Implement support for @stream directive

# Conflicts:
#	src/execution/execute.ts
#	src/validation/index.d.ts
#	src/validation/index.ts

src/validation/__tests__/DeferStreamDirectiveOnRootFieldRule-test.ts

@@ -36,6 +36,7 @@ const schema = buildSchema(`
 
   type QueryRoot {
     message: Message
+    messages: [Message]
   }
 
   schema {
@@ -167,4 +168,91 @@ describe('Validate: Defer/Stream directive on root field', () => {
       }
     `);
   });
+  it('Stream field on root query field', () => {
+    expectValid(`
+      {
+        messages @stream {
+          name
+        }
+      }
+    `);
+  });
+  it('Stream field on fragment on root query field', () => {
+    expectValid(`
+      {
+        ...rootFragment
+      }
+      fragment rootFragment on QueryType {
+        messages @stream {
+          name
+        }
+      }
+    `);
+  });
+  it('Stream field on root mutation field', () => {
+    expectErrors(`
+      mutation {
+        mutationListField @stream {
+          name
+        }
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Stream directive cannot be used on root mutation type "MutationRoot".',
+        locations: [{ line: 3, column: 27 }],
+      },
+    ]);
+  });
+  it('Stream field on fragment on root mutation field', () => {
+    expectErrors(`
+      mutation {
+        ...rootFragment
+      }
+      fragment rootFragment on MutationRoot {
+        mutationListField @stream {
+          name
+        }
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Stream directive cannot be used on root mutation type "MutationRoot".',
+        locations: [{ line: 6, column: 27 }],
+      },
+    ]);
+  });
+  it('Stream field on root subscription field', () => {
+    expectErrors(`
+      subscription {
+        subscriptionListField @stream {
+          name
+        }
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Stream directive cannot be used on root subscription type "SubscriptionRoot".',
+        locations: [{ line: 3, column: 31 }],
+      },
+    ]);
+  });
+  it('Stream field on fragment on root subscription field', () => {
+    expectErrors(`
+      subscription {
+        ...rootFragment
+      }
+      fragment rootFragment on SubscriptionRoot {
+        subscriptionListField @stream {
+          name
+        }
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Stream directive cannot be used on root subscription type "SubscriptionRoot".',
+        locations: [{ line: 6, column: 31 }],
+      },
+    ]);
+  });
 });

src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts

@@ -98,6 +98,123 @@ describe('Validate: Overlapping fields can be merged', () => {
     `);
   });
 
+  it('Same stream directives supported', () => {
+    expectValid(`
+      fragment differentDirectivesWithDifferentAliases on Dog {
+        name @stream(label: "streamLabel", initialCount: 1)
+        name @stream(label: "streamLabel", initialCount: 1)
+      }
+    `);
+  });
+
+  it('different stream directive label', () => {
+    expectErrors(`
+      fragment conflictingArgs on Dog {
+        name @stream(label: "streamLabel", initialCount: 1)
+        name @stream(label: "anotherLabel", initialCount: 1)
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "name" conflict because they have differing stream directives. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('different stream directive initialCount', () => {
+    expectErrors(`
+      fragment conflictingArgs on Dog {
+        name @stream(label: "streamLabel", initialCount: 1)
+        name @stream(label: "streamLabel", initialCount: 2)
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "name" conflict because they have differing stream directives. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('different stream directive first missing args', () => {
+    expectErrors(`
+      fragment conflictingArgs on Dog {
+        name @stream
+        name @stream(label: "streamLabel", initialCount: 1)
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "name" conflict because they have differing stream directives. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('different stream directive second missing args', () => {
+    expectErrors(`
+      fragment conflictingArgs on Dog {
+        name @stream(label: "streamLabel", initialCount: 1)
+        name @stream
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "name" conflict because they have differing stream directives. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('mix of stream and no stream', () => {
+    expectErrors(`
+      fragment conflictingArgs on Dog {
+        name @stream
+        name
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "name" conflict because they have differing stream directives. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('different stream directive both missing args', () => {
+    expectErrors(`
+      fragment conflictingArgs on Dog {
+        name @stream
+        name @stream
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "name" conflict because they have differing stream directives. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
   it('Same aliases with different field targets', () => {
     expectErrors(`
       fragment sameAliasesWithDifferentFieldTargets on Dog {

src/validation/__tests__/StreamDirectiveOnListFieldRule-test.ts

@@ -0,0 +1,79 @@
+import { describe, it } from 'mocha';
+
+import { StreamDirectiveOnListFieldRule } from '../rules/StreamDirectiveOnListFieldRule';
+
+import { expectValidationErrors } from './harness';
+
+function expectErrors(queryStr: string) {
+  return expectValidationErrors(StreamDirectiveOnListFieldRule, queryStr);
+}
+
+function expectValid(queryStr: string) {
+  expectErrors(queryStr).toDeepEqual([]);
+}
+
+describe('Validate: Stream directive on list field', () => {
+  it('Stream on list field', () => {
+    expectValid(`
+      fragment objectFieldSelection on Human {
+        pets @stream(initialCount: 0) {
+          name
+        }
+      }
+    `);
+  });
+
+  it('Stream on non-null list field', () => {
+    expectValid(`
+      fragment objectFieldSelection on Human {
+        relatives @stream(initialCount: 0) {
+          name
+        }
+      }
+    `);
+  });
+
+  it("Doesn't validate other directives on list fields", () => {
+    expectValid(`
+    fragment objectFieldSelection on Human {
+      pets @include(if: true) {
+        name
+      }
+    }
+    `);
+  });
+
+  it("Doesn't validate other directives on non-list fields", () => {
+    expectValid(`
+      fragment objectFieldSelection on Human {
+        pets {
+          name @include(if: true)
+        }
+      }
+    `);
+  });
+
+  it("Doesn't validate misplaced stream directives", () => {
+    expectValid(`
+      fragment objectFieldSelection on Human {
+        ... @stream(initialCount: 0) {
+          name
+        }
+      }
+    `);
+  });
+
+  it('reports errors when stream is used on non-list field', () => {
+    expectErrors(`
+      fragment objectFieldSelection on Human {
+        name @stream(initialCount: 0)
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Stream directive cannot be used on non-list field "name" on type "Human".',
+        locations: [{ line: 3, column: 14 }],
+      },
+    ]);
+  });
+});

src/validation/__tests__/harness.ts

@@ -58,7 +58,7 @@ export const testSchema: GraphQLSchema = buildSchema(`
   type Human {
     name(surname: Boolean): String
     pets: [Pet]
-    relatives: [Human]
+    relatives: [Human]!
   }
 
   enum FurColor {

src/validation/index.ts

@@ -60,6 +60,9 @@ export { ScalarLeafsRule } from './rules/ScalarLeafsRule';
 /** Spec Section: "Subscriptions with Single Root Field" */
 export { SingleFieldSubscriptionsRule } from './rules/SingleFieldSubscriptionsRule';
 
+/** Spec Section: "Stream Directives Are Used On List Fields" */
+export { StreamDirectiveOnListFieldRule } from './rules/StreamDirectiveOnListFieldRule';
+
 /** Spec Section: "Argument Uniqueness" */
 export { UniqueArgumentNamesRule } from './rules/UniqueArgumentNamesRule';
 

src/validation/rules/DeferStreamDirectiveOnRootFieldRule.ts

@@ -2,7 +2,10 @@ import { GraphQLError } from '../../error/GraphQLError';
 
 import type { ASTVisitor } from '../../language/visitor';
 
-import { GraphQLDeferDirective } from '../../type/directives';
+import {
+  GraphQLDeferDirective,
+  GraphQLStreamDirective,
+} from '../../type/directives';
 
 import type { ValidationContext } from '../ValidationContext';
 
@@ -37,6 +40,24 @@ export function DeferStreamDirectiveOnRootFieldRule(
           );
         }
       }
+      if (parentType && node.name.value === GraphQLStreamDirective.name) {
+        if (mutationType && parentType === mutationType) {
+          context.reportError(
+            new GraphQLError(
+              `Stream directive cannot be used on root mutation type "${parentType.name}".`,
+              node,
+            ),
+          );
+        }
+        if (subscriptionType && parentType === subscriptionType) {
+          context.reportError(
+            new GraphQLError(
+              `Stream directive cannot be used on root subscription type "${parentType.name}".`,
+              node,
+            ),
+          );
+        }
+      }
     },
   };
 }