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.

[LegNeato]

@nazar-pc I think what you saw should be fixed.

[nazar-pc]

Yes, clippy is happy now, tests are passing too

[fee1-dead]

cc @Firestar99 for some testing

[LegNeato]

@Firestar99 did you get a chance to test this?

[fee1-dead]

LGTM, had one last nit, otherwise this is ready to go and feel free to merge after CI green and testing (cc @Firestar99?)!

[fee1-dead]

nit: should move back to the let chain instead of putting another check inside.

[LegNeato]

Clippy caught it in CI, already fixed: 3cce05f#diff-0125001c97c174d9f3ce82c4aa79adbe742cfccdb92a38165daa7136952bb4e7R349

[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
• ✔️ bbb61f5 proc-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.