Fix layout detection

src/restic/backend/layout.go

@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"restic"
+	"restic/debug"
 	"restic/errors"
 	"restic/fs"
 )
@@ -140,28 +141,36 @@ func DetectLayout(repo Filesystem, dir string) (Layout, error) {
 	}
 
 	if foundKeysFile && foundDataFile && !foundKeyFile && !foundDataSubdirFile {
-		return &CloudLayout{}, nil
+		debug.Log("found cloud layout at %v", dir)
+		return &CloudLayout{
+			Path: dir,
+			Join: repo.Join,
+		}, nil
 	}
 
 	if foundKeysFile && foundDataSubdirFile && !foundKeyFile && !foundDataFile {
-		return &DefaultLayout{}, nil
+		debug.Log("found default layout at %v", dir)
+		return &DefaultLayout{
+			Path: dir,
+			Join: repo.Join,
+		}, nil
 	}
 
 	if foundKeyFile && foundDataFile && !foundKeysFile && !foundDataSubdirFile {
-		return &S3Layout{}, nil
+		debug.Log("found s3 layout at %v", dir)
+		return &S3Layout{
+			Path: dir,
+			Join: repo.Join,
+		}, nil
 	}
 
 	return nil, errors.New("auto-detecting the filesystem layout failed")
 }
 
 // ParseLayout parses the config string and returns a Layout. When layout is
-// the empty string, DetectLayout is used. If repo is nil, an instance of LocalFilesystem
-// is used.
+// the empty string, DetectLayout is used.
 func ParseLayout(repo Filesystem, layout, path string) (l Layout, err error) {
-	if repo == nil {
-		repo = &LocalFilesystem{}
-	}
-
+	debug.Log("parse layout string %q for backend at %v", layout, path)
 	switch layout {
 	case "default":
 		l = &DefaultLayout{

src/restic/backend/layout_test.go

@@ -271,7 +271,7 @@ func TestParseLayout(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.layoutName, func(t *testing.T) {
-			layout, err := ParseLayout(nil, test.layoutName, filepath.Join(path, "repo"))
+			layout, err := ParseLayout(&LocalFilesystem{}, test.layoutName, filepath.Join(path, "repo"))
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -280,6 +280,11 @@ func TestParseLayout(t *testing.T) {
 				t.Fatal("wanted some layout, but detect returned nil")
 			}
 
+			// test that the functions work (and don't panic)
+			_ = layout.Dirname(restic.Handle{Type: restic.DataFile})
+			_ = layout.Filename(restic.Handle{Type: restic.DataFile, Name: "1234"})
+			_ = layout.Paths()
+
 			layoutName := fmt.Sprintf("%T", layout)
 			if layoutName != test.want {
 				t.Fatalf("want layout %v, got %v", test.want, layoutName)