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Correctly transform spreads to use proper concat method (#9108)

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* Correctly transform spreads to use proper concat method

* Add tests to ensure array spread clones elements
This commit is contained in:
Daniel Tschinder
2018-12-13 23:24:43 -08:00
committed by GitHub
parent 72471aff63
commit 47da5cf75a
9 changed files with 62 additions and 5 deletions
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20
packages/babel-plugin-transform-spread/src/index.js
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@@ -57,13 +57,29 @@ export default declare((api, options) => {
if (!hasSpread(elements)) return;
const nodes = build(elements, scope);
const first = nodes.shift();
let first = nodes[0];
if (nodes.length === 0 && first !== elements[0].argument) {
// If there is only one element in the ArrayExpression and
// the element was transformed (Array.prototype.slice.call or toConsumableArray)
// we know that the transformed code already takes care of cloning the array.
// So we can simply return that element.
if (nodes.length === 1 && first !== elements[0].argument) {
path.replaceWith(first);
return;
}
// If the first element is a ArrayExpression we can directly call
// concat on it.
// `[..].concat(..)`
// If not then we have to use `[].concat(arr)` and not `arr.concat`
// because `arr` could be extended/modified (e.g. Immutable) and we do not know exactly
// what concat would produce.
if (!t.isArrayExpression(first)) {
first = t.arrayExpression([]);
} else {
nodes.shift();
}
path.replaceWith(
t.callExpression(
t.memberExpression(first, t.identifier("concat")),