Tracking Issue for `-Z patch-in-config`

[jonhoo]

Summary

Original issue: #5539
Implementation: #9204
Documentation: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#patch-in-config

The -Z patch-in-config flag enables the use of [patch] sections in cargo configuration files (.cargo/config.toml).

Unresolved issues

None known.

Future extensions

None known.

[jonhoo]

Documentation for feature in #9270

[jonhoo]

I'm trying to figure out the best way for me to test this feature, since I don't want to change cargo/rustc we use internally to be nightly, as it might cause developers to start adopting experimental features. I wonder, is there a way to use a cargo -Z feature on beta/stable specifically for this kind of testing? I'd like to be able to opt into just one feature rather than all of them, but "all" cargo features would probably also be fine. I'm thinking something like -Zallow-Zs :p

Alternatively, is there an "inverse" of RUST_BOOTSTRAP to disallow the use of nightly-only features on nightly? 😅

[alexcrichton]

I believe there's an [unstable] table in .cargo/config.toml which can globally enable nightly features, and then if you use nightly Cargo you should be able to use the feature without any opt-in anywhere else

[jyn514]

Alternatively, is there an "inverse" of RUST_BOOTSTRAP to disallow the use of nightly-only features on nightly? sweat_smile

I've suggested adding RUSTC_BOOTSTRAP=0 in the pass (a little whimsically, but I think the idea is good). https://rust-lang.zulipchat.com/#narrow/stream/233931-t-compiler.2Fmajor-changes/topic/Require.20users.20to.20confirm.20they.20know.20RUSTC_.E2.80.A6.20compiler-team.23350/near/212978290

[joshtriplett]

I would love to have a mechanism to prevent the use of nightly features, regardless of compiler branch. That'd be helpful, for instance, if using nightly for toolchain reasons (needing specific options or optimizations or targets), but not wanting to make code depend on nightly.

[jonhoo]

Ah, so, I specifically want to disallow all unstable features except one, since I want the ability to test a particular feature without opening the floodgates to all the others.

[jonhoo]

I started an internals discussion over in https://internals.rust-lang.org/t/mechanism-for-beta-testing-unstable-features/14280 for those interested in that line of discussion :)