Reuse wcswidth logic for rendered characters

crates/fallback/src/lib.rs

@@ -63,15 +63,19 @@ pub fn fish_wcwidth(c: char) -> isize {
     }
 }
 
-/// fish's internal versions of wcwidth and wcswidth
 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()) {
+    fish_wcswidth_canonicalizing(s, std::convert::identity)
+}
+
+pub fn fish_wcswidth_canonicalizing(s: &wstr, canonicalize: fn(char) -> char) -> isize {
+    // ascii fast path
+    let chars = s.chars().map(canonicalize);
+    if chars.clone().all(|c| c.is_ascii() && !c.is_ascii_control()) {
         return s.len() as isize;
     }
 
     let mut result = 0;
-    for c in s.chars() {
+    for c in chars {
         let w = fish_wcwidth(c);
         if w < 0 {
             return -1;