date: treat empty --file lines as midnight today like GNU

src/uu/date/src/date.rs

@@ -1157,7 +1157,17 @@ fn parse_dates_from_reader<R: Read + 'static>(
             bytes.pop();
         }
         match String::from_utf8(bytes) {
-            Ok(s) => parse_date(s, now, dbg_opts, allow_extended),
+            Ok(s) => {
+                let trimmed = s.trim();
+                if trimmed.is_empty() || trimmed == "-" {
+                    // GNU treats empty lines (and a lone "-", like `-d`) in
+                    // `--file`/stdin input as midnight today, not the
+                    // current time (issue #14498).
+                    Ok(ParsedDateTime::InRange(midnight_today(now)))
+                } else {
+                    parse_date(s, now, dbg_opts, allow_extended)
+                }
+            }
             // Report lines with invalid UTF-8 (with non-printable bytes
             // octal-escaped like GNU) instead of silently stopping the input
             Err(e) => Err((
@@ -1168,6 +1178,18 @@ fn parse_dates_from_reader<R: Read + 'static>(
     }))
 }
 
+/// Midnight at the start of `now`'s civil date, in its time zone.
+///
+/// Empty (whitespace-only or lone `-`) lines in `--file`/stdin input mean
+/// midnight today for GNU `date`, mirroring the `-d` handling above. Falls
+/// back to `now` itself on zones whose midnight does not exist.
+fn midnight_today(now: &Zoned) -> Zoned {
+    now.date()
+        .at(0, 0, 0, 0)
+        .to_zoned(now.time_zone().clone())
+        .unwrap_or_else(|_| now.clone())
+}
+
 /// Parse a string into either an in-range [`Zoned`] value or an extended date.
 fn parse_date<S: AsRef<str>>(
     s: S,

tests/by-util/test_date.rs

@@ -656,6 +656,19 @@ fn test_date_for_file_with_non_utf8_path() {
     ucmd.arg("--file").arg(file).succeeds().no_output();
 }
 
+#[test]
+fn test_date_file_empty_lines_are_midnight() {
+    // Empty, whitespace-only, and lone `-` lines mean midnight today,
+    // like GNU, not the current time (#14498).
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.write("dates", "\n   \n-\n");
+    ucmd.arg("--file")
+        .arg("dates")
+        .arg("+%H:%M")
+        .succeeds()
+        .stdout_is("00:00\n00:00\n00:00\n");
+}
+
 #[test]
 fn test_date_file_invalid_utf8_line() {
     let (at, mut ucmd) = at_and_ucmd!();