From a96efb5f41692ccacd6436c9cf8e12de440d206d Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Fri, 24 Aug 2018 18:17:04 +0100
Subject: [PATCH] Detect Fiber types to avoid inlining constants

---
 .../src/ReactSixteenAdapter.js                | 40 ++++++------
 .../src/detectFiberTags.js                    | 63 +++++++++++++++++++
 2 files changed, 81 insertions(+), 22 deletions(-)
 create mode 100644 packages/enzyme-adapter-react-16/src/detectFiberTags.js

diff --git a/packages/enzyme-adapter-react-16/src/ReactSixteenAdapter.js b/packages/enzyme-adapter-react-16/src/ReactSixteenAdapter.js
index 50aef74a7..ba4ab4b58 100644
--- a/packages/enzyme-adapter-react-16/src/ReactSixteenAdapter.js
+++ b/packages/enzyme-adapter-react-16/src/ReactSixteenAdapter.js
@@ -37,18 +37,10 @@ import {
   ensureKeyOrUndefined,
 } from 'enzyme-adapter-utils';
 import findCurrentFiberUsingSlowPath from './findCurrentFiberUsingSlowPath';
+import detectFiberTags from './detectFiberTags';
 
-const HostRoot = 3;
-const ClassComponent = 2;
-const FragmentType = 10;
-const FunctionalComponent = 1;
-const HostPortal = 4;
-const HostComponent = 5;
-const HostText = 6;
-const Mode = 11;
-const ContextConsumerType = 12;
-const ContextProviderType = 13;
-const ForwardRefType = 14;
+// Lazily populated if DOM is available.
+let FiberTags = null;
 
 function nodeAndSiblingsArray(nodeWithSibling) {
   const array = [];
@@ -115,9 +107,9 @@ function toTree(vnode) {
   // somewhere else. Should talk to sebastian about this perhaps
   const node = findCurrentFiberUsingSlowPath(vnode);
   switch (node.tag) {
-    case HostRoot: // 3
+    case FiberTags.HostRoot:
       return childrenToTree(node.child);
-    case HostPortal: { // 4
+    case FiberTags.HostPortal: {
       const {
         stateNode: { containerInfo },
         memoizedProps: children,
@@ -133,7 +125,7 @@ function toTree(vnode) {
         rendered: childrenToTree(node.child),
       };
     }
-    case ClassComponent:
+    case FiberTags.ClassComponent:
       return {
         nodeType: 'class',
         type: node.type,
@@ -143,7 +135,7 @@ function toTree(vnode) {
         instance: node.stateNode,
         rendered: childrenToTree(node.child),
       };
-    case FunctionalComponent: // 1
+    case FiberTags.FunctionalComponent:
       return {
         nodeType: 'function',
         type: node.type,
@@ -154,7 +146,7 @@ function toTree(vnode) {
         rendered: childrenToTree(node.child),
       };
 
-    case HostComponent: { // 5
+    case FiberTags.HostComponent: {
       let renderedNodes = flatten(nodeAndSiblingsArray(node.child).map(toTree));
       if (renderedNodes.length === 0) {
         renderedNodes = [node.memoizedProps.children];
@@ -169,14 +161,14 @@ function toTree(vnode) {
         rendered: renderedNodes,
       };
     }
-    case HostText: // 6
+    case FiberTags.HostText:
       return node.memoizedProps;
-    case FragmentType: // 10
-    case Mode: // 11
-    case ContextProviderType: // 13
-    case ContextConsumerType: // 12
+    case FiberTags.Fragment:
+    case FiberTags.Mode:
+    case FiberTags.ContextProvider:
+    case FiberTags.ContextConsumer:
       return childrenToTree(node.child);
-    case ForwardRefType: {
+    case FiberTags.ForwardRef: {
       return {
         nodeType: 'function',
         type: node.type,
@@ -255,6 +247,10 @@ class ReactSixteenAdapter extends EnzymeAdapter {
 
   createMountRenderer(options) {
     assertDomAvailable('mount');
+    if (FiberTags === null) {
+      // Requires DOM.
+      FiberTags = detectFiberTags();
+    }
     const { attachTo, hydrateIn } = options;
     const domNode = hydrateIn || attachTo || global.document.createElement('div');
     let instance = null;
diff --git a/packages/enzyme-adapter-react-16/src/detectFiberTags.js b/packages/enzyme-adapter-react-16/src/detectFiberTags.js
new file mode 100644
index 000000000..cffba524c
--- /dev/null
+++ b/packages/enzyme-adapter-react-16/src/detectFiberTags.js
@@ -0,0 +1,63 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+
+function getFiber(element) {
+  const container = global.document.createElement('div');
+  let inst = null;
+  class Tester extends React.Component {
+    render() {
+      inst = this;
+      return element;
+    }
+  }
+  ReactDOM.render(React.createElement(Tester), container);
+  return inst._reactInternalFiber.child;
+}
+
+module.exports = function detectFiberTags() {
+  const supportsMode = typeof React.StrictMode !== 'undefined';
+  const supportsContext = typeof React.createContext !== 'undefined';
+  const supportsForwardRef = typeof React.forwardRef !== 'undefined';
+
+  function Fn() {
+    return null;
+  }
+  // eslint-disable-next-line react/prefer-stateless-function
+  class Cls extends React.Component {
+    render() {
+      return null;
+    }
+  }
+  let Ctx = null;
+  let FwdRef = null;
+  if (supportsContext) {
+    Ctx = React.createContext();
+  }
+  if (supportsForwardRef) {
+    // React will warn if we don't have both arguments.
+    // eslint-disable-next-line no-unused-vars
+    FwdRef = React.forwardRef((props, ref) => null);
+  }
+
+  return {
+    HostRoot: getFiber('test').return.return.tag, // Go two levels above to find the root
+    ClassComponent: getFiber(React.createElement(Cls)).tag,
+    Fragment: getFiber([['nested']]).tag,
+    FunctionalComponent: getFiber(React.createElement(Fn)).tag,
+    HostPortal: getFiber(ReactDOM.createPortal(null, global.document.createElement('div'))).tag,
+    HostComponent: getFiber(React.createElement('span')).tag,
+    HostText: getFiber('text').tag,
+    Mode: supportsMode
+      ? getFiber(React.createElement(React.StrictMode)).tag
+      : -1,
+    ContextConsumer: supportsContext
+      ? getFiber(React.createElement(Ctx.Consumer, null, () => null)).tag
+      : -1,
+    ContextProvider: supportsContext
+      ? getFiber(React.createElement(Ctx.Provider, { value: null })).tag
+      : -1,
+    ForwardRef: supportsForwardRef
+      ? getFiber(React.createElement(FwdRef)).tag
+      : -1,
+  };
+}