Compiler Changes

• Within Vapor components
  • Transition is automatically rewritten as VaporTransition
  • TransitionGroup is automatically rewritten as VaporTransitionGroup
• When the root node of a Transition uses the v-if, the compiler automatically adds a $key property to the rendering result, making it easier for the runtime to track the element's leaving state using the key

  <Transition>
    <h1 v-if="show">
      <span>HI</span>
    </h1>
  </Transition>

will be compiled to

  const n4 = _createComponent(_VaporTransition, null, {
    "default": () => {
      const n1 = _createIf(() => (_ctx.show), () => {
        const n3 = t1()
        n3.$key = 3 // adds a `$key` 
        return n3
      })
      return n1
    }
  })

• When the root node of a Transition has an explicit key, the compiler generates code that includes createKeyedFragment, which creates a new DynamicFragment when the key changes, triggering transitions

  <Transition>
    <span :key="count">{{ count }}</span>
  </Transition>

will be compiled to

  const n1 = _createComponent(_VaporTransition, null, {
    "default": () => {
      return _createKeyedFragment(() => _ctx.count, () => {
        const n0 = t0()
        const x0 = _child(n0)
        _renderEffect(() => _setText(x0, _toDisplayString(_ctx.count)))
        n0.$key = _ctx.count
        return n0
      })
    }
  })

• When appear is set in the Transition and the root node uses v-show, it need to execute applyVShow after the Transition is created to ensure that the appear behavior works properly.

  <div>
    <transition appear>
      <div v-show="!toggle">content</div>
    </transition>
  </div>

will be compiled to

  const deferredApplyVShows = []
  const n2 = t1()
  const n1 = _createComponent(_VaporTransition, {
    appear: () => (""), 
    persisted: () => ("")
  }, {
    "default": () => {
      const n0 = t0()
      deferredApplyVShows.push(() => _applyVShow(n0, () => (!toggle.value)))
      return n0
    }
  })
  _insert(n1, n2)
  deferredApplyVShows.forEach(fn => fn())
  return n2

Runtime Changes

• Added VaporTransition and VaporTransitionGroup components that reuses most of the logic from runtime-dom/Transition
• Transition hooks are now stored on the block.$transition property
• DynamicFragment Update Logic Modification:
  • When removing old elements, leave animations are triggered
  • When rendering new elements, enter animations are triggered
• Extracted baseResolveTransitionHooks from the existing resolveTransitionHooks function to be shared between VaporTransition and Transition. Each component passes its own specific TransitionHooksContext
• Interop:
  • Existing Transition component now supports rendering Vapor components

Tests

• Ported all test cases except those related to KeepAlive, Suspense, and Teleport from packages/vue/tests/e2e/Transition.spec.ts
• Ported all test cases from packages/vue/tests/e2e/TransitionGroup.spec.ts