Simplify getDirectiveNames and remove flattenSelections helper.

Though it's possible that someone might have been using flattenSelections
directly, the function signature seems awfully specific to the needs of
the former implementation of getDirectiveNames.

CHANGELOG.md

@@ -8,6 +8,26 @@
   `graphql/language/printer`. If you need this functionality, import it
   directly: `import { print } from "graphql/language/printer"`
 
+### Apollo Cache In-Memory (vNext)
+
+- The `flattenSelections` helper function is no longer exported from
+  `apollo-utilities`, since `getDirectiveNames` has been reimplemented
+  without using `flattenSelections`, and `flattenSelections` has no clear
+  purpose now. If you need the old functionality, use a visitor:
+  ```ts
+  import { visit } from "graphql/language/visitor";
+
+  function flattenSelections(selection: SelectionNode) {
+    const selections: SelectionNode[] = [];
+    visit(selection, {
+      SelectionSet(ss) {
+        selections.push(...ss.selections);
+      }
+    });
+    return selections;
+  }
+  ```
+
 ## Apollo Client (2.4.9)
 
 ### Apollo Client (2.4.9)

packages/apollo-utilities/src/directives.ts

@@ -2,14 +2,15 @@
 // the `skip` and `include` directives within GraphQL.
 import {
   FieldNode,
-  OperationDefinitionNode,
   SelectionNode,
   VariableNode,
   BooleanValueNode,
   DirectiveNode,
   DocumentNode,
 } from 'graphql';
 
+import { visit } from 'graphql/language/visitor';
+
 import { argumentsObjectFromField } from './storeUtils';
 
 export type DirectiveInfo = {
@@ -95,45 +96,16 @@ export function shouldInclude(
   return res;
 }
 
-export function flattenSelections(selection: SelectionNode): SelectionNode[] {
-  if (
-    !(selection as FieldNode).selectionSet ||
-    !((selection as FieldNode).selectionSet.selections.length > 0)
-  )
-    return [selection];
-
-  return [selection].concat(
-    (selection as FieldNode).selectionSet.selections
-      .map(selectionNode =>
-        [selectionNode].concat(flattenSelections(selectionNode)),
-      )
-      .reduce((selections, selected) => selections.concat(selected), []),
-  );
-}
-
 export function getDirectiveNames(doc: DocumentNode) {
-  // operation => [names of directives];
-  const directiveNames = doc.definitions
-    .filter(
-      (definition: OperationDefinitionNode) =>
-        definition.selectionSet && definition.selectionSet.selections,
-    )
-    // operation => [[Selection]]
-    .map(x => flattenSelections(x as any))
-    // [[Selection]] => [Selection]
-    .reduce((selections, selected) => selections.concat(selected), [])
-    // [Selection] => [Selection with Directives]
-    .filter(
-      (selection: SelectionNode) =>
-        selection.directives && selection.directives.length > 0,
-    )
-    // [Selection with Directives] => [[Directives]]
-    .map((selection: SelectionNode) => selection.directives)
-    // [[Directives]] => [Directives]
-    .reduce((directives, directive) => directives.concat(directive), [])
-    // [Directives] => [Name]
-    .map((directive: DirectiveNode) => directive.name.value);
-  return directiveNames;
+  const names: string[] = [];
+
+  visit(doc, {
+    Directive(node) {
+      names.push(node.name.value);
+    },
+  });
+
+  return names;
 }
 
 export function hasDirectives(names: string[], doc: DocumentNode) {