errors: Ensure that errors.IsFatal(errors.Fatal("err")) == true

This fixes a few cases where restic output "Fatal: Fatal: [...]"

cmd/restic/main.go

@@ -102,7 +102,7 @@ func main() {
 		fmt.Fprintf(os.Stderr, "%v\nthe `unlock` command can be used to remove stale locks\n", err)
 	case err == ErrInvalidSourceData:
 		fmt.Fprintf(os.Stderr, "Warning: %v\n", err)
-	case errors.IsFatal(errors.Cause(err)):
+	case errors.IsFatal(err):
 		fmt.Fprintf(os.Stderr, "%v\n", err)
 	case err != nil:
 		fmt.Fprintf(os.Stderr, "%+v\n", err)

internal/errors/fatal.go

@@ -23,6 +23,8 @@ type Fataler interface {
 // IsFatal returns true if err is a fatal message that should be printed to the
 // user. Then, the program should exit.
 func IsFatal(err error) bool {
+	// unwrap "Wrap" method
+	err = Cause(err)
 	e, ok := err.(Fataler)
 	return ok && e.Fatal()
 }

internal/errors/fatal_test.go

@@ -0,0 +1,22 @@
+package errors_test
+
+import (
+	"testing"
+
+	"github.com/restic/restic/internal/errors"
+)
+
+func TestFatal(t *testing.T) {
+	for _, v := range []struct {
+		err      error
+		expected bool
+	}{
+		{errors.Fatal("broken"), true},
+		{errors.Fatalf("broken %d", 42), true},
+		{errors.New("error"), false},
+	} {
+		if errors.IsFatal(v.err) != v.expected {
+			t.Fatalf("IsFatal for %q, expected: %v, got: %v", v.err, v.expected, errors.IsFatal(v.err))
+		}
+	}
+}

internal/restic/config.go

@@ -78,7 +78,7 @@ func LoadConfig(ctx context.Context, r JSONUnpackedLoader) (Config, error) {
 	}
 
 	if cfg.Version != RepoVersion {
-		return Config{}, errors.New("unsupported repository version")
+		return Config{}, errors.Errorf("unsupported repository version %v", cfg.Version)
 	}
 
 	if checkPolynomial {