Pass LexerKind by reference.

[ltratt]

At the moment the code happens to work only because of an oversight in rustc: that oversight is likely to be fixed soon (rust-lang/rust#150681).

@meithecatte If you're able to do so, I'd be grateful if you can confirm this addresses the rustc issue properly. If so, I will then make a new release shortly after so that we're not blocking the rustc PR.

[ratmice]

I'm happy to approve.

I was able to reproduce the error from the crater log in #620 on current rustc by adding a second variant to LexerKind and compiling with cargo build --all-targets since the error only occurs with cfg(test).

Edit: The test worked as expected (failed on the master branch, and worked with this one)

[ltratt]

@ratmice Cool, and thanks! So we're confident with this PR merged, we won't trigger the upcoming-rustc change?

[ratmice]

If my understanding of the problem is right, adding another variant it should behave the same on both the new and old compilers, since the change seems to be making single variant #[non_exhaustive]` behave as they had multiple variants on the new compiler.

I'd still wait for feedback from @meithecatte before release, in case they can conveniently test on the new compiler though, or my understanding is flawed.

[meithecatte]

I can confirm that with this PR, the tests compile and pass with the compiler changes in question.

FWIW, considering that the error only happens under cfg(test), I'm not sure how important you'd consider actually creating the release – but that is entirely your decision.

[ltratt]

@meithecatte Thanks for confirming! You're right that it's not super important to release in this case, but at least then we know that no-one who clones the last release will get a surprise when rustc updates.