither is a string.
   240  // It returns the number of bytes written and any write error encountered.
   241  func Print(a ...interface{}) (n int, err error) {
   242  	return Fprint(os.Stdout, a...)
   243  }
   244  
   245  // Sprint formats using the default formats for its operands and returns the resulting string.
   246  // Spaces are added between operands when neither is a string.
   247  func Sprint(a ...interface{}) string {
   248  	p := newPrinter()
   249  	p.doPrint(a)
   250  	s := string(p.buf)
   251  	p.free()
   252  	return s
   253  }
   254  
   255  // These routines end in 'ln', do not take a format string,
   256  // always add spaces between operands, and add a newline
   257  // after the last operand.
   258  
   259  // Fprintln formats using the default formats for its operands and writes to w.
   260  // Spaces are always added between operands and a newline is appended.
   261  // It returns the number of bytes written and any write error encountered.
   262  func Fprintln(w io.Writer, a ...interface{}) (n int, err error) {
   263  	p := newPrinter()
   264  	p.doPrintln(a)
   265  	n, err = w.Write(p.buf)
   266  	p.free()
   267  	return
   268  }
   269  
   270  // Println formats using the default formats for its operands and writes to standard output.
   271  // Spaces are always added between operands and a newline is appended.
   272  // It returns the number of bytes written and any write error encountered.
   273  func Println(a ...interface{}) (n int, err error) {
   274  	return Fprintln(os.Stdout, a...)
   275  }
   276  
   277  // Sprintln formats using the default formats for its operands and returns the resulting string.
   278  // Spaces are always added between operands and a newline is appended.
   279  func Sprintln(a ...interface{}) string {
   280  	p := newPrinter()
   281  	p.doPrintln(a)
   282  	s := string(p.buf)
   283  	p.free()
   284  	return s
   285  }
   286  
   287  // getField gets the i'th field of the struct value.
   288  // If the field is itself is an interface, return a value for
   289  // the thing inside the interface, not the interface itself.
   290  func getField(v reflect.Value, i int) reflect.Value {
   291  	val := v.Field(i)
   292  	if val.Kind() == reflect.Interface && !val.IsNil() {
   293  		val = val.Elem()
   294  	}
   295  	return val
   296  }
   297  
   298  // tooLarge reports whether the magnitude of the integer is
   299  // too large to be used as a formatting width or precision.
   300  func tooLarge(x int) bool {
   301  	const max int = 1e6
   302  	return x > max || x < -max
   303  }
   304  
   305  // parsenum converts ASCII to integer.  num is 0 (and isnum is false) if no number present.
   306  func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
   307  	if start >= end {
   308  		return 0, false, end
   309  	}
   310  	for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
   311  		if tooLarge(num) {
   312  			return 0, false, end // Overflow; crazy long number most likely.
   313  		}
   314  		num = num*10 + int(s[newi]-'0')
   315  		isnum = true
   316  	}
   317  	return
   318  }
   319  
   320  func (p *pp) unknownType(v reflect.Value) {
   321  	if !v.IsValid() {
   322  		p.buf.writeString(nilAngleString)
   323  		return
   324  	}
   325  	p.buf.writeByte('?')
   326  	p.buf.writeString(v.Type().String())
   327  	p.buf.writeByte('?')
   328  }
   329  
   330  func (p *pp) badVerb(verb rune) {
   331  	p.erroring = true
   332  	p.buf.writeString(percentBangString)
   333  	p.buf.writeRune(verb)
   334  	p.buf.writeByte('(')
   335  	switch {
   336  	case p.arg != nil:
   337  		p.buf.writeString(reflect.TypeOf(p.arg).String())
   338  		p.buf.writeByte('=')
   339  		p.printArg(p.arg, 'v')
   340  	case p.value.IsValid():
   341  		p.buf.writeString(p.value.Type().String())
   342  		p.buf.writeByte('=')
   343  		p.printValue(p.value, 'v', 0)
   344  	default:
   345  		p.buf.writeString(nilAngleString)
   346  	}
   347  	p.buf.writeByte(')')
   348  	p.erroring = false
   349  }
   350  
   351  func (p *pp) fmtBool(v bool, verb rune) {
   352  	switch verb {
   353  	case 't', 'v':
   354  		p.fmt.fmtBoolean(v)
   355  	default:
   356  		p.badVerb(verb)
   357  	}
   358  }
   359  
   360  // fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
   361  // not, as requested, by temporarily setting the sharp flag.
   362  func (p *pp) fmt0x64(v uint64, leading0x bool) {
   363  	sharp := p.fmt.sharp
   364  	p.fmt.sharp = leading0x
   365  	p.fmt.fmtInteger(v, 16, unsigned, 'v', ldigits)
   366  	p.fmt.sharp = sharp
   367  }
   368  
   369  // fmtInteger formats a signed or unsigned integer.
   370  func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
   371  	switch verb {
   372  	case 'v':
   373  		if p.fmt.sharpV && !isSigned {
   374  			p.fmt0x64(v, true)
   375  		} else {
   376  			p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
   377  		}
   378  	case 'd':
   379  		p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
   380  	case 'b':
   381  		p.fmt.fmtInteger(v, 2, isSigned, verb, ldigits)
   382  	case 'o', 'O':
   383  		p.fmt.fmtInteger(v, 8, isSigned, verb, ldigits)
   384  	case 'x':
   385  		p.fmt.fmtInteger(v, 16, isSigned, verb, ldigits)
   386  	case 'X':
   387  		p.fmt.fmtInteger(v, 16, isSigned, verb, udigits)
   388  	case 'c':
   389  		p.fmt.fmtC(v)
   390  	case 'q':
   391  		p.fmt.fmtQc(v)
   392  	case 'U':
   393  		p.fmt.fmtUnicode(v)
   394  	default:
   395  		p.badVerb(verb)
   396  	}
   397  }
   398  
   399  // fmtFloat formats a float. The default precision for each verb
   400  // is specified as last argument in the call to fmt_float.
   401  func (p *pp) fmtFloat(v float64, size int, verb rune) {
   402  	switch verb {
   403  	case 'v':
   404  		p.fmt.fmtFloat(v, size, 'g', -1)
   405  	case 'b', 'g', 'G', 'x', 'X':
   406  		p.fmt.fmtFloat(v, size, verb, -1)
   407  	case 'f', 'e', 'E':
   408  		p.fmt.fmtFloat(v, size, verb, 6)
   409  	case 'F':
   410  		p.fmt.fmtFloat(v, size, 'f', 6)
   411  	default:
   412  		p.badVerb(verb)
   413  	}
   414  }
   415  
   416  // fmtComplex formats a complex number v with
   417  // r = real(v) and j = imag(v) as (r+ji) using
   418  // fmtFloat for r and j formatting.
   419  func (p *pp) fmtComplex(v complex128, size int, verb rune) {
   420  	// Make sure any unsupported verbs are found before the
   421  	// calls to fmtFloat to not generate an incorrect error string.
   422  	switch verb {
   423  	case 'v', 'b', 'g', 'G', 'x', 'X', 'f', 'F', 'e', 'E':
   424  		oldPlus := p.fmt.plus
   425  		p.buf.writeByte('(')
   426  		p.fmtFloat(real(v), size/2, verb)
   427  		// Imaginary part always has a sign.
   428  		p.fmt.plus = true
   429  		p.fmtFloat(imag(v), size/2, verb)
   430  		p.buf.writeString("i)")
   431  		p.fmt.plus = oldPlus
   432  	default:
   433  		p.badVerb(verb)
   434  	}
   435  }
   436  
   437  func (p *pp) fmtString(v string, verb rune) {
   438  	switch verb {
   439  	case 'v':
   440  		if p.fmt.sharpV {
   441  			p.fmt.fmtQ(v)
   442  		} else {
   443  			p.fmt.fmtS(v)
   444  		}
   445  	case 's':
   446  		p.fmt.fmtS(v)
   447  	case 'x':
   448  		p.fmt.fmtSx(v, ldigits)
   449  	case 'X':
   450  		p.fmt.fmtSx(v, udigits)
   451  	case 'q':
   452  		p.fmt.fmtQ(v)
   453  	default:
   454  		p.badVerb(verb)
   455  	}
   456  }
   457  
   458  func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
   459  	switch verb {
   460  	case 'v', 'd':
   461  		if p.fmt.sharpV {
   462  			p.buf.writeString(typeString)
   463  			if v == nil {
   464  				p.buf.writeString(nilParenString)
   465  				return
   466  			}
   467  			p.buf.writeByte('{')
   468  			for i, c := range v {
   469  				if i > 0 {
   470  					p.buf.writeString(commaSpaceString)
   471  				}
   472  				p.fmt0x64(uint64(c), true)
   473  			}
   474  			p.buf.writeByte('}')
   475  		} else {
   476  			p.buf.writeByte('[')
   477  			for i, c := range v {
   478  				if i > 0 {
   479  					p.buf.writeByte(' ')
   480  				}
   481  				p.fmt.fmtInteger(uint64(c), 10, unsigned, verb, ldigits)
   482  			}
   483  			p.buf.writeByte(']')
   484  		}
   485  	case 's':
   486  		p.fmt.fmtBs(v)
   487  	case 'x':
   488  		p.fmt.fmtBx(v, ldigits)
   489  	case 'X':
   490  		p.fmt.fmtBx(v, udigits)
   491  	case 'q':
   492  		p.fmt.fmtQ(string(v))
   493  	default:
   494  		p.printValue(reflect.ValueOf(v), verb, 0)
   495  	}
   496  }
   497  
   498  func (p *pp) fmtPointer(value reflect.Value, verb rune) {
   499  	var u uintptr
   500  	switch value.Kind() {
   501  	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
   502  		u = value.Pointer()
   503  	default:
   504  		p.badVerb(verb)
   505  		return
   506  	}
   507  
   508  	switch verb {
   509  	case 'v':
   510  		if p.fmt.sharpV {
   511  			p.buf.writeByte('(')
   512  			p.buf.writeString(value.Type().String())
   513  			p.buf.writeString(")(")
   514  			if u == 0 {
   515  				p.buf.writeString(nilString)
   516  			} else {
   517  				p.fmt0x64(uint64(u), true)
   518  			}
   519  			p.buf.writeByte(')')
   520  		} else {
   521  			if u == 0 {
   522  				p.fmt.padString(nilAngleString)
   523  			} else {
   524  				p.fmt0x64(uint64(u), !p.fmt.sharp)
   525  			}
   526  		}
   527  	case 'p':
   528  		p.fmt0x64(uint64(u), !p.fmt.sharp)
   529  	case 'b', 'o', 'd', 'x', 'X':
   530  		p.fmtInteger(uint64(u), unsigned, verb)
   531  	default:
   532  		p.badVerb(verb)
   533  	}
   534  }
   535  
   536  func (p *pp) catchPanic(arg interface{}, verb rune, method string) {
   537  	if err := recover(); err != nil {
   538  		// If it's a nil pointer, just say "<nil>". The likeliest causes are a
   539  		// Stringer that fails to guard against nil or a nil pointer for a
   540  		// value receiver, and in either case, "<nil>" is a nice result.
   541  		if v := reflect.ValueOf(arg); v.Kind() == reflect.Ptr && v.IsNil() {
   542  			p.buf.writeString(nilAngleString)
   543  			return
   544  		}
   545  		// Otherwise print a concise panic message. Most of the time the panic
   546  		// value will print itself nicely.
   547  		if p.panicking {
   548  			// Nested panics; the recursion in printArg cannot succeed.
   549  			panic(err)
   550  		}
   551  
   552  		oldFlags := p.fmt.fmtFlags
   553  		// For this output we want default behavior.
   554  		p.fmt.clearflags()
   555  
   556  		p.buf.writeString(percentBangString)
   557  		p.buf.writeRune(verb)
   558  		p.buf.writeString(panicString)
   559  		p.buf.writeString(method)
   560  		p.buf.writeString(" method: ")
   561  		p.panicking = true
   562  		p.printArg(err, 'v')
   563  		p.panicking = false
   564  		p.buf.writeByte(')')
   565  
   566  		p.fmt.fmtFlags = oldFlags
   567  	}
   568  }
   569  
   570  func (p *pp) handleMethods(verb rune) (handled bool) {
   571  	if p.erroring {
   572  		return
   573  	}
   574  	if verb == 'w' {
   575  		// It is invalid to use %w other than with Errorf, more than once,
   576  		// or with a non-error arg.
   577  		err, ok := p.arg.(error)
   578  		if !ok || !p.wrapErrs || p.wrappedErr != nil {
   579  			p.wrappedErr = nil
   580  			p.wrapErrs = false
   581  			p.badVerb(verb)
   582  			return true
   583  		}
   584  		p.wrappedErr = err
   585  		// If the arg is a Formatter, pass 'v' as the verb to it.
   586  		verb = 'v'
   587  	}
   588  
   589  	// Is it a Formatter?
   590  	if formatter, ok := p.arg.(Formatter); ok {
   591  		handled = true
   592  		defer p.catchPanic(p.arg, verb, "Format")
   593  		formatter.Format(p, verb)
   594  		return
   595  	}
   596  
   597  	// If we're doing Go syntax and the argument knows how to supply it, take care of it now.
   598  	if p.fmt.sharpV {
   599  		if stringer, ok := p.arg.(GoStringer); ok {
   600  			handled = true
   601  			defer p.catchPanic(p.arg, verb, "GoString")
   602  			// Print the result of GoString unadorned.
   603  			p.fmt.fmtS(stringer.GoString())
   604  			return
   605  		}
   606  	} else {
   607  		// If a string is acceptable according to the format, see if
   608  		// the value satisfies one of the string-valued interfaces.
   609  		// Println etc. set verb to %v, which is "stringable".
   610  		switch verb {
   611  		case 'v', 's', 'x', 'X', 'q':
   612  			// Is it an error or Stringer?
   613  			// The duplication in the bodies is necessary:
   614  			// setting handled and deferring catchPanic
   615  			// must happen before calling the method.
   616  			switch v := p.arg.(type) {
   617  			case error:
   618  				handled = true
   619  				defer p.catchPanic(p.arg, verb, "Error")
   620  				p.fmtString(v.Error(), verb)
   621  				return
   622  
   623  			case Stringer:
   624  				handled = true
   625  				defer p.catchPanic(p.arg, verb, "String")
   626  				p.fmtString(v.String(), verb)
   627  				return
   628  			}
   629  		}
   630  	}
   631  	return false
   632  }
   633  
   634  func (p *pp) printArg(arg interface{}, verb rune) {
   635  	p.arg = arg
   636  	p.value = reflect.Value{}
   637  
   638  	if arg == nil {
   639  		switch verb {
   640  		case 'T', 'v':
   641  			p.fmt.padString(nilAngleString)
   642  		default:
   643  			p.badVerb(verb)
   644  		}
   645  		return
   646  	}
   647  
   648  	// Special processing considerations.
   649  	// %T (the value's type) and %p (its address) are special; we always do them first.
   650  	switch verb {
   651  	case 'T':
   652  		p.fmt.fmtS(reflect.TypeOf(arg).String())
   653  		return
   654  	case 'p':
   655  		p.fmtPointer(reflect.ValueOf(arg), 'p')
   656  		return
   657  	}
   658  
   659  	// Some types can be done without reflection.
   660  	switch f := arg.(type) {
   661  	case bool:
   662  		p.fmtBool(f, verb)
   663  	case float32:
   664  		p.fmtFloat(float64(f), 32, verb)
   665  	case float64:
   666  		p.fmtFloat(f, 64, verb)
   667  	case complex64:
   668  		p.fmtComplex(complex128(f), 64, verb)
   669  	case complex128:
   670  		p.fmtComplex(f, 128, verb)
   671  	case int:
   672  		p.fmtInteger(uint64(f), signed, verb)
   673  	case int8:
   674  		p.fmtInteger(uint64(f), signed, verb)
   675  	case int16:
   676  		p.fmtInteger(uint64(f), signed, verb)
   677  	case int32:
   678  		p.fmtInteger(uint64(f), signed, verb)
   679  	case int64:
   680  		p.fmtInteger(uint64(f), signed, verb)
   681  	case uint:
   682  		p.fmtInteger(uint64(f), unsigned, verb)
   683  	case uint8:
   684  		p.fmtInteger(uint64(f), unsigned, verb)
   685  	case uint16:
   686  		p.fmtInteger(uint64(f), unsigned, verb)
   687  	case uint32:
   688  		p.fmtInteger(uint64(f), unsigned, verb)
   689  	case uint64:
   690  		p.fmtInteger(f, unsigned, verb)
   691  	case uintptr:
   692  		p.fmtInteger(uint64(f), unsigned, verb)
   693  	case string:
   694  		p.fmtString(f, verb)
   695  	case []byte:
   696  		p.fmtBytes(f, verb, "[]byte")
   697  	case reflect.Value:
   698  		// Handle extractable values with special methods
   699  		// since printValue does not handle them at depth 0.
   700  		if f.IsValid() && f.CanInterface() {
   701  			p.arg = f.Interface()
   702  			if p.handleMethods(verb) {
   703  				return
   704  			}
   705  		}
   706  		p.printValue(f, verb, 0)
   707  	default:
   708  		// If the type is not simple, it might have methods.
   709  		if !p.handleMethods(verb) {
   710  			// Need to use reflection, since the type had no
   711  			// interface methods that could be used for formatting.
   712  			p.printValue(reflect.ValueOf(f), verb, 0)
   713  		}
   714  	}
   715  }
   716  
   717  // printValue is similar to printArg but starts with a reflect value, not an interface{} value.
   718  // It does not handle 'p' and 'T' verbs because these should have been already handled by printArg.
   719  func (p *pp) printValue(value reflect.Value, verb rune, depth int) {
   720  	// Handle values with special methods if not already handled by printArg (depth == 0).
   721  	if depth > 0 && value.IsValid() && value.CanInterface() {
   722  		p.arg = value.Interface()
   723  		if p.handleMethods(verb) {
   724  			return
   725  		}
   726  	}
   727  	p.arg = nil
   728  	p.value = value
   729  
   730  	switch f := value; value.Kind() {
   731  	case reflect.Invalid:
   732  		if depth == 0 {
   733  			p.buf.writeString(invReflectString)
   734  		} else {
   735  			switch verb {
   736  			case 'v':
   737  				p.buf.writeString(nilAngleString)
   738  			default:
   739  				p.badVerb(verb)
   740  			}
   741  		}
   742  	case reflect.Bool:
   743  		p.fmtBool(f.Bool(), verb)
   744  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   745  		p.fmtInteger(uint64(f.Int()), signed, verb)
   746  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   747  		p.fmtInteger(f.Uint(), unsigned, verb)
   748  	case reflect.Float32:
   749  		p.fmtFloat(f.Float(), 32, verb)
   750  	case reflect.Float64:
   751  		p.fmtFloat(f.Float(), 64, verb)
   752  	case reflect.Complex64:
   753  		p.fmtComplex(f.Complex(), 64, verb)
   754  	case reflect.Complex128:
   755  		p.fmtComplex(f.Complex(), 128, verb)
   756  	case reflect.String:
   757  		p.fmtString(f.String(), verb)
   758  	case reflect.Map:
   759  		if p.fmt.sharpV {
   760  			p.buf.writeString(f.Type().String())
   761  			if f.IsNil() {
   762  				p.buf.writeString(nilParenString)
   763  				return
   764  			}
   765  			p.buf.writeByte('{')
   766  		} else {
   767  			p.buf.writeString(mapString)
   768  		}
   769  		sorted := fmtsort.Sort(f)
   770  		for i, key := range sorted.Key {
   771  			if i > 0 {
   772  				if p.fmt.sharpV {
   773  					p.buf.writeString(commaSpaceString)
   774  				} else {
   775  					p.buf.writeByte(' ')
   776  				}
   777  			}
   778  			p.printValue(key, verb, depth+1)
   779  			p.buf.writeByte(':')
   780  			p.printValue(sorted.Value[i], verb, depth+1)
   781  		}
   782  		if p.fmt.sharpV {
   783  			p.buf.writeByte('}')
   784  		} else {
   785  			p.buf.writeByte(']')
   786  		}
   787  	case reflect.Struct:
   788  		if p.fmt.sharpV {
   789  			p.buf.writeString(f.Type().String())
   790  		}
   791  		p.buf.writeByte('{')
   792  		for i := 0; i < f.NumField(); i++ {
   793  			if i > 0 {
   794  				if p.fmt.sharpV {
   795  					p.buf.writeString(commaSpaceString)
   796  				} else {
   797  					p.buf.writeByte(' ')
   798  				}
   799  			}
   800  			if p.fmt.plusV || p.fmt.sharpV {
   801  				if name := f.Type().Field(i).Name; name != "" {
   802  					p.buf.writeString(name)
   803  					p.buf.writeByte(':')
   804  				}
   805  			}
   806  			p.printValue(getField(f, i), verb, depth+1)
   807  		}
   808  		p.buf.writeByte('}')
   809  	case reflect.Interface:
   810  		value := f.Elem()
   811  		if !value.IsValid() {
   812  			if p.fmt.sharpV {
   813  				p.buf.writeString(f.Type().String())
   814  				p.buf.writeString(nilParenString)
   815  			} else {
   816  				p.buf.writeString(nilAngleString)
   817  			}
   818  		} else {
   819  			p.printValue(value, verb, depth+1)
   820  		}
   821  	case reflect.Array, reflect.Slice:
   822  		switch verb {
   823  		case 's', 'q', 'x', 'X':
   824  			// Handle byte and uint8 slices and arrays special for the above verbs.
   825  			t := f.Type()
   826  			if t.Elem().Kind() == reflect.Uint8 {
   827  				var bytes []byte
   828  				if f.Kind() == reflect.Slice {
   829  					bytes = f.Bytes()
   830  				} else if f.CanAddr() {
   831  					bytes = f.Slice(0, f.Len()).Bytes()
   832  				} else {
   833  					// We have an array, but we cannot Slice() a non-addressable array,
   834  					// so we build a slice by hand. This is a rare case but it would be nice
   835  					// if reflection could help a little more.
   836  					bytes = make([]byte, f.Len())
   837  					for i := range bytes {
   838  						bytes[i] = byte(f.Index(i).Uint())
   839  					}
   840  				}
   841  				p.fmtBytes(bytes, verb, t.String())
   842  				return
   843  			}
   844  		}
   845  		if p.fmt.sharpV {
   846  			p.buf.writeString(f.Type().String())
   847  			if f.Kind() == reflect.Slice && f.IsNil() {
   848  				p.buf.writeString(nilParenString)
   849  				return
   850  			}
   851  			p.buf.writeByte('{')
   852  			for i := 0; i < f.Len(); i++ {
   853  				if i > 0 {
   854  					p.buf.writeString(commaSpaceString)
   855  				}
   856  				p.printValue(f.Index(i), verb, depth+1)
   857  			}
   858  			p.buf.writeByte('}')
   859  		} else {
   860  			p.buf.writeByte('[')
   861  			for i := 0; i < f.Len(); i++ {
   862  				if i > 0 {
   863  					p.buf.writeByte(' ')
   864  				}
   865  				p.printValue(f.Index(i), verb, depth+1)
   866  			}
   867  			p.buf.writeByte(']')
   868  		}
   869  	case reflect.Ptr:
   870  		// pointer to array or slice or struct? ok at top level
   871  		// but not embedded (avoid loops)
   872  		if depth == 0 && f.Pointer() != 0 {
   873  			switch a := f.Elem(); a.Kind() {
   874  			case reflect.Array, reflect.Slice, reflect.Struct, reflect.Map:
   875  				p.buf.writeByte('&')
   876  				p.printValue(a, verb, depth+1)
   877  				return
   878  			}
   879  		}
   880  		fallthrough
   881  	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
   882  		p.fmtPointer(f, verb)
   883  	default:
   884  		p.unknownType(f)
   885  	}
   886  }
   887  
   888  // intFromArg gets the argNumth element of a. On return, isInt reports whether the argument has integer type.
   889  func intFromArg(a []interface{}, argNum int) (num int, isInt bool, newArgNum int) {
   890  	newArgNum = argNum
   891  	if argNum < len(a) {
   892  		num, isInt = a[argNum].(int) // Almost always OK.
   893  		if !isInt {
   894  			// Work harder.
   895  			switch v := reflect.ValueOf(a[argNum]); v.Kind() {
   896  			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   897  				n := v.Int()
   898  				if int64(int(n)) == n {
   899  					num = int(n)
   900  					isInt = true
   901  				}
   902  			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   903  				n := v.Uint()
   904  				if int64(n) >= 0 && uint64(int(n)) == n {
   905  					num = int(n)
   906  					isInt = true
   907  				}
   908  			default:
   909  				// Already 0, false.
   910  			}
   911  		}
   912  		newArgNum = argNum + 1
   913  		if tooLarge(num) {
   914  			num = 0
   915  			isInt = false
   916  		}
   917  	}
   918  	return
   919  }
   920  
   921  // parseArgNumber returns the value of the bracketed number, minus 1
   922  // (explicit argument numbers are one-indexed but we want zero-indexed).
   923  // The opening bracket is known to be present at format[0].
   924  // The returned values are the index, the number of bytes to consume
   925  // up to the closing paren, if present, and whether the number parsed
   926  // ok. The bytes to consume will be 1 if no closing paren is present.
   927  func parseArgNumber(format string) (index int, wid int, ok bool) {
   928  	// There must be at least 3 bytes: [n].
   929  	if len(format) < 3 {
   930  		return 0, 1, false
   931  	}
   932  
   933  	// Find closing bracket.
   934  	for i := 1; i < len(format); i++ {
   935  		if format[i] == ']' {
   936  			width, ok, newi := parsenum(format, 1, i)
   937  			if !ok || newi != i {
   938  				return 0, i + 1, false
   939  			}
   940  			return width - 1, i + 1, true // arg numbers are one-indexed and skip paren.
   941  		}
   942  	}
   943  	return 0, 1, false
   944  }
   945  
   946  // argNumber returns the next argument to evaluate, which is either the value of the passed-in
   947  // argNum or the value of the bracketed integer that begins format[i:]. It also returns
   948  // the new value of i, that is, the index of the next byte of the format to process.
   949  func (p *pp) argNumber(argNum int, format string, i int, numArgs int) (newArgNum, newi int, found bool) {
   950  	if len(format) <= i || format[i] != '[' {
   951  		return argNum, i, false
   952  	}
   953  	p.reordered = true
   954  	index, wid, ok := parseArgNumber(format[i:])
   955  	if ok && 0 <= index && index < numArgs {
   956  		return index, i + wid, true
   957  	}
   958  	p.goodArgNum = false
   959  	return argNum, i + wid, ok
   960  }
   961  
   962  func (p *pp) badArgNum(verb rune) {
   963  	p.buf.writeString(percentBangString)
   964  	p.buf.writeRune(verb)
   965  	p.buf.writeString(badIndexString)
   966  }
   967  
   968  func (p *pp) missingArg(verb rune) {
   969  	p.buf.writeString(percentBangString)
   970  	p.buf.writeRune(verb)
   971  	p.buf.writeString(missingString)
   972  }
   973  
   974  func (p *pp) doPrintf(format string, a []interface{}) {
   975  	end := len(format)
   976  	argNum := 0         // we process one argument per non-trivial format
   977  	afterIndex := false // previous item in format was an index like [3].
   978  	p.reordered = false
   979  formatLoop:
   980  	for i := 0; i < end; {
   981  		p.goodArgNum = true
   982  		lasti := i
   983  		for i < end && format[i] != '%' {
   984  			i++
   985  		}
   986  		if i > lasti {
   987  			p.buf.writeString(format[lasti:i])
   988  		}
   989  		if i >= end {
   990  			// done processing format string
   991  			break
   992  		}
   993  
   994  		// Process one verb
   995  		i++
   996  
   997  		// Do we have flags?
   998  		p.fmt.clearflags()
   999  	simpleFormat:
  1000  		for ; i < end; i++ {
  1001  			c := format[i]
  1002  			switch c {
  1003  			case '#':
  1004  				p.fmt.sharp = true
  1005  			case '0':
  1006  				p.fmt.zero = !p.fmt.minus // Only allow zero padding to the left.
  1007  			case '+':
  1008  				p.fmt.plus = true
  1009  			case '-':
  1010  				p.fmt.minus = true
  1011  				p.fmt.zero = false // Do not pad with zeros to the right.
  1012  			case ' ':
  1013  				p.fmt.space = true
  1014  			default:
  1015  				// Fast path for common case of ascii lower case simple verbs
  1016  				// without precision or width or argument indices.
  1017  				if 'a' <= c && c <= 'z' && argNum < len(a) {
  1018  					if c == 'v' {
  1019  						// Go syntax
  1020  						p.fmt.sharpV = p.fmt.sharp
  1021  						p.fmt.sharp = false
  1022  						// Struct-field syntax
  1023  						p.fmt.plusV = p.fmt.plus
  1024  						p.fmt.plus = false
  1025  					}
  1026  					p.printArg(a[argNum], rune(c))
  1027  					argNum++
  1028  					i++
  1029  					continue formatLoop
  1030  				}
  1031  				// Format is more complex than simple flags and a verb or is malformed.
  1032  				break simpleFormat
  1033  			}
  1034  		}
  1035  
  1036  		// Do we have an explicit argument index?
  1037  		argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  1038  
  1039  		// Do we have width?
  1040  		if i < end && format[i] == '*' {
  1041  			i++
  1042  			p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)
  1043  
  1044  			if !p.fmt.widPresent {
  1045  				p.buf.writeString(badWidthString)
  1046  			}
  1047  
  1048  			// We have a negative width, so take its value and ensure
  1049  			// that the minus flag is set
  1050  			if p.fmt.wid < 0 {
  1051  				p.fmt.wid = -p.fmt.wid
  1052  				p.fmt.minus = true
  1053  				p.fmt.zero = false // Do not pad with zeros to the right.
  1054  			}
  1055  			afterIndex = false
  1056  		} else {
  1057  			p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
  1058  			if afterIndex && p.fmt.widPresent { // "%[3]2d"
  1059  				p.goodArgNum = false
  1060  			}
  1061  		}
  1062  
  1063  		// Do we have precision?
  1064  		if i+1 < end && format[i] == '.' {
  1065  			i++
  1066  			if afterIndex { // "%[3].2d"
  1067  				p.goodArgNum = false
  1068  			}
  1069  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  1070  			if i < end && format[i] == '*' {
  1071  				i++
  1072  				p.fmt.prec, p.fmt.precPresent, argNum = intFromArg(a, argNum)
  1073  				// Negative precision arguments don't make sense
  1074  				if p.fmt.prec < 0 {
  1075  					p.fmt.prec = 0
  1076  					p.fmt.precPresent = false
  1077  				}
  1078  				if !p.fmt.precPresent {
  1079  					p.buf.writeString(badPrecString)
  1080  				}
  1081  				afterIndex = false
  1082  			} else {
  1083  				p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i, end)
  1084  				if !p.fmt.precPresent {
  1085  					p.fmt.prec = 0
  1086  					p.fmt.precPresent = true
  1087  				}
  1088  			}
  1089  		}
  1090  
  1091  		if !afterIndex {
  1092  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  1093  		}
  1094  
  1095  		if i >= end {
  1096  			p.buf.writeString(noVerbString)
  1097  			break
  1098  		}
  1099  
  1100  		verb, size := rune(format[i]), 1
  1101  		if verb >= utf8.RuneSelf {
  1102  			verb, size = utf8.DecodeRuneInString(format[i:])
  1103  		}
  1104  		i += size
  1105  
  1106  		switch {
  1107  		case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
  1108  			p.buf.writeByte('%')
  1109  		case !p.goodArgNum:
  1110  			p.badArgNum(verb)
  1111  		case argNum >= len(a): // No argument left over to print for the current verb.
  1112  			p.missingArg(verb)
  1113  		case verb == 'v':
  1114  			// Go syntax
  1115  			p.fmt.sharpV = p.fmt.sharp
  1116  			p.fmt.sharp = false
  1117  			// Struct-field syntax
  1118  			p.fmt.plusV = p.fmt.plus
  1119  			p.fmt.plus = false
  1120  			fallthrough
  1121  		default:
  1122  			p.printArg(a[argNum], verb)
  1123  			argNum++
  1124  		}
  1125  	}
  1126  
  1127  	// Check for extra arguments unless the call accessed the arguments
  1128  	// out of order, in which case it's too expensive to detect if they've all
  1129  	// been used and arguably OK if they're not.
  1130  	if !p.reordered && argNum < len(a) {
  1131  		p.fmt.clearflags()
  1132  		p.buf.writeString(extraString)
  1133  		for i, arg := range a[argNum:] {
  1134  			if i > 0 {
  1135  				p.buf.writeString(commaSpaceString)
  1136  			}
  1137  			if arg == nil {
  1138  				p.buf.writeString(nilAngleString)
  1139  			} else {
  1140  				p.buf.writeString(reflect.TypeOf(arg).String())
  1141  				p.buf.writeByte('=')
  1142  				p.printArg(arg, 'v')
  1143  			}
  1144  		}
  1145  		p.buf.writeByte(')')
  1146  	}
  1147  }
  1148  
  1149  func (p *pp) doPrint(a []interface{}) {
  1150  	prevString := false
  1151  	for argNum, arg := range a {
  1152  		isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
  1153  		// Add a space between two non-string arguments.
  1154  		if argNum > 0 && !isString && !prevString {
  1155  			p.buf.writeByte(' ')
  1156  		}
  1157  		p.printArg(arg, 'v')
  1158  		prevString = isString
  1159  	}
  1160  }
  1161  
  1162  // doPrintln is like doPrint but always adds a space between arguments
  1163  // and a newline after the last argument.
  1164  func (p *pp) doPrintln(a []interface{}) {
  1165  	for argNum, arg := range a {
  1166  		if argNum > 0 {
  1167  			p.buf.writeByte(' ')
  1168  		}
  1169  		p.printArg(arg, 'v')
  1170  	}
  1171  	p.buf.writeByte('\n')
  1172  }
  1173  

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