Doctest failure for custom quantity

[svartalf]

I've created a custom quantities system and for some weird reasons doc example for the quantity! macro somehow breaks the documentation tests in my crate with the following error:

$ cargo test --all
..

failures:

---- <::uom::system::system macros> - IEC (line 803) stdout ----
error[E0432]: unresolved import `mks`
  --> doctest.rs:861:5
   |
59 |     Q!(mks, f32/*, (centimeter, gram, second)*/);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `mks` external crate
   |
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

thread '<::uom::system::system macros> - IEC (line 803)' panicked at 'couldn't compile the test', src/librustdoc/test.rs:351:13

Commenting these lines in the uom sources removes an error completely.

rustc version: 1.33.0
uom version:

[dependencies.uom]
version = "0.21.1"
default-features = false
features = ["autoconvert", "usize", "u64", "f64", "si", "std"]

I guess, doc test for exported IEC! macro breaks for some unknown reasons?

So, here is what makes this bug "weird": it is reproducible in the existing code, but I can't reproduce it with a new cargo project.
Unfortunately, existing code is not public (yet), so at the moment I'm failing to find the way of how to show it.

@iliekturtles, any thoughts, maybe?

[iliekturtles]

This is an issue caused by edition="2018". I'm able to reproduce by copying the doc example into a new project. It fails to compile with edition="2018" but is successful with edition="2015". The $quantities! macro is generating code is that isn't compatible for edition="2018".

Short term it looks like changing the macro invocation to Q!(crate::mks, f32/*, (centimeter, gram, second)*/); is compatible with both editions. Long term I want to think about having uom documentation being generated on the $quantities! macro and inserted into the caller's crate. The doc comments for this macro should should possibly be specified in the system! macro call.

Cross-edition tests should also be added to uom so that issues like this get caught in the future.

[svartalf]

Yeah, this explains everything, thanks :)
I think I can manage the workaround until uom will be compatible with the edition="2018".

Not sure if this issue should be closed now, feel free to do that.

[iliekturtles]

Leave it open. I have some local changes to fix the generated code to be compatible with both editions. uom itself is going to remain 2015 to support older compilers but I should be able to make generated code compatible. I'll try to get the changes committed and released in the next couple days.

[iliekturtles]

v0.22.0 with the doc test fixes released to crates.io.