Allow fields with arguments in @requires (apollographql#2120)

If such field with arguments is used in a @requires, then that @requires
must provide a value for any required argument and may provide a value
for any non-required one (like in any normal graphQL selection set).

Additionally, this commit rejects aliases in @requires, @provides and
@key. Not because aliases cannot ever make sense in those directives,
but rather because it currently does not work (it breaks at runtime) but
wasn't rejected properly.

Fixes apollographql#1987

composition-js/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 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.
 
+- Allow fields with arguments in `@requires` [PR #2120](https://github.com/apollographql/federation/pull/2120).
+
 ## 2.1.0
 
 - Don't apply @shareable when upgrading fed1 supergraphs if it's already @shareable [PR #2043](https://github.com/apollographql/federation/pull/2043)

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

@@ -1529,6 +1529,78 @@ describe('composition', () => {
           'Argument "Query.q(a:)" is required in some subgraphs but does not appear in all subgraphs: it is required in subgraph "subgraphA" but does not appear in subgraph "subgraphB"']
       ]);
     });
+
+    it('errors if a subgraph argument is "@required" without arguments but that argument is mandatory in the supergraph', () => {
+      const subgraphA = {
+        typeDefs: gql`
+          type Query {
+            t: T
+          }
+
+          type T @key(fields: "id") {
+            id: ID!
+            x(arg: Int): Int @external
+            y: Int @requires(fields: "x")
+          }
+        `,
+        name: 'subgraphA',
+      };
+
+      const subgraphB = {
+        typeDefs: gql`
+          type T @key(fields: "id") {
+            id: ID!
+            x(arg: Int!): Int
+          }
+        `,
+        name: 'subgraphB',
+      };
+
+      const result = composeAsFed2Subgraphs([subgraphA, subgraphB]);
+
+      expect(result.errors).toBeDefined();
+      expect(errors(result)).toStrictEqual([
+        [
+          'REQUIRES_INVALID_FIELDS',
+          '[subgraphA] On field "T.y", for @requires(fields: "x"): no value provided for argument "arg" of field "T.x" but a value is mandatory as "arg" is required in subgraph "subgraphB"',
+        ]
+      ]);
+    });
+
+    it('errors if a subgraph argument is "@required" with an argument, but that argument is not in the supergraph', () => {
+      const subgraphA = {
+        typeDefs: gql`
+          type Query {
+            t: T
+          }
+
+          type T @key(fields: "id") {
+            id: ID!
+            x(arg: Int): Int @external
+            y: Int @requires(fields: "x(arg: 42)")
+          }
+        `,
+        name: 'subgraphA',
+      };
+
+      const subgraphB = {
+        typeDefs: gql`
+          type T @key(fields: "id") {
+            id: ID!
+            x: Int
+          }
+        `,
+        name: 'subgraphB',
+      };
+
+      const result = composeAsFed2Subgraphs([subgraphA, subgraphB]);
+      expect(errors(result)).toStrictEqual([
+        [
+          'REQUIRES_INVALID_FIELDS',
+          '[subgraphA] On field "T.y", for @requires(fields: "x(arg: 42)"): cannot provide a value for argument "arg" of field "T.x" as argument "arg" is not defined in subgraph "subgraphB"',
+        ]
+      ]);
+    });
   });
 
   describe('post-merge validation', () => {

composition-js/src/merging/merge.ts

@@ -65,6 +65,10 @@ import {
   filterTypesOfKind,
   isNonNullType,
   isExecutableDirectiveLocation,
+  parseFieldSetArgument,
+  isCompositeType,
+  isDefined,
+  addSubgraphToError,
 } from "@apollo/federation-internals";
 import { ASTNode, GraphQLError, DirectiveLocation } from "graphql";
 import {
@@ -74,6 +78,7 @@ import {
 } from "../hints";
 import { ComposeDirectiveManager } from '../composeDirectiveManager';
 import { MismatchReporter } from './reporter';
+import { inspect } from "util";
 
 
 const linkSpec = LINK_VERSIONS.latest();
@@ -2092,6 +2097,128 @@ class Merger {
         }
       }
     }
+
+    // We need to redo some validation for @requires after merge. The reason is that each subgraph validates that its own
+    // @requires are valid, but "requirements" are requested from _other_ subgraphs (by definition of @requires really),
+    // and there is a few situations (see details below) where a validity within the originated subgraph does not entail
+    // validity for all subgraph that would have to provide those "requirements".
+    // Long story short, we need to re-validate every @requires against the supergraph to guarantee it will always work
+    // at runtime.
+    for (const subgraph of this.subgraphs) {
+      for (const requiresApplication of subgraph.metadata().requiresDirective().applications()) {
+        const originalField = requiresApplication.parent as FieldDefinition<CompositeType>;
+        assert(originalField.kind === 'FieldDefinition', () => `Expected ${inspect(originalField)} to be a field`);
+        const mergedType = this.merged.type(originalField.parent.name);
+        // The type should exists: there is a few types we don't merge, but those are from specific core features and they shouldn't have @provides.
+        // In fact, if we were to not merge a type with a @provides, this would essentially mean that @provides cannot work, so worth catching
+        // the issue early if this ever happen for some reason. And of course, the type should be composite since it is in at least the one
+        // subgraph we're checking.
+        assert(mergedType && isCompositeType(mergedType), () => `Merged type ${originalField.parent.name} should exist should have field ${originalField.name}`)
+        assert(isCompositeType(mergedType), `${mergedType} should be a composite type but got ${mergedType.kind}`);
+        try {
+          parseFieldSetArgument({
+            parentType: mergedType,
+            directive: requiresApplication,
+            decorateValidationErrors: false,
+          });
+        } catch (e) {
+          if (!(e instanceof GraphQLError)) {
+            throw e;
+          }
+
+          // Providing a useful error message to the user here is tricky in the general case because what we checked is that
+          // a given subgraph @provides definition is invalid "on the supergraph", but the user seeing the error will not have
+          // the supergraph, so we need to express the error in terms of the subgraphs.
+          // But in practice, there is only a handful of cases that can trigger an error here. Indeed, at this point we know that
+          //  - the @require application is valid in its original subgraph.
+          //  - there was not merging errors (we don't call this whole method otherwise).
+          // This eliminate the risk of the error being due to some invalid syntax, of some subsection on a non-composite or missing
+          // on on a composite one (merging would have error), or of some unknown field in the selection (output types are merged
+          // by union, so any field that was in the subgraph will be in the supergraph), or even any error due to the types of fields
+          // involved (because the merged type is always a (non-strict) supertype of its counterpart in any subgraph, and anything
+          // that could be queried in a subtype can be queried on a supertype).
+          // As such, the only errors that we can have here are due to field arguments: because they are merged by intersection,
+          // it _is_ possible that something that is valid in a subgraph is not valid in the supergraph. And the only 2 things that
+          // can make such invalidity are:
+          //  1. an argument may not be in the supergraph: it is in the subgraph, but not in all the subgraphs having the field,
+          //    and the `@provides` passes a concrete value to that argument.
+          //  2. the type of an argument in the supergraph is a strict subtype the type that argument has in `subgraph` (the one
+          //    with the `@provides`) _and_ the `@provides` selection relies on the type difference. Now, argument types are input
+          //    types and the only subtyping difference input types is related to nullability (neither interfaces nor union are
+          //    input types in particular), so the only case this can happen is if a field `x` has some argument `a` type `A` in
+          //    `subgraph` but type `!A` with no default in the supergraph, _and_ the `@provides` queries that field `x` _without_
+          //    value for `a` (valid when `a` has type `A` but not with `!A` and no default).
+          // So to ensure we provide good error messages, we brute-force detecting those 2 possible cases and have a special
+          // treatment for each.
+          // Note that this detection is based on pattern-matching the error message, which is somewhat fragile, but because we
+          // only have 2 cases, we can easily cover them with unit tests, which means there is no practical risk of a message
+          // change breaking this code and being released undetected. A cleaner implementation would probably require having
+          // error codes and classes for all the graphqQL validations, but doing so cleanly is a fair amount of effort and probably
+          // no justified "just for this particular case".
+          const requireAST = requiresApplication.sourceAST ? [ addSubgraphToASTNode(requiresApplication.sourceAST, subgraph.name)] : [];
+
+          const that = this;
+          const registerError = (
+            arg: string,
+            field: string,
+            isIncompatible: (f: FieldDefinition<any>) => boolean,
+            makeMsg: (incompatibleSubgraphs: string) => string,
+          ) => {
+            const incompatibleSubgraphs = that.subgraphs.values().map((otherSubgraph) => {
+              if (otherSubgraph.name === subgraph.name) {
+                return undefined;
+              }
+              const fieldInOther = otherSubgraph.schema.elementByCoordinate(field);
+              const fieldIsIncompatible = fieldInOther
+                && fieldInOther instanceof FieldDefinition
+                && isIncompatible(fieldInOther);
+              return fieldIsIncompatible
+                ? {
+                  name: otherSubgraph.name,
+                  node: fieldInOther.sourceAST ? addSubgraphToASTNode(fieldInOther.sourceAST, otherSubgraph.name) : undefined,
+                }
+                : undefined;
+            }).filter(isDefined);
+            assert(incompatibleSubgraphs.length > 0, () => `Got error on ${arg} of ${field} but no "incompatible" subgraphs (error: ${e})`);
+            const nodes = requireAST.concat(incompatibleSubgraphs.map((s) => s.node).filter(isDefined));
+            const error = ERRORS.REQUIRES_INVALID_FIELDS.err(
+              `On field "${originalField.coordinate}", for ${requiresApplication}: ${makeMsg(printSubgraphNames(incompatibleSubgraphs.map((s) => s.name)))}`,
+              { nodes }
+            );
+            that.errors.push(addSubgraphToError(error, subgraph.name));
+          }
+
+          const unknownArgument = e.message.match(/Unknown argument \"(?<arg>[^"]*)\" found in value: \"(?<field>[^"]*)\" has no argument.*/);
+          if (unknownArgument) {
+            const arg = unknownArgument.groups?.arg!;
+            const field = unknownArgument.groups?.field!;
+            registerError(
+              arg,
+              field,
+              (f) => !f.argument(arg),
+              (incompatibleSubgraphs) => `cannot provide a value for argument "${arg}" of field "${field}" as argument "${arg}" is not defined in ${incompatibleSubgraphs}`,
+            );
+            continue;
+          }
+
+          const missingMandatory = e.message.match(/Missing mandatory value for argument \"(?<arg>[^"]*)\" of field \"(?<field>[^"]*)\".*/);
+          if (missingMandatory) {
+            const arg = missingMandatory.groups?.arg!;
+            const field = missingMandatory.groups?.field!;
+            registerError(
+              arg,
+              field,
+              (f) => !!f.argument(arg)?.isRequired(),
+              (incompatibleSubgraphs) => `no value provided for argument "${arg}" of field "${field}" but a value is mandatory as "${arg}" is required in ${incompatibleSubgraphs}`,
+            );
+            continue;
+          }
+
+          assert(false, () => `Unexpected error throw by ${requiresApplication} when evaluated on supergraph: ${e.message}`);
+        }
+      }
+    }
+
   }
 
   private updateInaccessibleErrorsWithLinkToSubgraphs(

docs/source/errors.md

@@ -76,7 +76,6 @@ The following errors might be raised during composition:
 | `REQUIRED_INACCESSIBLE` | An element is marked as @inaccessible but is required by an element visible in the API schema. | 2.0.0 |  |
 | `REQUIRED_INPUT_FIELD_MISSING_IN_SOME_SUBGRAPH` | A field of an input object type is mandatory in some subgraphs, but the field is not defined in all the subgraphs that define the input object type. | 2.0.0 |  |
 | `REQUIRES_DIRECTIVE_IN_FIELDS_ARG` | The `fields` argument of a `@requires` directive includes some directive applications. This is not supported | 2.1.0 |  |
-| `REQUIRES_FIELDS_HAS_ARGS` | The `fields` argument of a `@requires` directive includes a field defined with arguments (which is not currently supported). | 2.0.0 |  |
 | `REQUIRES_FIELDS_MISSING_EXTERNAL` | The `fields` argument of a `@requires` directive includes a field that is not marked as `@external`. | 0.x |  |
 | `REQUIRES_INVALID_FIELDS_TYPE` | The value passed to the `fields` argument of a `@requires` directive is not a string. | 2.0.0 |  |
 | `REQUIRES_INVALID_FIELDS` | The `fields` argument of a `@requires` directive is invalid (it has invalid syntax, includes unknown fields, ...). | 2.0.0 |  |
@@ -116,6 +115,7 @@ The following error codes have been removed and are no longer generated by the m
 | `NON_REPEATABLE_DIRECTIVE_ARGUMENTS_MISMATCH` | Since federation 2.1.0, the case this error used to cover is now a warning (with code `INCONSISTENT_NON_REPEATABLE_DIRECTIVE_ARGUMENTS`) instead of an error |
 | `PROVIDES_FIELDS_SELECT_INVALID_TYPE` | @provides can now be used on field of interface, union and list types |
 | `PROVIDES_NOT_ON_ENTITY` | @provides can now be used on any type. |
+| `REQUIRES_FIELDS_HAS_ARGS` | Since federation 2.1.1, using fields with arguments in a @requires is fully supported |
 | `REQUIRES_FIELDS_MISSING_ON_BASE` | Fields in @requires can now be from any subgraph. |
 | `REQUIRES_USED_ON_BASE` | As there is not type ownership anymore, there is also no particular limitation as to which subgraph can use a @requires. |
 | `RESERVED_FIELD_USED` | This error was previously not correctly enforced: the _service and _entities, if present, were overridden; this is still the case |

gateway-js/CHANGELOG.md

@@ -4,8 +4,11 @@ This CHANGELOG pertains only to Apollo Federation packages in the 2.x range. The
 
 ## vNext
 
+- Allow fields with arguments in `@requires` [PR #2120](https://github.com/apollographql/federation/pull/2120).
+
 ## 2.1.2-alpha.1
-- Fix potential inefficient planning due to __typename [PR #2137](https://github.com/apollographql/federation/pull/2137).
+
+- Fix potential inefficient planning due to `__typename` [PR #2137](https://github.com/apollographql/federation/pull/2137).
 - Fix potential assertion during query planning [PR #2133](https://github.com/apollographql/federation/pull/2133).
 
 ## 2.1.2-alpha.0