sortedmulti in descriptors does not work, always fails with error #18874

<!-- Describe the issue -->

The sortedmulti expression in descriptors seems to not be recognized.

Expected behavior

Take the sortedmulti example from the descriptor document and pass it to getdescriptorinfo.

$ bitcoin-cli getdescriptorinfo "wsh(sortedmulti(1,xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB/1/0/*,xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH/0/0/*))"
error code: -5
error message:
A function is needed within P2WSH

Actual behavior

Changing sortedmulti to multi no longer results in the error.

$ bitcoin-cli getdescriptorinfo "wsh(multi(1,xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB/1/0/*,xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH/0/0/*))"
{
  "descriptor": "wsh(multi(1,xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB/1/0/*,xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH/0/0/*))#t2zpj2eu",
  "checksum": "t2zpj2eu",
  "isrange": true,
  "issolvable": true,
  "hasprivatekeys": false
}

To reproduce

Run the above getdescriptorinfo command, or with any descriptor involving sortedmulti.

System information

Running Bitcoin Core version v0.19.0.1 (64-bit). Release version which I downloaded from bitcoincore.org

$ uname -a
Linux username 4.4.0-142-generic [#168](/bitcoin-bitcoin/168/)-Ubuntu SMP Wed Jan 16 21:00:45 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

sortedmulti is not available in 0.19.x. It was merged after it's release. It should be available in 0.20.0. Can you check 0.20.0rc1?

Ahh.

I just tried it with 0.20.0rc1, and it works perfectly.

Maybe only adding a note to the descriptor document is needed.

Either way, this isn't a bug in Core. Closing.