date: use PosixCustom formatting for GNU-compatible output (#10245)

src/uu/date/src/date.rs

@@ -8,7 +8,7 @@
 mod locale;
 
 use clap::{Arg, ArgAction, Command};
-use jiff::fmt::strtime;
+use jiff::fmt::strtime::{self, BrokenDownTime, Config, PosixCustom};
 use jiff::tz::{TimeZone, TimeZoneDatabase};
 use jiff::{Timestamp, Zoned};
 use std::collections::HashMap;
@@ -431,21 +431,23 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let mut stdout = BufWriter::new(std::io::stdout().lock());
 
     // Format all the dates
+    let config = Config::new().custom(PosixCustom::new()).lenient(true);
     for date in dates {
         match date {
-            // TODO: Switch to lenient formatting.
-            Ok(date) => match strtime::format(format_string, &date) {
-                Ok(s) => writeln!(stdout, "{s}").map_err(|e| {
-                    USimpleError::new(1, translate!("date-error-write", "error" => e))
-                })?,
-                Err(e) => {
-                    let _ = stdout.flush();
-                    return Err(USimpleError::new(
-                        1,
-                        translate!("date-error-invalid-format", "format" => format_string, "error" => e),
-                    ));
+            Ok(date) => {
+                match BrokenDownTime::from(&date).to_string_with_config(&config, format_string) {
+                    Ok(s) => writeln!(stdout, "{s}").map_err(|e| {
+                        USimpleError::new(1, translate!("date-error-write", "error" => e))
+                    })?,
+                    Err(e) => {
+                        let _ = stdout.flush();
+                        return Err(USimpleError::new(
+                            1,
+                            translate!("date-error-invalid-format", "format" => format_string, "error" => e),
+                        ));
+                    }
                 }
-            },
+            }
             Err((input, _err)) => {
                 let _ = stdout.flush();
                 show!(USimpleError::new(

tests/by-util/test_date.rs

@@ -480,9 +480,8 @@ fn test_date_set_valid_4() {
 
 #[test]
 fn test_invalid_format_string() {
-    let result = new_ucmd!().arg("+%!").fails();
-    result.no_stdout();
-    assert!(result.stderr_str().starts_with("date: invalid format "));
+    // With lenient mode, invalid format sequences are output literally (like GNU date)
+    new_ucmd!().arg("+%!").succeeds().stdout_is("%!\n");
 }
 
 #[test]
@@ -1446,3 +1445,27 @@ fn test_date_locale_fr_french() {
         "Output should include timezone information, got: {stdout}"
     );
 }
+
+#[test]
+fn test_date_posix_format_specifiers() {
+    let cases = [
+        // %r: 12-hour time with zero-padded hour (08:17:48 AM, not 8:17:48 AM)
+        ("%r", "08:17:48 AM"),
+        // %x: locale date in MM/DD/YY format
+        ("%x", "01/19/97"),
+        // %X: locale time in HH:MM:SS format
+        ("%X", "08:17:48"),
+        // %:8z: invalid format (width between : and z) should output literally (lenient mode)
+        ("%:8z", "%:8z"),
+    ];
+
+    for (format, expected) in cases {
+        new_ucmd!()
+            .env("TZ", "UTC")
+            .arg("-d")
+            .arg("1997-01-19 08:17:48")
+            .arg(format!("+{format}"))
+            .succeeds()
+            .stdout_is(format!("{expected}\n"));
+    }
+}