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Don't throw when destructuring into a var named as an import #10628

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merged 1 commit into from Nov 4, 2019
Merged

Don't throw when destructuring into a var named as an import #10628

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28 changes: 13 additions & 15 deletions packages/babel-helper-module-transforms/src/rewrite-live-references.js
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Expand Up @@ -224,6 +224,10 @@ const rewriteReferencesVisitor = {
seen.add(path.node);

const left = path.get("left");

// No change needed
if (left.isMemberExpression()) return;

if (left.isIdentifier()) {
// Simple update-assign foo += 1; export { foo };
// => exports.foo = (foo += 1);
Expand All @@ -234,9 +238,9 @@ const rewriteReferencesVisitor = {
return;
}

const exportedNames = exported.get(localName) || [];
const exportedNames = exported.get(localName);
const importData = imported.get(localName);
if (exportedNames.length > 0 || importData) {
if (exportedNames?.length > 0 || importData) {
assert(path.node.operator === "=", "Path was not simplified");

const assignment = path.node;
Expand All @@ -259,13 +263,14 @@ const rewriteReferencesVisitor = {
);
requeueInParent(path);
}
} else if (left.isMemberExpression()) {
// No change needed
} else {
const ids = left.getOuterBindingIdentifiers();
const id = Object.keys(ids)
.filter(localName => imported.has(localName))
.pop();
const programScopeIds = Object.keys(ids).filter(
localName =>
scope.getBinding(localName) === path.scope.getBinding(localName),
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nit: consider to guard with scope.hasBinding to avoid unnecessary path.scope.getBinding.

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I tried to do it and found a bug which, if fixed, would break @babel/plugin-transform-runtime <= 7.6 😢

This is what currently happens:

  1. The imports are analyzed
  2. The imports are removed -> The bindings are removed
  3. References to imported bindings are rewritten (this file)
    i) When we are comparing the bindings, the global one is undefined
    ii) If the local binding is undefined, it hasn't been redefined.

I tried to swap 2 and 3, but I still can optimize away the check for the local binding because @babel/transform-runtime doesn't register the import it injects in the scope tracker.

);
const id = programScopeIds.find(localName => imported.has(localName));

if (id) {
path.node.right = t.sequenceExpression([
path.node.right,
Expand All @@ -276,14 +281,7 @@ const rewriteReferencesVisitor = {
// Complex ({a, b, c} = {}); export { a, c };
// => ({a, b, c} = {}), (exports.a = a, exports.c = c);
const items = [];
Object.keys(ids).forEach(localName => {
// redeclared in this scope
if (
scope.getBinding(localName) !== path.scope.getBinding(localName)
) {
return;
}

programScopeIds.forEach(localName => {
const exportedNames = exported.get(localName) || [];
if (exportedNames.length > 0) {
items.push(
Expand Down
12 changes: 12 additions & 0 deletions ...bel-plugin-transform-modules-commonjs/test/fixtures/misc/import-shadowed-assign/input.mjs
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@@ -0,0 +1,12 @@
import { foo } from "x";

function f(foo) {
foo = 2;
[foo] = [];
({ foo } = {});
}


foo = 2;
[foo] = [];
({ foo } = {});
23 changes: 23 additions & 0 deletions ...bel-plugin-transform-modules-commonjs/test/fixtures/misc/import-shadowed-assign/output.js
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@@ -0,0 +1,23 @@
"use strict";

var _x = require("x");

function f(foo) {
foo = 2;
[foo] = [];
({
foo
} = {});
}

_x.foo = (2, function () {
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In a follow up PR, this could be left as foo since we are throwing anyway.

throw new Error('"' + "foo" + '" is read-only.');
}());
[foo] = ([], function () {
throw new Error('"' + "foo" + '" is read-only.');
}());
({
foo
} = ({}, function () {
throw new Error('"' + "foo" + '" is read-only.');
}()));