collectFields/collectSubfields refactor and export as part of public API

Motivated by graphql#3246

Author: IvanGoncharov

src/execution/collectFields.ts

@@ -22,8 +22,7 @@ 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.
+ * Given a selectionSet, collect all of the 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
@@ -37,9 +36,64 @@ export function collectFields(
   variableValues: { [variable: string]: unknown },
   runtimeType: GraphQLObjectType,
   selectionSet: SelectionSetNode,
+): Map<string, ReadonlyArray<FieldNode>> {
+  const fields = new Map();
+  collectFieldsImpl(
+    schema,
+    fragments,
+    variableValues,
+    runtimeType,
+    selectionSet,
+    fields,
+    new Set(),
+  );
+  return fields;
+}
+
+/**
+ * Given an array of field nodes, collects all of the subfields of the passed
+ * in fields, and returns it at the end.
+ *
+ * CollectFields requires the "return type" of an object. For a field which
+ * returns an Interface or Union type, the "return type" will be the actual
+ * Object type returned by that field.
+ *
+ * @internal
+ */
+export function collectSubfields(
+  schema: GraphQLSchema,
+  fragments: ObjMap<FragmentDefinitionNode>,
+  variableValues: { [variable: string]: unknown },
+  returnType: GraphQLObjectType,
+  fieldNodes: ReadonlyArray<FieldNode>,
+): Map<string, ReadonlyArray<FieldNode>> {
+  const subFieldNodes = new Map();
+  const visitedFragmentNames = new Set<string>();
+  for (const node of fieldNodes) {
+    if (node.selectionSet) {
+      collectFieldsImpl(
+        schema,
+        fragments,
+        variableValues,
+        returnType,
+        node.selectionSet,
+        subFieldNodes,
+        visitedFragmentNames,
+      );
+    }
+  }
+  return subFieldNodes;
+}
+
+function collectFieldsImpl(
+  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>> {
+): void {
   for (const selection of selectionSet.selections) {
     switch (selection.kind) {
       case Kind.FIELD: {
@@ -62,7 +116,7 @@ export function collectFields(
         ) {
           continue;
         }
-        collectFields(
+        collectFieldsImpl(
           schema,
           fragments,
           variableValues,
@@ -89,7 +143,7 @@ export function collectFields(
         ) {
           continue;
         }
-        collectFields(
+        collectFieldsImpl(
           schema,
           fragments,
           variableValues,
@@ -102,7 +156,6 @@ export function collectFields(
       }
     }
   }
-  return fields;
 }
 
 /**

src/execution/execute.ts

@@ -54,7 +54,30 @@ import {
 import { getOperationRootType } from '../utilities/getOperationRootType';
 
 import { getVariableValues, getArgumentValues } from './values';
-import { collectFields } from './collectFields';
+import {
+  collectFields,
+  collectSubfields as _collectSubfields,
+} from './collectFields';
+
+/**
+ * A memoized collection of relevant subfields with regard to the return
+ * type. Memoizing ensures the subfields are not repeatedly calculated, which
+ * saves overhead when resolving lists of values.
+ */
+const collectSubfields = memoize3(
+  (
+    exeContext: ExecutionContext,
+    returnType: GraphQLObjectType,
+    fieldNodes: ReadonlyArray<FieldNode>,
+  ) =>
+    _collectSubfields(
+      exeContext.schema,
+      exeContext.fragments,
+      exeContext.variableValues,
+      returnType,
+      fieldNodes,
+    ),
+);
 
 /**
  * Terminology
@@ -330,8 +353,6 @@ function executeOperation(
     exeContext.variableValues,
     type,
     operation.selectionSet,
-    new Map(),
-    new Set(),
   );
 
   const path = undefined;
@@ -921,35 +942,6 @@ function invalidReturnTypeError(
   );
 }
 
-/**
- * A memoized collection of relevant subfields with regard to the return
- * type. Memoizing ensures the subfields are not repeatedly calculated, which
- * saves overhead when resolving lists of values.
- */
-const collectSubfields = memoize3(_collectSubfields);
-function _collectSubfields(
-  exeContext: ExecutionContext,
-  returnType: GraphQLObjectType,
-  fieldNodes: ReadonlyArray<FieldNode>,
-): Map<string, ReadonlyArray<FieldNode>> {
-  let subFieldNodes = new Map();
-  const visitedFragmentNames = new Set<string>();
-  for (const node of fieldNodes) {
-    if (node.selectionSet) {
-      subFieldNodes = collectFields(
-        exeContext.schema,
-        exeContext.fragments,
-        exeContext.variableValues,
-        returnType,
-        node.selectionSet,
-        subFieldNodes,
-        visitedFragmentNames,
-      );
-    }
-  }
-  return subFieldNodes;
-}
-
 /**
  * If a resolveType function is not given, then a default resolve behavior is
  * used which attempts two strategies:

src/subscription/subscribe.ts

@@ -198,8 +198,6 @@ async function executeSubscription(
     variableValues,
     type,
     operation.selectionSet,
-    new Map(),
-    new Set(),
   );
   const [responseName, fieldNodes] = [...fields.entries()][0];
   const fieldDef = getFieldDef(schema, type, fieldNodes[0]);

src/validation/rules/SingleFieldSubscriptionsRule.ts

@@ -44,8 +44,6 @@ export function SingleFieldSubscriptionsRule(
             variableValues,
             subscriptionType,
             node.selectionSet,
-            new Map(),
-            new Set(),
           );
           if (fields.size > 1) {
             const fieldSelectionLists = [...fields.values()];