Cannot define a function using the try operator `?` in an `expect` statement

[ageron]

The following code fails with roc nightly pre-release, built from commit 9a4d556 on Mon Sep 9 09:02:33 UTC 2024:

app [main] {
    pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.15.0/SlwdbJ-3GR7uBWQo6zlmYWNYOxnvo8r6YABXD-45UOw.tar.br",
}

import pf.Stdout

inc = \i ->
    if i > 2 then
        Err MaxReached
    else
        Ok (i + 1)

expect
    run = \i ->
        newi =
            i
            |> inc?
            |> inc?
        Ok newi
    result = run 0
    result == Ok 2

main =
    Stdout.line! "Hello world"

The error is:

An internal compiler expectation was broken.
This is definitely a compiler bug.
Please file an issue here: <https://github.com/roc-lang/roc/issues/new/choose>
a Expr::TrySuffix expression was not completely removed in desugar_value_def_suffixed
Location: crates/compiler/can/src/expr.rs:1125:40

The problem disappears if I define the run function outside the expect statement. However, I'd like to avoid polluting the global scope, and I'd like to keep the function tied to the expect statement.

[ageron]

Here's a shorter example, in a module:

# Inc.roc
module [inc]

inc = \i -> if i > 2 then Err TooBig else Ok (i + 1)

expect
    result = inc? 0
    result == 1

Just run roc test Inc.roc

[ageron]

🥳 thanks @lukewilliamboswell !