Adding compile fail test for staged_api feature

[cseale]

Issue #39059
r? @est31

@est31 running the tests for this feature fails. Is that expected since this is the compile-failsuite?

I copied this test from the run-pass suite: rust/src/test/run-pass/reachable-unnameable-type-alias.rs. What are the differences between these suites in operation and why they are used?

[est31]

Is that expected since this is the compile-fail suite?

No, tests in the compile-fail suite are expected to fail compilation, but it will show up to you as "success". You need to tell it about the error messages that were excepted, if it encounters errors that didn't match it fails, which probably happened here. For how to mark the errors, you should read COMPILER_TESTS.md. Also, you can have a look at how #39700 did it.

What are the differences between these suites in operation and why they are used?

Run-pass is for tests that are expected to be compiled and not panic or segfault when they run, and compile-fail is for tests that fail to compile. There are other test suites as well, like parse-fail for tests that fail much earlier in compilation, during parsing. Usually though tests are in compile-fail and not parse-fail.

[aturon]

@bors delegate=est32

[bors]

✌️ @est32 can now approve this pull request

[aturon]

Helps if I get the user name right...

@bors delegate=est31

[bors]

✌️ @est31 can now approve this pull request

[aturon]

@bors r=est31

[bors]

📌 Commit 07b3a8b has been approved by est31