Add default parameter for array.{first, last} (#5970)

crates/typst-library/src/foundations/array.rs

@@ -172,17 +172,29 @@ impl Array {
     }
 
     /// Returns the first item in the array. May be used on the left-hand side
-    /// of an assignment. Fails with an error if the array is empty.
+    /// an assignment. Returns the default value if the array is empty
+    /// or fails with an error is no default value was specified.
     #[func]
-    pub fn first(&self) -> StrResult<Value> {
-        self.0.first().cloned().ok_or_else(array_is_empty)
+    pub fn first(
+        &self,
+        /// A default value to return if the array is empty.
+        #[named]
+        default: Option<Value>,
+    ) -> StrResult<Value> {
+        self.0.first().cloned().or(default).ok_or_else(array_is_empty)
     }
 
     /// Returns the last item in the array. May be used on the left-hand side of
-    /// an assignment. Fails with an error if the array is empty.
+    /// an assignment. Returns the default value if the array is empty
+    /// or fails with an error is no default value was specified.
     #[func]
-    pub fn last(&self) -> StrResult<Value> {
-        self.0.last().cloned().ok_or_else(array_is_empty)
+    pub fn last(
+        &self,
+        /// A default value to return if the array is empty.
+        #[named]
+        default: Option<Value>,
+    ) -> StrResult<Value> {
+        self.0.last().cloned().or(default).ok_or_else(array_is_empty)
     }
 
     /// Returns the item at the specified index in the array. May be used on the

tests/suite/foundations/array.typ

@@ -179,6 +179,10 @@
 #test((2,).last(), 2)
 #test((1, 2, 3).first(), 1)
 #test((1, 2, 3).last(), 3)
+#test((1, 2).first(default: 99), 1)
+#test(().first(default: 99), 99)
+#test((1, 2).last(default: 99), 2)
+#test(().last(default: 99), 99)
 
 --- array-first-empty ---
 // Error: 2-12 array is empty