feat: add deprecation notice interface (#399)

* feat: add deprecation notice interface

* fix: use a simple writer

* fix: use println

deb/deb.go

@@ -19,6 +19,7 @@ import (
 	"github.com/blakesmith/ar"
 	"github.com/goreleaser/chglog"
 	"github.com/goreleaser/nfpm/v2"
+	"github.com/goreleaser/nfpm/v2/deprecation"
 	"github.com/goreleaser/nfpm/v2/files"
 	"github.com/goreleaser/nfpm/v2/internal/sign"
 	"github.com/ulikunitz/xz"
@@ -170,7 +171,7 @@ func (*Deb) SetPackagerDefaults(info *nfpm.Info) {
 	// if in the long run we should be more strict about this and error when
 	// not set?
 	if info.Maintainer == "" {
-		fmt.Fprintf(os.Stderr, "DEPRECATION WARNING: Leaving the 'maintainer' field unset will not be allowed in a future version")
+		deprecation.Println("Leaving the 'maintainer' field unset will not be allowed in a future version")
 		info.Maintainer = "Unset Maintainer <unset@localhost>"
 	}
 }

deprecation/deprecation.go

@@ -0,0 +1,31 @@
+// Package deprecation provides centralized deprecation notice messaging for nfpm.
+package deprecation
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+type prefixed struct{ io.Writer }
+
+func (p prefixed) Write(b []byte) (int, error) {
+	return p.Writer.Write(append([]byte("DEPRECATION WARNING: "), b...))
+}
+
+var Noticer io.Writer = prefixed{os.Stderr}
+
+// Print prints the given string to the Noticer.
+func Print(s string) {
+	fmt.Fprint(Noticer, s)
+}
+
+// Println printslns the given string to the Noticer.
+func Println(s string) {
+	fmt.Fprintln(Noticer, s)
+}
+
+// Printf printfs the given string to the Noticer.
+func Printf(format string, a ...interface{}) {
+	fmt.Fprintf(Noticer, format, a...)
+}

deprecation/deprecation_test.go

@@ -0,0 +1,18 @@
+package deprecation
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNotice(t *testing.T) {
+	Print("before")
+	var b bytes.Buffer
+	Noticer = prefixed{&b}
+	Print("blah\n")
+	Printf("blah: %v\n", true)
+	Println("foobar")
+	require.Equal(t, "DEPRECATION WARNING: blah\nDEPRECATION WARNING: blah: true\nDEPRECATION WARNING: foobar\n", b.String())
+}

nfpm.go

@@ -11,6 +11,7 @@ import (
 	"github.com/AlekSi/pointer"
 	"github.com/Masterminds/semver/v3"
 	"github.com/goreleaser/chglog"
+	"github.com/goreleaser/nfpm/v2/deprecation"
 	"github.com/goreleaser/nfpm/v2/files"
 	"github.com/imdario/mergo"
 	"gopkg.in/yaml.v3"
@@ -375,8 +376,8 @@ func Validate(info *Info) (err error) {
 	}
 
 	if len(info.EmptyFolders) > 0 {
-		fmt.Fprintf(os.Stderr, "DEPRECATION WARNING: 'empty_folders' is deprecated and "+
-			"will be removed in a future version, create content with type 'dir' and "+
+		deprecation.Println("'empty_folders' is deprecated and " +
+			"will be removed in a future version, create content with type 'dir' and " +
 			"directoy name as 'dst' instead")
 
 		for _, emptyFolder := range info.EmptyFolders {