Treat errors as objects not strings to allow more detailed error information

[robdefeo]

Use Case

I am using open-tracing for all distributed tracing.

Problem

When I log an error with

errors.WithStack(err) 
ext.Error.Set(span, true) 
span.LogFields(log.Error(e))

It just gives the error string rather than stack trace or any supporting information.

Proposal

Treat errors as objects not strings
github.com/opentracing/opentracing-go/log/field.go
replace

case errorType:
		if err, ok := lf.interfaceVal.(error); ok {
			visitor.EmitString(lf.key, err.Error())
		} else {
			visitor.EmitString(lf.key, "<nil>")
		}

with

case errorType:
		if err, ok := lf.interfaceVal.(error); ok {
			visitor.EmitObject(lf.key, err)
		} else {
			visitor.EmitString(lf.key, "<nil>")
		}

the implementers are then free to use https://godoc.org/github.com/pkg/errors#hdr-Formatted_printing_of_errors just like is used in jaeger for EmitObject

func (ml fieldsAsMap) EmitObject(key string, value interface{}) {
	ml[key] = fmt.Sprintf("%+v", value)
}

Which will give all the information

Questions to address (if any)

[yurishkuro]

visitor.EmitString(lf.key, err) will not compile, did you mean EmitObject?

[robdefeo]

@yurishkuro yes you are correct thanks, i'll update the description. Thanks

[yurishkuro]

+1

[yurishkuro]

Related issue #199