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 _ "unsafe" // for go:linkname
     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  	interfaceString string
    23  	concreteString  string
    24  	assertedString  string
    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 := e.interfaceString
    32  	if inter == "" {
    33  		inter = "interface"
    34  	}
    35  	if e.concreteString == "" {
    36  		return "interface conversion: " + inter + " is nil, not " + e.assertedString
    37  	}
    38  	if e.missingMethod == "" {
    39  		return "interface conversion: " + inter + " is " + e.concreteString +
    40  			", not " + e.assertedString
    41  	}
    42  	return "interface conversion: " + e.concreteString + " is not " + e.assertedString +
    43  		": missing method " + e.missingMethod
    44  }
    45  
    46  // An errorString represents a runtime error described by a single string.
    47  type errorString string
    48  
    49  func (e errorString) RuntimeError() {}
    50  
    51  func (e errorString) Error() string {
    52  	return "runtime error: " + string(e)
    53  }
    54  
    55  // plainError represents a runtime error described a string without
    56  // the prefix "runtime error: " after invoking errorString.Error().
    57  // See Issue #14965.
    58  type plainError string
    59  
    60  func (e plainError) RuntimeError() {}
    61  
    62  func (e plainError) Error() string {
    63  	return string(e)
    64  }
    65  
    66  type stringer interface {
    67  	String() string
    68  }
    69  
    70  func typestring(x interface{}) string {
    71  	e := efaceOf(&x)
    72  	return e._type.string()
    73  }
    74  
    75  // printany prints an argument passed to panic.
    76  // If panic is called with a value that has a String or Error method,
    77  // it has already been converted into a string by preprintpanics.
    78  func printany(i interface{}) {
    79  	switch v := i.(type) {
    80  	case nil:
    81  		print("nil")
    82  	case bool:
    83  		print(v)
    84  	case int:
    85  		print(v)
    86  	case int8:
    87  		print(v)
    88  	case int16:
    89  		print(v)
    90  	case int32:
    91  		print(v)
    92  	case int64:
    93  		print(v)
    94  	case uint:
    95  		print(v)
    96  	case uint8:
    97  		print(v)
    98  	case uint16:
    99  		print(v)
   100  	case uint32:
   101  		print(v)
   102  	case uint64:
   103  		print(v)
   104  	case uintptr:
   105  		print(v)
   106  	case float32:
   107  		print(v)
   108  	case float64:
   109  		print(v)
   110  	case complex64:
   111  		print(v)
   112  	case complex128:
   113  		print(v)
   114  	case string:
   115  		print(v)
   116  	default:
   117  		print("(", typestring(i), ") ", i)
   118  	}
   119  }
   120  
   121  // strings.IndexByte is implemented in runtime/asm_$goarch.s
   122  // but amusingly we need go:linkname to get access to it here in the runtime.
   123  //go:linkname stringsIndexByte strings.IndexByte
   124  func stringsIndexByte(s string, c byte) int
   125  
   126  // panicwrap generates a panic for a call to a wrapped value method
   127  // with a nil pointer receiver.
   128  //
   129  // It is called from the generated wrapper code.
   130  func panicwrap() {
   131  	pc := getcallerpc()
   132  	name := funcname(findfunc(pc))
   133  	// name is something like "main.(*T).F".
   134  	// We want to extract pkg ("main"), typ ("T"), and meth ("F").
   135  	// Do it by finding the parens.
   136  	i := stringsIndexByte(name, '(')
   137  	if i < 0 {
   138  		throw("panicwrap: no ( in " + name)
   139  	}
   140  	pkg := name[:i-1]
   141  	if i+2 >= len(name) || name[i-1:i+2] != ".(*" {
   142  		throw("panicwrap: unexpected string after package name: " + name)
   143  	}
   144  	name = name[i+2:]
   145  	i = stringsIndexByte(name, ')')
   146  	if i < 0 {
   147  		throw("panicwrap: no ) in " + name)
   148  	}
   149  	if i+2 >= len(name) || name[i:i+2] != ")." {
   150  		throw("panicwrap: unexpected string after type name: " + name)
   151  	}
   152  	typ := name[:i]
   153  	meth := name[i+2:]
   154  	panic(plainError("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer"))
   155  }
   156
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