Experiment with a cttests_macro proc_macro.

[ratmice]

This was just a quick experiment with generating tests which parse cttest/src/*.test from a proc_macro to generate #[test] fragments.

1. Moving the cttests/build.rs helper functions to a file src/cgen_helper.rs
2. Adds a cttests_macro crate (doesn't need to live on crates.io, used as a path dependency)
3. Uses that macro to generate #[should_panic] tests calling the cgen_helper functions.

In #415 I know you said it probably would not be worth the effort, but I was curious if it would actually work.
You had mentioned using the lang_tester crate. But I'm just uncertain of how to go about that given the build.rs involvement and (moderate) dependence on cargo environment variables like OUT_DIR within the CTBuilders.

Not really sure if all the additional complexity is worthwhile however at least I learned some proc_macro things.

[ltratt]

Does this mean that the tests are always run now or ... ?

[ratmice]

Yeah, the additions to lrpar/src/lib.rs causes it to generate a bunch of #[test] functions that run along side all of the other #[tests]. So, even if the build.rs is never rebuilt these tests will now run when you cargo test.

There is a few things in this which i should probably investigate further, regarding the globbing/lossy string conversion which might cause an issue if someone uses a non-lossy convertible character in their home directory since the manifest path is absolute.
But it's a basic functioning proof of concept at how the proc-macro approach could work.

[ltratt]

Got it. I'm happy with this: do you want to do some of the tidying up you suggested before merge?

[ratmice]

I would like to tidy it up, I don't think the current master branch is affected by it so it likely is introducing a top-level cargo test regression, which could affect users with non-utf8 home directories.

It looks like both glob and globset have unresolved issues regarding this,

rust-lang/glob#78
BurntSushi/ripgrep#1250

In theory we can avoid non-utf8 characters by building a relative path, but it is complicated by proc_macros not having a specified working directory. Assuming it is in the workspace somewhere, we should be able to strip the common prefix between the working dir, and $CARGO_MANIFEST_DIR.

A bit hacky, but I think that is the only option short of fixing glob.
Edit: I guess we could also cd $CARGO_MANIFEST_PATH && glob(...) && cd -, while that would be simplest and avoids any string manipulation it seems like it isn't thread safe, I would probably rather avoid it even though it doesn't appear that the compiler is multi-threaded during proc_macro evaluation at the moment 🤷

[ltratt]

Presumably we haven't made the non-utf8 situation worse in this PR?

[ratmice]

Presumably we haven't made the non-utf8 situation worse in this PR?

It has or would, currently we only deal with known utf8 paths relative to the working dir.
The code in this branch has to deal with 2 conversions, one in and one out of glob. The one out of glob being
conversion of the path to tokens for the macro return value (I.e. there isn't a valid rust source code string which corresponds to all valid paths).

Previously we had known utf8 input, and never need to convert the output so it should be fine currently.

[ratmice]

I did my best to fix it in the obvious issues in that last patch, but i'm not really sure how to go about creating non-utf8 directory to test. I think though it should put us back on par with the current code on the master branch.

[ltratt]

I think this comes under "if the fix doesn't work for some edge cases, we'll deal with it when we find it"!

Please squash.

[ratmice]

Squashed.

[ltratt]

bors r+

[bors]

Build failed:

• buildbot/buildbot-build-script

[ratmice]

Oops, above commit msg should be rustfmt, but given it'll be squashed away i'll leave it for now.
Build failure should be fixed I believe.

[ltratt]

Please squash.

[ratmice]

Sorry. One last change to fix clippy.

[ltratt]

Please squash.

[ratmice]

Squashed -- hopefully for the last time!

[ltratt]

bors r+

[bors]

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• buildbot/buildbot-build-script