Selective Field Import

[q-uint]

It seems you can not import a file that uses selective field imports.

• feat: generalized imports supporting pattern matching and selective field import #3076 by @ggreif

---

src
├── X.mo
└── Y.mo

// X.mo
import { Array_init = init } = "mo:⛔";

// Y.mo
import X "X";

Error

src/X.mo:1.8-1.29: type error [M0015], only trivial patterns allowed in static expressions

Context

$(vessel bin)/moc --check $(vessel sources) src/Y.mo

• vessel 0.6.2
• Motoko compiler 0.6.21 (source wahvzdqw-grg3wqkh-0n8s7fj6-f4rxx0rh)

[nomeata]

Thanks for reporting! This needs
updates in https://github.com/dfinity/motoko/blob/master/src/mo_frontend/static.ml to allow more kinds of patterns.

I wonder if we need to be careful to not accept cyclic definitions, or if the definedness check prevents that. But it's too late today to think this through.

[nomeata]

Also, we shouldn't allow anything in libraries that cannot be compiled strategically, i.e. is const in the sense of https://github.com/dfinity/motoko/blob/master/src/ir_passes/const.ml. that handles object patterns already, so we should be good here. (This is important also so that function calls into libraries will be compiled to direct calls to known functions.)

[ggreif]

We already permit TupP in that context, can't see how allowing ObjP would be different. Working on a fix.

[ggreif]

Released as https://github.com/dfinity/motoko/releases/tag/0.6.22