I had forgotten the HeapBigInt part.
This is a bug introduced in https://bugs.webkit.org/show_bug.cgi?id=226676 (r278568)
Created attachment 430903 [details] Patch
Comment on attachment 430903 [details] Patch r=me
r=me too.
Committed r278642 (238624@main): <https://commits.webkit.org/238624@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 430903 [details].
<rdar://problem/79050304>