reintroduce 17 and 16.8

Author: phryneas

package.json

@@ -93,8 +93,8 @@
   "peerDependencies": {
     "@jest/globals": "*",
     "expect": "*",
-    "react": "^18.0.0 || >=19.0.0-rc",
-    "react-dom": "^18.0.0 || >=19.0.0-rc"
+    "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || >=19.0.0-rc",
+    "react-dom": "^16.8.0 || ^17.0.0 || ^18.0.0 || >=19.0.0-rc"
   },
   "scripts": {
     "build": "tsup",

src/renderStream/__tests__/passiveEffects.test.tsx

@@ -40,7 +40,7 @@ describe('passive effects', () => {
       const received: number[] = []
       const stream = createRenderStream<{value: number}>()
       let update: React.Dispatch<React.SetStateAction<number>>
-      let parentRenders = 0
+      let parentCommits = 0
       function Subscriber() {
         const [value, setValue] = React.useState(0)
         update = setValue
@@ -55,7 +55,9 @@ describe('passive effects', () => {
         return null
       }
       function Parent() {
-        parentRenders++
+        React.useLayoutEffect(() => {
+          parentCommits++
+        })
         return <Subscriber />
       }
 
@@ -67,7 +69,7 @@ describe('passive effects', () => {
 
       expect(render.snapshot).toEqual({value: 1})
       expect(received).toEqual([1])
-      expect(parentRenders).toBe(1)
+      expect(parentCommits).toBe(1)
     },
   )
 

src/renderStream/createRenderStream.tsx

@@ -242,6 +242,13 @@ export function createRenderStream<
       })
     } finally {
       pendingCommits.set(`${id}:${commitTime}`, stream.renders.length)
+      if (/^(16|17)\./.test(React.version)) {
+        // React 16/17 have no onPostCommit hook. Let the commit finish scheduling
+        // passive effects before yielding a task for them to run.
+        void Promise.resolve().then(() => {
+          setTimeout(() => profilerOnPostCommit(id, phase, 0, commitTime), 0)
+        })
+      }
     }
   }
 

src/renderWithoutAct.tsx

@@ -1,4 +1,5 @@
 import * as ReactDOMClient from 'react-dom/client'
+import * as ReactDOM from 'react-dom'
 import {type RenderOptions} from '@testing-library/react/pure.js'
 import {
   BoundFunction,
@@ -156,7 +157,11 @@ async function _renderWithoutAct(
   let root: ReturnType<typeof createConcurrentRoot>
   // eslint-disable-next-line no-negated-condition -- we want to map the evolution of this over time. The root is created first. Only later is it re-used so we don't want to read the case that happens later first.
   if (!mountedContainers.has(container)) {
-    root = createConcurrentRoot(container)
+    root = (
+      ReactDOM.version.startsWith('16') || ReactDOM.version.startsWith('17')
+        ? createLegacyRoot
+        : createConcurrentRoot
+    )(container)
     mountedRootEntries.push({container, root})
     // we'll add it to the mounted containers regardless of whether it's actually
     // added to document.body so the cleanup method works regardless of whether
@@ -182,6 +187,22 @@ async function _renderWithoutAct(
   })
 }
 
+function createLegacyRoot(container: ReactDOMClient.Container) {
+  // These runtime APIs are absent from React 19's types.
+  const legacyReactDOM = ReactDOM as unknown as {
+    render(element: React.ReactNode, container: ReactDOMClient.Container): void
+    unmountComponentAtNode(container: ReactDOMClient.Container): boolean
+  }
+  return {
+    render(element: React.ReactNode) {
+      legacyReactDOM.render(element, container)
+    },
+    unmount() {
+      legacyReactDOM.unmountComponentAtNode(container)
+    },
+  }
+}
+
 function createConcurrentRoot(container: ReactDOMClient.Container) {
   const anyThis = globalThis as any as {IS_REACT_ACT_ENVIRONMENT?: boolean}
   if (anyThis.IS_REACT_ACT_ENVIRONMENT) {

yarn.lock

@@ -2644,8 +2644,8 @@ __metadata:
   peerDependencies:
     "@jest/globals": "*"
     expect: "*"
-    react: ^18.0.0 || >=19.0.0-rc
-    react-dom: ^18.0.0 || >=19.0.0-rc
+    react: ^16.8.0 || ^17.0.0 || ^18.0.0 || >=19.0.0-rc
+    react-dom: ^16.8.0 || ^17.0.0 || ^18.0.0 || >=19.0.0-rc
   languageName: unknown
   linkType: soft