Stop using wcwidth entirely

wcwidth isn't a great idea - it returns "-1" for anything it doesn't
know and non-printables, which can easily break text.

It is also unclear that it would be accurate to the system console,
and that's a minority use-case over using ssh to access older systems.

Additionally, it means we use one less function from libc and
simplifies the code.

Closes #12562

crates/fallback/src/lib.rs

@@ -29,32 +29,9 @@
 
 static WC_LOOKUP_TABLE: LazyLock<WcLookupTable> = LazyLock::new(WcLookupTable::new);
 
-/// A safe wrapper around the system `wcwidth()` function
-#[cfg(not(cygwin))]
-pub fn wcwidth(c: char) -> isize {
-    unsafe extern "C" {
-        pub unsafe fn wcwidth(c: libc::wchar_t) -> libc::c_int;
-    }
-
-    const {
-        assert!(size_of::<libc::wchar_t>() >= size_of::<char>());
-    }
-
-    let width = unsafe { wcwidth(c as libc::wchar_t) };
-    isize::try_from(width).unwrap()
-}
-
 // Big hack to use our versions of wcswidth where we know them to be broken, which is
 // EVERYWHERE (https://github.com/fish-shell/fish-shell/issues/2199)
 pub fn fish_wcwidth(c: char) -> isize {
-    // The system version of wcwidth should accurately reflect the ability to represent characters
-    // in the console session, but knows nothing about the capabilities of other terminal emulators
-    // or ttys. Use it from the start only if we are logged in to the physical console.
-    #[cfg(not(cygwin))]
-    if fish_common::is_console_session() {
-        return wcwidth(c);
-    }
-
     // Check for VS16 which selects emoji presentation. This "promotes" a character like U+2764
     // (width 1) to an emoji (probably width 2). So treat it as width 1 so the sums work. See #2652.
     // VS15 selects text presentation.
@@ -75,18 +52,7 @@ pub fn fish_wcwidth(c: char) -> isize {
 
     let width = WC_LOOKUP_TABLE.classify(c);
     match width {
-        WcWidth::NonCharacter | WcWidth::NonPrint | WcWidth::Combining | WcWidth::Unassigned => {
+        WcWidth::NonCharacter | WcWidth::NonPrint | WcWidth::Combining | WcWidth::Unassigned => 0,
-            #[cfg(not(cygwin))]
-            {
-                // Fall back to system wcwidth in this case.
-                wcwidth(c)
-            }
-            #[cfg(cygwin)]
-            {
-                // No system wcwidth for UTF-32 on cygwin.
-                0
-            }
-        }
         WcWidth::Ambiguous | WcWidth::PrivateUse => {
             // TR11: "All private-use characters are by default classified as Ambiguous".
             FISH_AMBIGUOUS_WIDTH.load(Ordering::Relaxed)
@@ -97,8 +63,7 @@ pub fn fish_wcwidth(c: char) -> isize {
     }
 }
 
-/// fish's internal versions of wcwidth and wcswidth, which can use an internal implementation if
+/// fish's internal versions of wcwidth and wcswidth
-/// the system one is busted.
 pub fn fish_wcswidth(s: &wstr) -> isize {
     // ascii fast path; empty iterator returns true for .all()
     if s.chars().all(|c| c.is_ascii() && !c.is_ascii_control()) {

src/locale.rs

@@ -35,9 +35,6 @@ pub unsafe fn set_libc_locales(log_ok: bool) -> bool {
         }
         ok &= locale_string.is_some();
     };
-    // For wcwidth(3p)
-    set("LC_CTYPE", libc::LC_CTYPE, from_environment);
-    set("LC_CTYPE", libc::LC_CTYPE, c"C.UTF-8");
     // For strerror(3p) and strsignal(3p)
     set("LC_MESSAGES", libc::LC_MESSAGES, from_environment);
     // For builtin printf