date: Properly support %#z, instead of rejecting the format

It's easy to just replace %#z with %z as the capitalization makes
no sense anyway.

src/uu/date/src/date.rs

@@ -274,13 +274,6 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
             match date {
                 Ok(date) => {
                     let format_string = custom_time_format(format_string);
-                    // Refuse to pass this string to chrono as it is crashing in this crate
-                    if format_string.contains("%#z") {
-                        return Err(USimpleError::new(
-                            1,
-                            format!("invalid format {}", format_string.replace("%f", "%N")),
-                        ));
-                    }
                     // Hack to work around panic in chrono,
                     // TODO - remove when a fix for https://github.com/chronotope/chrono/issues/623 is released
                     let format_items = StrftimeItems::new(format_string.as_str());

src/uucore/src/lib/features/custom_tz_fmt.rs

@@ -35,8 +35,10 @@ fn timezone_abbreviation() -> String {
 /// A string that can be used as parameter of the chrono functions that use formats
 pub fn custom_time_format(fmt: &str) -> String {
     // TODO - Revisit when chrono 0.5 is released. https://github.com/chronotope/chrono/issues/970
+    // chrono crashes on %#z, but it's the same as %z anyway.
     // GNU `date` uses `%N` for nano seconds, however the `chrono` crate uses `%f`.
-    fmt.replace("%N", "%f")
+    fmt.replace("%#z", "%z")
+        .replace("%N", "%f")
         .replace("%Z", timezone_abbreviation().as_ref())
 }
 

tests/by-util/test_date.rs

@@ -381,10 +381,12 @@ fn test_invalid_format_string() {
 }
 
 #[test]
-fn test_unsupported_format() {
-    let result = new_ucmd!().arg("+%#z").fails();
-    result.no_stdout();
-    assert!(result.stderr_str().starts_with("date: invalid format %#z"));
+fn test_capitalized_numeric_time_zone() {
+    // %z     +hhmm numeric time zone (e.g., -0400)
+    // # is supposed to capitalize, which makes little sense here, but chrono crashes
+    // on such format so it's good to test.
+    let re = Regex::new(r"^[+-]\d{4,4}\n$").unwrap();
+    new_ucmd!().arg("+%#z").succeeds().stdout_matches(&re);
 }
 
 #[test]