date: skip '-' flag for composite strftime specifiers

GNU date treats composite strftime specifiers (%D, %F, %T, %r, %R, %c,
%x, %X) as atomic: flags like '-' apply to the whole expansion, not to
inner sub-fields. uutils let the '-' flag propagate into inner specifiers,
producing e.g. '6/15/24' for %-D instead of '06/15/24'.

Strip the '-' flag from composite specifiers before applying modifiers,
so inner fields keep their default padding while width and other flags
still work.

Fixes #11657

Author: Navaneeth Yadamreddy

src/uu/date/src/format_modifiers.rs

@@ -236,7 +236,25 @@ fn format_with_modifiers(
                 let formatted = broken_down.to_string_with_config(config, &base_format)?;
 
                 if !parsed.flags.is_empty() || parsed.width.is_some() {
-                    let modified = apply_modifiers(&formatted, &parsed)?;
+                    // Strip `-` from composite specifiers (D, F, T, etc.) so
+                    // apply_modifiers does not remove inner leading zeros.
+                    let effective =
+                        if is_composite_specifier(parsed.spec) && parsed.flags.contains('-') {
+                            ParsedSpec {
+                                flags: &parsed.flags.replace('-', ""),
+                                width: parsed.width,
+                                spec: parsed.spec,
+                                len: parsed.len,
+                            }
+                        } else {
+                            ParsedSpec {
+                                flags: parsed.flags,
+                                width: parsed.width,
+                                spec: parsed.spec,
+                                len: parsed.len,
+                            }
+                        };
+                    let modified = apply_modifiers(&formatted, &effective)?;
                     result.push_str(&modified);
                 } else {
                     result.push_str(&formatted);
@@ -256,6 +274,13 @@ fn format_with_modifiers(
     Ok(result)
 }
 
+/// Returns true if the specifier is composite (multi-field, e.g. %D = %m/%d/%y).
+fn is_composite_specifier(spec: &str) -> bool {
+    // strip leading colons (e.g. ":z" → "z")
+    let s = spec.trim_start_matches(':');
+    matches!(s, "D" | "F" | "T" | "r" | "R" | "c" | "x" | "X")
+}
+
 /// Returns true if the specifier produces text output (default pad is space)
 /// rather than numeric output (default pad is zero).
 fn is_text_specifier(specifier: &str) -> bool {

tests/by-util/test_date.rs

@@ -3148,3 +3148,27 @@ fn test_nanoseconds_width_prefix_ignored_issue12001() {
     // compare to 4 because of \n
     assert_eq!(result.stdout().len(), 4);
 }
+
+// Regression test for https://github.com/uutils/coreutils/issues/11657
+// strftime flags like `-` should not propagate into composite specifiers like %D
+#[test]
+fn test_date_format_composite_specifier_flags_issue11657() {
+    // GNU date treats %D as atomic — the `-` flag should NOT strip leading
+    // zeros from the month/day within the expansion of %D.
+    new_ucmd!()
+        .env("TZ", "UTC")
+        .arg("-d")
+        .arg("2024-06-15")
+        .arg("+%-D")
+        .succeeds()
+        .stdout_is("06/15/24\n");
+
+    // Same for %F (ISO date)
+    new_ucmd!()
+        .env("TZ", "UTC")
+        .arg("-d")
+        .arg("2024-01-05")
+        .arg("+%-F")
+        .succeeds()
+        .stdout_is("2024-01-05\n");
+}