source: code/trunk/vendor/golang.org/x/xerrors/frame.go@ 823

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package xerrors

import (
        "runtime"
)

// A Frame contains part of a call stack.
type Frame struct {
        // Make room for three PCs: the one we were asked for, what it called,
        // and possibly a PC for skipPleaseUseCallersFrames. See:
        // https://go.googlesource.com/go/+/032678e0fb/src/runtime/extern.go#169
        frames [3]uintptr
}

// Caller returns a Frame that describes a frame on the caller's stack.
// The argument skip is the number of frames to skip over.
// Caller(0) returns the frame for the caller of Caller.
func Caller(skip int) Frame {
        var s Frame
        runtime.Callers(skip+1, s.frames[:])
        return s
}

// location reports the file, line, and function of a frame.
//
// The returned function may be "" even if file and line are not.
func (f Frame) location() (function, file string, line int) {
        frames := runtime.CallersFrames(f.frames[:])
        if _, ok := frames.Next(); !ok {
                return "", "", 0
        }
        fr, ok := frames.Next()
        if !ok {
                return "", "", 0
        }
        return fr.Function, fr.File, fr.Line
}

// Format prints the stack as error detail.
// It should be called from an error's Format implementation
// after printing any other error detail.
func (f Frame) Format(p Printer) {
        if p.Detail() {
                function, file, line := f.location()
                if function != "" {
                        p.Printf("%s\n    ", function)
                }
                if file != "" {
                        p.Printf("%s:%d\n", file, line)
                }
        }
}