memory issues with expect

[Anton-4]

It's quite easy to hit a segmentation fault when using the expect keyword.

Example:

app [main!] {
    cli: platform "https://github.com/roc-lang/basic-cli/releases/download/0.19.0/Hj-J_zxz7V9YurCSTFcFdu6cQJie4guzsPMUi5kBYUk.tar.br",
}

import cli.Stdout

main! = |_args|
    Stdout.line!("ignore me")

expect
    actual = 1.0
    expected = 2.0
    actual == expected

Output:

$ roc test repro.roc
Segmentation fault (core dumped)

[Anton-4]

This is happening because we're sharing memory between processes in a brittle way.
We used to do this the same way for the dbg keyword, we modernized that but did not yet perform similar changes for expect.
Relevant links for the changes to dbg:

• Dbg with inspect #6116
• Dbg - Better Gen #6143
• fix off by one in roc_dbg #6166
• https://github.com/roc-lang/basic-cli/blame/0fda6456a16947681d4cf8634ec8c2d936b54ed4/crates/roc_host/src/lib.rs#L92

The core team is mostly occupied with working on the new compiler (which will also fix this issue) but a motivated individual could probably land this fix in the old compiler.

[Anton-4]

Important zulip conversation: #bugs > ✔ segfault on failing multi-line tests with a float def @ 💬

[Anton-4]

Other bugs caused by this issue:

• #beginners > Segmentation fault during exercism tests for phone-number @ 💬
• malloc_consolidate() error after tests finish #7797

[Anton-4]

Workaround for this issue; write your own inline test function like err_on_false here:

app [main!] { pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.19.0/Hj-J_zxz7V9YurCSTFcFdu6cQJie4guzsPMUi5kBYUk.tar.br" }

import pf.Stdout
import pf.Url
import pf.Arg exposing [Arg]

main! : List Arg => Result {} _
main! = |_args|
    Stdout.line!("Testing Url module functions...")?

    # Test Url.from_str and Url.to_str
    Stdout.line!("\nTesting Url.from_str and Url.to_str:")?
    url = Url.from_str("https://example.com")
    Stdout.line!("Created URL: ${Url.to_str(url)}")?
    err_on_false(Url.to_str(url) == "https://example.com")?

    Ok({})

err_on_false : Bool -> Result {} [StrErr Str]
err_on_false = |bool|
    if bool then
        Ok({})
    else
        Err(StrErr("Test failed"))

[Anton-4]

Would you be interested in taking a look at this @lukewilliamboswell? It may not be a lot of work, no promises though :p

[lukewilliamboswell]

@Anton-4 -- I'm not particularly motivated to look at this. I've spent a lot of time poking around in the shared memory stuff and it's a bit wild and difficult for me to debug anything.

I'm glad we had identified a workaround for now. If @kili-ilo needs help I could look into a more specific issue and try to help find another workaround.

[kili-ilo]

I'm not currently inconvenienced by this.