stat: print the -f block and free node counts signed, as GNU does

src/uu/stat/src/stat.rs

@@ -544,16 +544,18 @@ fn process_token_filesystem(
             format,
         } => {
             let output = match format {
+                // GNU prints the block and free node counts signed (`out_int`), so
+                // `+` and ` ` add a sign; the other counts are unsigned.
                 // free blocks available to non-superuser
-                'a' => OutputType::Unsigned(meta.avail_blocks()),
+                'a' => OutputType::Integer(meta.avail_blocks() as i64),
                 // total data blocks in file system
-                'b' => OutputType::Unsigned(meta.total_blocks()),
+                'b' => OutputType::Integer(meta.total_blocks() as i64),
                 // total file nodes in file system
                 'c' => OutputType::Unsigned(meta.total_file_nodes()),
                 // free file nodes in file system
-                'd' => OutputType::Unsigned(meta.free_file_nodes()),
+                'd' => OutputType::Integer(meta.free_file_nodes() as i64),
                 // free blocks in file system
-                'f' => OutputType::Unsigned(meta.free_blocks()),
+                'f' => OutputType::Integer(meta.free_blocks() as i64),
                 // file system ID in hex
                 'i' => OutputType::UnsignedHex(meta.fsid()),
                 // maximum length of filenames

tests/by-util/test_stat.rs

@@ -774,6 +774,25 @@ fn test_printf_invalid_directive() {
         .stderr_contains("'%9%': invalid directive");
 }
 
+#[test]
+#[cfg(any(target_os = "linux", target_os = "android", target_os = "macos"))]
+fn test_fs_signed_counts_take_sign_flags() {
+    // GNU prints %a, %b, %d and %f signed, so `+` and ` ` add a sign there,
+    // while the unsigned counts (%c, %s) ignore them.
+    let out = new_ucmd!()
+        .args(&["-f", "--printf=%+a|% b|%+d|%+f|%+c|%+s", "."])
+        .succeeds()
+        .stdout_move_str();
+    let fields: Vec<&str> = out.split('|').collect();
+    assert!(fields[0].starts_with('+'), "{out}");
+    assert!(fields[1].starts_with(' '), "{out}");
+    assert!(fields[2].starts_with('+'), "{out}");
+    assert!(fields[3].starts_with('+'), "{out}");
+    for unsigned in &fields[4..] {
+        assert!(unsigned.chars().all(|c| c.is_ascii_digit()), "{out}");
+    }
+}
+
 #[test]
 fn test_invalid_directive_after_multibyte_char() {
     let ts = TestScenario::new(util_name!());