Don't apply @shareable if it's already @shareable (#2043)

In the course of updating to fed2, it's feasible that subgraphs may want to add `@shareable` applications without `@link`ing to federation/2.0 and importing it from there.

Previously, this would throw an error because the schema upgrader will try to add a `@shareable` application that has already been manually added. Now we'll check first.

composition-js/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 This CHANGELOG pertains only to Apollo Federation packages in the 2.x range. The Federation v0.x equivalent for this package can be found [here](https://github.com/apollographql/federation/blob/version-0.x/federation-js/CHANGELOG.md) on the `version-0.x` branch of this repo.
 
+- Don't apply @shareable when upgrading fed1 supergraphs if it's already @shareable [PR #2043](https://github.com/apollographql/federation/pull/2043)
 - Update peer dependency `graphql` to `^16.5.0` to use `GraphQLErrorOptions` [PR #2060](https://github.com/apollographql/federation/pull/2060)
 
 ## 2.1.0-alpha.3

composition-js/src/__tests__/composeFed1Subgraphs.test.ts

@@ -583,6 +583,43 @@ describe('shareable', () => {
       }
     `);
   });
+
+  it('supports fed1 subgraphs that define @shareable', () => {
+    const subgraphA = {
+      name: 'subgraphA',
+      typeDefs: gql`
+        type Queryf {
+          friendlyFruit: Fruit!
+        }
+
+        directive @shareable on OBJECT | FIELD_DEFINITION
+
+        type Fruit @shareable {
+          id: ID!
+          name: String!
+        }
+      `
+    };
+
+    const subgraphB = {
+      name: 'subgraphB',
+      typeDefs: gql`
+        type Query {
+          forbiddenFruit: Fruit!
+        }
+
+        directive @shareable on OBJECT | FIELD_DEFINITION
+
+        type Fruit @shareable {
+          id: ID!
+          name: String!
+        }
+      `
+    };
+
+    const result = composeServices([subgraphA, subgraphB]);
+    assertCompositionSuccess(result);
+  });
 });
 
 describe('override', () => {

internals-js/src/schemaUpgrader.ts

@@ -676,14 +676,14 @@ class SchemaUpgrader {
             continue;
           }
           const otherResolvingSubgraphs = this.otherSubgraphs.filter((s) => resolvesField(s, field));
-          if (otherResolvingSubgraphs.length > 0) {
+          if (otherResolvingSubgraphs.length > 0 && !field.hasAppliedDirective(shareableDirective)) {
             field.applyDirective(shareableDirective);
             this.addChange(new ShareableFieldAddition(field.coordinate, otherResolvingSubgraphs.map((s) => s.name)));
           }
         }
       } else {
         const otherDeclaringSubgraphs = this.otherSubgraphs.filter((s) => s.schema.type(type.name));
-        if (otherDeclaringSubgraphs.length > 0) {
+        if (otherDeclaringSubgraphs.length > 0 && !type.hasAppliedDirective(shareableDirective)) {
           type.applyDirective(shareableDirective);
           this.addChange(new ShareableTypeAddition(type.coordinate, otherDeclaringSubgraphs.map((s) => s.name)));
         }