du: deduplicate the input

Should fix:
tests/du/hard-link.sh

src/uu/du/src/du.rs

@@ -649,6 +649,8 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
     let summarize = matches.get_flag(options::SUMMARIZE);
 
+    let count_links = matches.get_flag(options::COUNT_LINKS);
+
     let max_depth = parse_depth(
         matches
             .get_one::<String>(options::MAX_DEPTH)
@@ -669,15 +671,19 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         }
 
         read_files_from(file_from)?
-    } else {
+    } else if let Some(files) = matches.get_many::<String>(options::FILE) {
-        match matches.get_one::<String>(options::FILE) {
+        let files = files.map(PathBuf::from);
-            Some(_) => matches
+        if count_links {
-                .get_many::<String>(options::FILE)
+            files.collect()
-                .unwrap()
+        } else {
-                .map(PathBuf::from)
+            // Deduplicate while preserving order
-                .collect(),
+            let mut seen = std::collections::HashSet::new();
-            None => vec![PathBuf::from(".")],
+            files
+                .filter(|path| seen.insert(path.clone()))
+                .collect::<Vec<_>>()
         }
+    } else {
+        vec![PathBuf::from(".")]
     };
 
     let time = matches.contains_id(options::TIME).then(|| {
@@ -719,7 +725,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         } else {
             Deref::None
         },
-        count_links: matches.get_flag(options::COUNT_LINKS),
+        count_links,
         verbose: matches.get_flag(options::VERBOSE),
         excludes: build_exclude_patterns(&matches)?,
     };

tests/by-util/test_du.rs

@@ -1194,3 +1194,61 @@ fn test_human_size() {
         .succeeds()
         .stdout_contains(format!("1.0K	{dir}"));
 }
+
+#[cfg(not(target_os = "android"))]
+#[test]
+fn test_du_deduplicated_input_args() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+
+    at.mkdir("d");
+    at.mkdir("d/d");
+    at.touch("d/f");
+    at.hard_link("d/f", "d/h");
+
+    let result = ts
+        .ucmd()
+        .arg("--inodes")
+        .arg("d")
+        .arg("d")
+        .arg("d")
+        .succeeds();
+    result.no_stderr();
+
+    let result_seq: Vec<String> = result
+        .stdout_str()
+        .lines()
+        .map(|x| x.parse().unwrap())
+        .collect();
+    #[cfg(windows)]
+    assert_eq!(result_seq, ["1\td\\d", "3\td"]);
+    #[cfg(not(windows))]
+    assert_eq!(result_seq, ["1\td/d", "3\td"]);
+}
+
+#[cfg(not(target_os = "android"))]
+#[test]
+fn test_du_no_deduplicated_input_args() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+
+    at.mkdir("d");
+    at.touch("d/d");
+
+    let result = ts
+        .ucmd()
+        .arg("--inodes")
+        .arg("-l")
+        .arg("d")
+        .arg("d")
+        .arg("d")
+        .succeeds();
+    result.no_stderr();
+
+    let result_seq: Vec<String> = result
+        .stdout_str()
+        .lines()
+        .map(|x| x.parse().unwrap())
+        .collect();
+    assert_eq!(result_seq, ["2\td", "2\td", "2\td"]);
+}