Effects of `RUSTUP_WINDOWS_PATH_ADD_BIN` change about rustup HOT 14 OPEN

Thanks for filing this! This is essentially what nextest has too, specifically with test binaries built by proc-macro crates. Though this has been a long-standing issue with nextest (nextest-rs/nextest#267), because ideally nextest would work with Rust installations not managed by rustup.

We expect nextest-rs/nextest#1499 to fix this the right way, by querying rustc to obtain the target libdir and adding it manually to the dylib path variable.

This is now out as part of cargo-nextest 0.9.72. With this, nextest no longer depends on whether it's being invoked via a rustup-wrapped cargo.

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@smoelius thanks for the detailed description. Do you think the proposed path forward for nextest would also address the dylint use cases?

I'm not sure. Is RUSTUP_WINDOWS_PATH_ADD_BIN going away?

There are no concrete plans in that direction, but it'd be good to avoid depending on workarounds for deprecated features.

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There are no concrete plans in that direction, but it'd be good to avoid depending on workarounds for deprecated features.

OK. Dylint's CI still uses this environment variable to run one obscure doc test, but Dylint itself no longer uses it.

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This is in a super frustrating part of unix/windows difference; I'm sad we've created some pain - but the good news seems to be it is fairly limited - 3 projects out of the entire ecosystem is not terrible ;).

I have no strongly held view on what the right answer here is, but see #3036 (comment) - and there is a lot of previous discussion and work such as rust-lang/cargo#11917 and #3178

I do think its important that rustup is consistent on all platforms except where we really cannot (and the edge case of linked toolchains missing binaries is one such place). And we are now consistent again, so with the limited breakage, I'm inclined to suggest we shouldn't panic but should take some time to look at that the impact is on these downstream projects...

we could solve this by documenting what they need to do, or possibly by some sort of config they could opt-into ... but if we offer that, we should offer it for all platforms IMO.

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Thanks for filing this! This is essentially what nextest has too, specifically with test binaries built by proc-macro crates. Though this has been a long-standing issue with nextest (nextest-rs/nextest#267), because ideally nextest would work with Rust installations not managed by rustup.

We expect nextest-rs/nextest#1499 to fix this the right way, by querying rustc to obtain the target libdir and adding it manually to the dylib path variable.

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@sunshowers sounds good, thanks for chiming in!

@smoelius thanks for the detailed description. Do you think the proposed path forward for nextest would also address the dylint use cases?

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@smoelius thanks for the detailed description. Do you think the proposed path forward for nextest would also address the dylint use cases?

I'm not sure. Is RUSTUP_WINDOWS_PATH_ADD_BIN going away?

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I think a general decision to make is whether a tool needs to support Cargo installations not managed by rustup. For nextest the answer is yes, but it could be no for other tools.

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In servo we also hit this with our custom linter.

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This affected Tokio's CI setup too, and broke the case where we run tests on windows with proc macros. Not sure why exactly it broke us, but adding the flag seems to fix it.

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@ehuss do you think Rustup is responsible for this breakage?

Modifying PATH was originally done for various reasons that are complicated and not really relevant anymore.
https://internals.rust-lang.org/t/help-test-windows-behavior-between-rustup-and-cargo/20237

AFAIK, there have not been any indications of anyone having problems.
#3703

... unfortunately that's probably because few have actually tried 😅

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(Note that this introduces an inconsistency -- on Unix platforms, with rustup-managed cargo, you still don't need to do anything special with proc macro tests -- but on Windows you do.)

Wanted to reiterate that any projects that are broken by this are also probably broken by scenarios where rustup is not in use (e.g. distro-packaged cargo).

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@sunshowers I think that visible inconsistency is properly at a higher layer though: it is a symptom of dlopen semantics on the underlying platforms. Because PATH affects both command line lookup and dlopen, we can't have detach them,

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Is there a minimal example of the proc-macro test issue? This could perhaps be fixed on the rustc/cargo side of things by being more explicit about where to load a specific DLL from.

Maybe a possible workaround for rustup is to have a third mode that adds the bin path to the end of PATH?

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