README.md

@@ -139,6 +139,9 @@ matching.
 
 Moves or renames a secret within the current vault.
 - Fails if the destination already exists
+- Fails if the destination is the source under another name, such as `foo`
+  for `Foo` on a case-insensitive filesystem (the macOS default); there, to
+  change only the case of a name, move the secret to a third name first
 - Preserves all versions and metadata
 
 ### Version Management

TODO.md

@@ -25,6 +25,13 @@ Bring the repo into policy compliance in one commit:
 
 # Completed Steps
 
+- 2026-10-04: `secret mv` rejects a move whose destination is the source
+  under another name, such as `foo` for `Foo` on a case-insensitive
+  filesystem (the macOS default) or a name reached through a symbolic
+  link, before changing anything, with or without `--force`, within a
+  vault and between vaults; before, `--force` removed the destination and
+  so deleted the secret. A rename that changes only letter case works on a
+  case-sensitive filesystem as before.
 - 2026-10-04: Lint runs only in docker: `script/lint` builds
   `Dockerfile.lint`, where golangci-lint is a build step rebuilt on
   every run (`--no-cache-filter`), so an unchanged tree is linted too;

internal/cli/move_test.go

@@ -1,9 +1,15 @@
 package cli_test
 
 import (
+	"os"
+	"path/filepath"
 	"testing"
 
 	"git.eeqj.de/sneak/secret/internal/cli"
+	"git.eeqj.de/sneak/secret/internal/secret"
+	"git.eeqj.de/sneak/secret/internal/vault"
+	"github.com/awnumar/memguard"
+	"github.com/spf13/afero"
 	"github.com/spf13/cobra"
 	"github.com/stretchr/testify/require"
 )
@@ -97,3 +103,127 @@ func TestMoveWithinOtherVaultKeepsCurrentVault(t *testing.T) {
 	require.Contains(t, after, workSecrets+"y/")
 	require.NotContains(t, after, workSecrets+"x/")
 }
+
+// TestMoveOntoSameSecretUnderAnotherNameIsRejected is a regression test for
+// https://git.eeqj.de/sneak/secret/issues/78: on a case-insensitive
+// filesystem "Foo" and "foo" are one secret, and `secret mv --force Foo foo`
+// removed the destination, which was the source. Symbolic links on the real
+// filesystem give one secret two names here: in "default", "y" is a link to
+// the secret "x", and the secrets.d of "other" is a link to that of
+// "default", so other:x is default:x. Each move must be rejected and leave
+// the secret and the links as they were.
+//
+//nolint:paralleltest // t.Setenv
+func TestMoveOntoSameSecretUnderAnotherNameIsRejected(t *testing.T) {
+	t.Setenv(secret.EnvMnemonic, testMnemonic)
+
+	const isSame = "is the same secret on this filesystem"
+
+	tests := []struct {
+		command      string
+		source, dest string
+		force        bool
+		wantErr      string
+	}{
+		{
+			"mv --force y x", "y", "x", true,
+			"secret 'y' cannot be moved onto itself: 'x' " + isSame,
+		},
+		{
+			"mv --force x y", "x", "y", true,
+			"secret 'x' cannot be moved onto itself: 'y' " + isSame,
+		},
+		{
+			"mv x y", "x", "y", false,
+			"secret 'x' cannot be moved onto itself: 'y' " + isSame,
+		},
+		{
+			"mv --force default:x other:x", "default:x", "other:x", true,
+			"secret 'default:x' cannot be moved onto itself: 'other:x' " +
+				isSame,
+		},
+		{
+			"mv default:x other", "default:x", "other", false,
+			"secret 'default:x' cannot be moved onto itself: 'other:x' " +
+				isSame,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.command, func(t *testing.T) {
+			fs := afero.NewOsFs()
+			stateDir := t.TempDir()
+			vaultsDir := filepath.Join(stateDir, "vaults.d")
+
+			// "default" is created last, so it is the current vault.
+			_, err := vault.CreateVault(fs, stateDir, "other")
+			require.NoError(t, err)
+
+			vlt, err := vault.CreateVault(fs, stateDir, "default")
+			require.NoError(t, err)
+
+			err = vlt.AddSecret("x", memguard.NewBufferFromBytes([]byte("value")), false)
+			require.NoError(t, err)
+
+			defaultSecrets := filepath.Join(vaultsDir, "default", "secrets.d")
+			otherSecrets := filepath.Join(vaultsDir, "other", "secrets.d")
+			link := filepath.Join(defaultSecrets, "y")
+
+			require.NoError(t, os.Symlink("x", link))
+			require.NoError(t, os.Remove(otherSecrets))
+			require.NoError(t, os.Symlink(defaultSecrets, otherSecrets))
+
+			c := cli.NewCLIInstanceWithStateDir(fs, stateDir)
+			moveErr := c.MoveSecret(&cobra.Command{}, tt.source, tt.dest, tt.force)
+
+			value, err := vlt.GetSecret("x")
+			require.NoError(t, err)
+			require.Equal(t, "value", string(value))
+
+			target, err := os.Readlink(link)
+			require.NoError(t, err)
+			require.Equal(t, "x", target)
+
+			target, err = os.Readlink(otherSecrets)
+			require.NoError(t, err)
+			require.Equal(t, defaultSecrets, target)
+
+			require.EqualError(t, moveErr, tt.wantErr)
+		})
+	}
+}
+
+// TestForcedCaseOnlyMoveOnCaseSensitiveFilesystem checks that where "Foo"
+// and "foo" are two secrets, `secret mv --force Foo foo` still replaces "foo"
+// with "Foo".
+func TestForcedCaseOnlyMoveOnCaseSensitiveFilesystem(t *testing.T) {
+	t.Setenv(secret.EnvMnemonic, testMnemonic)
+
+	fs := afero.NewOsFs()
+	stateDir := t.TempDir()
+
+	vlt, err := vault.CreateVault(fs, stateDir, "default")
+	require.NoError(t, err)
+
+	err = vlt.AddSecret("Foo", memguard.NewBufferFromBytes([]byte("upper")), false)
+	require.NoError(t, err)
+
+	_, err = os.Stat(filepath.Join(stateDir, "vaults.d", "default", "secrets.d", "foo"))
+	if err == nil {
+		t.Skip("the temporary directory is on a case-insensitive filesystem")
+	}
+
+	err = vlt.AddSecret("foo", memguard.NewBufferFromBytes([]byte("lower")), false)
+	require.NoError(t, err)
+
+	c := cli.NewCLIInstanceWithStateDir(fs, stateDir)
+	err = c.MoveSecret(&cobra.Command{}, "Foo", "foo", true)
+	require.NoError(t, err)
+
+	value, err := vlt.GetSecret("foo")
+	require.NoError(t, err)
+	require.Equal(t, "upper", string(value))
+
+	_, err = vlt.GetSecret("Foo")
+	require.ErrorIs(t, err, vault.ErrSecretNotFound)
+}

internal/cli/secrets.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"os"
 	"path/filepath"
 	"slices"
 	"strings"
@@ -890,6 +891,18 @@ func (cli *Instance) moveSecretWithinVault(
 	destEncoded := strings.ReplaceAll(dest, "/", "%")
 	destDir := filepath.Join(vaultDir, "secrets.d", destEncoded)
 
+	// Removing a destination that is the source under another name, such as
+	// "foo" for "Foo" on a case-insensitive filesystem, would delete it too.
+	same, err := cli.sameDirectory(sourceDir, destDir)
+	if err != nil {
+		return err
+	}
+
+	if same {
+		return fmt.Errorf("secret '%s' %w: '%s' is the same secret on "+
+			"this filesystem", source, errMoveOntoItself, dest)
+	}
+
 	exists, err = afero.DirExists(cli.fs, destDir)
 	if err != nil {
 		return fmt.Errorf("failed to check if destination secret exists: %w", err)
@@ -916,6 +929,31 @@ func (cli *Instance) moveSecretWithinVault(
 	return nil
 }
 
+// sameDirectory reports whether the existing directory dir and the path
+// other are one directory under two names, as secrets.d/Foo and
+// secrets.d/foo are on a case-insensitive filesystem, or a directory and a
+// symbolic link to it. Removing other to make room for dir would then delete
+// dir. It is false if other does not exist, and always false on the
+// in-memory filesystem, which has no such aliasing and whose files
+// os.SameFile does not compare.
+func (cli *Instance) sameDirectory(dir, other string) (bool, error) {
+	dirInfo, err := cli.fs.Stat(dir)
+	if err != nil {
+		return false, fmt.Errorf("failed to check %s: %w", dir, err)
+	}
+
+	otherInfo, err := cli.fs.Stat(other)
+	if errors.Is(err, os.ErrNotExist) {
+		return false, nil
+	}
+
+	if err != nil {
+		return false, fmt.Errorf("failed to check %s: %w", other, err)
+	}
+
+	return os.SameFile(dirInfo, otherInfo), nil
+}
+
 // moveSecretCrossVault handles moving between two different vaults. Its
 // caller, MoveSecret, has already checked both secret names and that both
 // vaults exist.
@@ -940,6 +978,27 @@ func (cli *Instance) moveSecretCrossVault(
 			srcSecretName, errSecretNotFound, srcVault.Name)
 	}
 
+	// The source is removed after the copy, so a destination that is the
+	// source under another name would be lost with it.
+	destVaultDir, err := destVault.GetDirectory()
+	if err != nil {
+		return fmt.Errorf("failed to get destination vault directory: %w", err)
+	}
+
+	destStorageName := strings.ReplaceAll(destSecretName, "/", "%")
+	destSecretDir := filepath.Join(destVaultDir, "secrets.d", destStorageName)
+
+	same, err := cli.sameDirectory(srcSecretDir, destSecretDir)
+	if err != nil {
+		return err
+	}
+
+	if same {
+		return fmt.Errorf("secret '%s:%s' %w: '%s:%s' is the same secret on "+
+			"this filesystem", srcVault.Name, srcSecretName, errMoveOntoItself,
+			destVault.Name, destSecretName)
+	}
+
 	// Unlock destination vault (will fail if neither mnemonic nor unlocker available)
 	_, err = destVault.GetOrDeriveLongTermKey()
 	if err != nil {