frame.go

// This module mostly lifted from golang.org/x/xerrors
package cerrors

import (
	"fmt"
	"io"
	"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(s io.Writer, withFunctions bool) {
	function, file, line := f.location()
	if function != "" && withFunctions {
		fmt.Fprintf(s, "    %s\n    ", function)
	}
	if file != "" {
		fmt.Fprintf(s, "    %s:%d\n", file, line)
	}
}