bug: issue-4625 repro

[crusso]

Non-dfx repro for issue #4625

[ggreif]

LGTM, maybe you can add the 3 missing newlines too.

[ggreif]

Maybe this should be under test/fail, then?

[crusso]

I'm not sure how fixable this is. I wonder if design/IDL-Motoko.md is underspecified on how to translate Motoko/Candid references to type definitions, i.e. translate without or after expansion and that affects the translation of argument sequences.

In addition, both Motoko Null and () map to the Candid null.

so type X = () translates to type X = Null
but
func f(x : X) : async X has Candid type () -> ()
(I think), not, null -> null.

[github-actions]

Comparing from 9b67c0c to 79710b1:
The produced WebAssembly code seems to be completely unchanged.