build: bump Rust toolchain to nightly-2026-07-20

[robobun]

Bumps the pinned Rust nightly from nightly-2026-05-06 to nightly-2026-07-20.

	old	new
rustc	1.97.0-nightly (e95e73209 2026-05-05)	1.99.0-nightly (9f36de775 2026-07-19)
bundled LLVM	22.1.4	22.1.8

Notable upstream changes in this range

• v0 symbol mangling is now the default (rust#151994, 1.97). Rust symbols are now emitted with the _R prefix instead of legacy _ZN. std's own backtrace printer demangles both, but bun.report's server-side remapper and any external profiler/debugger tooling that reads Bun's Rust frames needs a v0-aware demangler. We do not pin -Csymbol-mangling-version, so this takes effect.
• linker_messages lint on by default (rust#153968, 1.97). Already handled: scripts/build/rust.ts and scripts/build/cargo-config.ts pass -Alinker_messages.
• Bundled LLVM 22.1.4 → 22.1.8 (same major). Cross-language LTO against our clang-21 is unaffected; the rust-lto-fix step still reads rustc-emitted bitcode with rustc's own llvm-tools.
• Windows WSAESHUTDOWN now maps to io::ErrorKind::BrokenPipe (rust#156063, 1.97). N/A for us: Bun's socket layer maps Win32 errors through bun_errno (which already maps WSAESHUTDOWN → EPIPE), not std's ErrorKind.
• Enum layout encoding changed for some repr(Rust) enums (rust#155473, 1.97). N/A: every enum we pass across FFI is repr(C)/repr(u*).
• {integer}::isolate_lowest_one / isolate_highest_one stabilised (1.97). Used in two of the clippy fixes below.
• core::mem::type_info nightly feature reshaped: core::intrinsics::type_id is now #[rustc_comptime] (compile-time only), and type_info::Type lost its size field in favour of TypeId::size(). bun_collections::MultiArrayList is the only user; fixed below.
• Of the nightly features we enable (adt_const_params, allocator_api, arbitrary_self_types_pointers, generic_const_exprs, hasher_prefixfree_extras, inherent_associated_types, macro_metavar_expr, sync_unsafe_cell, thread_local, type_info, core_intrinsics), only type_info/core_intrinsics changed shape.
• New rustc lint suspicious_runtime_symbol_definitions (1.99 nightly). Flags extern "C" declarations of runtime symbols (exit, etc.) whose Rust signature differs from std's own. Our bun_core::Global declares libc_exit as safe fn on purpose (no memory-safety preconditions); the ABI is identical, so #[allow] on the block.

Toolchain pin

• rust-toolchain.toml
• .github/workflows/{format,clippy,miri}.yml (RUSTUP_TOOLCHAIN)

Nightly API changes (core::mem::type_info)

bun_collections::MultiArrayList uses the experimental reflection API, which changed shape:

• core::intrinsics::type_id is now #[rustc_comptime] (callable only at compile time). Wrapped the call in a const { } block.
• type_info::Type no longer has a size field; the size now comes from TypeId::size().

New clippy lints

The new nightly promotes several lints that trip under the workspace's -D warnings. All fixes are mechanical and preserve behaviour:

• clippy::needless_late_init: convert late let x; if ... { x = ... } else { x = ... } to let x = if ... { ... } else { ... }; (bun_alloc, bun_collections, js_parser, js_printer, install, runtime/node/path, runtime/socket/udp, valkey_jsc, sql_jsc/mysql)
• clippy::chunks_exact_to_as_chunks: replace .chunks_exact(N) / .chunks_exact_mut(N) on const N with .as_chunks::<N>() (bun_core, boringssl, ast/char_freq, http_jsc websocket, runtime/cli/upgrade, runtime/image, runtime/webcore/encoding)
• clippy::manual_isolate_lowest_one: x & x.wrapping_neg() → x.isolate_lowest_one() (collections, css)
• clippy::manual_clear: truncate(0) → clear() (router)
• clippy::drain_collect: vec.drain(..).collect() → mem::take(&mut vec) (react_compiler)

Quiet rustup output

The build runs rustup toolchain install --force before cargo to self-heal partial toolchain installs. On a no-op this printed:

info: syncing channel updates for 'nightly-...-aarch64-apple-darwin'
info: latest update on ...
info: component 'rust-src' is up to date
info: self-update is disabled for this build of rustup
info: any updates to rustup will need to be fetched with your system package manager

Added -q (sets rustup log level to WARN) and --no-self-update to the three call sites (scripts/build/{rust.ts,source.ts,tools.ts}) so the info lines are suppressed while download/error output still surfaces.

Verification

• bun bd builds and bun-debug --revision runs
• cargo fmt --all --check is clean on the new nightly (no formatting drift)
• cargo clippy --workspace --no-deps --keep-going passes on the new nightly
• cargo test -p bun_collections multi_array passes (7/7)

Fixes #31414

[robobun]

^{Updated 11:38 PM PT - Jul 19th, 2026}

@robobun, your commit 53dc8ab is building: #76074

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📥 Commits

Reviewing files that changed from the base of the PR and between 5c28061 and 53dc8ab.

📒 Files selected for processing (29)

• .github/workflows/clippy.yml
• .github/workflows/format.yml
• .github/workflows/miri.yml
• rust-toolchain.toml
• scripts/build/rust.ts
• scripts/build/source.ts
• scripts/build/tools.ts
• src/ast/char_freq.rs
• src/boringssl/lib.rs
• src/bun_alloc/lib.rs
• src/bun_core/Global.rs
• src/bun_core/lib.rs
• src/collections/bit_set.rs
• src/collections/multi_array_list.rs
• src/css/values/color.rs
• src/http_jsc/websocket_client/WebSocketUpgradeClient.rs
• src/install/PackageManager/CommandLineArguments.rs
• src/install/resolvers/folder_resolver.rs
• src/js_parser/parse/parse_typescript.rs
• src/js_printer/lib.rs
• src/react_compiler/ssa/enter_ssa.rs
• src/router/lib.rs
• src/runtime/cli/upgrade_command.rs
• src/runtime/image/codecs.rs
• src/runtime/node/path.rs
• src/runtime/socket/udp_socket.rs
• src/runtime/valkey_jsc/valkey.rs
• src/runtime/webcore/encoding.rs
• src/sql_jsc/mysql/MySQLValue.rs

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[robobun]

No test/** changes in this PR: this is a toolchain version bump, and every src/** change is either a compile fix forced by the new nightly (the core::mem::type_info reshape) or a mechanical clippy-suggested rewrite for lints newly promoted under -D warnings. None of them change runtime behaviour, so there is no before/after observable to regression-test; correctness is covered by bun bd compiling, cargo clippy --workspace passing, and the existing test suite running unchanged on the new toolchain.

[github-actions]

Found 1 issue this PR may fix:

1. Perf: avoid using chunks_exact* when size is known statically #31414 - PR replaces .chunks_exact(N) / .chunks_exact_mut(N) with .as_chunks::<N>() / .as_chunks_mut::<N>() across ~7 files, which is exactly what this issue requests

If this is helpful, copy the block below into the PR description to auto-close this issue on merge.

Fixes #31414

🤖 Generated with Claude Code

[github-actions]

This PR may be a duplicate of:

1. perf: use as_chunks* instead of chunks_exact* for static chunk sizes #31415 - Also converts chunks_exact → as_chunks in 5 of the same files (src/bun_core/lib.rs, src/ast/char_freq.rs, src/http_jsc/websocket_client/WebSocketUpgradeClient.rs, src/runtime/image/codecs.rs, src/runtime/webcore/encoding.rs); merging both without rebasing will cause conflicts

🤖 Generated with Claude Code

[robobun]

Re the overlap with #31415: that PR is already in conflict with main and its const-N chunks_exact → as_chunks conversions are now enforced by clippy::chunks_exact_to_as_chunks on this nightly, so this PR supersedes that portion (covering the same five files plus two more clippy flagged). The only non-overlapping content in #31415 is the runtime-stride handling in src/install/lockfile/Package.rs (not a const generic, so the lint does not apply) and scripts/verify-baseline-static/src/main.rs, which can be rebased on top of this if still wanted.

[claude]

Beyond the pre-existing inline finding, I walked each chunks_exact → as_chunks site to confirm remainder handling is unchanged (every site either has an exact-multiple length or already discarded the remainder), checked that the bun_core as_chunks_mut borrow ends before the tail dst[copied..] reborrow, and confirmed folder_resolver.rs still assigns abs in both branches before the new rel expression uses it.

Extended reasoning...

The only finding is explicitly pre-existing (Time::to_binary off-by-one, unrelated to this PR's mechanical rewrite of the call site). I verified the less-obviously-mechanical lint fixes for behaviour preservation — in particular the as_chunks conversions (remainder semantics match chunks_exact at every site) and the needless_late_init rewrites where a second variable (abs in folder_resolver, minify_renamer/no_op_renamer in js_printer) is still assigned inside the branches. Deferring rather than approving because a toolchain bump touching 28 files plus build scripts should have the full BuildKite matrix confirmed green by a human before merge.

[robobun]

Rebased onto current main (102 commits) and bumped the target to nightly-2026-07-20 (rustc 1.99.0-nightly, 9f36de775 2026-07-19). The rebase applied cleanly; CI will surface any new lints or breakage introduced between 07-15 and 07-20.

[robobun]

Superseded by #34782, which folds this toolchain bump in alongside the CI pipeline changes and image bake. Closing in favour of that PR.