feat: Enhanced `get` template function (#513)

`get` is now able to take one more optional argument, that is used as the default value when the value for the key does not exist.

Resolves #465
Fixes #427
Fixes #357
Ref #460

tmpl/context_tmpl_test.go

@@ -110,11 +110,11 @@ func TestRenderTemplate_Defaulting(t *testing.T) {
 	}
 }
 
-func renderTemplateToString(s string) (string, error) {
+func renderTemplateToString(s string, data ...interface{}) (string, error) {
 	ctx := &Context{readFile: func(filename string) ([]byte, error) {
 		return nil, fmt.Errorf("unexpected call to readFile: filename=%s", filename)
 	}}
-	tplString, err := ctx.RenderTemplateToBuffer(s)
+	tplString, err := ctx.RenderTemplateToBuffer(s, data...)
 	if err != nil {
 		return "", err
 	}
@@ -125,6 +125,7 @@ func Test_renderTemplateToString(t *testing.T) {
 	type args struct {
 		s    string
 		envs map[string]string
+		data interface{}
 	}
 	tests := []struct {
 		name    string
@@ -177,6 +178,18 @@ func Test_renderTemplateToString(t *testing.T) {
 			want:    "7",
 			wantErr: false,
 		},
+		{
+			name: "get",
+			args: args{
+				s:    `{{ . | get "Foo" }}, {{ . | get "Bar" "2" }}`,
+				envs: map[string]string{},
+				data: map[string]interface{}{
+					"Foo": "1",
+				},
+			},
+			want:    "1, 2",
+			wantErr: false,
+		},
 		{
 			name: "env var not set",
 			args: args{
@@ -225,7 +238,7 @@ func Test_renderTemplateToString(t *testing.T) {
 					t.Error("renderTemplateToString() could not set env var for testing")
 				}
 			}
-			got, err := renderTemplateToString(tt.args.s)
+			got, err := renderTemplateToString(tt.args.s, tt.args.data)
 			if (err != nil) != tt.wantErr {
 				t.Errorf("renderTemplateToString() for %s error = %v, wantErr %v", tt.name, err, tt.wantErr)
 				return

tmpl/get_or_nil.go

@@ -14,36 +14,67 @@ func (e *noValueError) Error() string {
 	return e.msg
 }
 
-func get(path string, obj interface{}) (interface{}, error) {
+func get(path string, varArgs ...interface{}) (interface{}, error) {
+	var defSet bool
+	var def interface{}
+	var obj interface{}
+	switch len(varArgs) {
+	case 1:
+		defSet = false
+		def = nil
+		obj = varArgs[0]
+	case 2:
+		defSet = true
+		def = varArgs[0]
+		obj = varArgs[1]
+	default:
+		return nil, fmt.Errorf("unexpected number of args pased to the template function get(path, [def, ]obj): expected 1 or 2, got %d, args was %v", len(varArgs), varArgs)
+	}
+
 	if path == "" {
 		return obj, nil
 	}
 	keys := strings.Split(path, ".")
+	var v interface{}
+	var ok bool
 	switch typedObj := obj.(type) {
 	case map[string]interface{}:
-		v, ok := typedObj[keys[0]]
+		v, ok = typedObj[keys[0]]
 		if !ok {
+			if defSet {
+				return def, nil
+			}
 			return nil, &noValueError{fmt.Sprintf("no value exist for key \"%s\" in %v", keys[0], typedObj)}
 		}
-		return get(strings.Join(keys[1:], "."), v)
 	case map[interface{}]interface{}:
-		v, ok := typedObj[keys[0]]
+		v, ok = typedObj[keys[0]]
 		if !ok {
+			if defSet {
+				return def, nil
+			}
 			return nil, &noValueError{fmt.Sprintf("no value exist for key \"%s\" in %v", keys[0], typedObj)}
 		}
-		return get(strings.Join(keys[1:], "."), v)
 	default:
 		maybeStruct := reflect.ValueOf(typedObj)
-		if maybeStruct.NumField() < 1 {
+		if maybeStruct.Kind() != reflect.Struct {
 			return nil, &noValueError{fmt.Sprintf("unexpected type(%v) of value for key \"%s\": it must be either map[string]interface{} or any struct", reflect.TypeOf(obj), keys[0])}
+		} else if maybeStruct.NumField() < 1 {
+			return nil, &noValueError{fmt.Sprintf("no accessible struct fields for key \"%s\"", keys[0])}
 		}
 		f := maybeStruct.FieldByName(keys[0])
 		if !f.IsValid() {
+			if defSet {
+				return def, nil
+			}
 			return nil, &noValueError{fmt.Sprintf("no field named \"%s\" exist in %v", keys[0], typedObj)}
 		}
-		v := f.Interface()
+		v = f.Interface()
-		return get(strings.Join(keys[1:], "."), v)
 	}
+
+	if defSet {
+		return get(strings.Join(keys[1:], "."), def, v)
+	}
+	return get(strings.Join(keys[1:], "."), v)
 }
 
 func getOrNil(path string, o interface{}) (interface{}, error) {

tmpl/get_or_nil_test.go

@@ -4,6 +4,9 @@ import (
 	"testing"
 )
 
+type EmptyStruct struct {
+}
+
 func TestGetStruct(t *testing.T) {
 	type Foo struct{ Bar string }
 
@@ -23,6 +26,12 @@ func TestGetStruct(t *testing.T) {
 	if err == nil {
 		t.Errorf("expected error but was not occurred")
 	}
+
+	_, err = get("foo", EmptyStruct{})
+
+	if err == nil {
+		t.Errorf("expected error but was not occurred")
+	}
 }
 
 func TestGetMap(t *testing.T) {
@@ -44,6 +53,34 @@ func TestGetMap(t *testing.T) {
 	}
 }
 
+func TestGet_Default(t *testing.T) {
+	obj := map[string]interface{}{"Foo": map[string]interface{}{}, "foo": 1}
+
+	v1, err := get("Foo.Bar", "Bar", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v1 != "Bar" {
+		t.Errorf("unexpected value for path Foo.Bar in %v: expected=Bar, actual=%v", obj, v1)
+	}
+
+	v2, err := get("Baz", "Baz", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v2 != "Baz" {
+		t.Errorf("unexpected value for path Baz in %v: expected=Baz, actual=%v", obj, v2)
+	}
+
+	_, err = get("foo.Bar", "fooBar", obj)
+
+	if err == nil {
+		t.Errorf("expected error but was not occurred")
+	}
+}
+
 func TestGetOrNilStruct(t *testing.T) {
 	type Foo struct{ Bar string }