From 1250f978ce01cd8b94e2dd622f19e6acf52810bc Mon Sep 17 00:00:00 2001
From: Ivan Goncharov <ivan.goncharov.ua@gmail.com>
Date: Sat, 13 Mar 2021 13:36:53 +0200
Subject: [PATCH] ASTVisitor: use type intersection instead of type union

---
 src/language/visitor.d.ts | 16 +++++++---------
 src/language/visitor.js   | 20 +++++++++++---------
 2 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/src/language/visitor.d.ts b/src/language/visitor.d.ts
index 69261912799..8c48dba2601 100644
--- a/src/language/visitor.d.ts
+++ b/src/language/visitor.d.ts
@@ -6,17 +6,15 @@ import { ASTNode, ASTKindToNode } from './ast';
  * A visitor is provided to visit, it contains the collection of
  * relevant functions to be called during the visitor's traversal.
  */
-export type ASTVisitor = EnterLeave<ASTVisitFn<ASTNode>> | ShapeMapVisitor;
+export type ASTVisitor = EnterLeaveVisitor<ASTNode> & KindVisitor;
 
-interface EnterLeave<T> {
-  readonly enter?: T;
-  readonly leave?: T;
-}
+type KindVisitor = {
+  readonly [K in keyof ASTKindToNode]?: ASTVisitFn<K> | EnterLeaveVisitor<K>;
+};
 
-type ShapeMapVisitor = {
-  [K in keyof ASTKindToNode]?:
-    | ASTVisitFn<ASTKindToNode[K]>
-    | EnterLeave<ASTVisitFn<ASTKindToNode[K]>>;
+type EnterLeaveVisitor<TVisitedNode extends ASTNode> = {
+  readonly enter?: ASTVisitFn<TVisitedNode>;
+  readonly leave?: ASTVisitFn<TVisitedNode>;
 };
 
 /**
diff --git a/src/language/visitor.js b/src/language/visitor.js
index b8eac406133..582aaf4423f 100644
--- a/src/language/visitor.js
+++ b/src/language/visitor.js
@@ -7,14 +7,17 @@ import { isNode } from './ast';
  * A visitor is provided to visit, it contains the collection of
  * relevant functions to be called during the visitor's traversal.
  */
-export type ASTVisitor =
-  | EnterLeave<ASTVisitFn<ASTNode>>
-  | ShapeMap<
-      ASTKindToNode,
-      <Node>(Node) => ASTVisitFn<Node> | EnterLeave<ASTVisitFn<Node>>,
-    >;
-type EnterLeave<T> = {| +enter?: T, +leave?: T |};
-type ShapeMap<O, F> = $Shape<$ObjMap<O, F>>;
+export type ASTVisitor = $Shape<EnterLeaveVisitor<ASTNode> & KindVisitor>;
+
+type KindVisitor = $ObjMap<
+  ASTKindToNode,
+  <Node>(Node) => ASTVisitFn<Node> | EnterLeaveVisitor<Node>,
+>;
+
+type EnterLeaveVisitor<TVisitedNode: ASTNode> = {|
+  +enter?: ASTVisitFn<TVisitedNode>,
+  +leave?: ASTVisitFn<TVisitedNode>,
+|};
 
 /**
  * A visitor is comprised of visit functions, which are called on each node
@@ -389,7 +392,6 @@ export function getVisitFn(
       return kindSpecificVisitor;
     }
   } else {
-    // $FlowFixMe[prop-missing]
     const specificVisitor = isLeaving ? visitor.leave : visitor.enter;
     if (specificVisitor) {
       // { enter() {}, leave() {} }