frame.go

     1  // Copyright 2018 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 xerrors
     6  
     7  import (
     8  	"runtime"
     9  )
    10  
    11  // A Frame contains part of a call stack.
    12  type Frame struct {
    13  	// Make room for three PCs: the one we were asked for, what it called,
    14  	// and possibly a PC for skipPleaseUseCallersFrames. See:
    15  	// https://go.googlesource.com/go/+/032678e0fb/src/runtime/extern.go#169
    16  	frames [3]uintptr
    17  }
    18  
    19  // Caller returns a Frame that describes a frame on the caller's stack.
    20  // The argument skip is the number of frames to skip over.
    21  // Caller(0) returns the frame for the caller of Caller.
    22  func Caller(skip int) Frame {
    23  	var s Frame
    24  	runtime.Callers(skip+1, s.frames[:])
    25  	return s
    26  }
    27  
    28  // location reports the file, line, and function of a frame.
    29  //
    30  // The returned function may be "" even if file and line are not.
    31  func (f Frame) location() (function, file string, line int) {
    32  	frames := runtime.CallersFrames(f.frames[:])
    33  	if _, ok := frames.Next(); !ok {
    34  		return "", "", 0
    35  	}
    36  	fr, ok := frames.Next()
    37  	if !ok {
    38  		return "", "", 0
    39  	}
    40  	return fr.Function, fr.File, fr.Line
    41  }
    42  
    43  // Format prints the stack as error detail.
    44  // It should be called from an error's Format implementation
    45  // after printing any other error detail.
    46  func (f Frame) Format(p Printer) {
    47  	if p.Detail() {
    48  		function, file, line := f.location()
    49  		if function != "" {
    50  			p.Printf("%s\n    ", function)
    51  		}
    52  		if file != "" {
    53  			p.Printf("%s:%d\n", file, line)
    54  		}
    55  	}
    56  }
    57
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