Add import layers for testthat files

[lionel-]

Branched from #1259

Whereas scripts in tests/ folders are standalone, scripts in tests/testthat/ are sourced in an environment where:

• Setup and helper files are run.
• The package namespace is injected
• The testthat exports are attached

This PR detects testthat files and adjusts the import layers accordingly, so that symbols injected by testthat are visible in these files.

[DavisVaughan]

Cool

[DavisVaughan]

is this because https://example.com/foo/ sees that last / and returns an empty string for the (not really there) segment after the /?

[lionel-]

yep I've added this comment:

                    // A trailing slash (`.../foo/`) yields a final empty segment,
                    // meaning the URL points at a directory. Drop it so we return
                    // `None` rather than `""`.

[DavisVaughan]

"Only the file's own top-level library() calls"

GROSSSSSSSS, THE HORROR

[DavisVaughan]

LINT THIS?

[lionel-]

Possibly, but it feels to me more like Jarl's territory than Oak's.

[DavisVaughan]

is the cursor itself top level? not always right? like you can be in a test_that({<cursor>}) block and i wouldnt consider that top level?

i would also appreciate if this comment were rewritten as like a bulleted list of the 2 cases. it was very hard for me to mentally parse with the colon and semicolon

[lionel-]

This is now:

/// The file's `library()` / `require()` attaches as `Package` layers, in LIFO
/// order (latest-attached first). `before` selects which calls to include:
///
/// - `None`: every attach. The end-of-file view, used for lazy contexts.
/// - `Some(offset)`: only top-level (file-scope) calls that have run by
///   `offset`. Calls nested in a block (e.g. inside `test_that({})`) are
///   dropped, as are calls after the offset.

[DavisVaughan]

we should upgrade to 2024 edition rust at some point for let chains so you can do things like this

fn in_testthat_dir(path: &Utf8Path) -> bool {
    if let Some(parent) = path.parent() &&
        parent.file_name() == Some("testthat") &&
        let Some(parent) = parent.parent() &&
        parent.file_name() == Some("tests")
    {
        return true
    } else {
        return false
    }
}

[DavisVaughan]

What is the default? An empty Owned string i guess? can you just leave it as Option<Cow>? I have no idea if that would sort right

[lionel-]

Default but it's unreachable.

[DavisVaughan]

i wonder if it will be useful to have a specific field for testthat_scripts or something, so we dont have to tease them apart from regular scripts every time

[lionel-]

Potentially, but I'd rather have some kind of collation annotation to branch on (via a tracked query).