Add errorsext & Stack Frame helpers

Added Stack frame helper functions.

Author: Dean Karn

README.md

@@ -1,5 +1,5 @@
 # pkg
-![Project status](https://img.shields.io/badge/version-2.0.0-green.svg)
+![Project status](https://img.shields.io/badge/version-2.1.0-green.svg)
 [![Build Status](https://travis-ci.org/go-playground/pkg.svg?branch=master)](https://travis-ci.org/go-playground/pkg)
 [![Coverage Status](https://coveralls.io/repos/github/go-playground/pkg/badge.svg?branch=master)](https://coveralls.io/github/go-playground/pkg?branch=master)
 [![GoDoc](https://godoc.org/github.com/go-playground/pkg?status.svg)](https://godoc.org/github.com/go-playground/pkg)

errors/stack.go

@@ -0,0 +1,47 @@
+package errorsext
+
+import (
+	"runtime"
+	"strings"
+)
+
+// Frame wraps a runtime.Frame to provide some helper functions while still allowing access to
+// the original runtime.Frame
+type Frame struct {
+	runtime.Frame
+}
+
+// File is the runtime.Frame.File stripped down to just the filename
+func (f Frame) File() string {
+	name := f.Frame.File
+	i := strings.LastIndexByte(name, '/')
+	return name[i+1:]
+}
+
+// Line is the line of the runtime.Frame and exposed for convenience.
+func (f Frame) Line() int {
+	return f.Frame.Line
+}
+
+// Function is the runtime.Frame.Function stripped down to just the function name
+func (f Frame) Function() string {
+	name := f.Frame.Function
+	i := strings.LastIndexByte(name, '.')
+	return name[i+1:]
+}
+
+// Stack returns a stack Frame
+func Stack() Frame {
+	return StackLevel(1)
+}
+
+// StackLevel returns a stack Frame skipping the number of supplied frames.
+// This is primarily used by other libraries who use this package
+// internally as the additional.
+func StackLevel(skip int) (f Frame) {
+	var frame [3]uintptr
+	runtime.Callers(skip+2, frame[:])
+	frames := runtime.CallersFrames(frame[:])
+	f.Frame, _ = frames.Next()
+	return
+}

errors/stack_test.go

@@ -0,0 +1,54 @@
+package errorsext
+
+import (
+	"testing"
+)
+
+func nested(level int) Frame {
+	return StackLevel(level)
+}
+
+func TestStack(t *testing.T) {
+	tests := []struct {
+		name     string
+		frame    Frame
+		file     string
+		line     int
+		function string
+	}{
+		{
+			name:     "stack",
+			frame:    Stack(),
+			file:     "stack_test.go",
+			line:     21,
+			function: "TestStack",
+		},
+		{
+			name:     "stack-level1",
+			frame:    nested(1),
+			file:     "stack_test.go",
+			line:     28,
+			function: "TestStack",
+		},
+		{
+			name:     "stack-level0",
+			frame:    nested(0),
+			file:     "stack_test.go",
+			line:     8,
+			function: "nested",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.frame.File() != tt.file {
+				t.Errorf("TestStack File() = %s, want %s", tt.frame.File(), tt.file)
+			}
+			if tt.frame.Line() != tt.line {
+				t.Errorf("TestStack Line() = %d, want %d", tt.frame.Line(), tt.line)
+			}
+			if tt.frame.Function() != tt.function {
+				t.Errorf("TestStack Function() = %s, want %s", tt.frame.Function(), tt.function)
+			}
+		})
+	}
+}