regression: `zig test` on a std lib file errors with 'file exists in multiple packages'

[squeek502]

Zig Version

0.11.0-dev.1502+d6b430b52

Steps to Reproduce and Observed Behavior

Previously, something like the following worked, and only the tests within fs/test.zig would get run (at least after #12939):

zig test lib/std/fs/test.zig --zig-lib-dir lib --main-pkg-path lib/std

With current master branch, however, it will error:

lib/std/std.zig:1:1: error: file exists in multiple packages
lib/std/std.zig:1:1: note: root of package std
lib/std/fs/test.zig:1:21: note: imported from package root
const std = @import("../std.zig");
                    ^~~~~~~~~~~~
lib/std/multi_array_list.zig:1:21: note: imported from package std
const std = @import("std.zig");
                    ^~~~~~~~~

... (omitted a lot of notes) ...

lib/std/build/LibExeObjStep.zig:2:21: note: imported from package std
const std = @import("../std.zig");
                    ^~~~~~~~~~~~
lib/std/fs/test.zig:1:1: error: file exists in multiple packages
lib/std/fs/test.zig:1:1: note: root of package root
lib/std/fs.zig:3131:17: note: imported from package std
    _ = @import("fs/test.zig");
                ^~~~~~~~~~~~~

This is a use-case that I use quite often but I know isn't fully endorsed (some context: #2331 (comment), #9946). I expect some change similar to what caused it to regress before #12926 / #12939 has happened again.

Expected Behavior

$ zig test lib/std/fs/test.zig --main-pkg-path lib/std --zig-lib-dir lib
All 45 tests passed.

[mlugg]

This is an interesting case. The error is exactly what it says: files are now banned from being included in multiple packages. This isn't a needless restriction, it only sort of "worked" before - you could very easily cause issues by abusing multi-package files, and the "correct" fix was deemed unnecessary since in general having a file in multiple packages is very bad style. But indeed, the file test.zig in this case is in both your root package (or, pseudo-root; it's not the test runner, but the file being tested) and in std. We need std for the test runner, so we can't just eliminate it entirely when running partial tests on std, meaning the solution here is unclear.
A workaround would be to copy the std sources elsewhere and test those (a plain symlink might work in fact). This makes them truly separate packages, without files in common, preventing the issue. But that's certainly not an ideal solution, so I'll try and think about what can be done for this use case - maybe a special option of some sort for testing files in std.

[squeek502]

For what it's worth, I'd be totally fine with this permanently regressing if test-filter was powerful enough to replace it (i.e. test-filter being able to specify 'only compile and run tests within a particular file')

Otherwise, the solution here most likely will involve special casing for std (see #12939 for some special casing that was done to fix it once before)

[matu3ba]

A workaround would be to copy the std sources elsewhere and test those (a plain symlink might work in fact)

This workaround does not work on Windows on default: the user must enable symlinks (for security reasons).

[dweiller]

in general having a file in multiple packages is very bad style.

What is the reason this is bad style? If you have packages that share a common dependency (maybe some utils.zig containing some common helpers) it seems reasonable to have both of them import it as a file. I suppose the status quo is that you need to make that file a into a module and then they can both import it as a module. I don't really see why this would be better style than directly importing the file.

[erikarvstedt]

A workaround would be to copy the std sources elsewhere and test those (a plain symlink might work in fact).

This results in errors like error: expected type 'mem.Allocator', found 'mem.Allocator'.

[travisstaloch]

do you have different versions of the std lib being picked up? you might have to replace these lines

// const std = @import("../std.zig"); // <- maybe resolving to a different std.zig file?
const std = @import("std");

after making these replacements in 3 files. i was able to:

$ cp ../zig/lib/std/meta.zig /tmp
$ cp -pr ../zig/lib/std/meta /tmp
$ zig test /tmp/meta.zig 
All 55 tests passed.

[erikarvstedt]

@travisstaloch, yes, editing the test files fixes this.

But the regression discussed here is that it was previously possible to test single stdlib files without editing them.

[travisstaloch]

I didn't mean to suggest that the above is a solution to this problem, only a work around.