add tests for List.dropAt

compiler/builtins/bitcode/src/list.zig

@@ -833,8 +833,6 @@ pub fn listDrop(
     }
 }
 
-// GIESCH add type inference test
-// GIESCH add unit tests
 // GIESCH do a uniqueness check, and reuse the same array if possible
 // GIESCH figure out where to specify uniqueness of output, update builtins readme
 pub fn listDropAt(
@@ -848,7 +846,8 @@ pub fn listDropAt(
         const size = list.len();
 
         if (drop_index >= size) {
-            return RocList.empty();
+            // GIESCH should this still copy/reallocate if non-unique?
+            return list;
         }
 
         if (drop_index < size) {
@@ -856,11 +855,6 @@ pub fn listDropAt(
             dec(element);
         }
 
-        // GIESCH is this necessary?
-        if (size < 2 and drop_index == 0) {
-            return RocList.empty();
-        }
-
         const output = RocList.allocate(alignment, (size - 1), element_width);
         const target_ptr = output.bytes orelse unreachable;
 

compiler/solve/tests/solve_expr.rs

@@ -3709,6 +3709,18 @@ mod solve_expr {
         );
     }
 
+    #[test]
+    fn list_drop_at() {
+        infer_eq_without_problem(
+            indoc!(
+                r#"
+                List.dropAt
+                "#
+            ),
+            "List a, Nat -> List a",
+        );
+    }
+
     #[test]
     fn function_that_captures_nothing_is_not_captured() {
         // we should make sure that a function that doesn't capture anything it not itself captured

compiler/test_gen/src/gen_list.rs

@@ -198,6 +198,21 @@ fn list_drop() {
     assert_evals_to!("List.drop [1,2] 5", RocList::from_slice(&[]), RocList<i64>);
 }
 
+#[test]
+fn list_drop_at() {
+    assert_evals_to!(
+        "List.dropAt [1, 2, 3] 0",
+        RocList::from_slice(&[2, 3]),
+        RocList<i64>
+    );
+    assert_evals_to!(
+        "List.dropAt [0, 0, 0] 3",
+        RocList::from_slice(&[1, 2, 3]),
+        RocList<i64>
+    );
+    assert_evals_to!("List.dropAt [] 1", RocList::from_slice(&[]), RocList<i64>);
+}
+
 #[test]
 fn list_swap() {
     assert_evals_to!("List.swap [] 0 1", RocList::from_slice(&[]), RocList<i64>);