feat(compiler): generate patchFlags for runtime

packages/shared/src/index.ts

@@ -1,3 +1,5 @@
+export * from './patchFlags'
+
 export const EMPTY_OBJ: { readonly [key: string]: any } = __DEV__
   ? Object.freeze({})
   : {}

packages/shared/src/patchFlags.ts

@@ -0,0 +1,73 @@
+// Patch flags are optimization hints generated by the compiler.
+// when a block with dynamicChildren is encountered during diff, the algorithm
+// enters "optimized mode". In this mode, we know that the vdom is produced by
+// a render function generated by the compiler, so the algorithm only needs to
+// handle updates explicitly marked by these patch flags.
+
+// Patch flags can be combined using the | bitwise operator and can be checked
+// using the & operator, e.g.
+//
+//   const flag = TEXT | CLASS
+//   if (flag & TEXT) { ... }
+//
+// Check the `patchElement` function in './createRednerer.ts' to see how the
+// flags are handled during diff.
+
+export const enum PatchFlags {
+  // Indicates an element with dynamic textContent (children fast path)
+  TEXT = 1,
+
+  // Indicates an element with dynamic class binding.
+  CLASS = 1 << 1,
+
+  // Indicates an element with dynamic style
+  // The compiler pre-compiles static string styles into static objects
+  // + detects and hoists inline static objects
+  // e.g. style="color: red" and :style="{ color: 'red' }" both get hoisted as
+  //   const style = { color: 'red' }
+  //   render() { return e('div', { style }) }
+  STYLE = 1 << 2,
+
+  // Indicates an element that has non-class/style dynamic props.
+  // Can also be on a component that has any dynamic props (includes
+  // class/style). when this flag is present, the vnode also has a dynamicProps
+  // array that contains the keys of the props that may change so the runtime
+  // can diff them faster (without having to worry about removed props)
+  PROPS = 1 << 3,
+
+  // Indicates an element with props with dynamic keys. When keys change, a full
+  // diff is always needed to remove the old key. This flag is mutually
+  // exclusive with CLASS, STYLE and PROPS.
+  FULL_PROPS = 1 << 4,
+
+  // Indicates an element that only needs non-props patching, e.g. ref or
+  // directives (vnodeXXX hooks). It simply marks the vnode as "need patch",
+  // since every pathced vnode checks for refs and vnodeXXX hooks.
+  // This flag is never directly matched against, it simply serves as a non-zero
+  // value.
+  NEED_PATCH = 1 << 5,
+
+  // Indicates a fragment or element with keyed or partially-keyed v-for
+  // children
+  KEYED = 1 << 6,
+
+  // Indicates a fragment or element that contains unkeyed v-for children
+  UNKEYED = 1 << 7,
+
+  // Indicates a component with dynamic slots (e.g. slot that references a v-for
+  // iterated value, or dynamic slot names).
+  // Components with this flag are always force updated.
+  DYNAMIC_SLOTS = 1 << 8
+}
+
+// runtime object for public consumption
+export const PublicPatchFlags = {
+  TEXT: PatchFlags.TEXT,
+  CLASS: PatchFlags.CLASS,
+  STYLE: PatchFlags.STYLE,
+  PROPS: PatchFlags.PROPS,
+  NEED_PATCH: PatchFlags.NEED_PATCH,
+  FULL_PROPS: PatchFlags.FULL_PROPS,
+  KEYED: PatchFlags.KEYED,
+  UNKEYED: PatchFlags.UNKEYED
+}