template/interpolate: flip disable to enableenv

template/interpolate/funcs.go

@@ -51,7 +51,7 @@ func Funcs(ctx *Context) template.FuncMap {
 
 func funcGenEnv(ctx *Context) interface{} {
 	return func(k string) (string, error) {
-		if ctx.DisableEnv {
+		if !ctx.EnableEnv {
 			// The error message doesn't have to be that detailed since
 			// semantic checks should catch this.
 			return "", errors.New("env vars are not allowed here")

template/interpolate/funcs_test.go

@@ -26,7 +26,7 @@ func TestFuncEnv(t *testing.T) {
 	os.Setenv("PACKER_TEST_ENV", "foo")
 	defer os.Setenv("PACKER_TEST_ENV", "")
 
-	ctx := &Context{}
+	ctx := &Context{EnableEnv: true}
 	for _, tc := range cases {
 		i := &I{Value: tc.Input}
 		result, err := i.Render(ctx)
@@ -53,7 +53,7 @@ func TestFuncEnv_disable(t *testing.T) {
 		},
 	}
 
-	ctx := &Context{DisableEnv: true}
+	ctx := &Context{EnableEnv: false}
 	for _, tc := range cases {
 		i := &I{Value: tc.Input}
 		result, err := i.Render(ctx)

template/interpolate/i.go

@@ -15,8 +15,8 @@ type Context struct {
 	// "user" function reads from.
 	UserVariables map[string]string
 
-	// DisableEnv disables the env function
-	DisableEnv bool
+	// EnableEnv enables the env function
+	EnableEnv bool
 }
 
 // I stands for "interpolation" and is the main interpolation struct