Merge 'Fix updating single value' from Pedro Muniz

Closes #1482. I needed to change the `key_exists_in_index` function
because it zips the values from the records it is comparing, but if one
of the records is empty or not of the same length, the `all` function
could return true incorrectly.

Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>

Closes #1514

core/storage/btree.rs

@@ -3863,21 +3863,24 @@ impl BTreeCursor {
                 // Existing record found — compare prefix
                 let existing_key = &record.get_values()[..record.count().saturating_sub(1)];
                 let inserted_key_vals = &key.get_values();
-                if existing_key
-                    .iter()
-                    .zip(inserted_key_vals.iter())
-                    .all(|(a, b)| a == b)
-                {
-                    return Ok(CursorResult::Ok(true)); // duplicate
+                // Need this check because .all returns True on an empty iterator,
+                // So when record_opt is invalidated, it would always indicate show up as a duplicate key
+                if existing_key.len() != inserted_key_vals.len() {
+                    return Ok(CursorResult::Ok(false));
                 }
+
+                Ok(CursorResult::Ok(
+                    existing_key
+                        .iter()
+                        .zip(inserted_key_vals.iter())
+                        .all(|(a, b)| a == b),
+                ))
             }
             None => {
                 // Cursor not pointing at a record — table is empty or past last
-                return Ok(CursorResult::Ok(false));
+                Ok(CursorResult::Ok(false))
             }
         }
-
-        Ok(CursorResult::Ok(false)) // not a duplicate
     }
 
     pub fn exists(&mut self, key: &Value) -> Result<CursorResult<bool>> {

testing/cli_tests/constraint.py

@@ -347,6 +347,15 @@ def custom_test_2(limbo: TestLimboShell):
     )
 
 
+# Issue #1482
+def regression_test_update_single_key(limbo: TestLimboShell):
+    create = "CREATE TABLE t(a unique);"
+    first_insert = "INSERT INTO t VALUES (1);"
+    limbo.run_test("Create simple table with 1 unique value", create + first_insert, "")
+    update_single = "UPDATE t SET a=1 WHERE a=1;"
+    limbo.run_test("Update one single key to the same value", update_single, "")
+
+
 def all_tests() -> list[ConstraintTest]:
     tests: list[ConstraintTest] = []
     max_cols = 10
@@ -390,15 +399,17 @@ def main():
         cleanup(db_path)
 
     db_path = "testing/constraint.db"
-    try:
-        with TestLimboShell("") as limbo:
-            limbo.execute_dot(f".open {db_path}")
-            custom_test_2(limbo)
-    except Exception as e:
-        console.error(f"Test FAILED: {e}")
+    tests = [custom_test_2, regression_test_update_single_key]
+    for test in tests:
+        try:
+            with TestLimboShell("") as limbo:
+                limbo.execute_dot(f".open {db_path}")
+                test(limbo)
+        except Exception as e:
+            console.error(f"Test FAILED: {e}")
+            cleanup(db_path)
+            exit(1)
         cleanup(db_path)
-        exit(1)
-    cleanup(db_path)
     console.info("All tests passed successfully.")