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Fix stability of compare_strings_ascii #823

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Merged
lhecker merged 1 commit into from
Apr 27, 2026
+9 −4
Merged

Fix stability of compare_strings_ascii #823

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13 changes: 9 additions & 4 deletions crates/edit/src/icu.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -813,13 +813,15 @@ fn compare_strings_ascii(a: &[u8], b: &[u8]) -> Ordering {
// case-insensitive equal, because then we use that as a fallback.
while let Some((&a, &b)) = iter.next() {
if a != b {
let mut order = a.cmp(&b);
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@lhecker lhecker Apr 27, 2026

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The default value for order must always be la.cmp(&lb) (high weight: case-insensitive). Only if it's Equal must it fall back to a.cmp(&b) (low weight: case-sensitive).

let la = a.to_ascii_lowercase();
let lb = b.to_ascii_lowercase();
let mut order = la.cmp(&lb);

if order == Ordering::Equal {
// High weight: Find the first character which differs case-insensitively.
// Otherwise, it falls back to (or rather: defaults to) a case-sensitive comparison.
order = a.cmp(&b);

if la == lb {
// High weight: Find the first character which
// differs case-insensitively.
for (a, b) in iter {
let la = a.to_ascii_lowercase();
let lb = b.to_ascii_lowercase();
Expand Down Expand Up @@ -1378,6 +1380,9 @@ mod tests {
assert_eq!(compare_strings_ascii(b"abcd", b"abc"), Ordering::Greater);
// Same chars, different cases - 1st char wins
assert_eq!(compare_strings_ascii(b"AbC", b"aBc"), Ordering::Less);
// Different chars, different cases
assert_eq!(compare_strings_ascii(b"a", b"B"), Ordering::Less);
assert_eq!(compare_strings_ascii(b"B", b"a"), Ordering::Greater);
// Different chars, different cases - 2nd char wins, because it differs
assert_eq!(compare_strings_ascii(b"hallo", b"Hello"), Ordering::Less);
assert_eq!(compare_strings_ascii(b"Hello", b"hallo"), Ordering::Greater);
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