wip(ssr): reduce reactivity overhead during ssr

packages/reactivity/src/computed.ts

@@ -56,6 +56,10 @@ export function computed<T>(
     // expose effect so computed can be stopped
     effect: runner,
     get value() {
+      if (__SSR__) {
+        return getter()
+      }
+
       if (dirty) {
         value = runner()
         dirty = false

packages/reactivity/src/reactive.ts

@@ -1,4 +1,4 @@
-import { isObject, toRawType } from '@vue/shared'
+import { isObject, toRawType, EMPTY_OBJ } from '@vue/shared'
 import {
   mutableHandlers,
   readonlyHandlers,
@@ -117,9 +117,15 @@ function createReactiveObject(
   if (!canObserve(target)) {
     return target
   }
-  const handlers = collectionTypes.has(target.constructor)
-    ? collectionHandlers
-    : baseHandlers
+  const handlers = __SSR__
+    ? // disable reactivity in SSR.
+      // NOTE: a potential caveat here is isReactive check may return different
+      // values on nested values on client/server. This should be very rare but
+      // we should keep an eye on this.
+      EMPTY_OBJ
+    : collectionTypes.has(target.constructor)
+      ? collectionHandlers
+      : baseHandlers
   observed = new Proxy(target, handlers)
   toProxy.set(target, observed)
   toRaw.set(observed, target)

packages/reactivity/src/ref.ts

@@ -36,6 +36,14 @@ export function ref(raw?: unknown) {
     return raw
   }
   raw = convert(raw)
+
+  if (__SSR__) {
+    return {
+      _isRef: true,
+      value: raw
+    }
+  }
+
   const r = {
     _isRef: true,
     get value() {
@@ -58,7 +66,7 @@ export function ref(raw?: unknown) {
 export function toRefs<T extends object>(
   object: T
 ): { [K in keyof T]: Ref<T[K]> } {
-  if (__DEV__ && !isReactive(object)) {
+  if (__DEV__ && !__SSR__ && !isReactive(object)) {
     console.warn(`toRefs() expects a reactive object but received a plain one.`)
   }
   const ret: any = {}