install: show backup failure causes

src/uu/install/locales/en-US.ftl

@@ -29,7 +29,7 @@ install-error-chmod-failed-detailed = { $path }: chmod failed with error { $erro
 install-error-chown-failed = failed to chown { $path }: { $error }
 install-error-invalid-target = invalid target { $path }: No such file or directory
 install-error-target-not-dir = target { $path } is not a directory
-install-error-backup-failed = cannot backup { $from } to { $to }
+install-error-backup-failed = cannot backup { $from }: { $error }
 install-error-install-failed = cannot install { $from } to { $to }: { $error }
 install-error-strip-failed = strip program failed: { $error }
 install-error-strip-abnormal = strip process terminated abnormally - exit code: { $code }

src/uu/install/locales/fr-FR.ftl

@@ -29,7 +29,7 @@ install-error-chmod-failed-detailed = { $path } : échec du chmod avec l'erreur
 install-error-chown-failed = échec du chown { $path } : { $error }
 install-error-invalid-target = cible invalide { $path } : Aucun fichier ou répertoire de ce type
 install-error-target-not-dir = la cible { $path } n'est pas un répertoire
-install-error-backup-failed = impossible de sauvegarder { $from } vers { $to }
+install-error-backup-failed = impossible de sauvegarder { $from } : { $error }
 install-error-install-failed = impossible d'installer { $from } vers { $to }: { $error }
 install-error-strip-failed = échec du programme strip : { $error }
 install-error-strip-abnormal = le processus strip s'est terminé anormalement - code de sortie : { $code }

src/uu/install/src/install.rs

@@ -24,7 +24,7 @@ use uucore::backup_control::{self, BackupMode};
 use uucore::buf_copy::copy_fast;
 use uucore::display::Quotable;
 use uucore::entries::{grp2gid, usr2uid};
-use uucore::error::{FromIo, UError, UResult, UUsageError};
+use uucore::error::{FromIo, UError, UResult, UUsageError, strip_errno};
 use uucore::fs::dir_strip_dot_for_creation;
 use uucore::perms::{Verbosity, VerbosityLevel, wrap_chown};
 use uucore::process::{getegid, geteuid};
@@ -88,8 +88,8 @@ enum InstallError {
     #[error("{}", translate!("install-error-target-not-dir", "path" => .0.quote()))]
     TargetDirIsntDir(PathBuf),
 
-    #[error("{}", translate!("install-error-backup-failed", "from" => .0.quote(), "to" => .1.quote()))]
-    BackupFailed(PathBuf, PathBuf, #[source] std::io::Error),
+    #[error("{}", translate!("install-error-backup-failed", "from" => .0.quote(), "error" => strip_errno(.1)))]
+    BackupFailed(PathBuf, #[source] std::io::Error),
 
     #[error("{}", translate!("install-error-install-failed", "from" => .0.quote(), "to" => .1.quote(), "error" => .2.clone()))]
     InstallFailed(PathBuf, PathBuf, String),
@@ -916,9 +916,8 @@ fn perform_backup(to: &Path, b: &Behavior) -> UResult<Option<PathBuf>> {
         }
         let backup_path = backup_control::get_backup_path(b.backup_mode, to, &b.suffix);
         if let Some(ref backup_path) = backup_path {
-            fs::rename(to, backup_path).map_err(|err| {
-                InstallError::BackupFailed(to.to_path_buf(), backup_path.clone(), err)
-            })?;
+            fs::rename(to, backup_path)
+                .map_err(|err| InstallError::BackupFailed(to.to_path_buf(), err))?;
         }
         Ok(backup_path)
     } else {

tests/by-util/test_install.rs

@@ -17,6 +17,7 @@ use std::process;
 use std::sync::OnceLock;
 #[cfg(any(target_os = "linux", target_os = "android"))]
 use std::thread::sleep;
+use uucore::error::strip_errno;
 use uucore::process::{getegid, geteuid};
 #[cfg(all(
     feature = "feat_selinux",
@@ -1383,6 +1384,20 @@ fn test_install_backup_custom_suffix_via_env() {
     assert!(at.file_exists(format!("{file_b}{suffix}")));
 }
 
+#[test]
+fn test_install_backup_error_includes_cause() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.touch("source");
+    at.touch("target");
+    at.mkdir("target.backup");
+    let error = strip_errno(&fs::rename(at.plus("target"), at.plus("target.backup")).unwrap_err());
+
+    ucmd.env("SIMPLE_BACKUP_SUFFIX", ".backup")
+        .args(&["--backup", "source", "target"])
+        .fails()
+        .stderr_is(format!("install: cannot backup 'target': {error}\n"));
+}
+
 #[test]
 fn test_install_backup_numbered_with_t() {
     let scene = TestScenario::new(util_name!());