date: -d empty string should be treated as midnight today

src/uu/date/src/date.rs

@@ -205,6 +205,11 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     // Iterate over all dates - whether it's a single date or a file.
     let dates: Box<dyn Iterator<Item = _>> = match settings.date_source {
         DateSource::Human(ref input) => {
+            let input = input.trim();
+            // GNU compatibility (Empty string):
+            // An empty string (or whitespace-only) should be treated as midnight today.
+            let is_empty_or_whitespace = input.is_empty();
+
             // GNU compatibility (Military timezone 'J'):
             // 'J' is reserved for local time in military timezones.
             // GNU date accepts it and treats it as midnight today (00:00:00).
@@ -218,8 +223,8 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
             let is_pure_digits =
                 !input.is_empty() && input.len() <= 4 && input.chars().all(|c| c.is_ascii_digit());
 
-            let date = if is_military_j {
-                // Treat 'J' as midnight today (00:00:00) in local time
+            let date = if is_empty_or_whitespace || is_military_j {
+                // Treat empty string or 'J' as midnight today (00:00:00) in local time
                 let date_part =
                     strtime::format("%F", &now).unwrap_or_else(|_| String::from("1970-01-01"));
                 let offset = if settings.utc {

tests/by-util/test_date.rs

@@ -973,8 +973,7 @@ fn test_date_military_timezone_j_variations() {
 }
 
 #[test]
-#[ignore = "we use current time, GNU uses midnight"]
-fn test_date_fuzz_empty_string() {
+fn test_date_empty_string() {
     // Empty string should be treated as midnight today
     new_ucmd!()
         .env("TZ", "UTC+1")
@@ -984,6 +983,33 @@ fn test_date_fuzz_empty_string() {
         .stdout_contains("00:00:00");
 }
 
+#[test]
+fn test_date_empty_string_variations() {
+    // Test multiple variations of empty/whitespace strings
+    // All should produce midnight (00:00:00)
+    let test_cases = vec!["", " ", "  ", "\t", "\n", " \t ", "\t\n\t"];
+
+    for input in test_cases {
+        new_ucmd!()
+            .env("TZ", "UTC")
+            .arg("-d")
+            .arg(input)
+            .arg("+%T")
+            .succeeds()
+            .stdout_is("00:00:00\n");
+    }
+
+    // Test with -u flag to verify UTC behavior
+    new_ucmd!()
+        .arg("-u")
+        .arg("-d")
+        .arg("")
+        .arg("+%T %Z")
+        .succeeds()
+        .stdout_contains("00:00:00")
+        .stdout_contains("UTC");
+}
+
 #[test]
 #[ignore = "we produce year 0008, GNU gives today 12:00"]
 fn test_date_fuzz_relative_m9() {