Fix object spread runtime semantics #32514
Merged
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This fixes the runtime semantics for object spread for ES2017 and earlier.
We cannot call
__assign
with more than two elements, since any element could cause side effects. Forexample:
If we translate the above to
__assign({ a: 3 }, k, { b: k.a++ })
, thek.a++
will evaluate beforek
is spread and we end up with{ a: 2, b: 1 }
.This also occurs for spread elements, not just property assignments:
If we translate the above to
__assign({}, k, l)
, thel
will evaluate beforek
is spread and weend up with
{ a: 1, b: 2, c: 3 }
Fixes #31469