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* @file ComponentScope.js
* @description How a component resolves the names an expression uses.
*
* ## Why this is its own object
*
* Now that expressions are compiled at build time, the scope is what remains of
* the compiler/runtime boundary inside the runtime: the compiler emits closures
* that take one argument, and this is the thing it is given. Everything about
* what a component's expressions can see — its state, its computed values, its
* actions, its props, its bridges, its resources, the values injected into it,
* the names its own module imported — is decided here and nowhere else.
*
* It used to be four private methods and a cache field spread across a
* 2,900-line class, which made two things hard to see. It hid the ordering
* rule, which is load-bearing and easy to get wrong. And it hid the fact that a
* scope was being constructed *per evaluation*: on the compiled path that is
* one allocation and one layer walk per binding, per update, for an object
* whose contents almost never change.
*
* ## Precedence, and why it is what it is
*
* Layers are consulted highest first:
*
* 1. per-call extras — a `<@for>` item, an `event`, an action's `args`
* 2. injected values (`provide` / `inject`)
* 3. framework names — `props`, `styles`, `$route`, `$emit`, `$watch`, …
* 4. the component's own actions
* 5. state and computed values, read from the live reactive proxy
* 6. resources
* 7. bridges
* 8. mixin properties
* 9. `state` itself
* 10. the names the component's module imported
*
* Bridges sit below the component's own declarations so a bridge cannot
* silently shadow a `<state>` key or an action; the compiler reports such a
* collision separately. Imports sit last because an import is the least
* specific thing in scope.
*
* ## Nothing is read until it is named
*
* The layers are a Proxy, not a merged object. Spreading the reactive state
* into a plain object — which is what this replaced — read every key eagerly,
* which made bare identifiers non-reactive, reported cycles that did not exist,
* and tied every render to every state key. A `get` here resolves through the
* layers and, for a state or computed name, reads the live proxy inside
* whichever watcher is evaluating, so an expression depends on exactly the
* names it mentions.
*
* ## Caching
*
* The base scope — the one with no per-call extras — is built once and reused.
* It is invalidated when something changes what a name resolves to: the set of
* state keys, the action map, the injected values. A scope with extras derives
* from it rather than rebuilding, which is why {@link deriveScope} exists: a
* spread would reintroduce the eager read this whole design removes.
* @module lib/core/runtime/ComponentScope
*/
import {
createReactiveScope,
objectLayer,
stateLayer,
getterLayer,
deriveScope,
} from '../reactive/scopeProxy.js';
import { toRaw } from '../reactive/proxyHandler.js';
/**
* The evaluation scope of one component.
*/
export class ComponentScope {
/**
* @param {object} owner - The component this scope belongs to.
*/
constructor(owner) {
/** @type {object} */
this.owner = owner;
/**
* The base scope, built on first use and reused until invalidated.
* @type {object|null}
*/
this.base = null;
/**
* The names the state layer binds, cached because computing them is
* `Object.keys()` over the whole state object and a scope used to be built
* per expression evaluated.
* @type {string[]|null}
*/
this.stateKeys = null;
/**
* The method map the cached base scope was built against.
*
* A component's actions are established once, but `createMethodMap` hands
* the scope builder the map it is still filling, so the first scopes are
* built against an object that is not yet complete. Recording which map the
* cache belongs to is what stops a stale one being reused.
* @type {object|null}
*/
this.methods = null;
}
/**
* Discards the cached scope.
*
* Called when something changes what a name would resolve to. Cheap enough to
* call speculatively: the cost is one scope rebuild on the next evaluation.
*/
invalidate() {
this.base = null;
this.stateKeys = null;
}
/**
* Discards only the cached state-key list.
*
* A key being added to or removed from state changes what the state layer
* binds but not the shape of the scope, so the layers themselves survive.
*/
invalidateKeys() {
this.stateKeys = null;
}
/**
* The names state and computed values bind.
*
* Read from the raw target and the compiler's computed list rather than by
* enumerating the proxy, so building a scope registers no dependency and
* evaluates no computed value.
* @returns {string[]} The bound names.
*/
keys() {
if (this.stateKeys === null) {
const raw = toRaw(this.owner.state);
const names = raw && typeof raw === 'object' ? Object.keys(raw) : [];
this.stateKeys = names.concat(this.owner.__computedKeys());
}
return this.stateKeys;
}
/**
* The names `provide`/`inject` makes visible.
*
* The names are a property of the component's `inject` declaration and do not
* change; the values behind them do, because a provider higher up the tree
* can update one at any time. So the names are resolved once and the values
* are read live -- caching the values is what made a child keep rendering the
* theme its ancestor no longer provides.
* @returns {string[]} The injected names.
*/
#injectedNames() {
const owner = this.owner;
const option =
owner.inject ||
(typeof owner.constructor.inject === 'function' ? owner.constructor.inject() : owner.constructor.inject);
if (!option) {
return [];
}
const resolved = typeof option === 'function' ? option.call(owner) : option;
if (Array.isArray(resolved)) {
return resolved;
}
if (resolved && typeof resolved === 'object') {
return Object.keys(resolved);
}
return [];
}
/**
* Builds the layered scope.
* @param {object} methods - The component's executable actions.
* @returns {object} The scope proxy.
*/
#build(methods) {
const owner = this.owner;
const injected = {};
for (const name of this.#injectedNames()) {
injected[name] = () => owner[name];
}
// The set of resources is fixed once the constructor has run, but a scope
// can be built *during* construction -- `createMethodMap` asks for one --
// so the names are resolved on read rather than snapshotted here.
const resources = {
/**
* @param {string} key - The name to test.
* @returns {boolean} Whether a resource is declared under it.
*/
has: (key) => owner.__resourceNames().includes(key),
/**
* @param {string} key - The name to read.
* @returns {any} The resource's current value.
*/
get: (key) => owner.__readResource(key),
/**
* @returns {string[]} The declared resource names.
*/
keys: () => owner.__resourceNames(),
};
return createReactiveScope([
getterLayer(injected),
objectLayer({
props: owner.props,
styles: owner.styles,
$route: owner.$route,
$emit: (eventName, detail) => owner.$emit(eventName, detail),
$watch: (source, callback, options) => owner.$watch(source, callback, options),
$watchEffect: (effect, options) => owner.$watchEffect(effect, options),
$nextTick: (callback) => owner.$nextTick(callback),
}),
objectLayer(methods),
stateLayer(owner.state, () => this.keys()),
resources,
owner.__isIsolated() ? null : objectLayer(owner.__bridgeValues()),
objectLayer(owner._mixinProps),
objectLayer({ state: owner.state }),
// Omitted entirely when there are none, so a component that imports
// nothing resolves through exactly the layers it did before imports
// became part of a component's scope at all.
owner.__hasImports() ? objectLayer(owner.__importValues()) : null,
]);
}
/**
* The scope an expression should be evaluated against.
* @param {object} [methods] - The action map to expose. Defaults to the owner's.
* @param {object} [extras] - Per-call bindings layered on top.
* @returns {object} The scope.
*/
resolve(methods = this.owner.__methods(), extras = null) {
if (this.base === null || this.methods !== methods) {
this.base = this.#build(methods);
this.methods = methods;
}
if (!extras) {
return this.base;
}
// Derived rather than spread: a spread of a scope proxy reads every name it
// can enumerate, which is the eager read the layering exists to remove.
return deriveScope(this.base, extras);
}
}
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