Fix wcwidth on cygwin

src/env_dispatch.rs

@@ -199,7 +199,10 @@ fn guess_emoji_width(vars: &EnvStack) {
     } else {
         // Default to whatever the system's wcwidth gives for U+1F603, but only if it's at least
         // 1 and at most 2.
+        #[cfg(not(target_os = "cygwin"))]
         let width = crate::fallback::wcwidth('😃').clamp(1, 2);
+        #[cfg(target_os = "cygwin")]
+        let width = 2_isize;
         FISH_EMOJI_WIDTH.store(width, Ordering::Relaxed);
         FLOG!(term_support, "default emoji width:", width);
     }

src/fallback.rs

@@ -8,10 +8,10 @@
 use errno::{errno, Errno};
 use once_cell::sync::Lazy;
 use std::cmp;
+use std::ffi::CString;
 use std::fs::File;
 use std::os::fd::FromRawFd;
 use std::sync::atomic::{AtomicIsize, Ordering};
-use std::{ffi::CString, mem};
 
 /// Width of ambiguous East Asian characters and, as of TR11, all private-use characters.
 /// 1 is the typical default, but we accept any non-negative override via `$fish_ambiguous_width`.
@@ -32,12 +32,13 @@
 static WC_LOOKUP_TABLE: Lazy<WcLookupTable> = Lazy::new(WcLookupTable::new);
 
 /// A safe wrapper around the system `wcwidth()` function
+#[cfg(not(target_os = "cygwin"))]
 pub fn wcwidth(c: char) -> isize {
     extern "C" {
         pub fn wcwidth(c: libc::wchar_t) -> libc::c_int;
     }
 
-    const _: () = assert!(mem::size_of::<libc::wchar_t>() >= mem::size_of::<char>());
+    const _: () = assert!(std::mem::size_of::<libc::wchar_t>() >= std::mem::size_of::<char>());
     let width = unsafe { wcwidth(c as libc::wchar_t) };
     isize::try_from(width).unwrap()
 }
@@ -48,6 +49,7 @@ 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(target_os = "cygwin"))]
     if is_console_session() {
         return wcwidth(c);
     }
@@ -73,8 +75,16 @@ pub fn fish_wcwidth(c: char) -> isize {
     let width = WC_LOOKUP_TABLE.classify(c);
     match width {
         WcWidth::NonCharacter | WcWidth::NonPrint | WcWidth::Combining | WcWidth::Unassigned => {
-            // Fall back to system wcwidth in this case.
-            wcwidth(c)
+            #[cfg(not(target_os = "cygwin"))]
+            {
+                // Fall back to system wcwidth in this case.
+                wcwidth(c)
+            }
+            #[cfg(target_os = "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".