Fix GraphQL pagination ordering

This resolved an issue in the GraphQL API where the ordering of edges
was inconsistent when using `last`/`before` pagination arguments.
According to the GraphQL Cursor Connections Specification, the order of
edges should remain the same whether using `first`/`after` or
`last`/`before`, provided all other arguments are equal. Previously, our
API returned edges in reverse order when `last`/`before` was used, which
was contrary to the specification.

CHANGELOG.md

@@ -5,6 +5,17 @@ file is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and
 this project adheres to [Semantic
 Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- We've resolved an issue in the GraphQL API where the ordering of edges was
+  inconsistent when using `last`/`before` pagination arguments. According to the
+  GraphQL Cursor Connections Specification, the order of edges should remain the
+  same whether using `first`/`after` or `last`/`before`, provided all other
+  arguments are equal. Previously, our API returned edges in reverse order when
+  `last`/`before` was used, which was contrary to the specification.
+
 ## [0.17.0] - 2024-01-19
 
 ### Added
@@ -371,6 +382,7 @@ across our system.
 
 - An initial version.
 
+[Unreleased]: https://github.com/aicers/review-web/compare/0.17.0...main
 [0.17.0]: https://github.com/aicers/review-web/compare/0.16.0...0.17.0
 [0.16.0]: https://github.com/aicers/review-web/compare/0.15.0...0.16.0
 [0.15.0]: https://github.com/aicers/review-web/compare/0.14.5...0.15.0

src/graphql.rs

@@ -280,12 +280,13 @@ where
             map.iter_backward()?
         };
 
-        let (nodes, has_more) = if let Some(after) = after {
+        let (mut nodes, has_more) = if let Some(after) = after {
             let to = earliest_key(&after)?;
             iter_to_nodes_with_filter(iter, &to, cmp::Ordering::is_ge, filter, last)
         } else {
             iter_to_nodes_with_filter(iter, &[], always_true, filter, last)
         }?;
+        nodes.reverse();
         Ok((nodes, has_more, false))
     } else {
         let first = first.unwrap_or(DEFAULT_CONNECTION_SIZE);

src/graphql/account.rs

@@ -755,11 +755,6 @@ mod tests {
         };
         assert_eq!(username, "u2");
 
-        // Record the cursor of the first edge.
-        let Some(Value::String(cursor)) = edge.get("cursor") else {
-            panic!("unexpected response: {:?}", edge);
-        };
-
         // The last edge should be "u4".
         let Some(Value::Object(edge)) = edges.get(2) else {
             panic!("unexpected response: {:?}", edges);
@@ -772,11 +767,16 @@ mod tests {
         };
         assert_eq!(username, "u4");
 
+        // Record the cursor of the last edge.
+        let Some(Value::String(cursor)) = edge.get("cursor") else {
+            panic!("unexpected response: {:?}", edge);
+        };
+
         // Retrieve backward.
         let res = schema
             .execute(&format!(
                 "query {{
-                            accountList(last: 1, before: \"{cursor}\") {{
+                            accountList(last: 3, before: \"{cursor}\") {{
                                 edges {{
                                     node {{
                                         username
@@ -802,7 +802,7 @@ mod tests {
         let Some(Value::List(edges)) = account_list.get("edges") else {
             panic!("unexpected response: {:?}", account_list);
         };
-        assert_eq!(edges.len(), 1);
+        assert_eq!(edges.len(), 3);
         let Some(Value::Object(page_info)) = account_list.get("pageInfo") else {
             panic!("unexpected response: {:?}", account_list);
         };