error.go

Documentation: runtime

     1  // Copyright 2010 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 runtime
     6  
     7  import "internal/bytealg"
     8  
     9  // The Error interface identifies a run time error.
    10  type Error interface {
    11  	error
    12  
    13  	// RuntimeError is a no-op function but
    14  	// serves to distinguish types that are run time
    15  	// errors from ordinary errors: a type is a
    16  	// run time error if it has a RuntimeError method.
    17  	RuntimeError()
    18  }
    19  
    20  // A TypeAssertionError explains a failed type assertion.
    21  type TypeAssertionError struct {
    22  	_interface    *_type
    23  	concrete      *_type
    24  	asserted      *_type
    25  	missingMethod string // one method needed by Interface, missing from Concrete
    26  }
    27  
    28  func (*TypeAssertionError) RuntimeError() {}
    29  
    30  func (e *TypeAssertionError) Error() string {
    31  	inter := "interface"
    32  	if e._interface != nil {
    33  		inter = e._interface.string()
    34  	}
    35  	as := e.asserted.string()
    36  	if e.concrete == nil {
    37  		return "interface conversion: " + inter + " is nil, not " + as
    38  	}
    39  	cs := e.concrete.string()
    40  	if e.missingMethod == "" {
    41  		msg := "interface conversion: " + inter + " is " + cs + ", not " + as
    42  		if cs == as {
    43  			// provide slightly clearer error message
    44  			if e.concrete.pkgpath() != e.asserted.pkgpath() {
    45  				msg += " (types from different packages)"
    46  			} else {
    47  				msg += " (types from different scopes)"
    48  			}
    49  		}
    50  		return msg
    51  	}
    52  	return "interface conversion: " + cs + " is not " + as +
    53  		": missing method " + e.missingMethod
    54  }
    55  
    56  //go:nosplit
    57  // itoa converts val to a decimal representation. The result is
    58  // written somewhere within buf and the location of the result is returned.
    59  // buf must be at least 20 bytes.
    60  func itoa(buf []byte, val uint64) []byte {
    61  	i := len(buf) - 1
    62  	for val >= 10 {
    63  		buf[i] = byte(val%10 + '0')
    64  		i--
    65  		val /= 10
    66  	}
    67  	buf[i] = byte(val + '0')
    68  	return buf[i:]
    69  }
    70  
    71  // An errorString represents a runtime error described by a single string.
    72  type errorString string
    73  
    74  func (e errorString) RuntimeError() {}
    75  
    76  func (e errorString) Error() string {
    77  	return "runtime error: " + string(e)
    78  }
    79  
    80  type errorAddressString struct {
    81  	msg  string  // error message
    82  	addr uintptr // memory address where the error occurred
    83  }
    84  
    85  func (e errorAddressString) RuntimeError() {}
    86  
    87  func (e errorAddressString) Error() string {
    88  	return "runtime error: " + e.msg
    89  }
    90  
    91  // Addr returns the memory address where a fault occurred.
    92  // The address provided is best-effort.
    93  // The veracity of the result may depend on the platform.
    94  // Errors providing this method will only be returned as
    95  // a result of using runtime/debug.SetPanicOnFault.
    96  func (e errorAddressString) Addr() uintptr {
    97  	return e.addr
    98  }
    99  
   100  // plainError represents a runtime error described a string without
   101  // the prefix "runtime error: " after invoking errorString.Error().
   102  // See Issue #14965.
   103  type plainError string
   104  
   105  func (e plainError) RuntimeError() {}
   106  
   107  func (e plainError) Error() string {
   108  	return string(e)
   109  }
   110  
   111  // A boundsError represents an indexing or slicing operation gone wrong.
   112  type boundsError struct {
   113  	x int64
   114  	y int
   115  	// Values in an index or slice expression can be signed or unsigned.
   116  	// That means we'd need 65 bits to encode all possible indexes, from -2^63 to 2^64-1.
   117  	// Instead, we keep track of whether x should be interpreted as signed or unsigned.
   118  	// y is known to be nonnegative and to fit in an int.
   119  	signed bool
   120  	code   boundsErrorCode
   121  }
   122  
   123  type boundsErrorCode uint8
   124  
   125  const (
   126  	boundsIndex boundsErrorCode = iota // s[x], 0 <= x < len(s) failed
   127  
   128  	boundsSliceAlen // s[?:x], 0 <= x <= len(s) failed
   129  	boundsSliceAcap // s[?:x], 0 <= x <= cap(s) failed
   130  	boundsSliceB    // s[x:y], 0 <= x <= y failed (but boundsSliceA didn't happen)
   131  
   132  	boundsSlice3Alen // s[?:?:x], 0 <= x <= len(s) failed
   133  	boundsSlice3Acap // s[?:?:x], 0 <= x <= cap(s) failed
   134  	boundsSlice3B    // s[?:x:y], 0 <= x <= y failed (but boundsSlice3A didn't happen)
   135  	boundsSlice3C    // s[x:y:?], 0 <= x <= y failed (but boundsSlice3A/B didn't happen)
   136  
   137  	// Note: in the above, len(s) and cap(s) are stored in y
   138  )
   139  
   140  // boundsErrorFmts provide error text for various out-of-bounds panics.
   141  // Note: if you change these strings, you should adjust the size of the buffer
   142  // in boundsError.Error below as well.
   143  var boundsErrorFmts = [...]string{
   144  	boundsIndex:      "index out of range [%x] with length %y",
   145  	boundsSliceAlen:  "slice bounds out of range [:%x] with length %y",
   146  	boundsSliceAcap:  "slice bounds out of range [:%x] with capacity %y",
   147  	boundsSliceB:     "slice bounds out of range [%x:%y]",
   148  	boundsSlice3Alen: "slice bounds out of range [::%x] with length %y",
   149  	boundsSlice3Acap: "slice bounds out of range [::%x] with capacity %y",
   150  	boundsSlice3B:    "slice bounds out of range [:%x:%y]",
   151  	boundsSlice3C:    "slice bounds out of range [%x:%y:]",
   152  }
   153  
   154  // boundsNegErrorFmts are overriding formats if x is negative. In this case there's no need to report y.
   155  var boundsNegErrorFmts = [...]string{
   156  	boundsIndex:      "index out of range [%x]",
   157  	boundsSliceAlen:  "slice bounds out of range [:%x]",
   158  	boundsSliceAcap:  "slice bounds out of range [:%x]",
   159  	boundsSliceB:     "slice bounds out of range [%x:]",
   160  	boundsSlice3Alen: "slice bounds out of range [::%x]",
   161  	boundsSlice3Acap: "slice bounds out of range [::%x]",
   162  	boundsSlice3B:    "slice bounds out of range [:%x:]",
   163  	boundsSlice3C:    "slice bounds out of range [%x::]",
   164  }
   165  
   166  func (e boundsError) RuntimeError() {}
   167  
   168  func appendIntStr(b []byte, v int64, signed bool) []byte {
   169  	if signed && v < 0 {
   170  		b = append(b, '-')
   171  		v = -v
   172  	}
   173  	var buf [20]byte
   174  	b = append(b, itoa(buf[:], uint64(v))...)
   175  	return b
   176  }
   177  
   178  func (e boundsError) Error() string {
   179  	fmt := boundsErrorFmts[e.code]
   180  	if e.signed && e.x < 0 {
   181  		fmt = boundsNegErrorFmts[e.code]
   182  	}
   183  	// max message length is 99: "runtime error: slice bounds out of range [::%x] with capacity %y"
   184  	// x can be at most 20 characters. y can be at most 19.
   185  	b := make([]byte, 0, 100)
   186  	b = append(b, "runtime error: "...)
   187  	for i := 0; i < len(fmt); i++ {
   188  		c := fmt[i]
   189  		if c != '%' {
   190  			b = append(b, c)
   191  			continue
   192  		}
   193  		i++
   194  		switch fmt[i] {
   195  		case 'x':
   196  			b = appendIntStr(b, e.x, e.signed)
   197  		case 'y':
   198  			b = appendIntStr(b, int64(e.y), true)
   199  		}
   200  	}
   201  	return string(b)
   202  }
   203  
   204  type stringer interface {
   205  	String() string
   206  }
   207  
   208  // printany prints an argument passed to panic.
   209  // If panic is called with a value that has a String or Error method,
   210  // it has already been converted into a string by preprintpanics.
   211  func printany(i interface{}) {
   212  	switch v := i.(type) {
   213  	case nil:
   214  		print("nil")
   215  	case bool:
   216  		print(v)
   217  	case int:
   218  		print(v)
   219  	case int8:
   220  		print(v)
   221  	case int16:
   222  		print(v)
   223  	case int32:
   224  		print(v)
   225  	case int64:
   226  		print(v)
   227  	case uint:
   228  		print(v)
   229  	case uint8:
   230  		print(v)
   231  	case uint16:
   232  		print(v)
   233  	case uint32:
   234  		print(v)
   235  	case uint64:
   236  		print(v)
   237  	case uintptr:
   238  		print(v)
   239  	case float32:
   240  		print(v)
   241  	case float64:
   242  		print(v)
   243  	case complex64:
   244  		print(v)
   245  	case complex128:
   246  		print(v)
   247  	case string:
   248  		print(v)
   249  	default:
   250  		printanycustomtype(i)
   251  	}
   252  }
   253  
   254  func printanycustomtype(i interface{}) {
   255  	eface := efaceOf(&i)
   256  	typestring := eface._type.string()
   257  
   258  	switch eface._type.kind {
   259  	case kindString:
   260  		print(typestring, `("`, *(*string)(eface.data), `")`)
   261  	case kindBool:
   262  		print(typestring, "(", *(*bool)(eface.data), ")")
   263  	case kindInt:
   264  		print(typestring, "(", *(*int)(eface.data), ")")
   265  	case kindInt8:
   266  		print(typestring, "(", *(*int8)(eface.data), ")")
   267  	case kindInt16:
   268  		print(typestring, "(", *(*int16)(eface.data), ")")
   269  	case kindInt32:
   270  		print(typestring, "(", *(*int32)(eface.data), ")")
   271  	case kindInt64:
   272  		print(typestring, "(", *(*int64)(eface.data), ")")
   273  	case kindUint:
   274  		print(typestring, "(", *(*uint)(eface.data), ")")
   275  	case kindUint8:
   276  		print(typestring, "(", *(*uint8)(eface.data), ")")
   277  	case kindUint16:
   278  		print(typestring, "(", *(*uint16)(eface.data), ")")
   279  	case kindUint32:
   280  		print(typestring, "(", *(*uint32)(eface.data), ")")
   281  	case kindUint64:
   282  		print(typestring, "(", *(*uint64)(eface.data), ")")
   283  	case kindUintptr:
   284  		print(typestring, "(", *(*uintptr)(eface.data), ")")
   285  	case kindFloat32:
   286  		print(typestring, "(", *(*float32)(eface.data), ")")
   287  	case kindFloat64:
   288  		print(typestring, "(", *(*float64)(eface.data), ")")
   289  	case kindComplex64:
   290  		print(typestring, *(*complex64)(eface.data))
   291  	case kindComplex128:
   292  		print(typestring, *(*complex128)(eface.data))
   293  	default:
   294  		print("(", typestring, ") ", eface.data)
   295  	}
   296  }
   297  
   298  // panicwrap generates a panic for a call to a wrapped value method
   299  // with a nil pointer receiver.
   300  //
   301  // It is called from the generated wrapper code.
   302  func panicwrap() {
   303  	pc := getcallerpc()
   304  	name := funcname(findfunc(pc))
   305  	// name is something like "main.(*T).F".
   306  	// We want to extract pkg ("main"), typ ("T"), and meth ("F").
   307  	// Do it by finding the parens.
   308  	i := bytealg.IndexByteString(name, '(')
   309  	if i < 0 {
   310  		throw("panicwrap: no ( in " + name)
   311  	}
   312  	pkg := name[:i-1]
   313  	if i+2 >= len(name) || name[i-1:i+2] != ".(*" {
   314  		throw("panicwrap: unexpected string after package name: " + name)
   315  	}
   316  	name = name[i+2:]
   317  	i = bytealg.IndexByteString(name, ')')
   318  	if i < 0 {
   319  		throw("panicwrap: no ) in " + name)
   320  	}
   321  	if i+2 >= len(name) || name[i:i+2] != ")." {
   322  		throw("panicwrap: unexpected string after type name: " + name)
   323  	}
   324  	typ := name[:i]
   325  	meth := name[i+2:]
   326  	panic(plainError("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer"))
   327  }
   328
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