61 lines
2.1 KiB
JavaScript
61 lines
2.1 KiB
JavaScript
import { declare } from "@babel/helper-plugin-utils";
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import syntaxNullishCoalescingOperator from "@babel/plugin-syntax-nullish-coalescing-operator";
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import { types as t, template } from "@babel/core";
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export default declare((api, { loose = false }) => {
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api.assertVersion(7);
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const noDocumentAll = api.assumption("noDocumentAll") ?? loose;
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return {
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name: "proposal-nullish-coalescing-operator",
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inherits: syntaxNullishCoalescingOperator.default,
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visitor: {
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LogicalExpression(path) {
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const { node, scope } = path;
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if (node.operator !== "??") {
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return;
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}
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let ref;
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let assignment;
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// skip creating extra reference when `left` is static
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if (scope.isStatic(node.left)) {
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ref = node.left;
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assignment = t.cloneNode(node.left);
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} else if (scope.path.isPattern()) {
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// Replace `function (a, x = a.b ?? c) {}` to `function (a, x = (() => a.b ?? c)() ){}`
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// so the temporary variable can be injected in correct scope
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path.replaceWith(template.ast`(() => ${path.node})()`);
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// The injected nullish expression will be queued and eventually transformed when visited
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return;
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} else {
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ref = scope.generateUidIdentifierBasedOnNode(node.left);
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scope.push({ id: t.cloneNode(ref) });
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assignment = t.assignmentExpression("=", ref, node.left);
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}
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path.replaceWith(
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t.conditionalExpression(
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// We cannot use `!= null` in spec mode because
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// `document.all == null` and `document.all` is not "nullish".
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noDocumentAll
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? t.binaryExpression("!=", assignment, t.nullLiteral())
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: t.logicalExpression(
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"&&",
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t.binaryExpression("!==", assignment, t.nullLiteral()),
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t.binaryExpression(
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"!==",
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t.cloneNode(ref),
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scope.buildUndefinedNode(),
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),
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),
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t.cloneNode(ref),
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node.right,
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),
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);
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},
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},
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};
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});
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