BREAKING CHANGE: revert setup() result reactive conversion
Revert 6b10f0c & a840e7d. The motivation of the original change was
avoiding unnecessary deep conversions, but that can be achieved by
explicitly marking values non-reactive via `markNonReactive`.
Removing the reactive conversion behavior leads to an usability
issue in that plain objects containing refs (which is what most
composition functions will return), when exposed as a nested
property from `setup()`, will not unwrap the refs in templates. This
goes against the "no .value in template" intuition and the only
workaround requires users to manually wrap it again with `reactive()`.
So in this commit we are reverting to the previous behavior where
objects returned from `setup()` are implicitly wrapped with
`reactive()` for deep ref unwrapping.
BREAKING CHANGE: custom directive bindings no longer expose instance
This is a rarely used property that creates extra complexity in
ensuring it points to the correct instance. From a design
perspective, a custom directive should be scoped to the element and
data it is bound to and should not have access to the entire
instance in the first place.
BREAKING CHANGE: replae `watch(fn, options?)` with `watchEffect`
The `watch(fn, options?)` signature has been replaced by the new
`watchEffect` API, which has the same usage and behavior. `watch`
now only supports the `watch(source, cb, options?)` signautre.
BREAKING CHANGE: `watch` behavior has been adjusted.
- When using the `watch(source, callback, options?)` signature, the
callback now fires lazily by default (consistent with 2.x
behavior).
Note that the `watch(effect, options?)` signature is still eager,
since it must invoke the `effect` immediately to collect
dependencies.
- The `lazy` option has been replaced by the opposite `immediate`
option, which defaults to `false`. (It's ignored when using the
effect signature)
- Due to the above changes, the `watch` option in Options API now
behaves exactly the same as 2.x.
- When using the effect signature or `{ immediate: true }`, the
intital execution is now performed synchronously instead of
deferred until the component is mounted. This is necessary for
certain use cases to work properly with `async setup()` and
Suspense.
The side effect of this is the immediate watcher invocation will
no longer have access to the mounted DOM. However, the watcher can
be initiated inside `onMounted` to retain previous behavior.
Terser will aggressively inline hot functions in renderer.ts in order
to reduce "function" declarations, but the inlining leads to performance
overhead (small, but noticeable in benchmarks).
Since we cannot control user's minifier options, we have to avoid the
deopt in the source code by using arrow functions in hot paths.
