ls: finish the plug of mtime

Will help with tests/ls/ls-time

src/uu/ls/src/ls.rs

@@ -536,6 +536,7 @@ fn extract_time(options: &clap::ArgMatches) -> Time {
         match field.as_str() {
             "ctime" | "status" => Time::Change,
             "access" | "atime" | "use" => Time::Access,
+            "mtime" | "modification" => Time::Modification,
             "birth" | "creation" => Time::Birth,
             // below should never happen as clap already restricts the values.
             _ => unreachable!("Invalid field for --time"),
@@ -1442,12 +1443,14 @@ pub fn uu_app() -> Command {
                     "Show time in <field>:\n\
                         \taccess time (-u): atime, access, use;\n\
                         \tchange time (-t): ctime, status.\n\
+                        \tmodification time: mtime, modification.\n\
                         \tbirth time: birth, creation;",
                 )
                 .value_name("field")
                 .value_parser(ShortcutValueParser::new([
                     PossibleValue::new("atime").alias("access").alias("use"),
                     PossibleValue::new("ctime").alias("status"),
+                    PossibleValue::new("mtime").alias("modification"),
                     PossibleValue::new("birth").alias("creation"),
                 ]))
                 .hide_possible_values(true)

tests/by-util/test_ls.rs

@@ -2099,6 +2099,30 @@ fn test_ls_order_time() {
     }
 }
 
+#[test]
+fn test_ls_order_mtime() {
+    use std::time::SystemTime;
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    let f3 = at.make_file("test-3");
+    f3.set_modified(SystemTime::now()).unwrap();
+    let f4 = at.make_file("test-4");
+    f4.set_modified(SystemTime::now()).unwrap();
+    let f1 = at.make_file("test-1");
+    f1.set_modified(SystemTime::now()).unwrap();
+    let f2 = at.make_file("test-2");
+    f2.set_modified(SystemTime::now()).unwrap();
+
+    let result = scene.ucmd().arg("-t").arg("--time=mtime").succeeds();
+    result.stdout_only("test-2\ntest-1\ntest-4\ntest-3\n");
+    f3.set_modified(SystemTime::now()).unwrap();
+
+    f4.set_modified(SystemTime::now()).unwrap();
+    let result = scene.ucmd().arg("-t").arg("--time=mtime").succeeds();
+    result.stdout_only("test-4\ntest-3\ntest-2\ntest-1\n");
+}
+
 #[test]
 fn test_ls_non_existing() {
     new_ucmd!().arg("doesntexist").fails();