Set terminal title unconditionally

Terminal titles are set with an OSC 0 sequence.  I don't think we want to
support terminals that react badly to unknown OSC (or CSI) sequences.

So let's remove our feature detection.

This will fix future false negatives along the lines of
https://github.com/fish-shell/fish-shell/pull/10037

CHANGELOG.rst

@@ -102,7 +102,7 @@ Completions
 
 Improved terminal support
 ^^^^^^^^^^^^^^^^^^^^^^^^^
-- Fish now checks for the ``ts`` capability in terminfo to determine if a terminal supports setting the window title (:issue:`10037`).
+- Fish now sets the terminal window title unconditionally (:issue:`10037`).
 
 Other improvements
 ------------------

src/env_dispatch.rs

@@ -40,9 +40,6 @@ const CURSES_VARIABLES: [&wstr; 3] = [
 /// Whether to use `posix_spawn()` when possible.
 static USE_POSIX_SPAWN: AtomicBool = AtomicBool::new(false);
 
-/// Whether we think we can set the terminal title or not.
-static CAN_SET_TERM_TITLE: AtomicBool = AtomicBool::new(false);
-
 /// The variable dispatch table. This is set at startup and cannot be modified after.
 static VAR_DISPATCH_TABLE: once_cell::sync::Lazy<VarDispatchTable> =
     once_cell::sync::Lazy::new(|| {
@@ -601,62 +598,6 @@ fn apply_non_term_hacks(vars: &EnvStack) {
     }
 }
 
-/// This is a pretty lame heuristic for detecting terminals that do not support setting the title.
-/// If we recognise the terminal name as that of a virtual terminal, we assume it supports setting
-/// the title. If we recognise it as that of a console, we assume it does not support setting the
-/// title. Otherwise we check the ttyname and see if we believe it is a virtual terminal.
-///
-/// One situation in which this breaks down is with screen, since screen supports setting the
-/// terminal title if the underlying terminal does so, but will print garbage on terminals that
-/// don't. Since we can't see the underlying terminal below screen there is no way to fix this.
-fn does_term_support_setting_title(vars: &EnvStack) -> bool {
-    #[rustfmt::skip]
-    const TITLE_TERMS: &[&wstr] = &[
-        L!("xterm"), L!("screen"),    L!("tmux"),    L!("nxterm"),
-        L!("rxvt"),  L!("alacritty"), L!("wezterm"), L!("rio"),
-        L!("foot"),
-    ];
-
-    let Some(term) = vars.get_unless_empty(L!("TERM")).map(|v| v.as_string()) else {
-        return false;
-    };
-    let term: &wstr = term.as_ref();
-
-    if curses::term().map(|term| term.set_title.is_some()) == Some(true) {
-        return true;
-    }
-
-    let recognized = TITLE_TERMS.contains(&term)
-        || term.starts_with(L!("xterm-"))
-        || term.starts_with(L!("screen-"))
-        || term.starts_with(L!("tmux-"));
-    if !recognized {
-        if [
-            L!("linux"),
-            L!("dumb"),
-            L!("vt100"), // NetBSD
-            L!("wsvt25"),
-        ]
-        .contains(&term)
-        {
-            return false;
-        }
-
-        let mut buf = [b'\0'; libc::PATH_MAX as usize];
-        let retval =
-            unsafe { libc::ttyname_r(libc::STDIN_FILENO, buf.as_mut_ptr().cast(), buf.len()) };
-        let buf = &buf[..buf.iter().position(|c| *c == b'\0').unwrap()];
-        if retval != 0
-            || buf.windows(b"tty".len()).any(|w| w == b"tty")
-            || buf.windows(b"/vc/".len()).any(|w| w == b"/vc/")
-        {
-            return false;
-        }
-    }
-
-    true
-}
-
 // Initialize the curses subsystem
 fn init_curses(vars: &EnvStack) {
     for var_name in CURSES_VARIABLES {
@@ -697,7 +638,6 @@ fn init_curses(vars: &EnvStack) {
     apply_non_term_hacks(vars);
 
     // Store some global variables that reflect the term's capabilities
-    CAN_SET_TERM_TITLE.store(does_term_support_setting_title(vars), Ordering::Relaxed);
     if let Some(term) = curses::term() {
         TERM_HAS_XN.store(term.eat_newline_glitch, Ordering::Relaxed);
     }
@@ -845,8 +785,3 @@ const fn allow_use_posix_spawn() -> bool {
         true
     }
 }
-
-/// Returns true if we think the terminal support setting its title.
-pub fn term_supports_setting_title() -> bool {
-    CAN_SET_TERM_TITLE.load(Ordering::Relaxed)
-}

src/reader.rs

@@ -50,7 +50,6 @@ use crate::complete::{
 };
 use crate::editable_line::{Edit, EditableLine};
 use crate::env::{EnvMode, Environment, Statuses};
-use crate::env_dispatch::term_supports_setting_title;
 use crate::exec::exec_subshell;
 use crate::expand::{expand_string, expand_tilde, ExpandFlags, ExpandResultCode};
 use crate::fallback::fish_wcwidth;
@@ -3588,10 +3587,6 @@ pub fn reader_write_title(
     parser: &Parser,
     reset_cursor_position: bool, /* = true */
 ) {
-    if !term_supports_setting_title() {
-        return;
-    }
-
     let _noninteractive = scoped_push_replacer(
         |new_value| std::mem::replace(&mut parser.libdata_mut().pods.is_interactive, new_value),
         false,