date: handle parentheses as comments like GNU date

src/uu/date/src/date.rs

@@ -3,14 +3,15 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// spell-checker:ignore strtime ; (format) DATEFILE MMDDhhmm ; (vars) datetime datetimes getres AWST ACST AEST
+// spell-checker:ignore strtime ; (format) DATEFILE MMDDhhmm ; (vars) datetime datetimes getres AWST ACST AEST foobarbaz
 
 mod locale;
 
 use clap::{Arg, ArgAction, Command};
 use jiff::fmt::strtime::{self, BrokenDownTime, Config, PosixCustom};
 use jiff::tz::{TimeZone, TimeZoneDatabase};
 use jiff::{Timestamp, Zoned};
+use std::borrow::Cow;
 use std::collections::HashMap;
 use std::fs::File;
 use std::io::{BufRead, BufReader, BufWriter, Write};
@@ -130,6 +131,52 @@ enum DayDelta {
     Next,
 }
 
+/// Strip parenthesized comments from a date string.
+///
+/// GNU date removes balanced parentheses and their content, treating them as comments.
+/// If parentheses are unbalanced, everything from the unmatched '(' onwards is ignored.
+///
+/// Examples:
+/// - "2026(comment)-01-05" -> "2026-01-05"
+/// - "1(ignore comment to eol" -> "1"
+/// - "(" -> ""
+/// - "((foo)2026-01-05)" -> ""
+fn strip_parenthesized_comments(input: &str) -> Cow<'_, str> {
+    if !input.contains('(') {
+        return Cow::Borrowed(input);
+    }
+
+    let mut result = String::with_capacity(input.len());
+    let mut chars = input.chars();
+
+    while let Some(c) = chars.next() {
+        if c == '(' {
+            // Look for matching closing parenthesis
+            let mut depth = 1;
+            for inner_c in chars.by_ref() {
+                if inner_c == '(' {
+                    depth += 1;
+                } else if inner_c == ')' {
+                    depth -= 1;
+                    if depth == 0 {
+                        break;
+                    }
+                }
+            }
+
+            // If unmatched opening paren (depth > 0), stop processing entirely
+            if depth > 0 {
+                break;
+            }
+            // If balanced, the parentheses and their content are skipped (comment)
+        } else {
+            result.push(c);
+        }
+    }
+
+    Cow::Owned(result)
+}
+
 /// Parse military timezone with optional hour offset.
 /// Pattern: single letter (a-z except j) optionally followed by 1-2 digits.
 /// Returns Some(total_hours_in_utc) or None if pattern doesn't match.
@@ -286,7 +333,10 @@ 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) => {
+            // GNU compatibility (Comments in parentheses)
+            let input = strip_parenthesized_comments(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();
@@ -887,4 +937,38 @@ mod tests {
         assert_eq!(parse_military_timezone_with_offset("m999"), None); // Too long
         assert_eq!(parse_military_timezone_with_offset("9m"), None); // Starts with digit
     }
+
+    #[test]
+    fn test_strip_parenthesized_comments() {
+        assert_eq!(strip_parenthesized_comments("hello"), "hello");
+        assert_eq!(strip_parenthesized_comments("2026-01-05"), "2026-01-05");
+        assert_eq!(strip_parenthesized_comments("("), "");
+        assert_eq!(strip_parenthesized_comments("1(comment"), "1");
+        assert_eq!(
+            strip_parenthesized_comments("2026-01-05(this is a comment"),
+            "2026-01-05"
+        );
+        assert_eq!(
+            strip_parenthesized_comments("2026(comment)-01-05"),
+            "2026-01-05"
+        );
+        assert_eq!(strip_parenthesized_comments("()"), "");
+        assert_eq!(strip_parenthesized_comments("((foo)2026-01-05)"), "");
+
+        // These cases test the balanced parentheses removal feature
+        // which extends beyond what GNU date strictly supports
+        assert_eq!(strip_parenthesized_comments("a(b)c"), "ac");
+        assert_eq!(strip_parenthesized_comments("a(b)c(d)e"), "ace");
+        assert_eq!(strip_parenthesized_comments("(a)(b)"), "");
+
+        // When parentheses are unmatched, processing stops at the unmatched opening paren
+        // In this case "a(b)c(d", the (b) is balanced but (d is unmatched
+        // We process "a(b)c" and stop at the unmatched "(d"
+        assert_eq!(strip_parenthesized_comments("a(b)c(d"), "ac");
+
+        // Additional edge cases for nested and complex parentheses
+        assert_eq!(strip_parenthesized_comments("a(b(c)d)e"), "ae"); // Nested balanced
+        assert_eq!(strip_parenthesized_comments("a(b(c)d"), "a"); // Nested unbalanced
+        assert_eq!(strip_parenthesized_comments("a(b)c(d)e(f"), "ace"); // Multiple groups, last unmatched
+    }
 }

tests/by-util/test_date.rs

@@ -1497,3 +1497,40 @@ fn test_date_format_x_locale_aware() {
         .succeeds()
         .stdout_is("19/01/1997\n");
 }
+
+#[test]
+fn test_date_parenthesis_comment() {
+    // GNU compatibility: Text in parentheses is treated as a comment and removed.
+    let cases = [
+        // (input, format, expected_output)
+        ("(", "+%H:%M:%S", "00:00:00\n"),
+        ("1(ignore comment to eol", "+%H:%M:%S", "01:00:00\n"),
+        ("2026-01-05(this is a comment", "+%Y-%m-%d", "2026-01-05\n"),
+        ("2026(this is a comment)-01-05", "+%Y-%m-%d", "2026-01-05\n"),
+        ("((foo)2026-01-05)", "+%H:%M:%S", "00:00:00\n"), // Nested/unbalanced case
+        ("(2026-01-05(foo))", "+%H:%M:%S", "00:00:00\n"), // Balanced parentheses removed (empty result)
+    ];
+
+    for (input, format, expected) in cases {
+        new_ucmd!()
+            .env("TZ", "UTC")
+            .arg("-d")
+            .arg(input)
+            .arg("-u")
+            .arg(format)
+            .succeeds()
+            .stdout_only(expected);
+    }
+}
+
+#[test]
+fn test_date_parenthesis_vs_other_special_chars() {
+    // Ensure parentheses are special but other chars like [, ., ^ are still rejected
+    for special_char in ["[", ".", "^"] {
+        new_ucmd!()
+            .arg("-d")
+            .arg(special_char)
+            .fails()
+            .stderr_contains("invalid date");
+    }
+}