feat: allow experimental customization of execution algorithm

src/execution/__tests__/executor-test.ts

@@ -18,6 +18,7 @@ import {
   GraphQLUnionType,
 } from '../../type/definition';
 
+import { Executor } from '../executor';
 import { execute, executeSync } from '../execute';
 
 describe('Execute: Handles basic execution tasks', () => {
@@ -1151,6 +1152,32 @@ describe('Execute: Handles basic execution tasks', () => {
     expect(result).to.deep.equal({ data: { foo: null } });
   });
 
+  it('uses a custom Executor', () => {
+    const schema = new GraphQLSchema({
+      query: new GraphQLObjectType({
+        name: 'Query',
+        fields: {
+          foo: { type: GraphQLString },
+        },
+      }),
+    });
+    const document = parse('{ foo }');
+
+    class CustomExecutor extends Executor {
+      executeField() {
+        return 'foo';
+      }
+    }
+
+    const result = executeSync({
+      schema,
+      document,
+      CustomExecutor,
+    });
+
+    expect(result).to.deep.equal({ data: { foo: 'foo' } });
+  });
+
   it('uses a custom field resolver', () => {
     const schema = new GraphQLSchema({
       query: new GraphQLObjectType({

src/execution/collectFields.ts

@@ -0,0 +1,159 @@
+import type { ObjMap } from '../jsutils/ObjMap';
+
+import type {
+  SelectionSetNode,
+  FieldNode,
+  FragmentSpreadNode,
+  InlineFragmentNode,
+  FragmentDefinitionNode,
+} from '../language/ast';
+import { Kind } from '../language/kinds';
+
+import type { GraphQLSchema } from '../type/schema';
+import type { GraphQLObjectType } from '../type/definition';
+import {
+  GraphQLIncludeDirective,
+  GraphQLSkipDirective,
+} from '../type/directives';
+import { isAbstractType } from '../type/definition';
+
+import { typeFromAST } from '../utilities/typeFromAST';
+
+import { getDirectiveValues } from './values';
+
+/**
+ * Given a selectionSet, adds all of the fields in that selection to
+ * the passed in map of fields, and returns it at the end.
+ *
+ * CollectFields requires the "runtime type" of an object. For a field which
+ * returns an Interface or Union type, the "runtime type" will be the actual
+ * Object type returned by that field.
+ *
+ * @internal
+ */
+export function collectFields(
+  schema: GraphQLSchema,
+  fragments: ObjMap<FragmentDefinitionNode>,
+  variableValues: { [variable: string]: unknown },
+  runtimeType: GraphQLObjectType,
+  selectionSet: SelectionSetNode,
+  fields: Map<string, Array<FieldNode>>,
+  visitedFragmentNames: Set<string>,
+): Map<string, ReadonlyArray<FieldNode>> {
+  for (const selection of selectionSet.selections) {
+    switch (selection.kind) {
+      case Kind.FIELD: {
+        if (!shouldIncludeNode(variableValues, selection)) {
+          continue;
+        }
+        const name = getFieldEntryKey(selection);
+        const fieldList = fields.get(name);
+        if (fieldList !== undefined) {
+          fieldList.push(selection);
+        } else {
+          fields.set(name, [selection]);
+        }
+        break;
+      }
+      case Kind.INLINE_FRAGMENT: {
+        if (
+          !shouldIncludeNode(variableValues, selection) ||
+          !doesFragmentConditionMatch(schema, selection, runtimeType)
+        ) {
+          continue;
+        }
+        collectFields(
+          schema,
+          fragments,
+          variableValues,
+          runtimeType,
+          selection.selectionSet,
+          fields,
+          visitedFragmentNames,
+        );
+        break;
+      }
+      case Kind.FRAGMENT_SPREAD: {
+        const fragName = selection.name.value;
+        if (
+          visitedFragmentNames.has(fragName) ||
+          !shouldIncludeNode(variableValues, selection)
+        ) {
+          continue;
+        }
+        visitedFragmentNames.add(fragName);
+        const fragment = fragments[fragName];
+        if (
+          !fragment ||
+          !doesFragmentConditionMatch(schema, fragment, runtimeType)
+        ) {
+          continue;
+        }
+        collectFields(
+          schema,
+          fragments,
+          variableValues,
+          runtimeType,
+          fragment.selectionSet,
+          fields,
+          visitedFragmentNames,
+        );
+        break;
+      }
+    }
+  }
+  return fields;
+}
+
+/**
+ * Determines if a field should be included based on the @include and @skip
+ * directives, where @skip has higher precedence than @include.
+ */
+function shouldIncludeNode(
+  variableValues: { [variable: string]: unknown },
+  node: FragmentSpreadNode | FieldNode | InlineFragmentNode,
+): boolean {
+  const skip = getDirectiveValues(GraphQLSkipDirective, node, variableValues);
+  if (skip?.if === true) {
+    return false;
+  }
+
+  const include = getDirectiveValues(
+    GraphQLIncludeDirective,
+    node,
+    variableValues,
+  );
+  if (include?.if === false) {
+    return false;
+  }
+  return true;
+}
+
+/**
+ * Determines if a fragment is applicable to the given type.
+ */
+function doesFragmentConditionMatch(
+  schema: GraphQLSchema,
+  fragment: FragmentDefinitionNode | InlineFragmentNode,
+  type: GraphQLObjectType,
+): boolean {
+  const typeConditionNode = fragment.typeCondition;
+  if (!typeConditionNode) {
+    return true;
+  }
+  const conditionalType = typeFromAST(schema, typeConditionNode);
+  if (conditionalType === type) {
+    return true;
+  }
+  if (isAbstractType(conditionalType)) {
+    return schema.isSubType(conditionalType, type);
+  }
+  return false;
+}
+
+/**
+ * Implements the logic to compute the key of a given field's entry
+ */
+function getFieldEntryKey(node: FieldNode): string {
+  return node.alias ? node.alias.value : node.name.value;
+}