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strip rust src lines during normalization #247

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davidhewitt
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This adds a new normalization to trybuild to remove src lines which originate from rust-src. The rustup default profile does not contain the rust-src component, so I argue this normalization is justified as it makes the trybuild outputs consistent with what a user with a default rust install would see.

This is a follow-up to #126, which was resolved with a working alternative at the time.


For some context: As of this week, the PyO3 CI has ground to a halt, there is a bad interaction between rustup and GitHub Actions runner images which is causing rust-src component to fail to install, see rust-lang/rustup#3530

While there are several solutions we can employ to workaround the issue, this option seems like a potential plus for the ecosystem while also removing our need to install rust-src.

Comment on lines +329 to +331
self.numbers_to_hide_are_rust_src = is_rust_src;
self.hide_numbers = 0;
while let Some(next_line) = self.all_lines.get(index + self.hide_numbers + 1) {
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It seems to me that there was an off-by-one error here causing self.hide_numbers to be one higher than it needed to be. That didn't matter while the operation was just trimming leading numbers, resulted in a noop in the last line, but removing whole lines was more destructive.

@@ -32,8 +32,5 @@ error[E0599]: the method `to_cxx_exception` exists for reference `&NonError`, bu
which is required by `&NonError: ToCxxExceptionDefault`
note: the trait `std::fmt::Display` must be implemented
--> $RUST/core/src/fmt/mod.rs
|
| pub trait Display {
| ^^^^^^^^^^^^^^^^^
= note: this error originates in the macro `::cxx::map_rust_error_to_cxx_exception` (in Nightly builds, run with -Z macro-backtrace for more info)
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E.g. this = note: line would be removed without the off-by-one adjustment.

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@dtolnay dtolnay left a comment

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Thanks for the PR!

I would prefer not to make this change. The notes with which rustc annotates the standard library source snippet are potentially interesting to test. For example in that "rust-lib.rs" test touched by this PR: I would want to find out if that "doesn't satisfy `std::net::Ipv4Addr: quote::to_tokens::ToTokens`" message changes. Rustc occasionally does nutty things like _::_quote::to_tokens::ToTokens (rust-lang/rust#46991).

Hopefully the rust-src install bug is fixable in rustup.

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Understood, I can see the benefit of both sides of the coin.

We've unblocked the PyO3 CI but only by reverting the prior advice from #126 (comment) and removing the rust-toolchain.toml. In CI we can then install rust-src only when we want it using your rust-toolchain action. I'm not convinced the underlying bug is solved but it's got us off the ground at least.

Unfortunately this means that users running our trybuild tests will hit a necessary failure until they install the rust-src component. It's a small but annoying wart.

Is there a way you would accept this PR as an optional mode, perhaps by additional configuration to set on TestCases? Otherwise, I guess please just close this PR and we'll live with the pain.

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dtolnay commented Dec 27, 2023

I am glad you were able to unblock the PyO3 CI with PyO3/pyo3#3575. Also, surprised that deleting rust-toolchain.toml was necessary, because I have been using components = ["rust-src"] in rust-toolchain.toml in several repositories for over 2 years without ever hitting the rustup race condition:

I would be interested to find out if we can find any relevant difference between PyO3's CI and mine that would be exacerbating rust-lang/rustup#988.

@dtolnay dtolnay closed this Dec 27, 2023
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