Add little is_test_crate function

[blyxyas]

Ok, this is quite a story.
I'm mainly a Clippy contributor, so I was fixing this Clippy issue about a lint having to ignore test modules but that wasn't ignoring test files (integration test, test/ dirs and such).

As test files don't tend to have an inner #[cfg(test)] module inside them, I tried everything, looking for filenames, looking for item's parents in the HIR Map, doing black magic...

I even asked on Zulip, and jyn answered something about --cfg test. Aha! That's something that I might be looking for, so I started looking at rustc_driver_impl flag parsing and configuration and all that.

Then, I stumbled on this function right here, and noticed the argument config: Config. That's a hint.

So Config has the field opts: Options, and Options has the field test.

This journey has been ~7 or 8 hours in 3 days, it's a very hard thing to find, so this PR adds a mini-function to check if the current crate is a testing one. So that no one has to travel through the same as me, and can just search for is_test_crate in the documentation.

[rustbot]

r? @jackh726

(rustbot has picked a reviewer for you, use r? to override)

[compiler-errors]

If you want to test for --cfg test, then you're gonna have to do something like tcx.sess.parse_sess.config.contains(sym::test), I think. --test implies --cfg test, but --cfg test does not imply --test.

I don't have enough background about what you needed this for to know whether that's what you wanted.

Also, side-note, this should be squashed into one commit.

[blyxyas]

It seems like it isn't necessary.
Edit: It isn't necessary because it isn't searching for the specific --cfg test, but only if the compiler session is a test one. --cfg test was just an inspiration

[compiler-errors]

Please also migrate all of the other usages of sess.opts.test to use this helper -- there are 9 that I can see in the compiler source.

[compiler-errors]

@rustbot author

[blyxyas]

@rustbot ready

[compiler-errors]

@bors r+

[bors]

📌 Commit 2c97676 has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2c97676 with merge f036f34036470ab3d5cdc9e762051e9588ef9321...

[bors]

💔 Test failed - checks-actions

[ehuss]

@bors retry

crates.io network blip

[rust-log-analyzer]

The job dist-i686-msvc failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)