From b48d8643c5239692e15fd4ad6f6bfa44a9408782 Mon Sep 17 00:00:00 2001
From: Trevor Scheer <trevor.scheer@gmail.com>
Date: Wed, 7 Aug 2024 16:17:36 -0700
Subject: [PATCH 1/3] add test cases to show min join version is used for
 various fed versions

---
 composition-js/src/__tests__/compose.test.ts | 33 ++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/composition-js/src/__tests__/compose.test.ts b/composition-js/src/__tests__/compose.test.ts
index e0a538fab..fe2f5d066 100644
--- a/composition-js/src/__tests__/compose.test.ts
+++ b/composition-js/src/__tests__/compose.test.ts
@@ -4655,6 +4655,39 @@ describe('composition', () => {
     const authenticatedDirectiveExists = schema.directives().find(d => d.name === 'authenticated');
     expect(authenticatedDirectiveExists).toBeUndefined();
   });
+
+  describe('uses minimum required spec versions', () => {
+    function subgraphWithFederationSpecVersion(version: string) {
+      const schemaString = `
+        extend schema @link(url: "https://specs.apollo.dev/federation/v${version}", import: ["@key"])
+
+        type Query {
+          a: A
+        }
+
+        type A @key(fields: "id") {
+          id: ID!
+        }
+        `;
+      return {
+        typeDefs: gql`${schemaString}`,
+        name: 'subgraphA',
+      };
+    }
+
+    it.each([
+      { subgraphFedVersion: "2.4", expectedJoinVersion: "0.3"},
+      { subgraphFedVersion: "2.5", expectedJoinVersion: "0.3"},
+      { subgraphFedVersion: "2.6", expectedJoinVersion: "0.3"},
+      { subgraphFedVersion: "2.7", expectedJoinVersion: "0.4"},
+      { subgraphFedVersion: "2.8", expectedJoinVersion: "0.5" },
+    ])("federation -> join versions", ({ subgraphFedVersion, expectedJoinVersion }) => {
+      const subgraph = subgraphWithFederationSpecVersion(subgraphFedVersion);
+      const result = composeServices([subgraph]);
+      assertCompositionSuccess(result);
+      expect(result.supergraphSdl).toContain(`join/v${expectedJoinVersion}`);
+    });
+  });
 });
 
 describe('@source* directives', () => {

From b28555eb733dbf457f55d8ba1cc9b84b9af4453e Mon Sep 17 00:00:00 2001
From: Trevor Scheer <trevor.scheer@gmail.com>
Date: Thu, 8 Aug 2024 13:18:06 -0700
Subject: [PATCH 2/3] cover all fed versions

---
 composition-js/src/__tests__/compose.test.ts | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/composition-js/src/__tests__/compose.test.ts b/composition-js/src/__tests__/compose.test.ts
index fe2f5d066..879161d08 100644
--- a/composition-js/src/__tests__/compose.test.ts
+++ b/composition-js/src/__tests__/compose.test.ts
@@ -4676,10 +4676,14 @@ describe('composition', () => {
     }
 
     it.each([
-      { subgraphFedVersion: "2.4", expectedJoinVersion: "0.3"},
-      { subgraphFedVersion: "2.5", expectedJoinVersion: "0.3"},
-      { subgraphFedVersion: "2.6", expectedJoinVersion: "0.3"},
-      { subgraphFedVersion: "2.7", expectedJoinVersion: "0.4"},
+      { subgraphFedVersion: "2.0", expectedJoinVersion: "0.3" },
+      { subgraphFedVersion: "2.1", expectedJoinVersion: "0.3" },
+      { subgraphFedVersion: "2.2", expectedJoinVersion: "0.3" },
+      { subgraphFedVersion: "2.3", expectedJoinVersion: "0.3" },
+      { subgraphFedVersion: "2.4", expectedJoinVersion: "0.3" },
+      { subgraphFedVersion: "2.5", expectedJoinVersion: "0.3" },
+      { subgraphFedVersion: "2.6", expectedJoinVersion: "0.3" },
+      { subgraphFedVersion: "2.7", expectedJoinVersion: "0.4" },
       { subgraphFedVersion: "2.8", expectedJoinVersion: "0.5" },
     ])("federation -> join versions", ({ subgraphFedVersion, expectedJoinVersion }) => {
       const subgraph = subgraphWithFederationSpecVersion(subgraphFedVersion);

From 538444847ae6608f4f571f63d8f2ff8618471f54 Mon Sep 17 00:00:00 2001
From: Trevor Scheer <trevor.scheer@gmail.com>
Date: Thu, 8 Aug 2024 13:22:57 -0700
Subject: [PATCH 3/3] add a comment about why join v0.3 for fed 2.0

---
 internals-js/src/specs/joinSpec.ts | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/internals-js/src/specs/joinSpec.ts b/internals-js/src/specs/joinSpec.ts
index bd45fa212..cb4640000 100644
--- a/internals-js/src/specs/joinSpec.ts
+++ b/internals-js/src/specs/joinSpec.ts
@@ -287,6 +287,10 @@ export class JoinSpecDefinition extends FeatureDefinition {
 export const JOIN_VERSIONS = new FeatureDefinitions<JoinSpecDefinition>(joinIdentity)
   .add(new JoinSpecDefinition(new FeatureVersion(0, 1)))
   .add(new JoinSpecDefinition(new FeatureVersion(0, 2)))
+  // Though join v0.2 supports federation v2.0 as mentioned above, we should
+  // still prefer join v0.3 as a minimum for all of federation v2.0-2.6 since
+  // v0.3 offers improvements around union members and enum values that we're
+  // interested in.
   .add(new JoinSpecDefinition(new FeatureVersion(0, 3), new FeatureVersion(2, 0)))
   .add(new JoinSpecDefinition(new FeatureVersion(0, 4), new FeatureVersion(2, 7)))
   .add(new JoinSpecDefinition(new FeatureVersion(0, 5), new FeatureVersion(2, 8)));