rm: match GNU's error for a bad --preserve-root value

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

@@ -50,6 +50,7 @@ rm-error-and-preserve-root-all-in-effect = and --preserve-root=all is in effect
 rm-error-cannot-remove = cannot remove {$file}
 rm-error-cannot-remove-changed = cannot remove {$file}: File changed while removing
 rm-error-may-not-abbreviate-no-preserve-root = you may not abbreviate the --no-preserve-root option
+rm-error-unrecognized-preserve-root-argument = unrecognized --preserve-root argument: '{$arg}'
 rm-error-standard-output = standard output: {$error}
 
 # Verbose messages

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

@@ -48,6 +48,7 @@ rm-error-refusing-to-remove-directory = refus de supprimer le répertoire '.' ou
 rm-error-cannot-remove = impossible de supprimer {$file}
 rm-error-cannot-remove-changed = impossible de supprimer {$file} : Le fichier a changé pendant la suppression
 rm-error-may-not-abbreviate-no-preserve-root = Vous ne pouvez pas abréger l'option --no-preserve-root
+rm-error-unrecognized-preserve-root-argument = argument --preserve-root non reconnu : '{$arg}'
 rm-error-standard-output = sortie standard : {$error}
 
 # Messages verbeux

src/uu/rm/src/rm.rs

@@ -264,9 +264,16 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     };
 
     let preserve_root = !matches.get_flag(OPT_NO_PRESERVE_ROOT);
-    let preserve_root_all = matches
-        .get_one::<String>(OPT_PRESERVE_ROOT)
-        .is_some_and(|value| value == "all");
+    let preserve_root_all = match matches.get_one::<String>(OPT_PRESERVE_ROOT) {
+        Some(value) if value == "all" => true,
+        Some(value) => {
+            return Err(USimpleError::new(
+                1,
+                translate!("rm-error-unrecognized-preserve-root-argument", "arg" => value.clone()),
+            ));
+        }
+        None => false,
+    };
     let recursive = matches.get_flag(OPT_RECURSIVE);
 
     let options = Options {
@@ -428,8 +435,7 @@ pub fn uu_app() -> Command {
                 // additionally refuses to cross into another file system.
                 .num_args(0..=1)
                 .require_equals(true)
-                .value_name("all")
-                .value_parser(["all"]),
+                .value_name("all"),
         )
         .arg(
             Arg::new(OPT_RECURSIVE)

tests/by-util/test_rm.rs

@@ -249,7 +249,19 @@ fn test_preserve_root_rejects_unknown_value() {
         .arg("-rf")
         .arg("anything")
         .fails()
-        .stderr_contains("invalid value 'bogus'");
+        .stderr_is("rm: unrecognized --preserve-root argument: 'bogus'\n");
+}
+
+#[test]
+fn test_preserve_root_rejects_abbreviation() {
+    // Unlike --interactive and friends, --preserve-root does not accept
+    // abbreviations of its one value at all: GNU rejects even 'a'.
+    new_ucmd!()
+        .arg("--preserve-root=a")
+        .arg("-rf")
+        .arg("anything")
+        .fails()
+        .stderr_is("rm: unrecognized --preserve-root argument: 'a'\n");
 }
 
 #[test]