roc test: entered unreachable code: no borrow signature for LambdaName

[phtrivier]

• Using "ubuntu mate 24.04" on an x86_64

○ → lscpu
Architecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          39 bits physical, 48 bits virtual
  Byte Order:             Little Endian
CPU(s):                   8
  On-line CPU(s) list:    0-7
Vendor ID:                GenuineIntel
  Model name:             Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz

○ → lsb_release --all
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 24.04.1 LTS
Release:	24.04
Codename:	noble

• Using a recent nighly

○ → roc --version
roc nightly pre-release, built from commit a089cf2 on Di 07 Jan 2025 09:02:06 UTC

Given two files:

• Foo.roc :

module [
    foo,
]

foo = { bar: 42 }

• main.roc

app [main!] { pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.18.0/0APbwVN1_p1mJ96tXjaoiUCr8NBGamr8G8Ac_DrXR-o.tar.br" }

import pf.Stdout
import Foo

expect
    f = Foo.foo
    f.bar == 42

main! = \_args ->
    try Stdout.line! "Ok"
    Ok {}
    

When running roc test:

thread 'main' panicked at crates/compiler/mono/src/inc_dec.rs:984:33:
internal error: entered unreachable code: no borrow signature for LambdaName { name: `Foo.foo`, niche: Niche(Captures([])) } layout
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

If i replace the expectation with:

expect Foo.foo.bar == 42

Then test is successful:

○ → roc test
0 failed and 1 passed in 215 ms.

[Anton-4]

Thanks for the detailed error report @phtrivier :)

Notes for a future investigator: We have several issues with "no borrow signature for LambdaName" but this is the only one that panics in crates/compiler/mono/src/inc_dec.rs