Add support for compiler tests

[fuine]

This is an initial version of compiler tests. So far it should work on travis, appveyor is a bit harder to achieve, because there's no simple way to add testing with specified features only on nightly. Please don't merge yet, because I want to at least try to make them run on appveyor as well.

Moreover due to the design of compiletest crate and its implementation details there isn't any clear way to annotate warnings/errors in lines that are being expanded by the macro, but rather we are forced to use error-pattern general mechanism. I will document that in code later on, just wanted to highlight it here.

[fuine]

@KodrAus could you take a look at appveyor errors, because I'm starting to get out of ideas. I tried a lot of different things, including copying setup from rayon crate that works for them, but yields linker errors in our case.

[KodrAus]

@fuine Sure. I've got a Windows box handy so will do some troubleshooting over the weekend.

[fuine]

Cool, thanks. Just heads up: compile tests work on my machine using both Windows and Linux, they also work on travis, it's just that for some reason appveyor build refuses to find lazy_static crate even though it currently is implemented the same way rayon has it set up (or so I think)

[KodrAus]

So this is actually failing on my local environment too. Which is probably good news

[fuine]

That's great news, however could you test it as well on 60e11d8 ?

[KodrAus]

Yep, specifying the target directly when running the compile tests seems to cause it to fail to find the lazy_static crate. What if we remove the explicit --target calls from the script? We shouldn't actually need them since we only install the appropriate toolchain in each environment.

[fuine]

I don't have any indepth knowledge of appveyor's config, but if you don't specify target doesn't it fallback on w/e target it has set as default/finds first? Also if this is really a proble with --target flag then we should probably open an issue in cargo/rust repository

[fuine]

Actually at this point I'm willing to test that and just manually see the logs to check which targets are used if we don't specify them explicitly.

[KodrAus]

I don't have any indepth knowledge of appveyor's config, but if you don't specify target doesn't it fallback on w/e target it has set as default/finds first?

I think you're right, and since you're setting the default appropriately this should be fine.

My guess is that this is a problem with the rustflags we're giving compiletest, rather than a problem with compiletest itself. When cargo builds for a specific target, the results don't end up in the target/debug folder, they go into target/%TARGET%/debug, which isn't included in our script. It's probably easier to just exclude the target.

[fuine]

Thanks for the help, I've squashed previous commits and added some notes on the tests. I think it's potentially mergeable once CI goes green, but I can also squash the last commit with the first one - I want to preserve 6529b07 because it explicitly fixes a regression that I introduced in my previous PR.

[KodrAus]

That history looks good to me :+1: I'm happy to merge this in once it's all green.

Thanks for doing this @fuine! Your efforts to improve a bunch of aspects of the library are really appreciated! 😃