date: reject options to print and set the time together

src/uu/date/locales/en-US.ftl

@@ -108,3 +108,5 @@ date-error-format-modifier-width-too-large = format modifier width '{$width}' is
 date-error-format-missing-plus = the argument {$arg} lacks a leading '+';
   when using an option to specify date(s), any non-option
   argument must be a format string beginning with '+'
+
+date-error-print-and-set = the options to print and set the time may not be used together

src/uu/date/src/date.rs

@@ -24,7 +24,7 @@ use std::sync::OnceLock;
 use thiserror::Error;
 use uucore::display::Quotable;
 use uucore::error::FromIo;
-use uucore::error::{UError, UResult, strip_errno};
+use uucore::error::{UError, UResult, UUsageError, strip_errno};
 #[cfg(feature = "i18n-datetime")]
 use uucore::i18n::datetime::{localize_format_string, should_use_icu_locale};
 use uucore::translate;
@@ -351,6 +351,16 @@ fn parse_military_timezone_with_offset(s: &str) -> Option<(i32, DayDelta)> {
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let matches = uucore::clap_localization::handle_clap_result(uu_app(), args)?;
 
+    if matches.contains_id(OPT_SET)
+        && [OPT_DATE, OPT_FILE, OPT_REFERENCE, OPT_RESOLUTION]
+            .iter()
+            .any(|option| {
+                matches.value_source(option) == Some(clap::parser::ValueSource::CommandLine)
+            })
+    {
+        return Err(UUsageError::new(1, translate!("date-error-print-and-set")));
+    }
+
     let date_source = if let Some(date_os) = matches.get_one::<OsString>(OPT_DATE) {
         // Convert OsString to String, handling invalid UTF-8 with GNU-compatible error
         let date = date_os.to_str().ok_or_else(|| DateError::InvalidDate {

tests/by-util/test_date.rs

@@ -3446,3 +3446,28 @@ fn test_non_utf8_operands_are_octal_escaped() {
             .stderr_contains(expected);
     }
 }
+
+#[test]
+fn test_date_print_and_set_conflict() {
+    // Invalid set input also prevents any clock change if validation regresses.
+    for print_args in [
+        vec!["-d", "@0"],
+        vec!["-f", "missing"],
+        vec!["-r", "missing"],
+        vec!["--resolution"],
+    ] {
+        for set_first in [true, false] {
+            let mut args = vec!["-s", "not-a-date"];
+            if set_first {
+                args.extend(&print_args);
+            } else {
+                args.splice(0..0, print_args.iter().copied());
+            }
+            new_ucmd!()
+                .args(&args)
+                .fails_with_code(1)
+                .no_stdout()
+                .stderr_contains("the options to print and set the time may not be used together");
+        }
+    }
+}