Update toolchain nightly-2026-03-14

[LegNeato]

• cargo-gpu: update rust-gpu to PR #545 cargo-gpu#143
• rustc 1.94.0 destabilised json target specs, requiring -Ztarget-spec-json: Destabilise target-spec-json rust-lang/rust#150151

[LegNeato]

I think we want to use this rather than our own home-grown replacements, but didn't want to do it in this PR.

[nazar-pc]

cargo-gpu will need to be updated again to match this, custom target specs since recently require an unstable CLI option:

error: `.json` target specs require -Zjson-target-spec

[nazar-pc]

Tried to update with a patched cargo-gpu locally and it worked, but generated these warnings that were not present before:

Details

warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ptr/mod.rs:2086:9
|
2086 | / ub_checks::assert_unsafe_precondition!(
2087 | | check_language_ub,
2088 | | "ptr::read_volatile requires that the pointer argument is aligned",
... |
2092 | | ) => ub_checks::maybe_is_aligned(addr, align)
2093 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from panic entry-point call args
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ptr/mod.rs:531:5
|
531 | / ub_checks::assert_unsafe_precondition!(
532 | | check_language_ub,
533 | | "ptr::copy_nonoverlapping requires that both pointer arguments are aligned and non-null \
534 | | and the specified memory ranges do not overlap",
... |
547 | | );
| |_____^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from panic entry-point call args
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:240:9
|
240 | / assert_unsafe_precondition!(
241 | | check_language_ub, // okay because of the `assume` below
242 | | "slice::get_unchecked requires that the index is within the slice",
243 | | (this: usize = self, len: usize = slice.len()) => this < len
244 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(59851, 1387, [3516, 3517])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:240:9
|
240 | / assert_unsafe_precondition!(
241 | | check_language_ub, // okay because of the `assume` below
242 | | "slice::get_unchecked requires that the index is within the slice",
243 | | (this: usize = self, len: usize = slice.len()) => this < len
244 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(59882, 1390, [3522, 3523])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:260:9
|
260 | / assert_unsafe_precondition!(
261 | | check_library_ub,
262 | | "slice::get_unchecked_mut requires that the index is within the slice",
263 | | (this: usize = self, len: usize = slice.len()) => this < len
264 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(59911, 1381, [3527, 3528])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:240:9
|
240 | / assert_unsafe_precondition!(
241 | | check_language_ub, // okay because of the `assume` below
242 | | "slice::get_unchecked requires that the index is within the slice",
243 | | (this: usize = self, len: usize = slice.len()) => this < len
244 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(59936, 1393, [3533, 3534])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:240:9
|
240 | / assert_unsafe_precondition!(
241 | | check_language_ub, // okay because of the `assume` below
242 | | "slice::get_unchecked requires that the index is within the slice",
243 | | (this: usize = self, len: usize = slice.len()) => this < len
244 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(59967, 1396, [3539, 3540])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:240:9
|
240 | / assert_unsafe_precondition!(
241 | | check_language_ub, // okay because of the `assume` below
242 | | "slice::get_unchecked requires that the index is within the slice",
243 | | (this: usize = self, len: usize = slice.len()) => this < len
244 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(59998, 1399, [3545, 3546])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:260:9
|
260 | / assert_unsafe_precondition!(
261 | | check_library_ub,
262 | | "slice::get_unchecked_mut requires that the index is within the slice",
263 | | (this: usize = self, len: usize = slice.len()) => this < len
264 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(60027, 1384, [3550, 3551])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:240:9
|
240 | / assert_unsafe_precondition!(
241 | | check_language_ub, // okay because of the `assume` below
242 | | "slice::get_unchecked requires that the index is within the slice",
243 | | (this: usize = self, len: usize = slice.len()) => this < len
244 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(60052, 1402, [3556, 3557])])
warning: failed to find and remove `format_args!` construction for this `panic!`
--> /home/nazar-pc/.rustup/toolchains/nightly-2026-03-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/index.rs:326:9
|
326 | / assert_unsafe_precondition!(
327 | | check_library_ub,
328 | | "slice::get_unchecked_mut requires that the index is within the slice",
329 | | (end: usize = self.end(), len: usize = slice.len()) => end <= len
330 | | );
| |_________^
|
= note: compilation may later fail due to leftover `format_args!` internals
= note: [RUST-GPU BUG] bailed from fmt::Arguments::new call sequence ([Call(60985, 1071, [60970]), Call(60988, 1378, [3948, 3949])])

[LegNeato]

Cool, I'll take a look. There were some changes in this area.

[Firestar99]

Looks like cargo-gpu needs an update to work with this branch... I'll have a look tomorrow (and properly review this)

[Firestar99]

I found a good counter argument against updating to "in the middle" nightlies:

https://github.com/Rust-GPU/cargo-gpu/blob/7f1995823a82ee6e6b7a63b57313c4a829856e3d/.github/workflows/push.yaml#L56-L76

These are 4 old rust-gpu versions we no longer test cargo-gpu against due to them failing, of which 2 are broken due to using in-the-middle nightlies:

• ❌ 0.8.0: cargo-gpu builds rust-gpu without lockfiles, and these old cargo versions aren't msrv-aware, so it upgraded zmij to a too new version
• ✔️ cc75231 serde starts using #[diagnostic] attributes as it detects rustc 1.78.0. We're on nightly-2024-03-01, #[diagnostic] got stabilized on 2024-03-08 and rustc 1.78.0 branched on 2024-03-15
• ❌ 02cefd1 fails as target specs mismatch, they get changed a few commits later so I didn't bother
• ✔️ bbb61f5proc-macro2 starts using proc_macro::Literal::byte_character (from rustc_private proc_macro crate), stabilized in rustc 1.79.0. We're on nightly-2024-03-21, proc_macro::Literal::byte_character was stabilized on 2024-04-04 and rustc 1.79.0 branched on 2024-04-26.

These never showed up to end users since these revs are mostly in the middle of PR #249, the edition 2025 toolchain upgrade. I've specifically chosen to test revs before and after target spec changes to make sure (past) cargo-gpu's / (now) spirv-builder's backwards compat towards older rust-gpu versions works, as these are the most likely to break. (Also this PR is also not backwards compatible, see Rust-GPU/cargo-gpu@1e4487e ci failing, will fix soon)

This could also be fixed by making cargo-gpu's "rustc-codegen-spirv build" use rust-gpu's lockfile, and thus never use never deps then what we're using right now.

[Firestar99]

Had a read though it, skipping the format_args_disassembler cause that's entirely @eddyb's domain (I merely moved it to a separate mod at some point, if it shows me as having changed it).

Added some commits to make it work with cargo-gpu's backwards compat requirements.

Works for restir, nanite-at-home, rust-gpu-templates and builds nazar's abundance.

Still think we shouldn't upgrade to middle nightlies, see comment above.

[LegNeato]

Still think we shouldn't upgrade to middle nightlies, see comment above.

I don't want to optimize for cargo-gpu, I want to optimize for tracking nightly and detecting issues in upstream ASAP and perhaps having upstream revert or workaround rather than us dealing with them months later once things have solidified. cargo-gpu isn't even technically in alpha, it is on a best effort basis.

In my ideal world we are tracking rustc master. Perhaps this means cargo-gpu needs to be merged into this repo so users can depend on the same rev and have it all work (but have cargo-gpu able to compile with stable). I am not sure, that then feels a bit like SpirvBuilder? I feel like a tool that was supposed to be an add-on to make things easier is now a critical piece and seems to be slowing down the main project before we have even officially released it. That is not good.

[nazar-pc]

Perhaps this means cargo-gpu needs to be merged into this repo

Yes, please 🙏

[Firestar99]

Let's get this PR merged and I'll have a look at merging cargo-gpu into this repo once everything propagates through. @nazar-pc and I have discussed this before and I think it's a great idea.

On rustc in-the-middle nightlies, we decided to merge this and update again when 1.96.0 branches in 2 weeks