fix(doctest): warn only once if doctest xcompile is skipped

[progressive-galib]

as per issue/comment #12118 (comment) added warning about skipping doctest on xcompiling even when not under verbose flag

#this pr is an attempt at solving #12118. i tested them myself still might need a little work as concise waring shows every time we skip a test instead of once.

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[weihanglo]

Thanks for the contribution.

We need a test for this warning to make sure it doesn't emit excessive warnings.

#12118 (comment)

[progressive-galib]

currently it will show every time a doctest is passed over (i.e skipped)

else we are gonna need to use something like,

pub static ref WARNONCE: Mutex<bool> = Mutex::new(false);

(btw i really like lazy_static crate but i kinda admire low package count of a self hosted compiler)

[weihanglo]

This part of cargo is single-threaded, so perhaps a simple variable here serves the purpose.

cargo/src/cargo/ops/cargo_test.rs

Line 181 in 94d274d

[progressive-galib]

done, pushed it with without locally building.... man as someone working with very slow computer gotta say i just 💖 your CI/CD set up.

[progressive-galib]

done, all tests have passed

[ehuss]

I just want to mildly push back on this, since the original warning was hidden for a reason. It is difficult or impossible for the user to remove the warning. I suspect this will show up for everyone who runs cargo test --target which I suspect will be a large number. For example, I think it will start appearing in every CI run for rust-lang/rust. I understand the desire to bring awareness that something is being skipped, but if there is nothing the user can do about it, I'm not sure that is helpful. I'd like to better understand the motivation here.

[progressive-galib]

I just want to mildly push back on this, since the original warning was hidden for a reason. It is difficult or impossible for the user to remove the warning. I suspect this will show up for everyone who runs cargo test --target which I suspect will be a large number. For example, I think it will start appearing in every CI run for rust-lang/rust. I understand the desire to bring awareness that something is being skipped, but if there is nothing the user can do about it, I'm not sure that is helpful. I'd like to better understand the motivation here.

•)it will only warn only once on the first doctest, not for each doctest,
•)its just one line in a 10000 line CI log, I agree with you better to know it was skipped for those that need them
•)if users need the warning turned off there can be a flag for once users use it and ask for the flag