frame.Format: %+s prints more than "path of source file relative to the compile time GOPATH" about errors

[judwhite]

@davecheney @ChrisHines Playing with this a little more I noticed go vet complains about %n (and %#s).

What do you think about exposing these values as methods on Frame with stronger guarantees than Format?

[davecheney]

This commit was merged 6 months ago; might break people to change it now. Would you accept a PR to put the previous behavior under %#s and an update to the documentation?

It's probably too late to change the behaviour at this point. It'd be safer to document what exists now unless it's egregiously inconsistent.

[judwhite]

// Format accepts flags that alter the printing of some verbs, as follows:
//
//    %+s   path of source file relative to the compile time GOPATH
//    %+v   equivalent to %+s:%d

Current (248dadf):

func TestWrappedError(t *testing.T) {
	err := a()
	if st, ok := err.(stackTracer); ok {
		for _, frame := range st.StackTrace() {
			fmt.Printf("%+v\n", frame)
		}
	}
}

func a() error { return b() }
func b() error { return c() }
func c() error { return errors.Wrap(io.EOF, "unexpected eof") }

github.com/judwhite/httplog.c
        C:/Projects/go/src/github.com/judwhite/httplog/fallbackLogger_test.go:28
github.com/judwhite/httplog.b
        C:/Projects/go/src/github.com/judwhite/httplog/fallbackLogger_test.go:27
github.com/judwhite/httplog.a
        C:/Projects/go/src/github.com/judwhite/httplog/fallbackLogger_test.go:26
github.com/judwhite/httplog.TestWrappedError
        C:/Projects/go/src/github.com/judwhite/httplog/fallbackLogger_test.go:18
testing.tRunner
        C:/Go/src/testing/testing.go:610
runtime.goexit
        C:/Go/src/runtime/asm_amd64.s:2086

Previous (d4b5735):

github.com/judwhite/httplog/fallbackLogger_test.go:30
github.com/judwhite/httplog/fallbackLogger_test.go:29
github.com/judwhite/httplog/fallbackLogger_test.go:28
github.com/judwhite/httplog/fallbackLogger_test.go:18
testing/testing.go:610
runtime/asm_amd64.s:2086

[judwhite]

I would be happy with a change like this:

// File returns the path of the source file relative to the compile time GOPATH.
func (f Frame) File() string {
	pc := f.pc()
	fn := runtime.FuncForPC(pc)
	if fn == nil {
		return "unknown"
	}
	file, _ := fn.FileLine(pc)
	return trimGOPATH(fn.Name(), file)
}

// Func returns the function name.
func (f Frame) Func() string {
	name := runtime.FuncForPC(f.pc()).Name()
	return funcname(name)
}

// Line returns the source line.
func (f Frame) Line() int {
	return f.line()
}

If you're okay with this I'll submit a PR. The goal is to provide the user more control over stack trace formatting.

[ChrisHines]

Don't forget about #38. For reference see https://godoc.org/github.com/go-stack/stack#Call.Format and the code behind it.

[judwhite]

Closing.