Implicitly upgrade federation version to the max required by any used…

… directive (#2929)

# Overview

The recent addition of `SourceSpecDefinition` surfaced a case where a
subgraph with a `@link` to federation < 2.7 and a `@link` to the source
spec (which requires federation >= 2.7) results in an unexpected error
during composition. Validation for this case was introduced in
#2914, raising a
composition error when the versions are mismatched.

Since the existing behavior will implicitly upgrade to a later minor
version of federation when two subgraphs are mismatched, it makes sense
to do the same with feature requirements.

# Example

Subgraph A has a `@link` to fed version 2.5
Subgraph B has a `@link` to fed version 2.7
Subgraph C has a `@link` to fed version 2.5 and a separate `@link` to
the source spec

Previous behavior:
1. Composing Subgraph A and Subgraph B silently upgrades to fed version
2.7
2. Composing Subgraph A and Subgraph C results in a composition error

New behavior:
1. Composing Subgraph A and Subgraph B silently upgrades to fed version
2.7
2. Composing Subgraph A and Subgraph C upgrades to fed version 2.7 and
raises a hint explaining why

---------

Co-authored-by: Chris Lenfest <clenfest@apollographql.com>

.changeset/forty-dolls-type.md

@@ -0,0 +1,6 @@
+---
+"@apollo/composition": minor
+"@apollo/federation-internals": minor
+---
+
+When a linked directive requires a federation version higher than the linked federation spec, upgrade to the implied version and issue a hint

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

@@ -5101,10 +5101,6 @@ describe('@source* directives', () => {
 
       const messages = result.errors!.map(e => e.message);
 
-      expect(messages).toContain(
-        '[bad] Schemas that @link to https://specs.apollo.dev/source must also @link to federation version v2.7 or later (found v2.5)'
-      );
-
       expect(messages).toContain(
         '[bad] @sourceAPI(name: "A?!") must specify name using only [a-zA-Z0-9-_] characters'
       );

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

@@ -6,8 +6,9 @@ import {
   HINTS,
 } from '../hints';
 import { MergeResult, mergeSubgraphs } from '../merging';
-import { composeAsFed2Subgraphs } from './testHelper';
+import { assertCompositionSuccess, composeAsFed2Subgraphs } from './testHelper';
 import { formatExpectedToMatchReceived } from './matchers/toMatchString';
+import { composeServices } from '../compose';
 
 function mergeDocuments(...documents: DocumentNode[]): MergeResult {
   const subgraphs = new Subgraphs();
@@ -1177,3 +1178,121 @@ describe('when shared field has intersecting but non equal runtime types in diff
     );
   });
 });
+
+describe('when a directive causes an implicit federation version upgrade', () => {
+  const olderFederationSchema = gql`
+    extend schema
+      @link(url: "https://specs.apollo.dev/federation/v2.5", import: ["@key"])
+
+    type Query {
+      a: String!
+    }
+  `;
+
+  const newerFederationSchema = gql`
+    extend schema
+      @link(url: "https://specs.apollo.dev/federation/v2.7", import: ["@key"])
+
+    type Query {
+      b: String!
+    }
+  `;
+
+  const autoUpgradedSchema = gql`
+    extend schema
+      @link(url: "https://specs.apollo.dev/federation/v2.5", import: ["@key", "@shareable"])
+      @link(url: "https://specs.apollo.dev/source/v0.1", import: [
+        "@sourceAPI"
+        "@sourceType"
+        "@sourceField"
+      ])
+      @sourceAPI(
+        name: "A"
+        http: { baseURL: "https://api.a.com/v1" }
+      )
+      {
+        query: Query
+      }
+
+    type Query @shareable {
+      resources: [Resource!]! @sourceField(
+        api: "A"
+        http: { GET: "/resources" }
+      )
+    }
+
+    type Resource @shareable @key(fields: "id") @sourceType(
+      api: "A"
+      http: { GET: "/resources/{id}" }
+      selection: "id description"
+    ) {
+      id: ID!
+      description: String!
+    }
+  `;
+
+  it('should hint that the version was upgraded to satisfy directive requirements', () => {
+    const result = composeServices([
+      {
+        name: 'already-newest',
+        typeDefs: newerFederationSchema,
+      },
+      {
+        name: 'old-but-not-upgraded',
+        typeDefs: olderFederationSchema,
+      },
+      {
+        name: 'upgraded',
+        typeDefs: autoUpgradedSchema,
+      }
+    ]);
+
+    assertCompositionSuccess(result);
+    expect(result).toRaiseHint(
+      HINTS.IMPLICITLY_UPGRADED_FEDERATION_VERSION,
+      'Subgraph upgraded has been implicitly upgraded from federation v2.5 to v2.7',
+      '@link'
+    );
+  });
+
+  it('should show separate hints for each upgraded subgraph', () => {
+    const result = composeServices([
+      {
+        name: 'upgraded-1',
+        typeDefs: autoUpgradedSchema,
+      },
+      {
+        name: 'upgraded-2',
+        typeDefs: autoUpgradedSchema
+      },
+    ]);
+
+    assertCompositionSuccess(result);
+    expect(result).toRaiseHint(
+      HINTS.IMPLICITLY_UPGRADED_FEDERATION_VERSION,
+      'Subgraph upgraded-1 has been implicitly upgraded from federation v2.5 to v2.7',
+      '@link'
+    );
+    expect(result).toRaiseHint(
+      HINTS.IMPLICITLY_UPGRADED_FEDERATION_VERSION,
+      'Subgraph upgraded-2 has been implicitly upgraded from federation v2.5 to v2.7',
+      '@link'
+    );
+  });
+
+  it('should not raise hints if the only upgrade is caused by a link directly to the federation spec', () => {
+    const result = composeServices([
+      {
+        name: 'already-newest',
+        typeDefs: newerFederationSchema,
+      },
+      {
+        name: 'old-but-not-upgraded',
+        typeDefs: olderFederationSchema,
+      },
+    ]);
+
+    assertCompositionSuccess(result);
+    expect(result).toNotRaiseHints();
+  });
+})

composition-js/src/hints.ts

@@ -199,6 +199,13 @@ const INCONSISTENT_RUNTIME_TYPES_FOR_SHAREABLE_RETURN = makeCodeDefinition({
   description: 'Indicates that a @shareable field returns different sets of runtime types in the different subgraphs in which it is defined.',
 });
 
+const IMPLICITLY_UPGRADED_FEDERATION_VERSION = makeCodeDefinition({
+  code: 'IMPLICITLY_UPGRADED_FEDERATION_VERSION',
+  level: HintLevel.INFO,
+  description: 'Indicates that a directive requires a higher federation version than is explicitly linked.'
+    + ' In this case, the supergraph uses the federation version required by the directive.'
+});
+
 export const HINTS = {
   INCONSISTENT_BUT_COMPATIBLE_FIELD_TYPE,
   INCONSISTENT_BUT_COMPATIBLE_ARGUMENT_TYPE,
@@ -227,6 +234,7 @@ export const HINTS = {
   DIRECTIVE_COMPOSITION_INFO,
   DIRECTIVE_COMPOSITION_WARN,
   INCONSISTENT_RUNTIME_TYPES_FOR_SHAREABLE_RETURN,
+  IMPLICITLY_UPGRADED_FEDERATION_VERSION,
 }
 
 export class CompositionHint {

composition-js/src/merging/merge.ts

@@ -74,6 +74,8 @@ import {
   LinkDirectiveArgs,
   sourceIdentity,
   FeatureUrl,
+  CoreFeature,
+  Subgraph,
 } from "@apollo/federation-internals";
 import { ASTNode, GraphQLError, DirectiveLocation } from "graphql";
 import {
@@ -343,19 +345,56 @@ class Merger {
   }
 
   private getLatestFederationVersionUsed(): FeatureVersion {
-    const latestVersion =  this.subgraphs.values().reduce((latest: FeatureVersion | undefined, subgraph) => {
-      const version = subgraph.metadata()?.federationFeature()?.url?.version;
-      if (!latest) {
-        return version;
+    const versions = this.subgraphs.values()
+                        .map((s) => this.getLatestFederationVersionUsedInSubgraph(s))
+                        .filter(isDefined);
+
+    return FeatureVersion.max(versions) ?? FEDERATION_VERSIONS.latest().version;
+  }
+
+  private getLatestFederationVersionUsedInSubgraph(subgraph: Subgraph): FeatureVersion | undefined {
+    const linkedFederationVersion = subgraph.metadata()?.federationFeature()?.url.version;
+    if (!linkedFederationVersion) {
+      return undefined;
+    }
+
+    // Check if any of the directives imply a newer version of federation than is explicitly linked
+    const versionsFromFeatures: FeatureVersion[] = [];
+    for (const feature of subgraph.schema.coreFeatures?.allFeatures() ?? []) {
+      const version = feature.minimumFederationVersion();
+      if (version) {
+        versionsFromFeatures.push(version);
       }
-      if (!version) {
-        return latest;
+    }
+    const impliedFederationVersion = FeatureVersion.max(versionsFromFeatures);
+    if (!impliedFederationVersion?.satisfies(linkedFederationVersion) || linkedFederationVersion >= impliedFederationVersion) {
+      return linkedFederationVersion;
+    }
+
+    // If some of the directives are causing an implicit upgrade, put one in the hint
+    let featureCausingUpgrade: CoreFeature | undefined;
+    for (const feature of subgraph.schema.coreFeatures?.allFeatures() ?? []) {
+      if (feature.minimumFederationVersion() == impliedFederationVersion) {
+        featureCausingUpgrade = feature;
+        break;
       }
-      return latest >= version ? latest : version;
-    }, undefined);
-    return latestVersion ?? FEDERATION_VERSIONS.latest().version;
+    }
+
+    if (featureCausingUpgrade) {
+      this.hints.push(new CompositionHint(
+        HINTS.IMPLICITLY_UPGRADED_FEDERATION_VERSION,
+        `Subgraph ${subgraph.name} has been implicitly upgraded from federation ${linkedFederationVersion} to ${impliedFederationVersion}`,
+        featureCausingUpgrade.directive.definition,
+        featureCausingUpgrade.directive.sourceAST ?
+          addSubgraphToASTNode(featureCausingUpgrade.directive.sourceAST, subgraph.name) :
+          undefined
+      ));
+    }
+
+    return impliedFederationVersion;
   }
 
+
   private prepareSupergraph(): Map<string, string> {
     // TODO: we will soon need to look for name conflicts for @core and @join with potentially user-defined directives and
     // pass a `as` to the methods below if necessary. However, as we currently don't propagate any subgraph directives to

internals-js/src/definitions.ts

@@ -27,6 +27,7 @@ import {
   CoreSpecDefinition,
   extractCoreFeatureImports,
   FeatureUrl,
+  FeatureVersion,
   findCoreSpecVersion,
   isCoreSpecDirectiveApplication,
   removeAllCoreFeatures,
@@ -53,6 +54,7 @@ import { validateSchema } from "./validate";
 import { createDirectiveSpecification, createScalarTypeSpecification, DirectiveSpecification, TypeSpecification } from "./directiveAndTypeSpecification";
 import { didYouMean, suggestionList } from "./suggestions";
 import { aggregateError, ERRORS, withModifiedErrorMessage } from "./error";
+import { coreFeatureDefinitionIfKnown } from "./knownCoreFeatures";
 
 const validationErrorCode = 'GraphQLValidationFailed';
 const DEFAULT_VALIDATION_ERROR_MESSAGE = 'The schema is not a valid GraphQL schema.';
@@ -1014,6 +1016,10 @@ export class CoreFeature {
     const elementImport = this.imports.find((i) => i.name === name);
     return elementImport ? (elementImport.as ?? name) : this.nameInSchema + '__' + name;
   }
+
+  minimumFederationVersion(): FeatureVersion | undefined {
+    return coreFeatureDefinitionIfKnown(this.url)?.minimumFederationVersion;
+  }
 }
 
 export class CoreFeatures {

internals-js/src/specs/coreSpec.ts

@@ -640,6 +640,28 @@ export class FeatureVersion {
     return new this(+match[1], +match[2])
   }
 
+  /**
+   * Find the maximum version in a collection of versions, returning undefined in the case
+   * that the collection is empty.
+   *
+   * # Example
+   * ```
+   * expect(FeatureVersion.max([new FeatureVersion(1, 0), new FeatureVersion(2, 0)])).toBe(new FeatureVersion(2, 0))
+   * expect(FeatureVersion.max([])).toBe(undefined)
+   * ```
+   */
+  public static max(versions: Iterable<FeatureVersion>): FeatureVersion | undefined {
+    let max: FeatureVersion | undefined;
+
+    for (const version of versions) {
+      if (!max || version > max) {
+        max = version;
+      }
+    }
+
+    return max;
+  }
+
   /**
    * Return true if and only if this FeatureVersion satisfies the `required` version
    *

internals-js/src/specs/sourceSpec.ts

@@ -147,15 +147,13 @@ export class SourceSpecDefinition extends FeatureDefinition {
     return this.directive<SourceFieldDirectiveArgs>(schema, 'sourceField')!;
   }
 
-  private getSourceDirectives(schema: Schema, errors: GraphQLError[]) {
+  private getSourceDirectives(schema: Schema) {
     const result: {
       sourceAPI?: DirectiveDefinition<SourceAPIDirectiveArgs>;
       sourceType?: DirectiveDefinition<SourceTypeDirectiveArgs>;
       sourceField?: DirectiveDefinition<SourceFieldDirectiveArgs>;
     } = {};
 
-    let federationVersion: FeatureVersion | undefined;
-
     schema.schemaDefinition.appliedDirectivesOf<LinkDirectiveArgs>('link')
       .forEach(linkDirective => {
         const { url, import: imports } = linkDirective.arguments();
@@ -175,25 +173,8 @@ export class SourceSpecDefinition extends FeatureDefinition {
             }
           });
         }
-        if (featureUrl && featureUrl.name === 'federation') {
-          federationVersion = featureUrl.version;
-        }
       });
 
-    if (result.sourceAPI || result.sourceType || result.sourceField) {
-      // Since this subgraph uses at least one of the @source{API,Type,Field}
-      // directives, it must also use v2.7 or later of federation.
-      if (!federationVersion || federationVersion.lt(this.minimumFederationVersion)) {
-        errors.push(ERRORS.SOURCE_FEDERATION_VERSION_REQUIRED.err(
-          `Schemas that @link to ${
-            sourceIdentity
-          } must also @link to federation version ${
-            this.minimumFederationVersion
-          } or later (found ${federationVersion})`,
-        ));
-      }
-    }
-
     return result;
   }
 
@@ -203,7 +184,7 @@ export class SourceSpecDefinition extends FeatureDefinition {
       sourceAPI,
       sourceType,
       sourceField,
-    } = this.getSourceDirectives(schema, errors);
+    } = this.getSourceDirectives(schema);
 
     if (!(sourceAPI || sourceType || sourceField)) {
       // If none of the @source* directives are present, nothing needs