handle rollback error

Author: leafo

forbidden_test.go

@@ -1,5 +1,4 @@
 //go:build windows
-// +build windows
 
 package screw_test
 

screw_darwin.go

@@ -1,5 +1,4 @@
 //go:build darwin
-// +build darwin
 
 package screw
 
@@ -28,12 +27,17 @@ char *GetCanonicalPath(char *cInputPath) {
 import "C"
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
 	"unsafe"
 )
 
+// osRename is a test seam so darwin-only tests can deterministically exercise
+// fallback and rollback branches in doRename without relying on filesystem quirks.
+var osRename = os.Rename
+
 func sneakyLog(line string) {
 	// nothing
 }
@@ -54,7 +58,7 @@ func TrueBaseName(path string) string {
 }
 
 func doRename(oldpath, newpath string) error {
-	err := os.Rename(oldpath, newpath)
+	err := osRename(oldpath, newpath)
 	if err != nil {
 		// on macOS, renaming "foo" to "FOO" is fine,
 		// but renaming "foo/" to "FOO/" fails with "file exists"
@@ -63,15 +67,19 @@ func doRename(oldpath, newpath string) error {
 
 			tmppath := fmt.Sprintf("%s__rename_pid%d", oldpath, os.Getpid())
 
-			err = os.Rename(oldpath, tmppath)
+			err = osRename(oldpath, tmppath)
 			if err != nil {
 				return originalErr
 			}
-			err = os.Rename(tmppath, newpath)
+			err = osRename(tmppath, newpath)
 			if err != nil {
 				// attempt to rollback, ignore returned error,
 				// because what else can we do at this point?
-				_ = os.Rename(tmppath, oldpath)
+				rollbackErr := osRename(tmppath, oldpath)
+				if rollbackErr != nil {
+					return errors.Join(err, rollbackErr)
+				}
+				return err
 			}
 			// two-stage rename worked!
 			return nil

screw_darwin_test.go

@@ -0,0 +1,115 @@
+//go:build darwin
+
+package screw
+
+import (
+	"errors"
+	"os"
+	"strings"
+	"testing"
+)
+
+func stubRename(t *testing.T, fn func(oldpath, newpath string) error) {
+	t.Helper()
+
+	previous := osRename
+	osRename = fn
+	t.Cleanup(func() {
+		osRename = previous
+	})
+}
+
+func TestDoRename_DarwinSecondStageFailure(t *testing.T) {
+	oldpath := "/tmp/old"
+	newpath := "/tmp/new"
+	secondStageErr := errors.New("second stage failed")
+
+	var calls int
+	var tmppath string
+
+	stubRename(t, func(old, new string) error {
+		calls++
+		switch calls {
+		case 1:
+			if old != oldpath || new != newpath {
+				t.Fatalf("unexpected first rename call: %q => %q", old, new)
+			}
+			return os.ErrExist
+		case 2:
+			if old != oldpath {
+				t.Fatalf("unexpected second rename source: %q", old)
+			}
+			if !strings.HasPrefix(new, oldpath+"__rename_pid") {
+				t.Fatalf("unexpected second rename target: %q", new)
+			}
+			tmppath = new
+			return nil
+		case 3:
+			if old != tmppath || new != newpath {
+				t.Fatalf("unexpected third rename call: %q => %q", old, new)
+			}
+			return secondStageErr
+		case 4:
+			if old != tmppath || new != oldpath {
+				t.Fatalf("unexpected rollback call: %q => %q", old, new)
+			}
+			return nil
+		default:
+			t.Fatalf("unexpected extra rename call: %d", calls)
+			return nil
+		}
+	})
+
+	err := doRename(oldpath, newpath)
+	if !errors.Is(err, secondStageErr) {
+		t.Fatalf("expected second stage error, got: %v", err)
+	}
+	if calls != 4 {
+		t.Fatalf("expected 4 rename calls, got: %d", calls)
+	}
+}
+
+func TestDoRename_DarwinSecondStageAndRollbackFailure(t *testing.T) {
+	oldpath := "/tmp/old"
+	newpath := "/tmp/new"
+	secondStageErr := errors.New("second stage failed")
+	rollbackErr := errors.New("rollback failed")
+
+	var calls int
+	var tmppath string
+
+	stubRename(t, func(old, new string) error {
+		calls++
+		switch calls {
+		case 1:
+			return os.ErrExist
+		case 2:
+			tmppath = new
+			return nil
+		case 3:
+			if old != tmppath || new != newpath {
+				t.Fatalf("unexpected third rename call: %q => %q", old, new)
+			}
+			return secondStageErr
+		case 4:
+			if old != tmppath || new != oldpath {
+				t.Fatalf("unexpected rollback call: %q => %q", old, new)
+			}
+			return rollbackErr
+		default:
+			t.Fatalf("unexpected extra rename call: %d", calls)
+			return nil
+		}
+	})
+
+	err := doRename(oldpath, newpath)
+	if !errors.Is(err, secondStageErr) {
+		t.Fatalf("expected second stage error in chain, got: %v", err)
+	}
+	if !errors.Is(err, rollbackErr) {
+		t.Fatalf("expected rollback error in chain, got: %v", err)
+	}
+	if calls != 4 {
+		t.Fatalf("expected 4 rename calls, got: %d", calls)
+	}
+}

screw_linux.go

@@ -1,5 +1,4 @@
 //go:build linux
-// +build linux
 
 package screw
 

screw_windows.go

@@ -1,5 +1,4 @@
 //go:build windows
-// +build windows
 
 package screw