Don't scroll lock when a Transition + Dialog is mounted but hidden (#1681)

* Refer to context for initial Transition Tree state

* Update changelog

Author: thecrypticace

packages/@headlessui-react/CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Close `Menu` component when using `tab` key ([#1673](https://github.com/tailwindlabs/headlessui/pull/1673))
 - Resync input when display value changes ([#1679](https://github.com/tailwindlabs/headlessui/pull/1679))
 - Ensure controlled `Tabs` don't change automagically ([#1680](https://github.com/tailwindlabs/headlessui/pull/1680))
+- Don't scroll lock when a Transition + Dialog is mounted but hidden ([#1681](https://github.com/tailwindlabs/headlessui/pull/1681))
 
 ## [1.6.6] - 2022-07-07
 

packages/@headlessui-react/src/components/dialog/dialog.test.tsx

@@ -1,4 +1,4 @@
-import React, { createElement, useRef, useState } from 'react'
+import React, { createElement, useRef, useState, Fragment } from 'react'
 import { render } from '@testing-library/react'
 
 import { Dialog } from './dialog'
@@ -270,6 +270,44 @@ describe('Rendering', () => {
         expect(document.documentElement.style.overflow).toBe('hidden')
       })
     )
+
+    it(
+      'should wait to add a scroll lock to the html tag when unmount is false in a Transition',
+      suppressConsoleLogs(async () => {
+        function Example() {
+          let [isOpen, setIsOpen] = useState(false)
+
+          return (
+            <>
+              <button id="trigger" onClick={() => setIsOpen((v) => !v)}>
+                Trigger
+              </button>
+
+              <Transition as={Fragment} show={isOpen} unmount={false}>
+                <Dialog onClose={() => setIsOpen(false)} unmount={false}>
+                  <input id="a" type="text" />
+                  <input id="b" type="text" />
+                  <input id="c" type="text" />
+                </Dialog>
+              </Transition>
+            </>
+          )
+        }
+
+        render(<Example />)
+
+        // No overflow yet
+        expect(document.documentElement.style.overflow).toBe('')
+
+        let btn = document.getElementById('trigger')
+
+        // Open the dialog
+        await click(btn)
+
+        // Expect overflow
+        expect(document.documentElement.style.overflow).toBe('hidden')
+      })
+    )
   })
 
   describe('Dialog.Overlay', () => {

packages/@headlessui-react/src/components/transitions/transition.tsx

@@ -209,10 +209,12 @@ let TransitionChild = forwardRefWithAs(function TransitionChild<
   } = props as typeof props
   let container = useRef<HTMLElement | null>(null)
   let transitionRef = useSyncRefs(container, ref)
-  let [state, setState] = useState(TreeStates.Visible)
   let strategy = rest.unmount ? RenderStrategy.Unmount : RenderStrategy.Hidden
 
   let { show, appear, initial } = useTransitionContext()
+
+  let [state, setState] = useState(show ? TreeStates.Visible : TreeStates.Hidden)
+
   let { register, unregister } = useParentNesting()
   let prevShow = useRef<boolean | null>(null)
 

packages/@headlessui-vue/src/components/dialog/dialog.test.ts

@@ -391,6 +391,57 @@ describe('Rendering', () => {
         expect(document.documentElement.style.overflow).toBe('hidden')
       })
     )
+
+    it(
+      'should wait to add a scroll lock to the html tag when unmount is false in a Transition',
+      suppressConsoleLogs(async () => {
+        renderTemplate({
+          components: {
+            Dialog,
+            TransitionRoot,
+          },
+
+          template: `
+            <div>
+              <button id="trigger" @click="toggleOpen">
+                Trigger
+              </button>
+
+              <TransitionRoot :show="isOpen" :unmount="false">
+                <Dialog @close="setIsOpen" :unmount="false">
+                  <input id="a" type="text" />
+                  <input id="b" type="text" />
+                  <input id="c" type="text" />
+                </Dialog>
+              </TransitionRoot>
+            </div>
+          `,
+          setup() {
+            let isOpen = ref(false)
+            return {
+              isOpen,
+              setIsOpen(value: boolean) {
+                isOpen.value = value
+              },
+              toggleOpen() {
+                isOpen.value = !isOpen.value
+              },
+            }
+          },
+        })
+
+        // No overflow yet
+        expect(document.documentElement.style.overflow).toBe('')
+
+        let btn = document.getElementById('trigger')
+
+        // Open the dialog
+        await click(btn)
+
+        // Expect overflow
+        expect(document.documentElement.style.overflow).toBe('hidden')
+      })
+    )
   })
 
   describe('DialogOverlay', () => {