Implement lexicographic array comparison (#2827)

1 files changed, 21 insertions, 0 deletions

diff --git a/crates/typst/src/eval/ops.rs b/crates/typst/src/eval/ops.rs
index cb830614..8e8b6d29 100644
--- a/crates/typst/src/eval/ops.rs
+++ b/crates/typst/src/eval/ops.rs
@@ -551,6 +551,7 @@ pub fn compare(lhs: &Value, rhs: &Value) -> StrResult<Ordering> {
 
         (Duration(a), Duration(b)) => a.cmp(b),
         (Datetime(a), Datetime(b)) => try_cmp_datetimes(a, b)?,
+        (Array(a), Array(b)) => try_cmp_arrays(a.as_slice(), b.as_slice())?,
 
         _ => mismatch!("cannot compare {} and {}", lhs, rhs),
     })
@@ -568,6 +569,26 @@ fn try_cmp_datetimes(a: &Datetime, b: &Datetime) -> StrResult<Ordering> {
         .ok_or_else(|| eco_format!("cannot compare {} and {}", a.kind(), b.kind()))
 }
 
+/// Try to compare arrays of values lexicographically.
+fn try_cmp_arrays(a: &[Value], b: &[Value]) -> StrResult<Ordering> {
+    a.iter()
+        .zip(b.iter())
+        .find_map(|(first, second)| {
+            match compare(first, second) {
+                // Keep searching for a pair of elements that isn't equal.
+                Ok(Ordering::Equal) => None,
+                // Found a pair which either is not equal or not comparable, so
+                // we stop searching.
+                result => Some(result),
+            }
+        })
+        .unwrap_or_else(|| {
+            // The two arrays are equal up to the shortest array's extent,
+            // so compare their lengths instead.
+            Ok(a.len().cmp(&b.len()))
+        })
+}
+
 /// Test whether one value is "in" another one.
 pub fn in_(lhs: Value, rhs: Value) -> StrResult<Value> {
     if let Some(b) = contains(&lhs, &rhs) {