Fix source formatting (#13)

* fix source formatting

README.md

@@ -1,6 +1,6 @@
 Package errors
 ============
-![Project status](https://img.shields.io/badge/version-5.1.0-green.svg)
+![Project status](https://img.shields.io/badge/version-5.1.1-green.svg)
 [![Build Status](https://travis-ci.org/go-playground/errors.svg?branch=master)](https://travis-ci.org/go-playground/errors)
 [![Go Report Card](https://goreportcard.com/badge/github.com/go-playground/errors)](https://goreportcard.com/report/github.com/go-playground/errors)
 [![GoDoc](https://godoc.org/github.com/go-playground/errors?status.svg)](https://pkg.go.dev/github.com/go-playground/errors/v5)

benchmarks_test.go

@@ -10,6 +10,13 @@ func BenchmarkErrorNew(b *testing.B) {
 	}
 }
 
+func BenchmarkErrorWrap(b *testing.B) {
+	err := New("base error")
+	for i := 0; i < b.N; i++ {
+		_ = Wrap(err, "wrapped error")
+	}
+}
+
 func BenchmarkErrorParallelNew(b *testing.B) {
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {

chain.go

@@ -76,19 +76,37 @@ type Link struct {
 
 // formatError prints a single Links error
 func (l *Link) formatError(b []byte) []byte {
+	var funcName string
+
 	b = append(b, "source="...)
 	idx := strings.LastIndexByte(l.Source.Frame.Function, '.')
 	if idx == -1 {
 		b = append(b, l.Source.File()...)
 	} else {
-		b = append(b, l.Source.Frame.Function[:idx]...)
+		funcName = l.Source.Frame.Function[idx+1:]
+		remaining := l.Source.Frame.Function[:idx]
+
+		idx = strings.LastIndexByte(remaining, '/')
+		if idx > -1 {
+			b = append(b, l.Source.Frame.Function[:idx+1]...)
+			remaining = l.Source.Frame.Function[idx+1:]
+		}
+
+		idx = strings.IndexByte(remaining, '.')
+		if idx == -1 {
+			b = append(b, remaining...)
+		} else {
+			b = append(b, remaining[:idx]...)
+		}
 		b = append(b, '/')
 		b = append(b, l.Source.File()...)
 	}
 	b = append(b, ':')
 	b = strconv.AppendInt(b, int64(l.Source.Line()), 10)
-	b = append(b, ':')
-	b = append(b, l.Source.Frame.Function[idx+1:]...)
+	if funcName != "" {
+		b = append(b, ':')
+		b = append(b, funcName...)
+	}
 	b = append(b, ' ')
 	b = append(b, "error="...)