turbo-tasks: drop once_cell, const-init TRAIT_METHOD, ctor WORKER_TASKS#93090
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turbo-tasks: drop once_cell, const-init TRAIT_METHOD, ctor WORKER_TASKS#93090
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Merging this PR will degrade performance by 3.61%
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mmastrac
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Apr 21, 2026
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Apr 21, 2026
…_TASKS - Replace `once_cell::sync::Lazy` with `std::sync::LazyLock` throughout turbo-tasks and turbo-tasks-backend (registry, scope, macro_helpers, fuzz runtime). - Replace `once_cell::unsync::Lazy` with `std::cell::LazyCell` in update_cell.rs. - Remove the unused `OnceCell` and (now unused) `phf` re-exports from `macro_helpers`; drop `once_cell` and `phf` from turbo-tasks' Cargo deps (also drop `once_cell` from turbo-tasks-backend and its fuzz crate). - Change `TraitType::methods` from `phf::Map<&str, TraitMethod>` to `&'static [TraitMethod]` (parallel to `method_names`) and make `TraitType::get` a `const fn` using `index_of_name`. The `value_trait` macro now emits a slice literal instead of a `phf_map!`, and the `function` macro emits a plain `static TRAIT_METHOD: &'static TraitMethod = TRAIT.get(stringify!(..));` initialized at const-eval time instead of a `Lazy<&'static TraitMethod>`. - Bump `ctor` to 0.10 and convert `WORKER_TASKS` in scope.rs to a `#[ctor::ctor]` static so it's initialized once at program load with no per-access locking.
- Revert the workspace `ctor` bump from 0.10 back to 0.8. The
`#[ctor::ctor] static WORKER_TASKS: usize = unsafe { ... }` form is
supported in 0.8 when the RHS is a block expression, so no change to
the scope.rs call site is required.
- `TraitType::get` is now `#[cfg(test)]`-only. Production lookup is
inlined at the macro site: the `function` macro emits
`&TRAIT.methods[macro_helpers::index_of_name(TRAIT.method_names, "name")]`,
which resolves to a const index + array deref at compile time. Re-export
`index_of_name` from `macro_helpers`.
The perf win from moving WORKER_TASKS init to load time was minimal and not worth the ctor surface in this PR. Put it back under LazyLock and drop the now-unused ctor dep from turbo-tasks.
Both stored the same data already available on `TraitType.methods[i].method_name`. Replace them with a new `index_of_method_name(&'static [TraitMethod], &str)` const fn that scans the methods slice directly. `build_trait_vtable` picks up the methods array via `<B as RegistryDef<TraitType>>::DEF.methods`, so it no longer needs `NAMES`. Drops the old `index_of_name` free fn with them. The `value_trait` macro stops emitting the parallel name list entirely — one source of truth (`methods[i].method_name`) instead of two.
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What
Clean up the Lazy-locks we re-export or use internally in the turbo-tasks crates, migrating to
std::sync::LazyLock/std::cell::LazyCellwhere still needed and eliminating a couple of them where they weren't.Why
One less dep, using standard Rust features, a smaller number of Lazy items.
Details
macro_helpers::OnceCelland the now-unusedmacro_helpers::phf(sinceTraitTypeno longer stores aphf::Map). Replaceonce_cell::sync::Lazywithstd::sync::LazyLockinmacro_helpers::TRAIT_CAST_FNSand in the two macro-generated call sites.once_cell::sync::Lazy→std::sync::LazyLockinscope.rs,registry/mod.rs, andturbo-tasks-backend-fuzz'sgraph.rs.once_cell::unsync::Lazy→std::cell::LazyCellinupdate_cell.rs.TRAIT_METHOD→ plain const-init static:TraitType::methodschanges fromphf::Map<&'static str, TraitMethod>to&'static [TraitMethod](parallel tomethod_names), andTraitType::getbecomes aconst fnthat doesindex_of_name+ array indexing. Thevalue_traitmacro now emits a slice literal instead ofphf_map!, and thefunctionmacro emitsstatic TRAIT_METHOD: &'static TraitMethod = TRAIT.get(stringify!(..));— evaluated at const-eval time rather than behind aLazyLock<&TraitMethod>.once_cellandphfCargo deps fromturbo-tasks, andonce_cellfromturbo-tasks-backendand its fuzz crate.