stty: clear previous values when setting grouped flags

src/uu/stty/src/stty.rs

@@ -980,22 +980,23 @@ fn print_flags<T: TermiosFlag>(
 fn apply_setting(termios: &mut Termios, setting: &AllFlags) -> nix::Result<()> {
     match setting {
         AllFlags::Baud(_, _) => apply_baud_rate_flag(termios, setting)?,
-        AllFlags::ControlFlags((setting, disable)) => {
-            setting.flag.apply(termios, !disable);
-        }
-        AllFlags::InputFlags((setting, disable)) => {
-            setting.flag.apply(termios, !disable);
-        }
-        AllFlags::LocalFlags((setting, disable)) => {
-            setting.flag.apply(termios, !disable);
-        }
-        AllFlags::OutputFlags((setting, disable)) => {
-            setting.flag.apply(termios, !disable);
-        }
+        AllFlags::ControlFlags((setting, disable)) => apply_flag(termios, setting, !disable),
+        AllFlags::InputFlags((setting, disable)) => apply_flag(termios, setting, !disable),
+        AllFlags::LocalFlags((setting, disable)) => apply_flag(termios, setting, !disable),
+        AllFlags::OutputFlags((setting, disable)) => apply_flag(termios, setting, !disable),
     }
     Ok(())
 }
 
+fn apply_flag<T: TermiosFlag>(termios: &mut Termios, setting: &Flag<T>, val: bool) {
+    // A grouped flag selects one value of a multi-bit field (e.g. `cs7` in CSIZE),
+    // so the bits of the previously selected value have to be cleared first.
+    if val && let Some(group) = setting.group {
+        group.apply(termios, false);
+    }
+    setting.flag.apply(termios, val);
+}
+
 fn apply_baud_rate_flag(termios: &mut Termios, input: &AllFlags) -> nix::Result<()> {
     if let AllFlags::Baud(rate, baud_type) = input {
         match baud_type {
@@ -1586,6 +1587,40 @@ mod tests {
         assert!(!check_flag_group(&flag_without_group, false));
     }
 
+    // The character size is tested here rather than on a pseudo-terminal,
+    // because Linux pseudo-terminals always keep cs8.
+    #[test]
+    fn test_apply_grouped_flag_replaces_previous_value() {
+        // SAFETY: all-zero bytes are a valid `termios`.
+        let mut termios = Termios::from(unsafe { std::mem::zeroed::<nix::libc::termios>() });
+        let apply = |termios: &mut Termios, arg: &str| {
+            let flags = string_to_flag(arg)
+                .map_or_else(|| combo_to_flags(arg), |flag| vec![ArgOptions::Flags(flag)]);
+            for flag in flags {
+                if let ArgOptions::Flags(flag) = flag {
+                    apply_setting(termios, &flag).unwrap();
+                }
+            }
+        };
+
+        for (arg, expected) in [
+            ("cs8", ControlFlags::CS8),
+            ("cs7", ControlFlags::CS7),
+            ("cs5", ControlFlags::CS5),
+            ("cs6", ControlFlags::CS6),
+            ("cs8", ControlFlags::CS8),
+            ("evenp", ControlFlags::CS7),
+            ("-evenp", ControlFlags::CS8),
+        ] {
+            apply(&mut termios, arg);
+            assert_eq!(
+                termios.control_flags & ControlFlags::CSIZE,
+                expected,
+                "after {arg}"
+            );
+        }
+    }
+
     // Additional tests for get_sane_control_char
     #[test]
     fn test_get_sane_control_char_all_defined() {

tests/by-util/test_stty.rs

@@ -3,7 +3,7 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// spell-checker:ignore parenb parmrk ixany iuclc onlcr ofdel icanon noflsh econl igpar ispeed ospeed NCCS nonhex gstty notachar cbreak evenp oddp CSIZE
+// spell-checker:ignore parenb parmrk ixany iuclc onlcr ofdel icanon noflsh econl igpar ispeed ospeed NCCS nonhex gstty notachar cbreak evenp oddp CSIZE tabdly
 
 #![cfg(unix)]
 
@@ -64,6 +64,53 @@ fn test_sane() {
         .stdout_str_check(|s| !s.contains("intr = ^A"));
 }
 
+/// Returns the settings from `group` that `stty --all` reports for the terminal at `path`.
+#[cfg(any(
+    target_vendor = "apple",
+    target_os = "android",
+    target_os = "haiku",
+    target_os = "linux"
+))]
+fn shown_settings(path: &str, group: &[&'static str]) -> Vec<&'static str> {
+    let stdout = new_ucmd!()
+        .args(&["--all", "--file", path])
+        .succeeds()
+        .stdout_move_str();
+    let words: Vec<&str> = stdout.split_whitespace().collect();
+    group
+        .iter()
+        .copied()
+        .filter(|s| words.contains(s))
+        .collect()
+}
+
+#[test]
+#[cfg(any(
+    target_vendor = "apple",
+    target_os = "android",
+    target_os = "haiku",
+    target_os = "linux"
+))]
+fn test_grouped_output_flag_replaces_previous_value() {
+    let (path, _controller, _replica) = pty_path();
+    let tabdly = ["tab0", "tab1", "tab2", "tab3"];
+
+    for (setting, expected) in [
+        ("tab1", "tab1"),
+        ("tab2", "tab2"),
+        ("tab0", "tab0"),
+        ("tab3", "tab3"),
+        ("sane", "tab0"),
+    ] {
+        new_ucmd!().args(&["--file", &path, setting]).succeeds();
+        assert_eq!(
+            shown_settings(&path, &tabdly),
+            [expected],
+            "after {setting}"
+        );
+    }
+}
+
 #[test]
 fn save_and_setting() {
     new_ucmd!()