Fix relayStylePagination bug when using after

src/utilities/policies/__tests__/relayStylePagination.test.ts

@@ -153,6 +153,28 @@ describe('relayStylePagination', () => {
       });
     });
 
+    it("replaces the existing data if a query using `after` is repeated", () => {
+      const page = {
+        edges: [{ cursor: "alpha", node: makeReference("fakeAlpha") }],
+        pageInfo: {
+          hasPreviousPage: false,
+          hasNextPage: true,
+          startCursor: "alpha",
+          endCursor: "alpha",
+        },
+      };
+
+      const result = merge(page, page, {
+        ...options,
+        args: {
+          // Represents the cursor that comes immediately before 'alpha'
+          after: "zeta",
+        },
+      });
+
+      expect(result).toEqual(page);
+    });
+
     it('should maintain existing PageInfo when adding a page', () => {
       const existingEdges = [
         { cursor: 'alpha', node: makeReference("fakeAlpha") },

src/utilities/policies/pagination.ts

@@ -188,27 +188,33 @@ export function relayStylePagination<TNode = Reference>(
         }
       }
 
-      let prefix = existing.edges;
-      let suffix: typeof prefix = [];
+      let prefix: TRelayEdge<TNode>[] = [];
+      let suffix: TRelayEdge<TNode>[] = [];
 
       if (args && args.after) {
         // This comparison does not need to use readField("cursor", edge),
         // because we stored the cursor field of any Reference edges as an
         // extra property of the Reference object.
-        const index = prefix.findIndex(edge => edge.cursor === args.after);
+        const index = existing.edges.findIndex(
+          edge => edge.cursor === args.after,
+        );
         if (index >= 0) {
-          prefix = prefix.slice(0, index + 1);
+          prefix = existing.edges.slice(0, index + 1);
           // suffix = []; // already true
         }
       } else if (args && args.before) {
-        const index = prefix.findIndex(edge => edge.cursor === args.before);
-        suffix = index < 0 ? prefix : prefix.slice(index);
-        prefix = [];
+        const index = existing.edges.findIndex(
+          edge => edge.cursor === args.before,
+        );
+        suffix = index < 0 ? existing.edges : existing.edges.slice(index);
+        // prefix = []; // already true
       } else if (incoming.edges) {
         // If we have neither args.after nor args.before, the incoming
         // edges cannot be spliced into the existing edges, so they must
         // replace the existing edges. See #6592 for a motivating example.
-        prefix = [];
+        // prefix = []; // already true
+      } else {
+        prefix = existing.edges;
       }
 
       const edges = [