77 lines
2.2 KiB
JavaScript
77 lines
2.2 KiB
JavaScript
export default function({ types: t }) {
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const HOISTED = new WeakSet();
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const immutabilityVisitor = {
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enter(path, state) {
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const stop = () => {
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state.isImmutable = false;
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path.stop();
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};
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if (path.isJSXClosingElement()) {
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path.skip();
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return;
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}
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// Elements with refs are not safe to hoist.
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if (
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path.isJSXIdentifier({ name: "ref" }) &&
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path.parentPath.isJSXAttribute({ name: path.node })
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) {
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return stop();
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}
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// Ignore identifiers & JSX expressions.
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if (
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path.isJSXIdentifier() ||
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path.isIdentifier() ||
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path.isJSXMemberExpression()
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) {
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return;
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}
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if (!path.isImmutable()) {
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// If it's not immutable, it may still be a pure expression, such as string concatenation.
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// It is still safe to hoist that, so long as its result is immutable.
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// If not, it is not safe to replace as mutable values (like objects) could be mutated after render.
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// https://github.com/facebook/react/issues/3226
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if (path.isPure()) {
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const expressionResult = path.evaluate();
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if (expressionResult.confident) {
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// We know the result; check its mutability.
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const { value } = expressionResult;
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const isMutable =
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(value && typeof value === "object") ||
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typeof value === "function";
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if (!isMutable) {
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// It evaluated to an immutable value, so we can hoist it.
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return;
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}
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} else if (t.isIdentifier(expressionResult.deopt)) {
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// It's safe to hoist here if the deopt reason is an identifier (e.g. func param).
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// The hoister will take care of how high up it can be hoisted.
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return;
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}
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}
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stop();
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}
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},
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};
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return {
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visitor: {
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JSXElement(path) {
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if (HOISTED.has(path.node)) return;
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HOISTED.add(path.node);
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const state = { isImmutable: true };
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path.traverse(immutabilityVisitor, state);
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if (state.isImmutable) {
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path.hoist();
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}
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},
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},
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};
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}
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