Implement Null Propagation Operator
This commit is contained in:
Justin Ridgewell
@@ -1,161 +1,105 @@
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export default function ({ types: t }) {
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const optionalNodesTransformed = new WeakSet();
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const nilIdentifier = t.unaryExpression("void", t.numericLiteral(0));
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function setOptionalTransformed(node) {
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t.assertMemberExpression(node); // Dev
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optionalNodesTransformed.add(node);
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}
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function isOptionalTransformed(node) {
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t.assertMemberExpression(node); // Dev
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return optionalNodesTransformed.has(node);
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}
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function createCondition(ref, access, nextProperty, bailout) {
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return t.conditionalExpression(
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createCheckAgainstNull(
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t.AssignmentExpression("=", ref, access)
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),
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t.memberExpression(ref, nextProperty),
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bailout,
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);
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}
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function createCheckAgainstNull(left) {
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return t.BinaryExpression("!=", left, t.NullLiteral());
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}
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function isNodeOptional(node) {
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return node.optional === true;
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}
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return {
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visitor: {
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AssignmentExpression(path, state) {
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const { left } = path.node;
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if (!isNodeOptional(left) || isOptionalTransformed(left)) {
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return;
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}
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if (!state.optionalTemp) {
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const id = path.scope.generateUidIdentifier();
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state.optionalTemp = id;
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path.scope.push({ id });
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}
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const { object, property } = left;
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const isChainNil = t.BinaryExpression(
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"!=",
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createCondition(
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state.optionalTemp,
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object,
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property,
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nilIdentifier,
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),
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nilIdentifier,
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);
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// FIXME(sven): if will be a ConditionalExpression for childs, only top level will be ifStatement
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const replacement = t.ifStatement(isChainNil, t.blockStatement([t.expressionStatement(path.node)]));
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setOptionalTransformed(left);
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path.traverse({
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MemberExpression({ node }) {
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setOptionalTransformed(node);
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},
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});
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path.parentPath.replaceWith(replacement);
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},
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UnaryExpression(path, state) {
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const { operator, argument } = path.node;
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if (operator !== "delete") {
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return;
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}
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if (!isNodeOptional(argument) || isOptionalTransformed(argument)) {
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return;
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}
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if (!state.optionalTemp) {
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const id = path.scope.generateUidIdentifier();
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state.optionalTemp = id;
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path.scope.push({ id });
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}
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const { object, property } = argument;
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const isChainNil = t.BinaryExpression(
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"!=",
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createCondition(
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state.optionalTemp,
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object,
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property,
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nilIdentifier,
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),
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nilIdentifier,
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);
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const replacement = t.ifStatement(isChainNil, t.blockStatement([t.expressionStatement(path.node)]));
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setOptionalTransformed(argument);
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path.parentPath.replaceWith(replacement);
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},
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MemberExpression(path, state) {
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if (!isNodeOptional(path.node) || isOptionalTransformed(path.node)) {
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return;
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}
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const { object, property } = path.node;
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if (!state.optionalTemp) {
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const id = path.scope.generateUidIdentifier();
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state.optionalTemp = id;
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path.scope.push({ id });
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}
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if (t.isAssignmentExpression(path.parent)) {
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return;
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} else if (t.isUnaryExpression(path.parent)) {
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return;
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} else if (t.isCallExpression(path.parent)) {
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const replacement = createCondition(
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state.optionalTemp,
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object,
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property,
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t.callExpression(t.identifier("Function"), []),
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);
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setOptionalTransformed(path.node);
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path.replaceWith(replacement);
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} else {
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const replacement = createCondition(
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state.optionalTemp,
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object,
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property,
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nilIdentifier,
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);
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setOptionalTransformed(path.node);
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// DO NOT SUBMIT. This is until the parser is complete
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const fixer = {
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NewExpression: {
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exit(path) {
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const { callee } = path.node;
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if (t.isCallExpression(callee)) {
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const replacement = t.newExpression(callee.callee, callee.arguments);
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replacement.optional = true;
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path.replaceWith(replacement);
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}
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},
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},
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CallExpression(path) {
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const { node } = path;
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if (!node.optional || node.callee) {
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return;
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}
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const callee = t.clone(node.arguments[0]);
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if (t.isMemberExpression(callee)) {
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callee.optional = node.arguments[1].value;
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}
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node.callee = callee;
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},
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};
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// END DO NOT SUBMIT
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const visitor = {
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Program(path) {
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path.traverse(fixer);
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},
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MemberExpression(path) {
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if (!path.node.optional) {
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return;
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}
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const { scope, node } = path;
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const { object } = node;
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node.optional = false;
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const ref = scope.generateUidIdentifierBasedOnNode(object);
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scope.push({ id: ref });
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node.object = ref;
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let parent = path;
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let expression;
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do {
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expression = parent;
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parent = parent.parentPath;
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} while (!parent.container);
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const replace = parent.isExpression() ? parent : expression;
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replace.replaceWith(t.conditionalExpression(
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t.binaryExpression("==", t.assignmentExpression("=", ref, object), t.nullLiteral()),
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scope.buildUndefinedNode(),
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replace.node
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));
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},
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"NewExpression|CallExpression": {
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exit(path) {
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if (!path.node.optional) {
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return;
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}
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const { scope, node } = path;
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const { callee } = node;
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node.optional = false;
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const ref = scope.generateUidIdentifierBasedOnNode(callee);
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scope.push({ id: ref });
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node.callee = ref;
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if (t.isMemberExpression(callee) && !t.isNewExpression(node)) {
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const context = scope.generateUidIdentifierBasedOnNode(callee.object);
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scope.push({ id: context });
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callee.object = t.assignmentExpression("=", context, callee.object);
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node.arguments.unshift(context);
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node.callee = t.memberExpression(node.callee, t.identifier("call"));
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}
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path.replaceWith(t.conditionalExpression(
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t.binaryExpression("==", t.assignmentExpression("=", ref, callee), t.nullLiteral()),
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scope.buildUndefinedNode(),
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node
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));
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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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manipulateOptions(opts, parserOpts) {
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parserOpts.plugins.push("optionalChaining");
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},
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};
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}
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