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optimize: Simplify the export-default-from transform #14768

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merged 2 commits into from Jul 19, 2022
Merged

optimize: Simplify the export-default-from transform #14768

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5853c90
optimize: Simplify the `export-default-from` transform
magic-akari Jul 19, 2022
e8852da
chore: merge specifiers if possible
magic-akari Jul 19, 2022
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21 changes: 7 additions & 14 deletions packages/babel-plugin-proposal-export-default-from/src/index.ts
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Expand Up @@ -11,33 +11,26 @@ export default declare(api => {

visitor: {
ExportNamedDeclaration(path) {
const { node, scope } = path;
const { specifiers } = node;
const { node } = path;
const { specifiers, source } = node;
if (!t.isExportDefaultSpecifier(specifiers[0])) return;

const specifier = specifiers.shift();
const { exported } = specifier;
const uid = scope.generateUidIdentifier(
// @ts-expect-error Identifier ?? StringLiteral
exported.name ?? exported.value,
);

const nodes = [
t.importDeclaration(
[t.importDefaultSpecifier(uid)],
t.cloneNode(node.source),
t.exportNamedDeclaration(
null,
[t.exportSpecifier(t.identifier("default"), exported)],
t.cloneNode(source),
),
t.exportNamedDeclaration(null, [
t.exportSpecifier(t.cloneNode(uid), exported),
]),
];

if (specifiers.length >= 1) {
nodes.push(node);
}

const [importDeclaration] = path.replaceWithMultiple(nodes);
path.scope.registerDeclaration(importDeclaration);
path.replaceWithMultiple(nodes);
},
},
};
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3 changes: 1 addition & 2 deletions ...proposal-export-default-from/test/fixtures/export-default/default-compound-es6/output.mjs
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@@ -1,3 +1,2 @@
import _v from "mod";
export { _v as v };
export { default as v } from "mod";
export { x, y as w } from "mod";
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Further optimization idea: we can merge { default as v } with the next specifier if exists.

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Sure. And here come a case

export v, * as ns, { x, y as w } from "mod";

if there is a namespace compound, should we merge it?

// a.js
export { default as v,  x, y as w} from "mod";
export * as ns from "mod";

The export order will change.

import * as ns from "a.js";
Object.keys(ns) // order changed

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Ok, it will be merged if there is no namespace export.

3 changes: 1 addition & 2 deletions ...l-plugin-proposal-export-default-from/test/fixtures/export-default/default-es6/output.mjs
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@@ -1,2 +1 @@
import _foo from "bar";
export { _foo as foo };
export { default as foo } from "bar";
3 changes: 1 addition & 2 deletions ...n-proposal-export-default-from/test/fixtures/export-default/default-typescript/output.mjs
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@@ -1,2 +1 @@
import _foo from "bar";
export { _foo as foo };
export { default as foo } from "bar";