mv: 'mv source hardlink' should fail

fixes: tests/mv/force.sh

src/uu/mv/Cargo.toml

@@ -18,7 +18,7 @@ path = "src/mv.rs"
 clap = { workspace=true }
 fs_extra = { workspace=true }
 indicatif = { workspace=true }
-uucore = { workspace=true }
+uucore = { workspace=true, features=["fs"] }
 
 [[bin]]
 name = "mv"

src/uu/mv/src/mv.rs

@@ -25,6 +25,7 @@ use std::path::{Path, PathBuf};
 use uucore::backup_control::{self, BackupMode};
 use uucore::display::Quotable;
 use uucore::error::{set_exit_code, FromIo, UError, UResult, USimpleError, UUsageError};
+use uucore::fs::are_hardlinks_to_same_file;
 use uucore::update_control::{self, UpdateMode};
 use uucore::{format_usage, help_about, help_section, help_usage, prompt_yes, show};
 
@@ -268,7 +269,7 @@ fn exec(files: &[OsString], b: &Behavior) -> UResult<()> {
             }
 
             // GNU semantics are: if the source and target are the same, no move occurs and we print an error
-            if source.eq(target) {
+            if source.eq(target) || are_hardlinks_to_same_file(source, target) {
                 // Done to match GNU semantics for the dot file
                 if source.eq(Path::new(".")) || source.ends_with("/.") || source.is_file() {
                     return Err(MvError::SameFile(

tests/by-util/test_mv.rs

@@ -400,6 +400,23 @@ fn test_mv_same_file() {
         .stderr_is(format!("mv: '{file_a}' and '{file_a}' are the same file\n",));
 }
 
+#[test]
+#[cfg(unix)]
+fn test_mv_same_hardlink() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    let file_a = "test_mv_same_file_a";
+    let file_b = "test_mv_same_file_b";
+    at.touch(file_a);
+
+    at.hard_link(file_a, file_b);
+
+    at.touch(file_a);
+    ucmd.arg(file_a)
+        .arg(file_b)
+        .fails()
+        .stderr_is(format!("mv: '{file_a}' and '{file_b}' are the same file\n",));
+}
+
 #[test]
 fn test_mv_same_file_not_dot_dir() {
     let (at, mut ucmd) = at_and_ucmd!();