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