extract IncrementalExecutor from Executor (#4545)

such that `IncrementalExecutor` extends a base Executor class that
ignores the incremental directives.

In contrast, the `ExecutorThrowingOnIncremental` subclass should throw
on encountering incremental directives, to be used in the standard
`execute` function, signaling that these directives are disabled unless
used intentionally with the new experimental behavior via the new
function.

Tests are reorganized/moved, not changed.

Author: yaacovCR

src/execution/Executor.ts

@@ -0,0 +1,114 @@
+import { invariant } from '../jsutils/invariant.js';
+import type { ObjMap } from '../jsutils/ObjMap.js';
+import type { Path } from '../jsutils/Path.js';
+import type { PromiseOrValue } from '../jsutils/PromiseOrValue.js';
+
+import { OperationTypeNode } from '../language/ast.js';
+
+import type {
+  GraphQLList,
+  GraphQLObjectType,
+  GraphQLOutputType,
+} from '../type/index.js';
+
+import type {
+  DeferUsage,
+  FieldDetailsList,
+  GroupedFieldSet,
+} from './collectFields.js';
+import { Executor, getStreamUsage } from './Executor.js';
+import type { ResolveInfo } from './ResolveInfo.js';
+
+const UNEXPECTED_MULTIPLE_PAYLOADS =
+  'Executing this GraphQL operation would unexpectedly produce multiple payloads (due to @defer or @stream directive)';
+
+/** @internal */
+export class ExecutorThrowingOnIncremental extends Executor {
+  override executeCollectedRootFields(
+    operation: OperationTypeNode,
+    rootType: GraphQLObjectType,
+    rootValue: unknown,
+    originalGroupedFieldSet: GroupedFieldSet,
+    newDeferUsages: ReadonlyArray<DeferUsage>,
+  ): PromiseOrValue<ObjMap<unknown>> {
+    if (newDeferUsages.length > 0) {
+      invariant(
+        this.validatedExecutionArgs.operation.operation !==
+          OperationTypeNode.SUBSCRIPTION,
+        '`@defer` directive not supported on subscription operations. Disable `@defer` by setting the `if` argument to `false`.',
+      );
+      const reason = new Error(UNEXPECTED_MULTIPLE_PAYLOADS);
+      this.cancel(reason);
+      throw reason;
+    }
+    return this.executeRootGroupedFieldSet(
+      operation,
+      rootType,
+      rootValue,
+      originalGroupedFieldSet,
+      undefined,
+    );
+  }
+
+  override executeCollectedSubfields(
+    parentType: GraphQLObjectType,
+    sourceValue: unknown,
+    path: Path | undefined,
+    originalGroupedFieldSet: GroupedFieldSet,
+    newDeferUsages: ReadonlyArray<DeferUsage>,
+  ): PromiseOrValue<ObjMap<unknown>> {
+    if (newDeferUsages.length > 0) {
+      invariant(
+        this.validatedExecutionArgs.operation.operation !==
+          OperationTypeNode.SUBSCRIPTION,
+        '`@defer` directive not supported on subscription operations. Disable `@defer` by setting the `if` argument to `false`.',
+      );
+      const reason = new Error(UNEXPECTED_MULTIPLE_PAYLOADS);
+      this.cancel(reason);
+      throw reason;
+    }
+
+    return this.executeFields(
+      parentType,
+      sourceValue,
+      path,
+      originalGroupedFieldSet,
+      undefined,
+    );
+  }
+
+  // eslint-disable-next-line max-params
+  override completeListValue(
+    returnType: GraphQLList<GraphQLOutputType>,
+    fieldDetailsList: FieldDetailsList,
+    info: ResolveInfo,
+    path: Path,
+    result: unknown,
+    positionContext: undefined,
+  ): PromiseOrValue<ReadonlyArray<unknown>> {
+    const streamUsage = getStreamUsage(
+      this.validatedExecutionArgs,
+      fieldDetailsList,
+    );
+    if (streamUsage !== undefined) {
+      invariant(
+        this.validatedExecutionArgs.operation.operation !==
+          OperationTypeNode.SUBSCRIPTION,
+        '`@stream` directive not supported on subscription operations. Disable `@stream` by setting the `if` argument to `false`.',
+      );
+
+      const reason = new Error(UNEXPECTED_MULTIPLE_PAYLOADS);
+      this.cancel(reason);
+      throw reason;
+    }
+
+    return super.completeListValue(
+      returnType,
+      fieldDetailsList,
+      info,
+      path,
+      result,
+      positionContext,
+    );
+  }
+}