add Wrap function (#1)

.travis.yml

@@ -7,8 +7,6 @@ language: go
 # You don't need to test on very old version of the Go compiler. It's the user's
 # responsibility to keep their compilers up to date.
 go:
-  - 1.11.x
-  - 1.12.x
   - 1.13.x
 
 env:

README.md

@@ -5,6 +5,8 @@
 [![GoDoc](https://godoc.org/github.com/spyzhov/safe?status.svg)](https://godoc.org/github.com/spyzhov/safe)
 [![Coverage Status](https://coveralls.io/repos/github/spyzhov/safe/badge.svg?branch=master)](https://coveralls.io/github/spyzhov/safe?branch=master)
 
+Golang Minimal Version: **1.13**
+
 Package safe is a minimal project with safe methods to write clean code.
 
 ## safe.Close
@@ -36,12 +38,22 @@ Full description of the problem in article ["Go-tcha: When nil != nil"](https://
 
 ```go
 func Foo(str fmt.Stringer) {
-    if !IsNil(str) {
+    if !safe.IsNil(str) {
         // ...
     }
 }
 ```
 
+## safe.Wrap
+
+`Wrap` will wrap current error with the scope value, or return `nil` if error wasn't set.
+
+```go
+func Unmarshal(data []byte) (value interface{}, err error) {
+	return value, safe.Wrap(json.Unmarshal(data, &value), "broken json")
+}
+```
+
 # License
 
 Licensed under the MIT license, see [LICENSE](LICENSE) for details.

wrap.go

@@ -0,0 +1,11 @@
+package safe
+
+import "fmt"
+
+// Wrap will wrap current error with the scope value, or return nil if error wasn't set.
+func Wrap(err error, scope string) error {
+	if !IsNil(err) {
+		return fmt.Errorf("%s: %w", scope, err)
+	}
+	return nil
+}

wrap_example_test.go

@@ -0,0 +1,14 @@
+package safe
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+func ExampleWrap() {
+	var value interface{}
+	err := Wrap(json.Unmarshal([]byte(`[broken`), &value), "broken json")
+	fmt.Println(err)
+	// Output:
+	// broken json: invalid character 'b' looking for beginning of value
+}

wrap_test.go

@@ -0,0 +1,43 @@
+package safe
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestWrap(t *testing.T) {
+	simple := fmt.Errorf("error")
+	type args struct {
+		err   error
+		scope string
+	}
+	tests := []struct {
+		name   string
+		args   args
+		result error
+	}{
+		{
+			name:   "nil",
+			args:   args{nil, ""},
+			result: nil,
+		},
+		{
+			name:   "nil/scope",
+			args:   args{nil, "scope"},
+			result: nil,
+		},
+		{
+			name:   "error/scope",
+			args:   args{simple, "scope"},
+			result: simple,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := Wrap(tt.args.err, tt.args.scope); err != tt.result && !errors.Is(err, tt.result) {
+				t.Errorf("Wrap() error = %v, wanted %v", err, tt.result)
+			}
+		})
+	}
+}