arrayCompact UB for nan, nan + Null

[den-crane]

in some cases nan === nan

SELECT arrayCompact([1, 1, nan, nan, 2, 3, 3, 3]) AS x

┌─x───────────────┐
│ [1,nan,nan,2,3] │
└─────────────────┘

SELECT arrayCompact([1, 1, nan, nan, 2, 3, 3, inf, inf, 3]) AS x

┌─x─────────────────────┐
│ [1,nan,nan,2,3,inf,3] │
└───────────────────────┘

SELECT arrayCompact([1, 1, nan, nan, 2, 3, 3, inf, inf, 3, NULL, NULL]) AS x

┌─x──────────────────────┐
│ [1,nan,2,3,inf,3,NULL] │ ???
└────────────────────────┘

SELECT arrayCompact([1, 1, inf, nan, NULL, nan, nan]) AS x

┌─x────────────────────┐
│ [1,inf,nan,NULL,nan] │  ???
└──────────────────────┘

[alexey-milovidov]

I see, it is falling back to generic implementation if the type is Nullable,
and generic implementation uses the same comparison operator as for sorting, that requires total order.

[alexey-milovidov]

Implementation specific behaviour for nans is generally Ok.

[alexey-milovidov]

I can stratify it in the way that nans will be compared for bit equality.