printf: pad octal numbers with zeros on the left

src/uucore/src/lib/features/format/num_format.rs

@@ -143,11 +143,13 @@ impl Formatter for UnsignedInt {
             UnsignedIntVariant::Octal(Prefix::No) => format!("{x:o}"),
             UnsignedIntVariant::Octal(Prefix::Yes) => {
                 // The prefix that rust uses is `0o`, but GNU uses `0`.
-                // We also need to take into account that 0 should not be 00
+                // We also need to take into account that 0 should not be 00 and
+                // that GNU pads prefixed octals with zeros.
+                //
                 // Since this is an unsigned int, we do not need to take the minus
                 // sign into account.
-                if x == 0 {
+                if x < 8u64.pow(self.precision.saturating_sub(1) as u32) {
-                    format!("{x:o}")
+                    format!("{x:0>width$o}", width = self.precision)
                 } else {
                     format!("0{x:o}")
                 }

tests/by-util/test_printf.rs

@@ -680,3 +680,31 @@ fn char_as_byte() {
 fn no_infinite_loop() {
     new_ucmd!().args(&["a", "b"]).succeeds().stdout_only("a");
 }
+
+#[test]
+fn pad_octal_with_prefix() {
+    new_ucmd!()
+        .args(&[">%#15.6o<", "0"])
+        .succeeds()
+        .stdout_only(">         000000<");
+
+    new_ucmd!()
+        .args(&[">%#15.6o<", "01"])
+        .succeeds()
+        .stdout_only(">         000001<");
+
+    new_ucmd!()
+        .args(&[">%#15.6o<", "01234"])
+        .succeeds()
+        .stdout_only(">         001234<");
+
+    new_ucmd!()
+        .args(&[">%#15.6o<", "012345"])
+        .succeeds()
+        .stdout_only(">         012345<");
+
+    new_ucmd!()
+        .args(&[">%#15.6o<", "0123456"])
+        .succeeds()
+        .stdout_only(">        0123456<");
+}